]> git.sesse.net Git - bcachefs-tools-debian/blobdiff - libbcachefs/fsck.c
Move c_src dirs back to toplevel
[bcachefs-tools-debian] / libbcachefs / fsck.c
index 7ea1a41ac637fa02a1160b10ee929280cd36d73f..4f0ecd60567570b7364cef517225ea0e3dfa5575 100644 (file)
 
 #include "bcachefs.h"
 #include "bkey_buf.h"
+#include "btree_cache.h"
 #include "btree_update.h"
+#include "buckets.h"
+#include "darray.h"
 #include "dirent.h"
 #include "error.h"
 #include "fs-common.h"
 #include "fsck.h"
 #include "inode.h"
 #include "keylist.h"
+#include "recovery.h"
+#include "snapshot.h"
 #include "super.h"
 #include "xattr.h"
 
 #include <linux/bsearch.h>
 #include <linux/dcache.h> /* struct qstr */
 
-#define QSTR(n) { { { .len = strlen(n) } }, .name = n }
+/*
+ * XXX: this is handling transaction restarts without returning
+ * -BCH_ERR_transaction_restart_nested, this is not how we do things anymore:
+ */
+static s64 bch2_count_inode_sectors(struct btree_trans *trans, u64 inum,
+                                   u32 snapshot)
+{
+       u64 sectors = 0;
+
+       int ret = for_each_btree_key_upto(trans, iter, BTREE_ID_extents,
+                               SPOS(inum, 0, snapshot),
+                               POS(inum, U64_MAX),
+                               0, k, ({
+               if (bkey_extent_is_allocation(k.k))
+                       sectors += k.k->size;
+               0;
+       }));
+
+       return ret ?: sectors;
+}
+
+static s64 bch2_count_subdirs(struct btree_trans *trans, u64 inum,
+                                   u32 snapshot)
+{
+       u64 subdirs = 0;
+
+       int ret = for_each_btree_key_upto(trans, iter, BTREE_ID_dirents,
+                                   SPOS(inum, 0, snapshot),
+                                   POS(inum, U64_MAX),
+                                   0, k, ({
+               if (k.k->type == KEY_TYPE_dirent &&
+                   bkey_s_c_to_dirent(k).v->d_type == DT_DIR)
+                       subdirs++;
+               0;
+       }));
+
+       return ret ?: subdirs;
+}
+
+static int subvol_lookup(struct btree_trans *trans, u32 subvol,
+                        u32 *snapshot, u64 *inum)
+{
+       struct bch_subvolume s;
+       int ret;
 
-static s64 bch2_count_inode_sectors(struct btree_trans *trans, u64 inum)
+       ret = bch2_subvolume_get(trans, subvol, false, 0, &s);
+
+       *snapshot = le32_to_cpu(s.snapshot);
+       *inum = le64_to_cpu(s.inode);
+       return ret;
+}
+
+static int lookup_first_inode(struct btree_trans *trans, u64 inode_nr,
+                             struct bch_inode_unpacked *inode)
 {
-       struct btree_iter *iter;
+       struct btree_iter iter;
        struct bkey_s_c k;
-       u64 sectors = 0;
        int ret;
 
-       for_each_btree_key(trans, iter, BTREE_ID_extents,
-                          POS(inum, 0), 0, k, ret) {
-               if (k.k->p.inode != inum)
-                       break;
+       bch2_trans_iter_init(trans, &iter, BTREE_ID_inodes,
+                            POS(0, inode_nr),
+                            BTREE_ITER_ALL_SNAPSHOTS);
+       k = bch2_btree_iter_peek(&iter);
+       ret = bkey_err(k);
+       if (ret)
+               goto err;
 
-               if (bkey_extent_is_allocation(k.k))
-                       sectors += k.k->size;
+       if (!k.k || !bkey_eq(k.k->p, POS(0, inode_nr))) {
+               ret = -BCH_ERR_ENOENT_inode;
+               goto err;
        }
 
-       bch2_trans_iter_free(trans, iter);
-
-       return ret ?: sectors;
+       ret = bch2_inode_unpack(k, inode);
+err:
+       bch_err_msg(trans->c, ret, "fetching inode %llu", inode_nr);
+       bch2_trans_iter_exit(trans, &iter);
+       return ret;
 }
 
-static int __lookup_inode(struct btree_trans *trans, u64 inode_nr,
+static int lookup_inode(struct btree_trans *trans, u64 inode_nr,
                          struct bch_inode_unpacked *inode,
                          u32 *snapshot)
 {
-       struct btree_iter *iter;
+       struct btree_iter iter;
        struct bkey_s_c k;
        int ret;
 
-       iter = bch2_trans_get_iter(trans, BTREE_ID_inodes,
-                       POS(0, inode_nr), 0);
-       k = bch2_btree_iter_peek_slot(iter);
+       k = bch2_bkey_get_iter(trans, &iter, BTREE_ID_inodes,
+                              SPOS(0, inode_nr, *snapshot), 0);
        ret = bkey_err(k);
        if (ret)
                goto err;
 
-       if (snapshot)
-               *snapshot = iter->pos.snapshot;
-       ret = k.k->type == KEY_TYPE_inode
-               ? bch2_inode_unpack(bkey_s_c_to_inode(k), inode)
-               : -ENOENT;
+       ret = bkey_is_inode(k.k)
+               ? bch2_inode_unpack(k, inode)
+               : -BCH_ERR_ENOENT_inode;
+       if (!ret)
+               *snapshot = iter.pos.snapshot;
 err:
-       bch2_trans_iter_free(trans, iter);
+       bch_err_msg(trans->c, ret, "fetching inode %llu:%u", inode_nr, *snapshot);
+       bch2_trans_iter_exit(trans, &iter);
        return ret;
 }
 
-static int lookup_inode(struct btree_trans *trans, u64 inode_nr,
-                       struct bch_inode_unpacked *inode,
-                       u32 *snapshot)
+static int __lookup_dirent(struct btree_trans *trans,
+                          struct bch_hash_info hash_info,
+                          subvol_inum dir, struct qstr *name,
+                          u64 *target, unsigned *type)
 {
-       return lockrestart_do(trans, __lookup_inode(trans, inode_nr, inode, snapshot));
+       struct btree_iter iter;
+       struct bkey_s_c_dirent d;
+       int ret;
+
+       ret = bch2_hash_lookup(trans, &iter, bch2_dirent_hash_desc,
+                              &hash_info, dir, name, 0);
+       if (ret)
+               return ret;
+
+       d = bkey_s_c_to_dirent(bch2_btree_iter_peek_slot(&iter));
+       *target = le64_to_cpu(d.v->d_inum);
+       *type = d.v->d_type;
+       bch2_trans_iter_exit(trans, &iter);
+       return 0;
 }
 
 static int __write_inode(struct btree_trans *trans,
                         struct bch_inode_unpacked *inode,
                         u32 snapshot)
 {
-       struct btree_iter *inode_iter =
-               bch2_trans_get_iter(trans, BTREE_ID_inodes,
-                                   SPOS(0, inode->bi_inum, snapshot),
-                                   BTREE_ITER_INTENT);
-       int ret = bch2_btree_iter_traverse(inode_iter) ?:
-               bch2_inode_write(trans, inode_iter, inode);
-       bch2_trans_iter_put(trans, inode_iter);
-       return ret;
+       struct bkey_inode_buf *inode_p =
+               bch2_trans_kmalloc(trans, sizeof(*inode_p));
+
+       if (IS_ERR(inode_p))
+               return PTR_ERR(inode_p);
+
+       bch2_inode_pack(inode_p, inode);
+       inode_p->inode.k.p.snapshot = snapshot;
+
+       return bch2_btree_insert_nonextent(trans, BTREE_ID_inodes,
+                               &inode_p->inode.k_i,
+                               BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE);
 }
 
-static int write_inode(struct btree_trans *trans,
-                      struct bch_inode_unpacked *inode,
-                      u32 snapshot)
+static int fsck_write_inode(struct btree_trans *trans,
+                           struct bch_inode_unpacked *inode,
+                           u32 snapshot)
 {
-       int ret = __bch2_trans_do(trans, NULL, NULL,
-                                 BTREE_INSERT_NOFAIL|
-                                 BTREE_INSERT_LAZY_RW,
-                                 __write_inode(trans, inode, snapshot));
-       if (ret)
-               bch_err(trans->c, "error in fsck: error %i updating inode", ret);
+       int ret = commit_do(trans, NULL, NULL, BCH_TRANS_COMMIT_no_enospc,
+                           __write_inode(trans, inode, snapshot));
+       bch_err_fn(trans->c, ret);
        return ret;
 }
 
 static int __remove_dirent(struct btree_trans *trans, struct bpos pos)
 {
        struct bch_fs *c = trans->c;
-       struct btree_iter *iter;
+       struct btree_iter iter;
        struct bch_inode_unpacked dir_inode;
        struct bch_hash_info dir_hash_info;
        int ret;
 
-       ret = lookup_inode(trans, pos.inode, &dir_inode, NULL);
+       ret = lookup_first_inode(trans, pos.inode, &dir_inode);
        if (ret)
-               return ret;
+               goto err;
 
        dir_hash_info = bch2_hash_info_init(c, &dir_inode);
 
-       iter = bch2_trans_get_iter(trans, BTREE_ID_dirents, pos, BTREE_ITER_INTENT);
+       bch2_trans_iter_init(trans, &iter, BTREE_ID_dirents, pos, BTREE_ITER_INTENT);
 
        ret = bch2_hash_delete_at(trans, bch2_dirent_hash_desc,
-                                 &dir_hash_info, iter);
-       bch2_trans_iter_put(trans, iter);
-       return ret;
-}
-
-static int remove_dirent(struct btree_trans *trans, struct bpos pos)
-{
-       int ret = __bch2_trans_do(trans, NULL, NULL,
-                                 BTREE_INSERT_NOFAIL|
-                                 BTREE_INSERT_LAZY_RW,
-                                 __remove_dirent(trans, pos));
-       if (ret)
-               bch_err(trans->c, "remove_dirent: err %i deleting dirent", ret);
+                                 &dir_hash_info, &iter,
+                                 BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE);
+       bch2_trans_iter_exit(trans, &iter);
+err:
+       bch_err_fn(c, ret);
        return ret;
 }
 
 /* Get lost+found, create if it doesn't exist: */
-static int lookup_lostfound(struct btree_trans *trans,
+static int lookup_lostfound(struct btree_trans *trans, u32 snapshot,
                            struct bch_inode_unpacked *lostfound)
 {
        struct bch_fs *c = trans->c;
-       struct bch_inode_unpacked root;
-       struct bch_hash_info root_hash_info;
        struct qstr lostfound_str = QSTR("lost+found");
-       u64 inum;
-       u32 snapshot;
+       u64 inum = 0;
+       unsigned d_type = 0;
        int ret;
 
-       ret = lookup_inode(trans, BCACHEFS_ROOT_INO, &root, &snapshot);
-       if (ret && ret != -ENOENT)
+       struct bch_snapshot_tree st;
+       ret = bch2_snapshot_tree_lookup(trans,
+                       bch2_snapshot_tree(c, snapshot), &st);
+       if (ret)
+               return ret;
+
+       subvol_inum root_inum = { .subvol = le32_to_cpu(st.master_subvol) };
+       u32 subvol_snapshot;
+
+       ret = subvol_lookup(trans, le32_to_cpu(st.master_subvol),
+                           &subvol_snapshot, &root_inum.inum);
+       bch_err_msg(c, ret, "looking up root subvol");
+       if (ret)
+               return ret;
+
+       struct bch_inode_unpacked root_inode;
+       struct bch_hash_info root_hash_info;
+       ret = lookup_inode(trans, root_inum.inum, &root_inode, &snapshot);
+       bch_err_msg(c, ret, "looking up root inode");
+       if (ret)
                return ret;
 
-       root_hash_info = bch2_hash_info_init(c, &root);
-       inum = bch2_dirent_lookup(c, BCACHEFS_ROOT_INO, &root_hash_info,
-                                 &lostfound_str);
-       if (!inum) {
-               bch_notice(c, "creating lost+found");
+       root_hash_info = bch2_hash_info_init(c, &root_inode);
+
+       ret = __lookup_dirent(trans, root_hash_info, root_inum,
+                             &lostfound_str, &inum, &d_type);
+       if (bch2_err_matches(ret, ENOENT))
                goto create_lostfound;
-       }
 
-       ret = lookup_inode(trans, inum, lostfound, &snapshot);
-       if (ret && ret != -ENOENT) {
-               /*
-                * The check_dirents pass has already run, dangling dirents
-                * shouldn't exist here:
-                */
-               bch_err(c, "error looking up lost+found: %i", ret);
+       bch_err_fn(c, ret);
+       if (ret)
                return ret;
+
+       if (d_type != DT_DIR) {
+               bch_err(c, "error looking up lost+found: not a directory");
+               return -BCH_ERR_ENOENT_not_directory;
        }
 
-       if (ret == -ENOENT) {
+       /*
+        * The bch2_check_dirents pass has already run, dangling dirents
+        * shouldn't exist here:
+        */
+       return lookup_inode(trans, inum, lostfound, &snapshot);
+
 create_lostfound:
-               bch2_inode_init_early(c, lostfound);
-
-               ret = __bch2_trans_do(trans, NULL, NULL,
-                                     BTREE_INSERT_NOFAIL|
-                                     BTREE_INSERT_LAZY_RW,
-                       bch2_create_trans(trans,
-                                         BCACHEFS_ROOT_INO, &root,
-                                         lostfound,
-                                         &lostfound_str,
-                                         0, 0, S_IFDIR|0700, 0, NULL, NULL));
-               if (ret)
-                       bch_err(c, "error creating lost+found: %i", ret);
-       }
+       /*
+        * XXX: we could have a nicer log message here  if we had a nice way to
+        * walk backpointers to print a path
+        */
+       bch_notice(c, "creating lost+found in snapshot %u", le32_to_cpu(st.root_snapshot));
 
-       return 0;
+       u64 now = bch2_current_time(c);
+       struct btree_iter lostfound_iter = { NULL };
+       u64 cpu = raw_smp_processor_id();
+
+       bch2_inode_init_early(c, lostfound);
+       bch2_inode_init_late(lostfound, now, 0, 0, S_IFDIR|0700, 0, &root_inode);
+       lostfound->bi_dir = root_inode.bi_inum;
+
+       root_inode.bi_nlink++;
+
+       ret = bch2_inode_create(trans, &lostfound_iter, lostfound, snapshot, cpu);
+       if (ret)
+               goto err;
+
+       bch2_btree_iter_set_snapshot(&lostfound_iter, snapshot);
+       ret = bch2_btree_iter_traverse(&lostfound_iter);
+       if (ret)
+               goto err;
+
+       ret =   bch2_dirent_create_snapshot(trans,
+                               root_inode.bi_inum, snapshot, &root_hash_info,
+                               mode_to_type(lostfound->bi_mode),
+                               &lostfound_str,
+                               lostfound->bi_inum,
+                               &lostfound->bi_dir_offset,
+                               BCH_HASH_SET_MUST_CREATE) ?:
+               bch2_inode_write_flags(trans, &lostfound_iter, lostfound,
+                                      BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE);
+err:
+       bch_err_msg(c, ret, "creating lost+found");
+       bch2_trans_iter_exit(trans, &lostfound_iter);
+       return ret;
 }
 
 static int reattach_inode(struct btree_trans *trans,
-                         struct bch_inode_unpacked *inode)
+                         struct bch_inode_unpacked *inode,
+                         u32 inode_snapshot)
 {
        struct bch_hash_info dir_hash;
        struct bch_inode_unpacked lostfound;
@@ -193,14 +304,14 @@ static int reattach_inode(struct btree_trans *trans,
        u64 dir_offset = 0;
        int ret;
 
-       ret = lookup_lostfound(trans, &lostfound);
+       ret = lookup_lostfound(trans, inode_snapshot, &lostfound);
        if (ret)
                return ret;
 
        if (S_ISDIR(inode->bi_mode)) {
                lostfound.bi_nlink++;
 
-               ret = write_inode(trans, &lostfound, U32_MAX);
+               ret = __write_inode(trans, &lostfound, U32_MAX);
                if (ret)
                        return ret;
        }
@@ -210,82 +321,386 @@ static int reattach_inode(struct btree_trans *trans,
        snprintf(name_buf, sizeof(name_buf), "%llu", inode->bi_inum);
        name = (struct qstr) QSTR(name_buf);
 
-       ret = __bch2_trans_do(trans, NULL, NULL, BTREE_INSERT_LAZY_RW,
-               bch2_dirent_create(trans, lostfound.bi_inum, &dir_hash,
-                                  mode_to_type(inode->bi_mode),
-                                  &name, inode->bi_inum, &dir_offset,
-                                  BCH_HASH_SET_MUST_CREATE));
-       if (ret) {
-               bch_err(trans->c, "error %i reattaching inode %llu",
-                       ret, inode->bi_inum);
+       ret = bch2_dirent_create_snapshot(trans,
+                               lostfound.bi_inum, inode_snapshot,
+                               &dir_hash,
+                               inode_d_type(inode),
+                               &name, inode->bi_inum, &dir_offset,
+                               BCH_HASH_SET_MUST_CREATE);
+       if (ret)
                return ret;
-       }
 
        inode->bi_dir           = lostfound.bi_inum;
        inode->bi_dir_offset    = dir_offset;
 
-       return write_inode(trans, inode, U32_MAX);
+       return __write_inode(trans, inode, inode_snapshot);
 }
 
 static int remove_backpointer(struct btree_trans *trans,
                              struct bch_inode_unpacked *inode)
 {
-       struct btree_iter *iter;
-       struct bkey_s_c k;
+       struct btree_iter iter;
+       struct bkey_s_c_dirent d;
        int ret;
 
-       iter = bch2_trans_get_iter(trans, BTREE_ID_dirents,
-                                  POS(inode->bi_dir, inode->bi_dir_offset), 0);
-       k = bch2_btree_iter_peek_slot(iter);
-       ret = bkey_err(k);
+       d = bch2_bkey_get_iter_typed(trans, &iter, BTREE_ID_dirents,
+                                    POS(inode->bi_dir, inode->bi_dir_offset), 0,
+                                    dirent);
+       ret =   bkey_err(d) ?:
+               __remove_dirent(trans, d.k->p);
+       bch2_trans_iter_exit(trans, &iter);
+       return ret;
+}
+
+struct snapshots_seen_entry {
+       u32                             id;
+       u32                             equiv;
+};
+
+struct snapshots_seen {
+       struct bpos                     pos;
+       DARRAY(struct snapshots_seen_entry) ids;
+};
+
+static inline void snapshots_seen_exit(struct snapshots_seen *s)
+{
+       darray_exit(&s->ids);
+}
+
+static inline void snapshots_seen_init(struct snapshots_seen *s)
+{
+       memset(s, 0, sizeof(*s));
+}
+
+static int snapshots_seen_add_inorder(struct bch_fs *c, struct snapshots_seen *s, u32 id)
+{
+       struct snapshots_seen_entry *i, n = {
+               .id     = id,
+               .equiv  = bch2_snapshot_equiv(c, id),
+       };
+       int ret = 0;
+
+       __darray_for_each(s->ids, i) {
+               if (i->id == id)
+                       return 0;
+               if (i->id > id)
+                       break;
+       }
+
+       ret = darray_insert_item(&s->ids, i - s->ids.data, n);
        if (ret)
-               goto out;
-       if (k.k->type != KEY_TYPE_dirent) {
-               ret = -ENOENT;
-               goto out;
+               bch_err(c, "error reallocating snapshots_seen table (size %zu)",
+                       s->ids.size);
+       return ret;
+}
+
+static int snapshots_seen_update(struct bch_fs *c, struct snapshots_seen *s,
+                                enum btree_id btree_id, struct bpos pos)
+{
+       struct snapshots_seen_entry n = {
+               .id     = pos.snapshot,
+               .equiv  = bch2_snapshot_equiv(c, pos.snapshot),
+       };
+       int ret = 0;
+
+       if (!bkey_eq(s->pos, pos))
+               s->ids.nr = 0;
+
+       s->pos = pos;
+       s->pos.snapshot = n.equiv;
+
+       darray_for_each(s->ids, i) {
+               if (i->id == n.id)
+                       return 0;
+
+               /*
+                * We currently don't rigorously track for snapshot cleanup
+                * needing to be run, so it shouldn't be a fsck error yet:
+                */
+               if (i->equiv == n.equiv) {
+                       bch_err(c, "snapshot deletion did not finish:\n"
+                               "  duplicate keys in btree %s at %llu:%llu snapshots %u, %u (equiv %u)\n",
+                               bch2_btree_id_str(btree_id),
+                               pos.inode, pos.offset,
+                               i->id, n.id, n.equiv);
+                       set_bit(BCH_FS_need_delete_dead_snapshots, &c->flags);
+                       return bch2_run_explicit_recovery_pass(c, BCH_RECOVERY_PASS_delete_dead_snapshots);
+               }
        }
 
-       ret = remove_dirent(trans, k.k->p);
-out:
-       bch2_trans_iter_put(trans, iter);
+       ret = darray_push(&s->ids, n);
+       if (ret)
+               bch_err(c, "error reallocating snapshots_seen table (size %zu)",
+                       s->ids.size);
        return ret;
 }
 
-struct inode_walker {
-       bool                    first_this_inode;
-       bool                    have_inode;
-       u64                     cur_inum;
-       u32                     snapshot;
+/**
+ * key_visible_in_snapshot - returns true if @id is a descendent of @ancestor,
+ * and @ancestor hasn't been overwritten in @seen
+ *
+ * @c:         filesystem handle
+ * @seen:      list of snapshot ids already seen at current position
+ * @id:                descendent snapshot id
+ * @ancestor:  ancestor snapshot id
+ *
+ * Returns:    whether key in @ancestor snapshot is visible in @id snapshot
+ */
+static bool key_visible_in_snapshot(struct bch_fs *c, struct snapshots_seen *seen,
+                                   u32 id, u32 ancestor)
+{
+       ssize_t i;
+
+       EBUG_ON(id > ancestor);
+       EBUG_ON(!bch2_snapshot_is_equiv(c, id));
+       EBUG_ON(!bch2_snapshot_is_equiv(c, ancestor));
+
+       /* @ancestor should be the snapshot most recently added to @seen */
+       EBUG_ON(ancestor != seen->pos.snapshot);
+       EBUG_ON(ancestor != seen->ids.data[seen->ids.nr - 1].equiv);
+
+       if (id == ancestor)
+               return true;
+
+       if (!bch2_snapshot_is_ancestor(c, id, ancestor))
+               return false;
+
+       /*
+        * We know that @id is a descendant of @ancestor, we're checking if
+        * we've seen a key that overwrote @ancestor - i.e. also a descendent of
+        * @ascestor and with @id as a descendent.
+        *
+        * But we already know that we're scanning IDs between @id and @ancestor
+        * numerically, since snapshot ID lists are kept sorted, so if we find
+        * an id that's an ancestor of @id we're done:
+        */
+
+       for (i = seen->ids.nr - 2;
+            i >= 0 && seen->ids.data[i].equiv >= id;
+            --i)
+               if (bch2_snapshot_is_ancestor(c, id, seen->ids.data[i].equiv))
+                       return false;
+
+       return true;
+}
+
+/**
+ * ref_visible - given a key with snapshot id @src that points to a key with
+ * snapshot id @dst, test whether there is some snapshot in which @dst is
+ * visible.
+ *
+ * @c:         filesystem handle
+ * @s:         list of snapshot IDs already seen at @src
+ * @src:       snapshot ID of src key
+ * @dst:       snapshot ID of dst key
+ * Returns:    true if there is some snapshot in which @dst is visible
+ *
+ * Assumes we're visiting @src keys in natural key order
+ */
+static bool ref_visible(struct bch_fs *c, struct snapshots_seen *s,
+                       u32 src, u32 dst)
+{
+       return dst <= src
+               ? key_visible_in_snapshot(c, s, dst, src)
+               : bch2_snapshot_is_ancestor(c, src, dst);
+}
+
+static int ref_visible2(struct bch_fs *c,
+                       u32 src, struct snapshots_seen *src_seen,
+                       u32 dst, struct snapshots_seen *dst_seen)
+{
+       src = bch2_snapshot_equiv(c, src);
+       dst = bch2_snapshot_equiv(c, dst);
+
+       if (dst > src) {
+               swap(dst, src);
+               swap(dst_seen, src_seen);
+       }
+       return key_visible_in_snapshot(c, src_seen, dst, src);
+}
+
+#define for_each_visible_inode(_c, _s, _w, _snapshot, _i)                              \
+       for (_i = (_w)->inodes.data; _i < (_w)->inodes.data + (_w)->inodes.nr &&        \
+            (_i)->snapshot <= (_snapshot); _i++)                                       \
+               if (key_visible_in_snapshot(_c, _s, _i->snapshot, _snapshot))
+
+struct inode_walker_entry {
        struct bch_inode_unpacked inode;
+       u32                     snapshot;
+       bool                    seen_this_pos;
+       u64                     count;
+};
+
+struct inode_walker {
+       bool                            first_this_inode;
+       bool                            recalculate_sums;
+       struct bpos                     last_pos;
+
+       DARRAY(struct inode_walker_entry) inodes;
 };
 
+static void inode_walker_exit(struct inode_walker *w)
+{
+       darray_exit(&w->inodes);
+}
+
 static struct inode_walker inode_walker_init(void)
 {
-       return (struct inode_walker) {
-               .cur_inum       = -1,
-               .have_inode     = false,
-       };
+       return (struct inode_walker) { 0, };
 }
 
-static int walk_inode(struct btree_trans *trans,
-                     struct inode_walker *w, u64 inum)
+static int add_inode(struct bch_fs *c, struct inode_walker *w,
+                    struct bkey_s_c inode)
 {
-       if (inum != w->cur_inum) {
-               int ret = lookup_inode(trans, inum, &w->inode, &w->snapshot);
+       struct bch_inode_unpacked u;
 
-               if (ret && ret != -ENOENT)
-                       return ret;
+       BUG_ON(bch2_inode_unpack(inode, &u));
 
-               w->have_inode   = !ret;
-               w->cur_inum     = inum;
-               w->first_this_inode = true;
-       } else {
-               w->first_this_inode = false;
+       return darray_push(&w->inodes, ((struct inode_walker_entry) {
+               .inode          = u,
+               .snapshot       = bch2_snapshot_equiv(c, inode.k->p.snapshot),
+       }));
+}
+
+static int get_inodes_all_snapshots(struct btree_trans *trans,
+                                   struct inode_walker *w, u64 inum)
+{
+       struct bch_fs *c = trans->c;
+       struct btree_iter iter;
+       struct bkey_s_c k;
+       int ret;
+
+       w->recalculate_sums = false;
+       w->inodes.nr = 0;
+
+       for_each_btree_key_norestart(trans, iter, BTREE_ID_inodes, POS(0, inum),
+                                    BTREE_ITER_ALL_SNAPSHOTS, k, ret) {
+               if (k.k->p.offset != inum)
+                       break;
+
+               if (bkey_is_inode(k.k))
+                       add_inode(c, w, k);
        }
+       bch2_trans_iter_exit(trans, &iter);
+
+       if (ret)
+               return ret;
 
+       w->first_this_inode = true;
        return 0;
 }
 
+static struct inode_walker_entry *
+lookup_inode_for_snapshot(struct bch_fs *c, struct inode_walker *w,
+                         u32 snapshot, bool is_whiteout)
+{
+       struct inode_walker_entry *i;
+
+       snapshot = bch2_snapshot_equiv(c, snapshot);
+
+       __darray_for_each(w->inodes, i)
+               if (bch2_snapshot_is_ancestor(c, snapshot, i->snapshot))
+                       goto found;
+
+       return NULL;
+found:
+       BUG_ON(snapshot > i->snapshot);
+
+       if (snapshot != i->snapshot && !is_whiteout) {
+               struct inode_walker_entry new = *i;
+               size_t pos;
+               int ret;
+
+               new.snapshot = snapshot;
+               new.count = 0;
+
+               bch_info(c, "have key for inode %llu:%u but have inode in ancestor snapshot %u",
+                        w->last_pos.inode, snapshot, i->snapshot);
+
+               while (i > w->inodes.data && i[-1].snapshot > snapshot)
+                       --i;
+
+               pos = i - w->inodes.data;
+               ret = darray_insert_item(&w->inodes, pos, new);
+               if (ret)
+                       return ERR_PTR(ret);
+
+               i = w->inodes.data + pos;
+       }
+
+       return i;
+}
+
+static struct inode_walker_entry *walk_inode(struct btree_trans *trans,
+                                            struct inode_walker *w, struct bpos pos,
+                                            bool is_whiteout)
+{
+       if (w->last_pos.inode != pos.inode) {
+               int ret = get_inodes_all_snapshots(trans, w, pos.inode);
+               if (ret)
+                       return ERR_PTR(ret);
+       } else if (bkey_cmp(w->last_pos, pos)) {
+               darray_for_each(w->inodes, i)
+                       i->seen_this_pos = false;
+       }
+
+       w->last_pos = pos;
+
+       return lookup_inode_for_snapshot(trans->c, w, pos.snapshot, is_whiteout);
+}
+
+static int __get_visible_inodes(struct btree_trans *trans,
+                               struct inode_walker *w,
+                               struct snapshots_seen *s,
+                               u64 inum)
+{
+       struct bch_fs *c = trans->c;
+       struct btree_iter iter;
+       struct bkey_s_c k;
+       int ret;
+
+       w->inodes.nr = 0;
+
+       for_each_btree_key_norestart(trans, iter, BTREE_ID_inodes, POS(0, inum),
+                          BTREE_ITER_ALL_SNAPSHOTS, k, ret) {
+               u32 equiv = bch2_snapshot_equiv(c, k.k->p.snapshot);
+
+               if (k.k->p.offset != inum)
+                       break;
+
+               if (!ref_visible(c, s, s->pos.snapshot, equiv))
+                       continue;
+
+               if (bkey_is_inode(k.k))
+                       add_inode(c, w, k);
+
+               if (equiv >= s->pos.snapshot)
+                       break;
+       }
+       bch2_trans_iter_exit(trans, &iter);
+
+       return ret;
+}
+
+static int check_key_has_snapshot(struct btree_trans *trans,
+                                 struct btree_iter *iter,
+                                 struct bkey_s_c k)
+{
+       struct bch_fs *c = trans->c;
+       struct printbuf buf = PRINTBUF;
+       int ret = 0;
+
+       if (mustfix_fsck_err_on(!bch2_snapshot_equiv(c, k.k->p.snapshot), c,
+                               bkey_in_missing_snapshot,
+                               "key in missing snapshot: %s",
+                               (bch2_bkey_val_to_text(&buf, c, k), buf.buf)))
+               ret = bch2_btree_delete_at(trans, iter,
+                                           BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE) ?: 1;
+fsck_err:
+       printbuf_exit(&buf);
+       return ret;
+}
+
 static int hash_redo_key(struct btree_trans *trans,
                         const struct bch_hash_desc desc,
                         struct bch_hash_info *hash_info,
@@ -298,37 +713,20 @@ static int hash_redo_key(struct btree_trans *trans,
        if (IS_ERR(delete))
                return PTR_ERR(delete);
 
-       tmp = bch2_trans_kmalloc(trans, bkey_bytes(k.k));
+       tmp = bch2_bkey_make_mut_noupdate(trans, k);
        if (IS_ERR(tmp))
                return PTR_ERR(tmp);
 
-       bkey_reassemble(tmp, k);
-
        bkey_init(&delete->k);
        delete->k.p = k_iter->pos;
        return  bch2_btree_iter_traverse(k_iter) ?:
                bch2_trans_update(trans, k_iter, delete, 0) ?:
-               bch2_hash_set(trans, desc, hash_info, k_iter->pos.inode, tmp, 0);
-}
-
-static int fsck_hash_delete_at(struct btree_trans *trans,
-                              const struct bch_hash_desc desc,
-                              struct bch_hash_info *info,
-                              struct btree_iter *iter)
-{
-       int ret;
-retry:
-       ret   = bch2_hash_delete_at(trans, desc, info, iter) ?:
-               bch2_trans_commit(trans, NULL, NULL,
-                                 BTREE_INSERT_NOFAIL|
-                                 BTREE_INSERT_LAZY_RW);
-       if (ret == -EINTR) {
-               ret = bch2_btree_iter_traverse(iter);
-               if (!ret)
-                       goto retry;
-       }
-
-       return ret;
+               bch2_hash_set_snapshot(trans, desc, hash_info,
+                                      (subvol_inum) { 0, k.k->p.inode },
+                                      k.k->p.snapshot, tmp,
+                                      BCH_HASH_SET_MUST_CREATE,
+                                      BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE) ?:
+               bch2_trans_commit(trans, NULL, NULL, BCH_TRANS_COMMIT_no_enospc);
 }
 
 static int hash_check_key(struct btree_trans *trans,
@@ -337,8 +735,8 @@ static int hash_check_key(struct btree_trans *trans,
                          struct btree_iter *k_iter, struct bkey_s_c hash_k)
 {
        struct bch_fs *c = trans->c;
-       struct btree_iter *iter = NULL;
-       char buf[200];
+       struct btree_iter iter = { NULL };
+       struct printbuf buf = PRINTBUF;
        struct bkey_s_c k;
        u64 hash;
        int ret = 0;
@@ -354,795 +752,1354 @@ static int hash_check_key(struct btree_trans *trans,
        if (hash_k.k->p.offset < hash)
                goto bad_hash;
 
-       for_each_btree_key(trans, iter, desc.btree_id, POS(hash_k.k->p.inode, hash),
-                          BTREE_ITER_SLOTS, k, ret) {
-               if (!bkey_cmp(k.k->p, hash_k.k->p))
+       for_each_btree_key_norestart(trans, iter, desc.btree_id,
+                                    SPOS(hash_k.k->p.inode, hash, hash_k.k->p.snapshot),
+                                    BTREE_ITER_SLOTS, k, ret) {
+               if (bkey_eq(k.k->p, hash_k.k->p))
                        break;
 
                if (fsck_err_on(k.k->type == desc.key_type &&
                                !desc.cmp_bkey(k, hash_k), c,
+                               hash_table_key_duplicate,
                                "duplicate hash table keys:\n%s",
-                               (bch2_bkey_val_to_text(&PBUF(buf), c,
-                                                      hash_k), buf))) {
-                       ret = fsck_hash_delete_at(trans, desc, hash_info, k_iter);
-                       if (ret)
-                               return ret;
-                       ret = 1;
+                               (printbuf_reset(&buf),
+                                bch2_bkey_val_to_text(&buf, c, hash_k),
+                                buf.buf))) {
+                       ret = bch2_hash_delete_at(trans, desc, hash_info, k_iter, 0) ?: 1;
                        break;
                }
 
                if (bkey_deleted(k.k)) {
-                       bch2_trans_iter_free(trans, iter);
+                       bch2_trans_iter_exit(trans, &iter);
                        goto bad_hash;
                }
-
        }
-       bch2_trans_iter_free(trans, iter);
+out:
+       bch2_trans_iter_exit(trans, &iter);
+       printbuf_exit(&buf);
        return ret;
 bad_hash:
-       if (fsck_err(c, "hash table key at wrong offset: btree %u inode %llu offset %llu, "
-                    "hashed to %llu\n%s",
-                    desc.btree_id, hash_k.k->p.inode, hash_k.k->p.offset, hash,
-                    (bch2_bkey_val_to_text(&PBUF(buf), c, hash_k), buf)) == FSCK_ERR_IGNORE)
-               return 0;
-
-       ret = __bch2_trans_do(trans, NULL, NULL,
-                             BTREE_INSERT_NOFAIL|BTREE_INSERT_LAZY_RW,
-               hash_redo_key(trans, desc, hash_info, k_iter, hash_k));
-       if (ret) {
-               bch_err(c, "hash_redo_key err %i", ret);
-               return ret;
+       if (fsck_err(c, hash_table_key_wrong_offset,
+                    "hash table key at wrong offset: btree %s inode %llu offset %llu, hashed to %llu\n%s",
+                    bch2_btree_id_str(desc.btree_id), hash_k.k->p.inode, hash_k.k->p.offset, hash,
+                    (printbuf_reset(&buf),
+                     bch2_bkey_val_to_text(&buf, c, hash_k), buf.buf))) {
+               ret = hash_redo_key(trans, desc, hash_info, k_iter, hash_k);
+               bch_err_fn(c, ret);
+               if (ret)
+                       return ret;
+               ret = -BCH_ERR_transaction_restart_nested;
        }
-       return -EINTR;
 fsck_err:
-       return ret;
+       goto out;
 }
 
-static int check_inode(struct btree_trans *trans,
-                      struct btree_iter *iter,
-                      struct bkey_s_c_inode inode)
+static int check_inode_deleted_list(struct btree_trans *trans, struct bpos p)
+{
+       struct btree_iter iter;
+       struct bkey_s_c k = bch2_bkey_get_iter(trans, &iter, BTREE_ID_deleted_inodes, p, 0);
+       int ret = bkey_err(k);
+       if (ret)
+               return ret;
+
+       bch2_trans_iter_exit(trans, &iter);
+       return k.k->type == KEY_TYPE_set;
+}
+
+static int check_inode(struct btree_trans *trans,
+                      struct btree_iter *iter,
+                      struct bkey_s_c k,
+                      struct bch_inode_unpacked *prev,
+                      struct snapshots_seen *s,
+                      bool full)
 {
        struct bch_fs *c = trans->c;
        struct bch_inode_unpacked u;
        bool do_update = false;
-       int ret = 0;
+       int ret;
 
-       ret = bch2_inode_unpack(inode, &u);
+       ret = check_key_has_snapshot(trans, iter, k);
+       if (ret < 0)
+               goto err;
+       if (ret)
+               return 0;
 
-       if (bch2_fs_inconsistent_on(ret, c,
-                        "error unpacking inode %llu in fsck",
-                        inode.k->p.inode))
-               return ret;
+       ret = snapshots_seen_update(c, s, iter->btree_id, k.k->p);
+       if (ret)
+               goto err;
 
-       if (u.bi_flags & BCH_INODE_UNLINKED &&
-           (!c->sb.clean ||
-            fsck_err(c, "filesystem marked clean, but inode %llu unlinked",
-                     u.bi_inum))) {
-               bch_verbose(c, "deleting inode %llu", u.bi_inum);
+       if (!bkey_is_inode(k.k))
+               return 0;
+
+       BUG_ON(bch2_inode_unpack(k, &u));
+
+       if (!full &&
+           !(u.bi_flags & (BCH_INODE_i_size_dirty|
+                           BCH_INODE_i_sectors_dirty|
+                           BCH_INODE_unlinked)))
+               return 0;
+
+       if (prev->bi_inum != u.bi_inum)
+               *prev = u;
+
+       if (fsck_err_on(prev->bi_hash_seed      != u.bi_hash_seed ||
+                       inode_d_type(prev)      != inode_d_type(&u),
+                       c, inode_snapshot_mismatch,
+                       "inodes in different snapshots don't match")) {
+               bch_err(c, "repair not implemented yet");
+               return -BCH_ERR_fsck_repair_unimplemented;
+       }
+
+       if ((u.bi_flags & (BCH_INODE_i_size_dirty|BCH_INODE_unlinked)) &&
+           bch2_key_has_snapshot_overwrites(trans, BTREE_ID_inodes, k.k->p)) {
+               struct bpos new_min_pos;
+
+               ret = bch2_propagate_key_to_snapshot_leaves(trans, iter->btree_id, k, &new_min_pos);
+               if (ret)
+                       goto err;
 
-               bch2_trans_unlock(trans);
-               bch2_fs_lazy_rw(c);
+               u.bi_flags &= ~BCH_INODE_i_size_dirty|BCH_INODE_unlinked;
 
-               ret = bch2_inode_rm(c, u.bi_inum, false);
+               ret = __write_inode(trans, &u, iter->pos.snapshot);
+               bch_err_msg(c, ret, "in fsck updating inode");
                if (ret)
-                       bch_err(c, "error in fsck: error %i while deleting inode", ret);
+                       return ret;
+
+               if (!bpos_eq(new_min_pos, POS_MIN))
+                       bch2_btree_iter_set_pos(iter, bpos_predecessor(new_min_pos));
+               return 0;
+       }
+
+       if (u.bi_flags & BCH_INODE_unlinked) {
+               ret = check_inode_deleted_list(trans, k.k->p);
+               if (ret < 0)
+                       return ret;
+
+               fsck_err_on(ret, c, unlinked_inode_not_on_deleted_list,
+                           "inode %llu:%u unlinked, but not on deleted list",
+                           u.bi_inum, k.k->p.snapshot);
+               ret = 0;
+       }
+
+       if (u.bi_flags & BCH_INODE_unlinked &&
+           (!c->sb.clean ||
+            fsck_err(c, inode_unlinked_but_clean,
+                     "filesystem marked clean, but inode %llu unlinked",
+                     u.bi_inum))) {
+               ret = bch2_inode_rm_snapshot(trans, u.bi_inum, iter->pos.snapshot);
+               bch_err_msg(c, ret, "in fsck deleting inode");
                return ret;
        }
 
-       if (u.bi_flags & BCH_INODE_I_SIZE_DIRTY &&
+       if (u.bi_flags & BCH_INODE_i_size_dirty &&
            (!c->sb.clean ||
-            fsck_err(c, "filesystem marked clean, but inode %llu has i_size dirty",
+            fsck_err(c, inode_i_size_dirty_but_clean,
+                     "filesystem marked clean, but inode %llu has i_size dirty",
                      u.bi_inum))) {
                bch_verbose(c, "truncating inode %llu", u.bi_inum);
 
-               bch2_trans_unlock(trans);
-               bch2_fs_lazy_rw(c);
-
                /*
                 * XXX: need to truncate partial blocks too here - or ideally
                 * just switch units to bytes and that issue goes away
                 */
                ret = bch2_btree_delete_range_trans(trans, BTREE_ID_extents,
-                               POS(u.bi_inum, round_up(u.bi_size, block_bytes(c)) >> 9),
+                               SPOS(u.bi_inum, round_up(u.bi_size, block_bytes(c)) >> 9,
+                                    iter->pos.snapshot),
                                POS(u.bi_inum, U64_MAX),
-                               NULL);
-               if (ret) {
-                       bch_err(c, "error in fsck: error %i truncating inode", ret);
+                               0, NULL);
+               bch_err_msg(c, ret, "in fsck truncating inode");
+               if (ret)
                        return ret;
-               }
 
                /*
                 * We truncated without our normal sector accounting hook, just
                 * make sure we recalculate it:
                 */
-               u.bi_flags |= BCH_INODE_I_SECTORS_DIRTY;
+               u.bi_flags |= BCH_INODE_i_sectors_dirty;
 
-               u.bi_flags &= ~BCH_INODE_I_SIZE_DIRTY;
+               u.bi_flags &= ~BCH_INODE_i_size_dirty;
                do_update = true;
        }
 
-       if (u.bi_flags & BCH_INODE_I_SECTORS_DIRTY &&
+       if (u.bi_flags & BCH_INODE_i_sectors_dirty &&
            (!c->sb.clean ||
-            fsck_err(c, "filesystem marked clean, but inode %llu has i_sectors dirty",
+            fsck_err(c, inode_i_sectors_dirty_but_clean,
+                     "filesystem marked clean, but inode %llu has i_sectors dirty",
                      u.bi_inum))) {
                s64 sectors;
 
                bch_verbose(c, "recounting sectors for inode %llu",
                            u.bi_inum);
 
-               sectors = bch2_count_inode_sectors(trans, u.bi_inum);
+               sectors = bch2_count_inode_sectors(trans, u.bi_inum, iter->pos.snapshot);
                if (sectors < 0) {
-                       bch_err(c, "error in fsck: error %i recounting inode sectors",
-                               (int) sectors);
+                       bch_err_msg(c, sectors, "in fsck recounting inode sectors");
                        return sectors;
                }
 
                u.bi_sectors = sectors;
-               u.bi_flags &= ~BCH_INODE_I_SECTORS_DIRTY;
+               u.bi_flags &= ~BCH_INODE_i_sectors_dirty;
                do_update = true;
        }
 
-       if (u.bi_flags & BCH_INODE_BACKPTR_UNTRUSTED) {
+       if (u.bi_flags & BCH_INODE_backptr_untrusted) {
                u.bi_dir = 0;
                u.bi_dir_offset = 0;
-               u.bi_flags &= ~BCH_INODE_BACKPTR_UNTRUSTED;
+               u.bi_flags &= ~BCH_INODE_backptr_untrusted;
                do_update = true;
        }
 
        if (do_update) {
-               ret = __bch2_trans_do(trans, NULL, NULL,
-                                     BTREE_INSERT_NOFAIL|
-                                     BTREE_INSERT_LAZY_RW,
-                               bch2_btree_iter_traverse(iter) ?:
-                               bch2_inode_write(trans, iter, &u));
+               ret = __write_inode(trans, &u, iter->pos.snapshot);
+               bch_err_msg(c, ret, "in fsck updating inode");
                if (ret)
-                       bch_err(c, "error in fsck: error %i "
-                               "updating inode", ret);
+                       return ret;
        }
+err:
 fsck_err:
+       bch_err_fn(c, ret);
        return ret;
 }
 
-noinline_for_stack
-static int check_inodes(struct bch_fs *c, bool full)
+int bch2_check_inodes(struct bch_fs *c)
 {
-       struct btree_trans trans;
-       struct btree_iter *iter;
-       struct bkey_s_c k;
-       struct bkey_s_c_inode inode;
-       int ret;
+       bool full = c->opts.fsck;
+       struct bch_inode_unpacked prev = { 0 };
+       struct snapshots_seen s;
 
-       bch2_trans_init(&trans, c, BTREE_ITER_MAX, 0);
+       snapshots_seen_init(&s);
+
+       int ret = bch2_trans_run(c,
+               for_each_btree_key_commit(trans, iter, BTREE_ID_inodes,
+                               POS_MIN,
+                               BTREE_ITER_PREFETCH|BTREE_ITER_ALL_SNAPSHOTS, k,
+                               NULL, NULL, BCH_TRANS_COMMIT_no_enospc,
+                       check_inode(trans, &iter, k, &prev, &s, full)));
+
+       snapshots_seen_exit(&s);
+       bch_err_fn(c, ret);
+       return ret;
+}
 
-       for_each_btree_key(&trans, iter, BTREE_ID_inodes, POS_MIN,
-                          BTREE_ITER_INTENT|
-                          BTREE_ITER_PREFETCH, k, ret) {
-               if (k.k->type != KEY_TYPE_inode)
+static struct bkey_s_c_dirent dirent_get_by_pos(struct btree_trans *trans,
+                                               struct btree_iter *iter,
+                                               struct bpos pos)
+{
+       return bch2_bkey_get_iter_typed(trans, iter, BTREE_ID_dirents, pos, 0, dirent);
+}
+
+static bool inode_points_to_dirent(struct bch_inode_unpacked *inode,
+                                  struct bkey_s_c_dirent d)
+{
+       return  inode->bi_dir           == d.k->p.inode &&
+               inode->bi_dir_offset    == d.k->p.offset;
+}
+
+static bool dirent_points_to_inode(struct bkey_s_c_dirent d,
+                                  struct bch_inode_unpacked *inode)
+{
+       return d.v->d_type == DT_SUBVOL
+               ? le32_to_cpu(d.v->d_child_subvol)      == inode->bi_subvol
+               : le64_to_cpu(d.v->d_inum)              == inode->bi_inum;
+}
+
+static int check_i_sectors(struct btree_trans *trans, struct inode_walker *w)
+{
+       struct bch_fs *c = trans->c;
+       u32 restart_count = trans->restart_count;
+       int ret = 0;
+       s64 count2;
+
+       darray_for_each(w->inodes, i) {
+               if (i->inode.bi_sectors == i->count)
                        continue;
 
-               inode = bkey_s_c_to_inode(k);
+               count2 = bch2_count_inode_sectors(trans, w->last_pos.inode, i->snapshot);
 
-               if (full ||
-                   (inode.v->bi_flags & (BCH_INODE_I_SIZE_DIRTY|
-                                         BCH_INODE_I_SECTORS_DIRTY|
-                                         BCH_INODE_UNLINKED))) {
-                       ret = check_inode(&trans, iter, inode);
+               if (w->recalculate_sums)
+                       i->count = count2;
+
+               if (i->count != count2) {
+                       bch_err(c, "fsck counted i_sectors wrong for inode %llu:%u: got %llu should be %llu",
+                               w->last_pos.inode, i->snapshot, i->count, count2);
+                       return -BCH_ERR_internal_fsck_err;
+               }
+
+               if (fsck_err_on(!(i->inode.bi_flags & BCH_INODE_i_sectors_dirty),
+                               c, inode_i_sectors_wrong,
+                               "inode %llu:%u has incorrect i_sectors: got %llu, should be %llu",
+                               w->last_pos.inode, i->snapshot,
+                               i->inode.bi_sectors, i->count)) {
+                       i->inode.bi_sectors = i->count;
+                       ret = fsck_write_inode(trans, &i->inode, i->snapshot);
                        if (ret)
                                break;
                }
        }
-       bch2_trans_iter_put(&trans, iter);
+fsck_err:
+       bch_err_fn(c, ret);
+       return ret ?: trans_was_restarted(trans, restart_count);
+}
+
+struct extent_end {
+       u32                     snapshot;
+       u64                     offset;
+       struct snapshots_seen   seen;
+};
+
+struct extent_ends {
+       struct bpos                     last_pos;
+       DARRAY(struct extent_end)       e;
+};
+
+static void extent_ends_reset(struct extent_ends *extent_ends)
+{
+       darray_for_each(extent_ends->e, i)
+               snapshots_seen_exit(&i->seen);
+       extent_ends->e.nr = 0;
+}
+
+static void extent_ends_exit(struct extent_ends *extent_ends)
+{
+       extent_ends_reset(extent_ends);
+       darray_exit(&extent_ends->e);
+}
+
+static void extent_ends_init(struct extent_ends *extent_ends)
+{
+       memset(extent_ends, 0, sizeof(*extent_ends));
+}
+
+static int extent_ends_at(struct bch_fs *c,
+                         struct extent_ends *extent_ends,
+                         struct snapshots_seen *seen,
+                         struct bkey_s_c k)
+{
+       struct extent_end *i, n = (struct extent_end) {
+               .offset         = k.k->p.offset,
+               .snapshot       = k.k->p.snapshot,
+               .seen           = *seen,
+       };
 
-       BUG_ON(ret == -EINTR);
+       n.seen.ids.data = kmemdup(seen->ids.data,
+                             sizeof(seen->ids.data[0]) * seen->ids.size,
+                             GFP_KERNEL);
+       if (!n.seen.ids.data)
+               return -BCH_ERR_ENOMEM_fsck_extent_ends_at;
+
+       __darray_for_each(extent_ends->e, i) {
+               if (i->snapshot == k.k->p.snapshot) {
+                       snapshots_seen_exit(&i->seen);
+                       *i = n;
+                       return 0;
+               }
 
-       return bch2_trans_exit(&trans) ?: ret;
+               if (i->snapshot >= k.k->p.snapshot)
+                       break;
+       }
+
+       return darray_insert_item(&extent_ends->e, i - extent_ends->e.data, n);
 }
 
-static int fix_overlapping_extent(struct btree_trans *trans,
-                                      struct bkey_s_c k, struct bpos cut_at)
+static int overlapping_extents_found(struct btree_trans *trans,
+                                    enum btree_id btree,
+                                    struct bpos pos1, struct snapshots_seen *pos1_seen,
+                                    struct bkey pos2,
+                                    bool *fixed,
+                                    struct extent_end *extent_end)
 {
-       struct btree_iter *iter;
-       struct bkey_i *u;
+       struct bch_fs *c = trans->c;
+       struct printbuf buf = PRINTBUF;
+       struct btree_iter iter1, iter2 = { NULL };
+       struct bkey_s_c k1, k2;
        int ret;
 
-       u = bch2_trans_kmalloc(trans, bkey_bytes(k.k));
-       ret = PTR_ERR_OR_ZERO(u);
+       BUG_ON(bkey_le(pos1, bkey_start_pos(&pos2)));
+
+       bch2_trans_iter_init(trans, &iter1, btree, pos1,
+                            BTREE_ITER_ALL_SNAPSHOTS|
+                            BTREE_ITER_NOT_EXTENTS);
+       k1 = bch2_btree_iter_peek_upto(&iter1, POS(pos1.inode, U64_MAX));
+       ret = bkey_err(k1);
        if (ret)
-               return ret;
+               goto err;
 
-       bkey_reassemble(u, k);
-       bch2_cut_front(cut_at, u);
+       prt_str(&buf, "\n  ");
+       bch2_bkey_val_to_text(&buf, c, k1);
 
+       if (!bpos_eq(pos1, k1.k->p)) {
+               prt_str(&buf, "\n  wanted\n  ");
+               bch2_bpos_to_text(&buf, pos1);
+               prt_str(&buf, "\n  ");
+               bch2_bkey_to_text(&buf, &pos2);
 
-       /*
-        * We don't want to go through the extent_handle_overwrites path:
-        *
-        * XXX: this is going to screw up disk accounting, extent triggers
-        * assume things about extent overwrites - we should be running the
-        * triggers manually here
-        */
-       iter = bch2_trans_get_iter(trans, BTREE_ID_extents, u->k.p,
-                                  BTREE_ITER_INTENT|BTREE_ITER_NOT_EXTENTS);
-
-       BUG_ON(iter->flags & BTREE_ITER_IS_EXTENTS);
-       ret   = bch2_btree_iter_traverse(iter) ?:
-               bch2_trans_update(trans, iter, u, BTREE_TRIGGER_NORUN) ?:
-               bch2_trans_commit(trans, NULL, NULL,
-                                 BTREE_INSERT_NOFAIL|
-                                 BTREE_INSERT_LAZY_RW);
-       bch2_trans_iter_put(trans, iter);
+               bch_err(c, "%s: error finding first overlapping extent when repairing, got%s",
+                       __func__, buf.buf);
+               ret = -BCH_ERR_internal_fsck_err;
+               goto err;
+       }
+
+       bch2_trans_copy_iter(&iter2, &iter1);
+
+       while (1) {
+               bch2_btree_iter_advance(&iter2);
+
+               k2 = bch2_btree_iter_peek_upto(&iter2, POS(pos1.inode, U64_MAX));
+               ret = bkey_err(k2);
+               if (ret)
+                       goto err;
+
+               if (bpos_ge(k2.k->p, pos2.p))
+                       break;
+       }
+
+       prt_str(&buf, "\n  ");
+       bch2_bkey_val_to_text(&buf, c, k2);
+
+       if (bpos_gt(k2.k->p, pos2.p) ||
+           pos2.size != k2.k->size) {
+               bch_err(c, "%s: error finding seconding overlapping extent when repairing%s",
+                       __func__, buf.buf);
+               ret = -BCH_ERR_internal_fsck_err;
+               goto err;
+       }
+
+       prt_printf(&buf, "\n  overwriting %s extent",
+                  pos1.snapshot >= pos2.p.snapshot ? "first" : "second");
+
+       if (fsck_err(c, extent_overlapping,
+                    "overlapping extents%s", buf.buf)) {
+               struct btree_iter *old_iter = &iter1;
+               struct disk_reservation res = { 0 };
+
+               if (pos1.snapshot < pos2.p.snapshot) {
+                       old_iter = &iter2;
+                       swap(k1, k2);
+               }
+
+               trans->extra_disk_res += bch2_bkey_sectors_compressed(k2);
+
+               ret =   bch2_trans_update_extent_overwrite(trans, old_iter,
+                               BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE,
+                               k1, k2) ?:
+                       bch2_trans_commit(trans, &res, NULL, BCH_TRANS_COMMIT_no_enospc);
+               bch2_disk_reservation_put(c, &res);
+
+               if (ret)
+                       goto err;
+
+               *fixed = true;
+
+               if (pos1.snapshot == pos2.p.snapshot) {
+                       /*
+                        * We overwrote the first extent, and did the overwrite
+                        * in the same snapshot:
+                        */
+                       extent_end->offset = bkey_start_offset(&pos2);
+               } else if (pos1.snapshot > pos2.p.snapshot) {
+                       /*
+                        * We overwrote the first extent in pos2's snapshot:
+                        */
+                       ret = snapshots_seen_add_inorder(c, pos1_seen, pos2.p.snapshot);
+               } else {
+                       /*
+                        * We overwrote the second extent - restart
+                        * check_extent() from the top:
+                        */
+                       ret = -BCH_ERR_transaction_restart_nested;
+               }
+       }
+fsck_err:
+err:
+       bch2_trans_iter_exit(trans, &iter2);
+       bch2_trans_iter_exit(trans, &iter1);
+       printbuf_exit(&buf);
        return ret;
 }
 
-static int inode_backpointer_exists(struct btree_trans *trans,
-                                   struct bch_inode_unpacked *inode)
+static int check_overlapping_extents(struct btree_trans *trans,
+                             struct snapshots_seen *seen,
+                             struct extent_ends *extent_ends,
+                             struct bkey_s_c k,
+                             u32 equiv,
+                             struct btree_iter *iter,
+                             bool *fixed)
 {
-       struct btree_iter *iter;
-       struct bkey_s_c k;
-       int ret;
+       struct bch_fs *c = trans->c;
+       int ret = 0;
 
-       iter = bch2_trans_get_iter(trans, BTREE_ID_dirents,
-                                  POS(inode->bi_dir, inode->bi_dir_offset), 0);
-       k = bch2_btree_iter_peek_slot(iter);
-       ret = bkey_err(k);
+       /* transaction restart, running again */
+       if (bpos_eq(extent_ends->last_pos, k.k->p))
+               return 0;
+
+       if (extent_ends->last_pos.inode != k.k->p.inode)
+               extent_ends_reset(extent_ends);
+
+       darray_for_each(extent_ends->e, i) {
+               if (i->offset <= bkey_start_offset(k.k))
+                       continue;
+
+               if (!ref_visible2(c,
+                                 k.k->p.snapshot, seen,
+                                 i->snapshot, &i->seen))
+                       continue;
+
+               ret = overlapping_extents_found(trans, iter->btree_id,
+                                               SPOS(iter->pos.inode,
+                                                    i->offset,
+                                                    i->snapshot),
+                                               &i->seen,
+                                               *k.k, fixed, i);
+               if (ret)
+                       goto err;
+       }
+
+       ret = extent_ends_at(c, extent_ends, seen, k);
        if (ret)
-               goto out;
-       if (k.k->type != KEY_TYPE_dirent)
-               goto out;
+               goto err;
 
-       ret = le64_to_cpu(bkey_s_c_to_dirent(k).v->d_inum) == inode->bi_inum;
-out:
-       bch2_trans_iter_free(trans, iter);
+       extent_ends->last_pos = k.k->p;
+err:
        return ret;
 }
 
-static bool inode_backpointer_matches(struct bkey_s_c_dirent d,
-                                     struct bch_inode_unpacked *inode)
+static int check_extent_overbig(struct btree_trans *trans, struct btree_iter *iter,
+                               struct bkey_s_c k)
 {
-       return d.k->p.inode == inode->bi_dir &&
-               d.k->p.offset == inode->bi_dir_offset;
+       struct bch_fs *c = trans->c;
+       struct bkey_ptrs_c ptrs = bch2_bkey_ptrs_c(k);
+       struct bch_extent_crc_unpacked crc;
+       const union bch_extent_entry *i;
+       unsigned encoded_extent_max_sectors = c->opts.encoded_extent_max >> 9;
+
+       bkey_for_each_crc(k.k, ptrs, crc, i)
+               if (crc_is_encoded(crc) &&
+                   crc.uncompressed_size > encoded_extent_max_sectors) {
+                       struct printbuf buf = PRINTBUF;
+
+                       bch2_bkey_val_to_text(&buf, c, k);
+                       bch_err(c, "overbig encoded extent, please report this:\n  %s", buf.buf);
+                       printbuf_exit(&buf);
+               }
+
+       return 0;
+}
+
+static int check_extent(struct btree_trans *trans, struct btree_iter *iter,
+                       struct bkey_s_c k,
+                       struct inode_walker *inode,
+                       struct snapshots_seen *s,
+                       struct extent_ends *extent_ends)
+{
+       struct bch_fs *c = trans->c;
+       struct inode_walker_entry *i;
+       struct printbuf buf = PRINTBUF;
+       struct bpos equiv = k.k->p;
+       int ret = 0;
+
+       equiv.snapshot = bch2_snapshot_equiv(c, k.k->p.snapshot);
+
+       ret = check_key_has_snapshot(trans, iter, k);
+       if (ret) {
+               ret = ret < 0 ? ret : 0;
+               goto out;
+       }
+
+       if (inode->last_pos.inode != k.k->p.inode) {
+               ret = check_i_sectors(trans, inode);
+               if (ret)
+                       goto err;
+       }
+
+       i = walk_inode(trans, inode, equiv, k.k->type == KEY_TYPE_whiteout);
+       ret = PTR_ERR_OR_ZERO(i);
+       if (ret)
+               goto err;
+
+       ret = snapshots_seen_update(c, s, iter->btree_id, k.k->p);
+       if (ret)
+               goto err;
+
+       if (k.k->type != KEY_TYPE_whiteout) {
+               if (fsck_err_on(!i, c, extent_in_missing_inode,
+                               "extent in missing inode:\n  %s",
+                               (printbuf_reset(&buf),
+                                bch2_bkey_val_to_text(&buf, c, k), buf.buf)))
+                       goto delete;
+
+               if (fsck_err_on(i &&
+                               !S_ISREG(i->inode.bi_mode) &&
+                               !S_ISLNK(i->inode.bi_mode),
+                               c, extent_in_non_reg_inode,
+                               "extent in non regular inode mode %o:\n  %s",
+                               i->inode.bi_mode,
+                               (printbuf_reset(&buf),
+                                bch2_bkey_val_to_text(&buf, c, k), buf.buf)))
+                       goto delete;
+
+               ret = check_overlapping_extents(trans, s, extent_ends, k,
+                                               equiv.snapshot, iter,
+                                               &inode->recalculate_sums);
+               if (ret)
+                       goto err;
+       }
+
+       /*
+        * Check inodes in reverse order, from oldest snapshots to newest,
+        * starting from the inode that matches this extent's snapshot. If we
+        * didn't have one, iterate over all inodes:
+        */
+       if (!i)
+               i = inode->inodes.data + inode->inodes.nr - 1;
+
+       for (;
+            inode->inodes.data && i >= inode->inodes.data;
+            --i) {
+               if (i->snapshot > equiv.snapshot ||
+                   !key_visible_in_snapshot(c, s, i->snapshot, equiv.snapshot))
+                       continue;
+
+               if (k.k->type != KEY_TYPE_whiteout) {
+                       if (fsck_err_on(!(i->inode.bi_flags & BCH_INODE_i_size_dirty) &&
+                                       k.k->p.offset > round_up(i->inode.bi_size, block_bytes(c)) >> 9 &&
+                                       !bkey_extent_is_reservation(k),
+                                       c, extent_past_end_of_inode,
+                                       "extent type past end of inode %llu:%u, i_size %llu\n  %s",
+                                       i->inode.bi_inum, i->snapshot, i->inode.bi_size,
+                                       (bch2_bkey_val_to_text(&buf, c, k), buf.buf))) {
+                               struct btree_iter iter2;
+
+                               bch2_trans_copy_iter(&iter2, iter);
+                               bch2_btree_iter_set_snapshot(&iter2, i->snapshot);
+                               ret =   bch2_btree_iter_traverse(&iter2) ?:
+                                       bch2_btree_delete_at(trans, &iter2,
+                                               BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE);
+                               bch2_trans_iter_exit(trans, &iter2);
+                               if (ret)
+                                       goto err;
+
+                               iter->k.type = KEY_TYPE_whiteout;
+                       }
+
+                       if (bkey_extent_is_allocation(k.k))
+                               i->count += k.k->size;
+               }
+
+               i->seen_this_pos = true;
+       }
+out:
+err:
+fsck_err:
+       printbuf_exit(&buf);
+       bch_err_fn(c, ret);
+       return ret;
+delete:
+       ret = bch2_btree_delete_at(trans, iter, BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE);
+       goto out;
 }
 
 /*
  * Walk extents: verify that extents have a corresponding S_ISREG inode, and
  * that i_size an i_sectors are consistent
  */
-noinline_for_stack
-static int check_extents(struct bch_fs *c)
+int bch2_check_extents(struct bch_fs *c)
 {
        struct inode_walker w = inode_walker_init();
-       struct btree_trans trans;
-       struct btree_iter *iter;
-       struct bkey_s_c k;
-       struct bkey_buf prev;
-       u64 i_sectors = 0;
+       struct snapshots_seen s;
+       struct extent_ends extent_ends;
+       struct disk_reservation res = { 0 };
+
+       snapshots_seen_init(&s);
+       extent_ends_init(&extent_ends);
+
+       int ret = bch2_trans_run(c,
+               for_each_btree_key_commit(trans, iter, BTREE_ID_extents,
+                               POS(BCACHEFS_ROOT_INO, 0),
+                               BTREE_ITER_PREFETCH|BTREE_ITER_ALL_SNAPSHOTS, k,
+                               &res, NULL,
+                               BCH_TRANS_COMMIT_no_enospc, ({
+                       bch2_disk_reservation_put(c, &res);
+                       check_extent(trans, &iter, k, &w, &s, &extent_ends) ?:
+                       check_extent_overbig(trans, &iter, k);
+               })) ?:
+               check_i_sectors(trans, &w));
+
+       bch2_disk_reservation_put(c, &res);
+       extent_ends_exit(&extent_ends);
+       inode_walker_exit(&w);
+       snapshots_seen_exit(&s);
+
+       bch_err_fn(c, ret);
+       return ret;
+}
+
+int bch2_check_indirect_extents(struct bch_fs *c)
+{
+       struct disk_reservation res = { 0 };
+
+       int ret = bch2_trans_run(c,
+               for_each_btree_key_commit(trans, iter, BTREE_ID_reflink,
+                               POS_MIN,
+                               BTREE_ITER_PREFETCH, k,
+                               &res, NULL,
+                               BCH_TRANS_COMMIT_no_enospc, ({
+                       bch2_disk_reservation_put(c, &res);
+                       check_extent_overbig(trans, &iter, k);
+               })));
+
+       bch2_disk_reservation_put(c, &res);
+       bch_err_fn(c, ret);
+       return ret;
+}
+
+static int check_subdir_count(struct btree_trans *trans, struct inode_walker *w)
+{
+       struct bch_fs *c = trans->c;
+       u32 restart_count = trans->restart_count;
        int ret = 0;
+       s64 count2;
 
-       bch2_bkey_buf_init(&prev);
-       prev.k->k = KEY(0, 0, 0);
-       bch2_trans_init(&trans, c, BTREE_ITER_MAX, 0);
+       darray_for_each(w->inodes, i) {
+               if (i->inode.bi_nlink == i->count)
+                       continue;
 
-       bch_verbose(c, "checking extents");
+               count2 = bch2_count_subdirs(trans, w->last_pos.inode, i->snapshot);
+               if (count2 < 0)
+                       return count2;
 
-       iter = bch2_trans_get_iter(&trans, BTREE_ID_extents,
-                                  POS(BCACHEFS_ROOT_INO, 0),
-                                  BTREE_ITER_INTENT|
-                                  BTREE_ITER_PREFETCH);
-retry:
-       while ((k = bch2_btree_iter_peek(iter)).k &&
-              !(ret = bkey_err(k))) {
-               if (w.have_inode &&
-                   w.cur_inum != k.k->p.inode &&
-                   !(w.inode.bi_flags & BCH_INODE_I_SECTORS_DIRTY) &&
-                   fsck_err_on(w.inode.bi_sectors != i_sectors, c,
-                               "inode %llu has incorrect i_sectors: got %llu, should be %llu",
-                               w.inode.bi_inum,
-                               w.inode.bi_sectors, i_sectors)) {
-                       w.inode.bi_sectors = i_sectors;
-
-                       ret = write_inode(&trans, &w.inode, w.snapshot);
+               if (i->count != count2) {
+                       bch_err(c, "fsck counted subdirectories wrong: got %llu should be %llu",
+                               i->count, count2);
+                       i->count = count2;
+                       if (i->inode.bi_nlink == i->count)
+                               continue;
+               }
+
+               if (fsck_err_on(i->inode.bi_nlink != i->count,
+                               c, inode_dir_wrong_nlink,
+                               "directory %llu:%u with wrong i_nlink: got %u, should be %llu",
+                               w->last_pos.inode, i->snapshot, i->inode.bi_nlink, i->count)) {
+                       i->inode.bi_nlink = i->count;
+                       ret = fsck_write_inode(trans, &i->inode, i->snapshot);
                        if (ret)
                                break;
                }
+       }
+fsck_err:
+       bch_err_fn(c, ret);
+       return ret ?: trans_was_restarted(trans, restart_count);
+}
 
-               if (bkey_cmp(prev.k->k.p, bkey_start_pos(k.k)) > 0) {
-                       char buf1[200];
-                       char buf2[200];
-
-                       bch2_bkey_val_to_text(&PBUF(buf1), c, bkey_i_to_s_c(prev.k));
-                       bch2_bkey_val_to_text(&PBUF(buf2), c, k);
+static int check_dirent_target(struct btree_trans *trans,
+                              struct btree_iter *iter,
+                              struct bkey_s_c_dirent d,
+                              struct bch_inode_unpacked *target,
+                              u32 target_snapshot)
+{
+       struct bch_fs *c = trans->c;
+       struct bkey_i_dirent *n;
+       struct printbuf buf = PRINTBUF;
+       struct btree_iter bp_iter = { NULL };
+       int ret = 0;
 
-                       if (fsck_err(c, "overlapping extents:\n%s\n%s", buf1, buf2))
-                               return fix_overlapping_extent(&trans, k, prev.k->k.p) ?: -EINTR;
-               }
+       if (!target->bi_dir &&
+           !target->bi_dir_offset) {
+               target->bi_dir          = d.k->p.inode;
+               target->bi_dir_offset   = d.k->p.offset;
 
-               ret = walk_inode(&trans, &w, k.k->p.inode);
+               ret = __write_inode(trans, target, target_snapshot);
                if (ret)
-                       break;
+                       goto err;
+       }
+
+       if (!inode_points_to_dirent(target, d)) {
+               struct bkey_s_c_dirent bp_dirent = dirent_get_by_pos(trans, &bp_iter,
+                                     SPOS(target->bi_dir, target->bi_dir_offset, target_snapshot));
+               ret = bkey_err(bp_dirent);
+               if (ret && !bch2_err_matches(ret, ENOENT))
+                       goto err;
+
+               bool backpointer_exists = !ret;
+               ret = 0;
 
-               if (w.first_this_inode)
-                       i_sectors = 0;
-
-               if (fsck_err_on(!w.have_inode, c,
-                               "extent type %u for missing inode %llu",
-                               k.k->type, k.k->p.inode) ||
-                   fsck_err_on(w.have_inode &&
-                               !S_ISREG(w.inode.bi_mode) && !S_ISLNK(w.inode.bi_mode), c,
-                               "extent type %u for non regular file, inode %llu mode %o",
-                               k.k->type, k.k->p.inode, w.inode.bi_mode)) {
-                       bch2_fs_lazy_rw(c);
-                       return bch2_btree_delete_range_trans(&trans, BTREE_ID_extents,
-                                                      POS(k.k->p.inode, 0),
-                                                      POS(k.k->p.inode, U64_MAX),
-                                                      NULL) ?: -EINTR;
+               bch2_bkey_val_to_text(&buf, c, d.s_c);
+               prt_newline(&buf);
+               if (backpointer_exists)
+                       bch2_bkey_val_to_text(&buf, c, bp_dirent.s_c);
+
+               if (fsck_err_on(S_ISDIR(target->bi_mode) && backpointer_exists,
+                               c, inode_dir_multiple_links,
+                               "directory %llu:%u with multiple links\n%s",
+                               target->bi_inum, target_snapshot, buf.buf)) {
+                       ret = __remove_dirent(trans, d.k->p);
+                       goto out;
+               }
+
+               /*
+                * hardlinked file with nlink 0:
+                * We're just adjusting nlink here so check_nlinks() will pick
+                * it up, it ignores inodes with nlink 0
+                */
+               if (fsck_err_on(backpointer_exists && !target->bi_nlink,
+                               c, inode_multiple_links_but_nlink_0,
+                               "inode %llu:%u type %s has multiple links but i_nlink 0\n%s",
+                               target->bi_inum, target_snapshot, bch2_d_types[d.v->d_type], buf.buf)) {
+                       target->bi_nlink++;
+                       target->bi_flags &= ~BCH_INODE_unlinked;
+
+                       ret = __write_inode(trans, target, target_snapshot);
+                       if (ret)
+                               goto err;
                }
 
-               if (fsck_err_on(w.have_inode &&
-                               !(w.inode.bi_flags & BCH_INODE_I_SIZE_DIRTY) &&
-                               k.k->type != KEY_TYPE_reservation &&
-                               k.k->p.offset > round_up(w.inode.bi_size, block_bytes(c)) >> 9, c,
-                               "extent type %u offset %llu past end of inode %llu, i_size %llu",
-                               k.k->type, k.k->p.offset, k.k->p.inode, w.inode.bi_size)) {
-                       bch2_fs_lazy_rw(c);
-                       return bch2_btree_delete_range_trans(&trans, BTREE_ID_extents,
-                                       POS(k.k->p.inode, round_up(w.inode.bi_size, block_bytes(c)) >> 9),
-                                       POS(k.k->p.inode, U64_MAX),
-                                       NULL) ?: -EINTR;
+               if (fsck_err_on(!backpointer_exists,
+                               c, inode_wrong_backpointer,
+                               "inode %llu:%u has wrong backpointer:\n"
+                               "got       %llu:%llu\n"
+                               "should be %llu:%llu",
+                               target->bi_inum, target_snapshot,
+                               target->bi_dir,
+                               target->bi_dir_offset,
+                               d.k->p.inode,
+                               d.k->p.offset)) {
+                       target->bi_dir          = d.k->p.inode;
+                       target->bi_dir_offset   = d.k->p.offset;
+
+                       ret = __write_inode(trans, target, target_snapshot);
+                       if (ret)
+                               goto err;
                }
+       }
 
-               if (bkey_extent_is_allocation(k.k))
-                       i_sectors += k.k->size;
-               bch2_bkey_buf_reassemble(&prev, c, k);
+       if (fsck_err_on(d.v->d_type != inode_d_type(target),
+                       c, dirent_d_type_wrong,
+                       "incorrect d_type: got %s, should be %s:\n%s",
+                       bch2_d_type_str(d.v->d_type),
+                       bch2_d_type_str(inode_d_type(target)),
+                       (printbuf_reset(&buf),
+                        bch2_bkey_val_to_text(&buf, c, d.s_c), buf.buf))) {
+               n = bch2_trans_kmalloc(trans, bkey_bytes(d.k));
+               ret = PTR_ERR_OR_ZERO(n);
+               if (ret)
+                       goto err;
+
+               bkey_reassemble(&n->k_i, d.s_c);
+               n->v.d_type = inode_d_type(target);
+
+               ret = bch2_trans_update(trans, iter, &n->k_i, 0);
+               if (ret)
+                       goto err;
 
-               bch2_btree_iter_advance(iter);
+               d = dirent_i_to_s_c(n);
        }
+
+       if (fsck_err_on(d.v->d_type == DT_SUBVOL &&
+                       target->bi_parent_subvol != le32_to_cpu(d.v->d_parent_subvol),
+                       c, dirent_d_parent_subvol_wrong,
+                       "dirent has wrong d_parent_subvol field: got %u, should be %u",
+                       le32_to_cpu(d.v->d_parent_subvol),
+                       target->bi_parent_subvol)) {
+               n = bch2_trans_kmalloc(trans, bkey_bytes(d.k));
+               ret = PTR_ERR_OR_ZERO(n);
+               if (ret)
+                       goto err;
+
+               bkey_reassemble(&n->k_i, d.s_c);
+               n->v.d_parent_subvol = cpu_to_le32(target->bi_parent_subvol);
+
+               ret = bch2_trans_update(trans, iter, &n->k_i, 0);
+               if (ret)
+                       goto err;
+
+               d = dirent_i_to_s_c(n);
+       }
+out:
+err:
 fsck_err:
-       if (ret == -EINTR)
-               goto retry;
-       bch2_trans_iter_put(&trans, iter);
-       bch2_bkey_buf_exit(&prev, c);
-       return bch2_trans_exit(&trans) ?: ret;
+       bch2_trans_iter_exit(trans, &bp_iter);
+       printbuf_exit(&buf);
+       bch_err_fn(c, ret);
+       return ret;
 }
 
-/*
* Walk dirents: verify that they all have a corresponding S_ISDIR inode,
- * validate d_type
- */
-noinline_for_stack
-static int check_dirents(struct bch_fs *c)
+static int check_dirent(struct btree_trans *trans, struct btree_iter *iter,
                      struct bkey_s_c k,
+                       struct bch_hash_info *hash_info,
+                       struct inode_walker *dir,
+                       struct inode_walker *target,
+                       struct snapshots_seen *s)
 {
-       struct inode_walker w = inode_walker_init();
-       struct bch_hash_info hash_info;
-       struct btree_trans trans;
-       struct btree_iter *iter;
-       struct bkey_s_c k;
-       char buf[200];
-       unsigned nr_subdirs = 0;
+       struct bch_fs *c = trans->c;
+       struct bkey_s_c_dirent d;
+       struct inode_walker_entry *i;
+       struct printbuf buf = PRINTBUF;
+       struct bpos equiv;
        int ret = 0;
 
-       bch_verbose(c, "checking dirents");
+       ret = check_key_has_snapshot(trans, iter, k);
+       if (ret) {
+               ret = ret < 0 ? ret : 0;
+               goto out;
+       }
+
+       equiv = k.k->p;
+       equiv.snapshot = bch2_snapshot_equiv(c, k.k->p.snapshot);
+
+       ret = snapshots_seen_update(c, s, iter->btree_id, k.k->p);
+       if (ret)
+               goto err;
+
+       if (k.k->type == KEY_TYPE_whiteout)
+               goto out;
+
+       if (dir->last_pos.inode != k.k->p.inode) {
+               ret = check_subdir_count(trans, dir);
+               if (ret)
+                       goto err;
+       }
+
+       BUG_ON(!btree_iter_path(trans, iter)->should_be_locked);
+
+       i = walk_inode(trans, dir, equiv, k.k->type == KEY_TYPE_whiteout);
+       ret = PTR_ERR_OR_ZERO(i);
+       if (ret < 0)
+               goto err;
+
+       if (dir->first_this_inode && dir->inodes.nr)
+               *hash_info = bch2_hash_info_init(c, &dir->inodes.data[0].inode);
+       dir->first_this_inode = false;
+
+       if (fsck_err_on(!i, c, dirent_in_missing_dir_inode,
+                       "dirent in nonexisting directory:\n%s",
+                       (printbuf_reset(&buf),
+                        bch2_bkey_val_to_text(&buf, c, k), buf.buf))) {
+               ret = bch2_btree_delete_at(trans, iter,
+                               BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE);
+               goto out;
+       }
+
+       if (!i)
+               goto out;
+
+       if (fsck_err_on(!S_ISDIR(i->inode.bi_mode),
+                       c, dirent_in_non_dir_inode,
+                       "dirent in non directory inode type %s:\n%s",
+                       bch2_d_type_str(inode_d_type(&i->inode)),
+                       (printbuf_reset(&buf),
+                        bch2_bkey_val_to_text(&buf, c, k), buf.buf))) {
+               ret = bch2_btree_delete_at(trans, iter, 0);
+               goto out;
+       }
+
+       ret = hash_check_key(trans, bch2_dirent_hash_desc, hash_info, iter, k);
+       if (ret < 0)
+               goto err;
+       if (ret) {
+               /* dirent has been deleted */
+               ret = 0;
+               goto out;
+       }
+
+       if (k.k->type != KEY_TYPE_dirent)
+               goto out;
 
-       bch2_trans_init(&trans, c, BTREE_ITER_MAX, 0);
+       d = bkey_s_c_to_dirent(k);
 
-       iter = bch2_trans_get_iter(&trans, BTREE_ID_dirents,
-                                  POS(BCACHEFS_ROOT_INO, 0),
-                                  BTREE_ITER_INTENT|
-                                  BTREE_ITER_PREFETCH);
-retry:
-       while ((k = bch2_btree_iter_peek(iter)).k &&
-              !(ret = bkey_err(k))) {
-               struct bkey_s_c_dirent d;
-               struct bch_inode_unpacked target;
+       if (d.v->d_type == DT_SUBVOL) {
+               struct bch_inode_unpacked subvol_root;
+               u32 target_subvol = le32_to_cpu(d.v->d_child_subvol);
                u32 target_snapshot;
-               bool have_target;
-               bool backpointer_exists = true;
-               u64 d_inum;
-
-               if (w.have_inode &&
-                   w.cur_inum != k.k->p.inode &&
-                   fsck_err_on(w.inode.bi_nlink != nr_subdirs, c,
-                               "directory %llu with wrong i_nlink: got %u, should be %u",
-                               w.inode.bi_inum, w.inode.bi_nlink, nr_subdirs)) {
-                       w.inode.bi_nlink = nr_subdirs;
-                       ret = write_inode(&trans, &w.inode, w.snapshot);
-                       if (ret)
-                               break;
+               u64 target_inum;
+
+               ret = subvol_lookup(trans, target_subvol,
+                                     &target_snapshot, &target_inum);
+               if (ret && !bch2_err_matches(ret, ENOENT))
+                       goto err;
+
+               if (fsck_err_on(ret, c, dirent_to_missing_subvol,
+                               "dirent points to missing subvolume %u",
+                               le32_to_cpu(d.v->d_child_subvol))) {
+                       ret = __remove_dirent(trans, d.k->p);
+                       goto err;
                }
 
-               ret = walk_inode(&trans, &w, k.k->p.inode);
-               if (ret)
-                       break;
+               ret = lookup_inode(trans, target_inum,
+                                  &subvol_root, &target_snapshot);
+               if (ret && !bch2_err_matches(ret, ENOENT))
+                       goto err;
+
+               if (fsck_err_on(ret, c, subvol_to_missing_root,
+                               "subvolume %u points to missing subvolume root %llu",
+                               target_subvol,
+                               target_inum)) {
+                       bch_err(c, "repair not implemented yet");
+                       ret = -EINVAL;
+                       goto err;
+               }
 
-               if (w.first_this_inode)
-                       nr_subdirs = 0;
-
-               if (fsck_err_on(!w.have_inode, c,
-                               "dirent in nonexisting directory:\n%s",
-                               (bch2_bkey_val_to_text(&PBUF(buf), c,
-                                                      k), buf)) ||
-                   fsck_err_on(!S_ISDIR(w.inode.bi_mode), c,
-                               "dirent in non directory inode type %u:\n%s",
-                               mode_to_type(w.inode.bi_mode),
-                               (bch2_bkey_val_to_text(&PBUF(buf), c,
-                                                      k), buf))) {
-                       ret = __bch2_trans_do(&trans, NULL, NULL, 0,
-                                       bch2_btree_delete_at(&trans, iter, 0));
+               if (fsck_err_on(subvol_root.bi_subvol != target_subvol,
+                               c, subvol_root_wrong_bi_subvol,
+                               "subvol root %llu has wrong bi_subvol field: got %u, should be %u",
+                               target_inum,
+                               subvol_root.bi_subvol, target_subvol)) {
+                       subvol_root.bi_subvol = target_subvol;
+                       ret = __write_inode(trans, &subvol_root, target_snapshot);
                        if (ret)
                                goto err;
-                       goto next;
                }
 
-               if (!w.have_inode)
-                       goto next;
-
-               if (w.first_this_inode)
-                       hash_info = bch2_hash_info_init(c, &w.inode);
-
-               ret = hash_check_key(&trans, bch2_dirent_hash_desc,
-                                    &hash_info, iter, k);
-               if (ret > 0) {
-                       ret = 0;
-                       goto next;
-               }
+               ret = check_dirent_target(trans, iter, d, &subvol_root,
+                                         target_snapshot);
                if (ret)
-                       goto fsck_err;
-
-               if (k.k->type != KEY_TYPE_dirent)
-                       goto next;
-
-               d = bkey_s_c_to_dirent(k);
-               d_inum = le64_to_cpu(d.v->d_inum);
-
-               ret = lookup_inode(&trans, d_inum, &target, &target_snapshot);
-               if (ret && ret != -ENOENT)
-                       break;
-
-               have_target = !ret;
-               ret = 0;
-
-               if (fsck_err_on(!have_target, c,
-                               "dirent points to missing inode:\n%s",
-                               (bch2_bkey_val_to_text(&PBUF(buf), c,
-                                                      k), buf))) {
-                       ret = remove_dirent(&trans, d.k->p);
+                       goto err;
+       } else {
+               ret = __get_visible_inodes(trans, target, s, le64_to_cpu(d.v->d_inum));
+               if (ret)
+                       goto err;
+
+               if (fsck_err_on(!target->inodes.nr,
+                               c, dirent_to_missing_inode,
+                               "dirent points to missing inode: (equiv %u)\n%s",
+                               equiv.snapshot,
+                               (printbuf_reset(&buf),
+                                bch2_bkey_val_to_text(&buf, c, k),
+                                buf.buf))) {
+                       ret = __remove_dirent(trans, d.k->p);
                        if (ret)
                                goto err;
-                       goto next;
                }
 
-               if (!have_target)
-                       goto next;
-
-               if (!target.bi_dir &&
-                   !target.bi_dir_offset) {
-                       target.bi_dir           = k.k->p.inode;
-                       target.bi_dir_offset    = k.k->p.offset;
-
-                       ret = write_inode(&trans, &target, target_snapshot);
+               darray_for_each(target->inodes, i) {
+                       ret = check_dirent_target(trans, iter, d,
+                                                 &i->inode, i->snapshot);
                        if (ret)
                                goto err;
                }
+       }
 
-               if (!inode_backpointer_matches(d, &target)) {
-                       ret = inode_backpointer_exists(&trans, &target);
-                       if (ret < 0)
-                               goto err;
-
-                       backpointer_exists = ret;
-                       ret = 0;
+       if (d.v->d_type == DT_DIR)
+               for_each_visible_inode(c, s, dir, equiv.snapshot, i)
+                       i->count++;
 
-                       if (fsck_err_on(S_ISDIR(target.bi_mode) &&
-                                       backpointer_exists, c,
-                                       "directory %llu with multiple links",
-                                       target.bi_inum)) {
-                               ret = remove_dirent(&trans, d.k->p);
-                               if (ret)
-                                       goto err;
-                               continue;
-                       }
+out:
+err:
+fsck_err:
+       printbuf_exit(&buf);
+       bch_err_fn(c, ret);
+       return ret;
+}
 
-                       if (fsck_err_on(backpointer_exists &&
-                                       !target.bi_nlink, c,
-                                       "inode %llu has multiple links but i_nlink 0",
-                                       d_inum)) {
-                               target.bi_nlink++;
-                               target.bi_flags &= ~BCH_INODE_UNLINKED;
+/*
+ * Walk dirents: verify that they all have a corresponding S_ISDIR inode,
+ * validate d_type
+ */
+int bch2_check_dirents(struct bch_fs *c)
+{
+       struct inode_walker dir = inode_walker_init();
+       struct inode_walker target = inode_walker_init();
+       struct snapshots_seen s;
+       struct bch_hash_info hash_info;
 
-                               ret = write_inode(&trans, &target, target_snapshot);
-                               if (ret)
-                                       goto err;
-                       }
+       snapshots_seen_init(&s);
+
+       int ret = bch2_trans_run(c,
+               for_each_btree_key_commit(trans, iter, BTREE_ID_dirents,
+                               POS(BCACHEFS_ROOT_INO, 0),
+                               BTREE_ITER_PREFETCH|BTREE_ITER_ALL_SNAPSHOTS,
+                               k,
+                               NULL, NULL,
+                               BCH_TRANS_COMMIT_no_enospc,
+                       check_dirent(trans, &iter, k, &hash_info, &dir, &target, &s)));
+
+       snapshots_seen_exit(&s);
+       inode_walker_exit(&dir);
+       inode_walker_exit(&target);
+       bch_err_fn(c, ret);
+       return ret;
+}
 
-                       if (fsck_err_on(!backpointer_exists, c,
-                                       "inode %llu has wrong backpointer:\n"
-                                       "got       %llu:%llu\n"
-                                       "should be %llu:%llu",
-                                       d_inum,
-                                       target.bi_dir,
-                                       target.bi_dir_offset,
-                                       k.k->p.inode,
-                                       k.k->p.offset)) {
-                               target.bi_dir           = k.k->p.inode;
-                               target.bi_dir_offset    = k.k->p.offset;
-
-                               ret = write_inode(&trans, &target, target_snapshot);
-                               if (ret)
-                                       goto err;
-                       }
-               }
+static int check_xattr(struct btree_trans *trans, struct btree_iter *iter,
+                      struct bkey_s_c k,
+                      struct bch_hash_info *hash_info,
+                      struct inode_walker *inode)
+{
+       struct bch_fs *c = trans->c;
+       struct inode_walker_entry *i;
+       int ret;
 
-               if (fsck_err_on(d.v->d_type != mode_to_type(target.bi_mode), c,
-                               "incorrect d_type: should be %u:\n%s",
-                               mode_to_type(target.bi_mode),
-                               (bch2_bkey_val_to_text(&PBUF(buf), c,
-                                                      k), buf))) {
-                       struct bkey_i_dirent *n;
+       ret = check_key_has_snapshot(trans, iter, k);
+       if (ret)
+               return ret;
 
-                       n = kmalloc(bkey_bytes(d.k), GFP_KERNEL);
-                       if (!n) {
-                               ret = -ENOMEM;
-                               goto err;
-                       }
+       i = walk_inode(trans, inode, k.k->p, k.k->type == KEY_TYPE_whiteout);
+       ret = PTR_ERR_OR_ZERO(i);
+       if (ret)
+               return ret;
 
-                       bkey_reassemble(&n->k_i, d.s_c);
-                       n->v.d_type = mode_to_type(target.bi_mode);
+       if (inode->first_this_inode && inode->inodes.nr)
+               *hash_info = bch2_hash_info_init(c, &inode->inodes.data[0].inode);
+       inode->first_this_inode = false;
 
-                       ret = __bch2_trans_do(&trans, NULL, NULL,
-                                             BTREE_INSERT_NOFAIL|
-                                             BTREE_INSERT_LAZY_RW,
-                               bch2_btree_iter_traverse(iter) ?:
-                               bch2_trans_update(&trans, iter, &n->k_i, 0));
-                       kfree(n);
-                       if (ret)
-                               goto err;
+       if (fsck_err_on(!i, c, xattr_in_missing_inode,
+                       "xattr for missing inode %llu",
+                       k.k->p.inode))
+               return bch2_btree_delete_at(trans, iter, 0);
 
-               }
+       if (!i)
+               return 0;
 
-               nr_subdirs += d.v->d_type == DT_DIR;
-next:
-               bch2_btree_iter_advance(iter);
-       }
-err:
+       ret = hash_check_key(trans, bch2_xattr_hash_desc, hash_info, iter, k);
 fsck_err:
-       if (ret == -EINTR)
-               goto retry;
-
-       bch2_trans_iter_put(&trans, iter);
-       return bch2_trans_exit(&trans) ?: ret;
+       bch_err_fn(c, ret);
+       return ret;
 }
 
 /*
  * Walk xattrs: verify that they all have a corresponding inode
  */
-noinline_for_stack
-static int check_xattrs(struct bch_fs *c)
+int bch2_check_xattrs(struct bch_fs *c)
 {
-       struct inode_walker w = inode_walker_init();
+       struct inode_walker inode = inode_walker_init();
        struct bch_hash_info hash_info;
-       struct btree_trans trans;
-       struct btree_iter *iter;
-       struct bkey_s_c k;
        int ret = 0;
 
-       bch_verbose(c, "checking xattrs");
+       ret = bch2_trans_run(c,
+               for_each_btree_key_commit(trans, iter, BTREE_ID_xattrs,
+                       POS(BCACHEFS_ROOT_INO, 0),
+                       BTREE_ITER_PREFETCH|BTREE_ITER_ALL_SNAPSHOTS,
+                       k,
+                       NULL, NULL,
+                       BCH_TRANS_COMMIT_no_enospc,
+               check_xattr(trans, &iter, k, &hash_info, &inode)));
+       bch_err_fn(c, ret);
+       return ret;
+}
 
-       bch2_trans_init(&trans, c, BTREE_ITER_MAX, 0);
+static int check_root_trans(struct btree_trans *trans)
+{
+       struct bch_fs *c = trans->c;
+       struct bch_inode_unpacked root_inode;
+       u32 snapshot;
+       u64 inum;
+       int ret;
 
-       iter = bch2_trans_get_iter(&trans, BTREE_ID_xattrs,
-                                  POS(BCACHEFS_ROOT_INO, 0),
-                                  BTREE_ITER_INTENT|
-                                  BTREE_ITER_PREFETCH);
-retry:
-       while ((k = bch2_btree_iter_peek(iter)).k &&
-              !(ret = bkey_err(k))) {
-               ret = walk_inode(&trans, &w, k.k->p.inode);
-               if (ret)
-                       break;
+       ret = subvol_lookup(trans, BCACHEFS_ROOT_SUBVOL, &snapshot, &inum);
+       if (ret && !bch2_err_matches(ret, ENOENT))
+               return ret;
 
-               if (fsck_err_on(!w.have_inode, c,
-                               "xattr for missing inode %llu",
-                               k.k->p.inode)) {
-                       ret = bch2_btree_delete_at(&trans, iter, 0);
-                       if (ret)
-                               break;
-                       continue;
-               }
+       if (mustfix_fsck_err_on(ret, c, root_subvol_missing,
+                               "root subvol missing")) {
+               struct bkey_i_subvolume root_subvol;
 
-               if (w.first_this_inode && w.have_inode)
-                       hash_info = bch2_hash_info_init(c, &w.inode);
+               snapshot        = U32_MAX;
+               inum            = BCACHEFS_ROOT_INO;
 
-               ret = hash_check_key(&trans, bch2_xattr_hash_desc,
-                                    &hash_info, iter, k);
+               bkey_subvolume_init(&root_subvol.k_i);
+               root_subvol.k.p.offset = BCACHEFS_ROOT_SUBVOL;
+               root_subvol.v.flags     = 0;
+               root_subvol.v.snapshot  = cpu_to_le32(snapshot);
+               root_subvol.v.inode     = cpu_to_le64(inum);
+               ret = bch2_btree_insert_trans(trans, BTREE_ID_subvolumes, &root_subvol.k_i, 0);
+               bch_err_msg(c, ret, "writing root subvol");
                if (ret)
-                       break;
+                       goto err;
+       }
+
+       ret = lookup_inode(trans, BCACHEFS_ROOT_INO, &root_inode, &snapshot);
+       if (ret && !bch2_err_matches(ret, ENOENT))
+               return ret;
 
-               bch2_btree_iter_advance(iter);
+       if (mustfix_fsck_err_on(ret, c, root_dir_missing,
+                               "root directory missing") ||
+           mustfix_fsck_err_on(!S_ISDIR(root_inode.bi_mode),
+                               c, root_inode_not_dir,
+                               "root inode not a directory")) {
+               bch2_inode_init(c, &root_inode, 0, 0, S_IFDIR|0755,
+                               0, NULL);
+               root_inode.bi_inum = inum;
+
+               ret = __write_inode(trans, &root_inode, snapshot);
+               bch_err_msg(c, ret, "writing root inode");
        }
+err:
 fsck_err:
-       if (ret == -EINTR)
-               goto retry;
-
-       bch2_trans_iter_put(&trans, iter);
-       return bch2_trans_exit(&trans) ?: ret;
+       return ret;
 }
 
 /* Get root directory, create if it doesn't exist: */
-static int check_root(struct bch_fs *c, struct bch_inode_unpacked *root_inode)
+int bch2_check_root(struct bch_fs *c)
 {
-       struct bkey_inode_buf packed;
-       u32 snapshot;
-       int ret;
-
-       bch_verbose(c, "checking root directory");
-
-       ret = bch2_trans_do(c, NULL, NULL, 0,
-               lookup_inode(&trans, BCACHEFS_ROOT_INO, root_inode, &snapshot));
-       if (ret && ret != -ENOENT)
-               return ret;
-
-       if (fsck_err_on(ret, c, "root directory missing"))
-               goto create_root;
-
-       if (fsck_err_on(!S_ISDIR(root_inode->bi_mode), c,
-                       "root inode not a directory"))
-               goto create_root;
-
-       return 0;
-fsck_err:
+       int ret = bch2_trans_do(c, NULL, NULL, BCH_TRANS_COMMIT_no_enospc,
+               check_root_trans(trans));
+       bch_err_fn(c, ret);
        return ret;
-create_root:
-       bch2_inode_init(c, root_inode, 0, 0, S_IFDIR|0755,
-                       0, NULL);
-       root_inode->bi_inum = BCACHEFS_ROOT_INO;
-
-       bch2_inode_pack(c, &packed, root_inode);
-
-       return bch2_btree_insert(c, BTREE_ID_inodes, &packed.inode.k_i,
-                                NULL, NULL,
-                                BTREE_INSERT_NOFAIL|
-                                BTREE_INSERT_LAZY_RW);
 }
 
-struct pathbuf {
-       size_t          nr;
-       size_t          size;
-
-       struct pathbuf_entry {
-               u64     inum;
-       }               *entries;
+struct pathbuf_entry {
+       u64     inum;
+       u32     snapshot;
 };
 
-static int path_down(struct pathbuf *p, u64 inum)
+typedef DARRAY(struct pathbuf_entry) pathbuf;
+
+static bool path_is_dup(pathbuf *p, u64 inum, u32 snapshot)
 {
-       if (p->nr == p->size) {
-               size_t new_size = max_t(size_t, 256UL, p->size * 2);
-               void *n = krealloc(p->entries,
-                                  new_size * sizeof(p->entries[0]),
-                                  GFP_KERNEL);
-               if (!n) {
-                       return -ENOMEM;
-               }
+       darray_for_each(*p, i)
+               if (i->inum     == inum &&
+                   i->snapshot == snapshot)
+                       return true;
+       return false;
+}
 
-               p->entries = n;
-               p->size = new_size;
-       };
+static int path_down(struct bch_fs *c, pathbuf *p,
+                    u64 inum, u32 snapshot)
+{
+       int ret = darray_push(p, ((struct pathbuf_entry) {
+               .inum           = inum,
+               .snapshot       = snapshot,
+       }));
 
-       p->entries[p->nr++] = (struct pathbuf_entry) {
-               .inum = inum,
-       };
-       return 0;
+       if (ret)
+               bch_err(c, "fsck: error allocating memory for pathbuf, size %zu",
+                       p->size);
+       return ret;
 }
 
+/*
+ * Check that a given inode is reachable from the root:
+ *
+ * XXX: we should also be verifying that inodes are in the right subvolumes
+ */
 static int check_path(struct btree_trans *trans,
-                     struct pathbuf *p,
-                     struct bch_inode_unpacked *inode)
+                     pathbuf *p,
+                     struct bch_inode_unpacked *inode,
+                     u32 snapshot)
 {
        struct bch_fs *c = trans->c;
-       u32 snapshot;
-       size_t i;
        int ret = 0;
 
+       snapshot = bch2_snapshot_equiv(c, snapshot);
        p->nr = 0;
 
-       while (inode->bi_inum != BCACHEFS_ROOT_INO) {
-               ret = lockrestart_do(trans,
-                       inode_backpointer_exists(trans, inode));
-               if (ret < 0)
+       while (!(inode->bi_inum == BCACHEFS_ROOT_INO &&
+                inode->bi_subvol == BCACHEFS_ROOT_SUBVOL)) {
+               struct btree_iter dirent_iter;
+               struct bkey_s_c_dirent d;
+               u32 parent_snapshot = snapshot;
+
+               if (inode->bi_subvol) {
+                       u64 inum;
+
+                       ret = subvol_lookup(trans, inode->bi_parent_subvol,
+                                           &parent_snapshot, &inum);
+                       if (ret)
+                               break;
+               }
+
+               d = dirent_get_by_pos(trans, &dirent_iter,
+                                     SPOS(inode->bi_dir, inode->bi_dir_offset,
+                                          parent_snapshot));
+               ret = bkey_err(d.s_c);
+               if (ret && !bch2_err_matches(ret, ENOENT))
                        break;
 
-               if (!ret) {
-                       if (fsck_err(c,  "unreachable inode %llu, type %u nlink %u backptr %llu:%llu",
-                                    inode->bi_inum,
-                                    mode_to_type(inode->bi_mode),
+               if (!ret && !dirent_points_to_inode(d, inode)) {
+                       bch2_trans_iter_exit(trans, &dirent_iter);
+                       ret = -BCH_ERR_ENOENT_dirent_doesnt_match_inode;
+               }
+
+               if (bch2_err_matches(ret, ENOENT)) {
+                       if (fsck_err(c,  inode_unreachable,
+                                    "unreachable inode %llu:%u, type %s nlink %u backptr %llu:%llu",
+                                    inode->bi_inum, snapshot,
+                                    bch2_d_type_str(inode_d_type(inode)),
                                     inode->bi_nlink,
                                     inode->bi_dir,
                                     inode->bi_dir_offset))
-                               ret = reattach_inode(trans, inode);
+                               ret = reattach_inode(trans, inode, snapshot);
                        break;
                }
-               ret = 0;
+
+               bch2_trans_iter_exit(trans, &dirent_iter);
 
                if (!S_ISDIR(inode->bi_mode))
                        break;
 
-               ret = path_down(p, inode->bi_inum);
+               ret = path_down(c, p, inode->bi_inum, snapshot);
                if (ret) {
                        bch_err(c, "memory allocation failure");
                        return ret;
                }
 
-               for (i = 0; i < p->nr; i++) {
-                       if (inode->bi_dir != p->entries[i].inum)
-                               continue;
+               snapshot = parent_snapshot;
+
+               ret = lookup_inode(trans, inode->bi_dir, inode, &snapshot);
+               if (ret) {
+                       /* Should have been caught in dirents pass */
+                       if (!bch2_err_matches(ret, BCH_ERR_transaction_restart))
+                               bch_err(c, "error looking up parent directory: %i", ret);
+                       break;
+               }
 
+               if (path_is_dup(p, inode->bi_inum, snapshot)) {
                        /* XXX print path */
-                       if (!fsck_err(c, "directory structure loop"))
+                       bch_err(c, "directory structure loop");
+
+                       darray_for_each(*p, i)
+                               pr_err("%llu:%u", i->inum, i->snapshot);
+                       pr_err("%llu:%u", inode->bi_inum, snapshot);
+
+                       if (!fsck_err(c, dir_loop, "directory structure loop"))
                                return 0;
 
-                       ret = lockrestart_do(trans,
-                                        remove_backpointer(trans, inode));
-                       if (ret) {
-                               bch_err(c, "error removing dirent: %i", ret);
+                       ret = remove_backpointer(trans, inode);
+                       if (ret && !bch2_err_matches(ret, BCH_ERR_transaction_restart))
+                               bch_err_msg(c, ret, "removing dirent");
+                       if (ret)
                                break;
-                       }
-
-                       ret = reattach_inode(trans, inode);
-                       break;
-               }
 
-               ret = lookup_inode(trans, inode->bi_dir, inode, &snapshot);
-               if (ret) {
-                       /* Should have been caught in dirents pass */
-                       bch_err(c, "error looking up parent directory: %i", ret);
+                       ret = reattach_inode(trans, inode, snapshot);
+                       if (ret && !bch2_err_matches(ret, BCH_ERR_transaction_restart))
+                               bch_err_msg(c, ret, "reattaching inode %llu", inode->bi_inum);
                        break;
                }
        }
 fsck_err:
-       if (ret)
-               bch_err(c, "%s: err %i", __func__, ret);
+       bch_err_fn(c, ret);
        return ret;
 }
 
 /*
  * Check for unreachable inodes, as well as loops in the directory structure:
- * After check_dirents(), if an inode backpointer doesn't exist that means it's
+ * After bch2_check_dirents(), if an inode backpointer doesn't exist that means it's
  * unreachable:
  */
-static int check_directory_structure(struct bch_fs *c)
+int bch2_check_directory_structure(struct bch_fs *c)
 {
-       struct btree_trans trans;
-       struct btree_iter *iter;
-       struct bkey_s_c k;
        struct bch_inode_unpacked u;
-       struct pathbuf path = { 0, 0, NULL };
+       pathbuf path = { 0, };
        int ret;
 
-       bch2_trans_init(&trans, c, BTREE_ITER_MAX, 0);
-
-       for_each_btree_key(&trans, iter, BTREE_ID_inodes, POS_MIN,
-                          BTREE_ITER_INTENT|
-                          BTREE_ITER_PREFETCH, k, ret) {
-               if (k.k->type != KEY_TYPE_inode)
-                       continue;
-
-               ret = bch2_inode_unpack(bkey_s_c_to_inode(k), &u);
-               if (ret) {
-                       /* Should have been caught earlier in fsck: */
-                       bch_err(c, "error unpacking inode %llu: %i", k.k->p.offset, ret);
-                       break;
-               }
+       ret = bch2_trans_run(c,
+               for_each_btree_key_commit(trans, iter, BTREE_ID_inodes, POS_MIN,
+                                         BTREE_ITER_INTENT|
+                                         BTREE_ITER_PREFETCH|
+                                         BTREE_ITER_ALL_SNAPSHOTS, k,
+                                         NULL, NULL, BCH_TRANS_COMMIT_no_enospc, ({
+                       if (!bkey_is_inode(k.k))
+                               continue;
 
-               ret = check_path(&trans, &path, &u);
-               if (ret)
-                       break;
-       }
-       bch2_trans_iter_put(&trans, iter);
+                       BUG_ON(bch2_inode_unpack(k, &u));
 
-       BUG_ON(ret == -EINTR);
+                       if (u.bi_flags & BCH_INODE_unlinked)
+                               continue;
 
-       kfree(path.entries);
+                       check_path(trans, &path, &u, iter.pos.snapshot);
+               })));
+       darray_exit(&path);
 
-       return bch2_trans_exit(&trans) ?: ret;
+       bch_err_fn(c, ret);
+       return ret;
 }
 
 struct nlink_table {
@@ -1156,13 +2113,17 @@ struct nlink_table {
        }               *d;
 };
 
-static int add_nlink(struct nlink_table *t, u64 inum, u32 snapshot)
+static int add_nlink(struct bch_fs *c, struct nlink_table *t,
+                    u64 inum, u32 snapshot)
 {
        if (t->nr == t->size) {
                size_t new_size = max_t(size_t, 128UL, t->size * 2);
-               void *d = kvmalloc(new_size * sizeof(t->d[0]), GFP_KERNEL);
+               void *d = kvmalloc_array(new_size, sizeof(t->d[0]), GFP_KERNEL);
+
                if (!d) {
-                       return -ENOMEM;
+                       bch_err(c, "fsck: error allocating memory for nlink_table, size %zu",
+                               new_size);
+                       return -BCH_ERR_ENOMEM_fsck_add_nlink;
                }
 
                if (t->d)
@@ -1187,11 +2148,12 @@ static int nlink_cmp(const void *_l, const void *_r)
        const struct nlink *l = _l;
        const struct nlink *r = _r;
 
-       return cmp_int(l->inum, r->inum) ?: cmp_int(l->snapshot, r->snapshot);
+       return cmp_int(l->inum, r->inum);
 }
 
-static void inc_link(struct bch_fs *c, struct nlink_table *links,
-                    u64 range_start, u64 range_end, u64 inum)
+static void inc_link(struct bch_fs *c, struct snapshots_seen *s,
+                    struct nlink_table *links,
+                    u64 range_start, u64 range_end, u64 inum, u32 snapshot)
 {
        struct nlink *link, key = {
                .inum = inum, .snapshot = U32_MAX,
@@ -1202,8 +2164,18 @@ static void inc_link(struct bch_fs *c, struct nlink_table *links,
 
        link = __inline_bsearch(&key, links->d, links->nr,
                                sizeof(links->d[0]), nlink_cmp);
-       if (link)
-               link->count++;
+       if (!link)
+               return;
+
+       while (link > links->d && link[0].inum == link[-1].inum)
+               --link;
+
+       for (; link < links->d + links->nr && link->inum == inum; link++)
+               if (ref_visible(c, s, snapshot, link->snapshot)) {
+                       link->count++;
+                       if (link->snapshot >= snapshot)
+                               break;
+               }
 }
 
 noinline_for_stack
@@ -1211,51 +2183,39 @@ static int check_nlinks_find_hardlinks(struct bch_fs *c,
                                       struct nlink_table *t,
                                       u64 start, u64 *end)
 {
-       struct btree_trans trans;
-       struct btree_iter *iter;
-       struct bkey_s_c k;
-       struct bkey_s_c_inode inode;
-       struct bch_inode_unpacked u;
-       int ret = 0;
-
-       bch2_trans_init(&trans, c, BTREE_ITER_MAX, 0);
-
-       for_each_btree_key(&trans, iter, BTREE_ID_inodes,
-                          POS(0, start),
-                          BTREE_ITER_INTENT|
-                          BTREE_ITER_PREFETCH, k, ret) {
-               if (k.k->type != KEY_TYPE_inode)
-                       continue;
-
-               inode = bkey_s_c_to_inode(k);
-
-               /*
-                * Backpointer and directory structure checks are sufficient for
-                * directories, since they can't have hardlinks:
-                */
-               if (S_ISDIR(le16_to_cpu(inode.v->bi_mode)))
-                       continue;
-
-               /* Should never fail, checked by bch2_inode_invalid: */
-               BUG_ON(bch2_inode_unpack(inode, &u));
+       int ret = bch2_trans_run(c,
+               for_each_btree_key(trans, iter, BTREE_ID_inodes,
+                                  POS(0, start),
+                                  BTREE_ITER_INTENT|
+                                  BTREE_ITER_PREFETCH|
+                                  BTREE_ITER_ALL_SNAPSHOTS, k, ({
+                       if (!bkey_is_inode(k.k))
+                               continue;
 
-               if (!u.bi_nlink)
-                       continue;
+                       /* Should never fail, checked by bch2_inode_invalid: */
+                       struct bch_inode_unpacked u;
+                       BUG_ON(bch2_inode_unpack(k, &u));
 
-               ret = add_nlink(t, k.k->p.offset, k.k->p.snapshot);
-               if (ret) {
-                       *end = k.k->p.offset;
-                       ret = 0;
-                       break;
-               }
+                       /*
+                        * Backpointer and directory structure checks are sufficient for
+                        * directories, since they can't have hardlinks:
+                        */
+                       if (S_ISDIR(u.bi_mode))
+                               continue;
 
-       }
-       bch2_trans_iter_put(&trans, iter);
-       bch2_trans_exit(&trans);
+                       if (!u.bi_nlink)
+                               continue;
 
-       if (ret)
-               bch_err(c, "error in fsck: btree error %i while walking inodes", ret);
+                       ret = add_nlink(c, t, k.k->p.offset, k.k->p.snapshot);
+                       if (ret) {
+                               *end = k.k->p.offset;
+                               ret = 0;
+                               break;
+                       }
+                       0;
+               })));
 
+       bch_err_fn(c, ret);
        return ret;
 }
 
@@ -1263,111 +2223,106 @@ noinline_for_stack
 static int check_nlinks_walk_dirents(struct bch_fs *c, struct nlink_table *links,
                                     u64 range_start, u64 range_end)
 {
-       struct btree_trans trans;
-       struct btree_iter *iter;
-       struct bkey_s_c k;
-       struct bkey_s_c_dirent d;
-       int ret;
+       struct snapshots_seen s;
 
-       bch2_trans_init(&trans, c, BTREE_ITER_MAX, 0);
+       snapshots_seen_init(&s);
 
-       for_each_btree_key(&trans, iter, BTREE_ID_dirents, POS_MIN,
-                          BTREE_ITER_INTENT|
-                          BTREE_ITER_PREFETCH, k, ret) {
-               switch (k.k->type) {
-               case KEY_TYPE_dirent:
-                       d = bkey_s_c_to_dirent(k);
+       int ret = bch2_trans_run(c,
+               for_each_btree_key(trans, iter, BTREE_ID_dirents, POS_MIN,
+                                  BTREE_ITER_INTENT|
+                                  BTREE_ITER_PREFETCH|
+                                  BTREE_ITER_ALL_SNAPSHOTS, k, ({
+                       ret = snapshots_seen_update(c, &s, iter.btree_id, k.k->p);
+                       if (ret)
+                               break;
 
-                       if (d.v->d_type != DT_DIR)
-                               inc_link(c, links, range_start, range_end,
-                                        le64_to_cpu(d.v->d_inum));
-                       break;
-               }
+                       if (k.k->type == KEY_TYPE_dirent) {
+                               struct bkey_s_c_dirent d = bkey_s_c_to_dirent(k);
 
-               bch2_trans_cond_resched(&trans);
-       }
-       bch2_trans_iter_put(&trans, iter);
+                               if (d.v->d_type != DT_DIR &&
+                                   d.v->d_type != DT_SUBVOL)
+                                       inc_link(c, &s, links, range_start, range_end,
+                                                le64_to_cpu(d.v->d_inum),
+                                                bch2_snapshot_equiv(c, d.k->p.snapshot));
+                       }
+                       0;
+               })));
 
-       ret = bch2_trans_exit(&trans) ?: ret;
-       if (ret)
-               bch_err(c, "error in fsck: btree error %i while walking dirents", ret);
+       snapshots_seen_exit(&s);
 
+       bch_err_fn(c, ret);
        return ret;
 }
 
-noinline_for_stack
-static int check_nlinks_update_hardlinks(struct bch_fs *c,
-                              struct nlink_table *links,
-                              u64 range_start, u64 range_end)
+static int check_nlinks_update_inode(struct btree_trans *trans, struct btree_iter *iter,
+                                    struct bkey_s_c k,
+                                    struct nlink_table *links,
+                                    size_t *idx, u64 range_end)
 {
-       struct btree_trans trans;
-       struct btree_iter *iter;
-       struct bkey_s_c k;
-       struct bkey_s_c_inode inode;
+       struct bch_fs *c = trans->c;
        struct bch_inode_unpacked u;
-       struct nlink *link = links->d;
+       struct nlink *link = &links->d[*idx];
        int ret = 0;
 
-       bch2_trans_init(&trans, c, BTREE_ITER_MAX, 0);
-
-       for_each_btree_key(&trans, iter, BTREE_ID_inodes,
-                          POS(0, range_start),
-                          BTREE_ITER_INTENT|
-                          BTREE_ITER_PREFETCH, k, ret) {
-               if (k.k->p.offset >= range_end)
-                       break;
+       if (k.k->p.offset >= range_end)
+               return 1;
 
-               if (k.k->type != KEY_TYPE_inode)
-                       continue;
+       if (!bkey_is_inode(k.k))
+               return 0;
 
-               inode = bkey_s_c_to_inode(k);
-               if (S_ISDIR(le16_to_cpu(inode.v->bi_mode)))
-                       continue;
+       BUG_ON(bch2_inode_unpack(k, &u));
 
-               BUG_ON(bch2_inode_unpack(inode, &u));
+       if (S_ISDIR(u.bi_mode))
+               return 0;
 
-               if (!u.bi_nlink)
-                       continue;
+       if (!u.bi_nlink)
+               return 0;
 
-               while (link->inum < k.k->p.offset) {
-                       link++;
-                       BUG_ON(link >= links->d + links->nr);
-               }
+       while ((cmp_int(link->inum, k.k->p.offset) ?:
+               cmp_int(link->snapshot, k.k->p.snapshot)) < 0) {
+               BUG_ON(*idx == links->nr);
+               link = &links->d[++*idx];
+       }
 
-               if (fsck_err_on(bch2_inode_nlink_get(&u) != link->count, c,
-                               "inode %llu has wrong i_nlink (type %u i_nlink %u, should be %u)",
-                               u.bi_inum, mode_to_type(u.bi_mode),
-                               bch2_inode_nlink_get(&u), link->count)) {
-                       bch2_inode_nlink_set(&u, link->count);
-
-                       ret = __bch2_trans_do(&trans, NULL, NULL,
-                                             BTREE_INSERT_NOFAIL|
-                                             BTREE_INSERT_LAZY_RW,
-                                             bch2_btree_iter_traverse(iter) ?:
-                                       bch2_inode_write(&trans, iter, &u));
-                       if (ret)
-                               bch_err(c, "error in fsck: error %i updating inode", ret);
-               }
+       if (fsck_err_on(bch2_inode_nlink_get(&u) != link->count,
+                       c, inode_wrong_nlink,
+                       "inode %llu type %s has wrong i_nlink (%u, should be %u)",
+                       u.bi_inum, bch2_d_types[mode_to_type(u.bi_mode)],
+                       bch2_inode_nlink_get(&u), link->count)) {
+               bch2_inode_nlink_set(&u, link->count);
+               ret = __write_inode(trans, &u, k.k->p.snapshot);
        }
 fsck_err:
-       bch2_trans_iter_put(&trans, iter);
-       bch2_trans_exit(&trans);
-
-       if (ret)
-               bch_err(c, "error in fsck: btree error %i while walking inodes", ret);
-
        return ret;
 }
 
 noinline_for_stack
-static int check_nlinks(struct bch_fs *c)
+static int check_nlinks_update_hardlinks(struct bch_fs *c,
+                              struct nlink_table *links,
+                              u64 range_start, u64 range_end)
+{
+       size_t idx = 0;
+
+       int ret = bch2_trans_run(c,
+               for_each_btree_key_commit(trans, iter, BTREE_ID_inodes,
+                               POS(0, range_start),
+                               BTREE_ITER_INTENT|BTREE_ITER_PREFETCH|BTREE_ITER_ALL_SNAPSHOTS, k,
+                               NULL, NULL, BCH_TRANS_COMMIT_no_enospc,
+                       check_nlinks_update_inode(trans, &iter, k, links, &idx, range_end)));
+       if (ret < 0) {
+               bch_err(c, "error in fsck walking inodes: %s", bch2_err_str(ret));
+               return ret;
+       }
+
+       return 0;
+}
+
+int bch2_check_nlinks(struct bch_fs *c)
 {
        struct nlink_table links = { 0 };
        u64 this_iter_range_start, next_iter_range_start = 0;
        int ret = 0;
 
-       bch_verbose(c, "checking inode nlinks");
-
        do {
                this_iter_range_start = next_iter_range_start;
                next_iter_range_start = U64_MAX;
@@ -1392,28 +2347,48 @@ static int check_nlinks(struct bch_fs *c)
        } while (next_iter_range_start != U64_MAX);
 
        kvfree(links.d);
-
+       bch_err_fn(c, ret);
        return ret;
 }
 
-/*
- * Checks for inconsistencies that shouldn't happen, unless we have a bug.
- * Doesn't fix them yet, mainly because they haven't yet been observed:
- */
-int bch2_fsck_full(struct bch_fs *c)
+static int fix_reflink_p_key(struct btree_trans *trans, struct btree_iter *iter,
+                            struct bkey_s_c k)
 {
-       struct bch_inode_unpacked root_inode;
+       struct bkey_s_c_reflink_p p;
+       struct bkey_i_reflink_p *u;
+
+       if (k.k->type != KEY_TYPE_reflink_p)
+               return 0;
+
+       p = bkey_s_c_to_reflink_p(k);
+
+       if (!p.v->front_pad && !p.v->back_pad)
+               return 0;
+
+       u = bch2_trans_kmalloc(trans, sizeof(*u));
+       int ret = PTR_ERR_OR_ZERO(u);
+       if (ret)
+               return ret;
 
-       return  check_inodes(c, true) ?:
-               check_extents(c) ?:
-               check_dirents(c) ?:
-               check_xattrs(c) ?:
-               check_root(c, &root_inode) ?:
-               check_directory_structure(c) ?:
-               check_nlinks(c);
+       bkey_reassemble(&u->k_i, k);
+       u->v.front_pad  = 0;
+       u->v.back_pad   = 0;
+
+       return bch2_trans_update(trans, iter, &u->k_i, BTREE_TRIGGER_NORUN);
 }
 
-int bch2_fsck_walk_inodes_only(struct bch_fs *c)
+int bch2_fix_reflink_p(struct bch_fs *c)
 {
-       return check_inodes(c, false);
+       if (c->sb.version >= bcachefs_metadata_version_reflink_p_fix)
+               return 0;
+
+       int ret = bch2_trans_run(c,
+               for_each_btree_key_commit(trans, iter,
+                               BTREE_ID_extents, POS_MIN,
+                               BTREE_ITER_INTENT|BTREE_ITER_PREFETCH|
+                               BTREE_ITER_ALL_SNAPSHOTS, k,
+                               NULL, NULL, BCH_TRANS_COMMIT_no_enospc,
+                       fix_reflink_p_key(trans, &iter, k)));
+       bch_err_fn(c, ret);
+       return ret;
 }