Remove mount entries that will be pruned away due to prunefs.

[plocate] / bind-mount.cpp

diff --git a/bind-mount.cpp b/bind-mount.cpp
index 899bf3bd5f9a5496fbdb9d11e8e09d4a86493633..b3c1bd29194fe9f945499ce5db652f1cba9c5343 100644 (file)
--- a/bind-mount.cpp
+++ b/bind-mount.cpp
@@ -25,6 +25,7 @@ any later version.
 #include "conf.h"
 #include "lib.h"
 
+#include <algorithm>
 #include <atomic>
 #include <fcntl.h>
 #include <limits.h>
@@ -39,6 +40,7 @@ any later version.
 #include <sys/time.h>
 #include <thread>
 #include <optional>
+#include <unordered_map>
 
 using namespace std;
 
@@ -52,6 +54,10 @@ struct mount {
        string mount_point;
        string fs_type;
        string source;
+
+       // Derived properties.
+       bool pruned_due_to_fs_type;
+       bool to_remove;
 };
 
 /* Path to mountinfo */
@@ -167,6 +173,29 @@ static bool read_mount_entry(FILE *f, mount *me)
        return true;
 }
 
+static bool find_whether_under_pruned(
+       int id,
+       const unordered_map<int, mount *> &id_to_mount,
+       unordered_map<int, bool> *id_to_pruned_cache)
+{
+       auto cache_it = id_to_pruned_cache->find(id);
+       if (cache_it != id_to_pruned_cache->end()) {
+               return cache_it->second;
+       }
+       auto mount_it = id_to_mount.find(id);
+       if (mount_it == id_to_mount.end()) {
+               // Should not happen.
+               return false;
+       }
+
+       bool result = mount_it->second->pruned_due_to_fs_type ||
+               (mount_it->second->parent_id != 0 &&
+                find_whether_under_pruned(mount_it->second->parent_id,
+                                          id_to_mount, id_to_pruned_cache));
+       id_to_pruned_cache->emplace(id, result);
+       return result;
+}
+
 /* Read mount information from mountinfo_path, update mount_entries and
    num_mount_entries.
    Return std::nullopt on error. */
@@ -179,17 +208,53 @@ static optional<MountEntries> read_mount_entries(void)
 
        MountEntries mount_entries;
 
-       mount me;
-       while (read_mount_entry(f, &me)) {
-               if (conf_debug_pruning) {
-                       fprintf(stderr,
-                               " `%s' (%d on %d) is `%s' of `%s' (%u:%u), type `%s'\n",
-                               me.mount_point.c_str(), me.id, me.parent_id, me.root.c_str(), me.source.c_str(),
-                               me.dev_major, me.dev_minor, me.fs_type.c_str());
+       {
+               mount me;
+               while (read_mount_entry(f, &me)) {
+                       string fs_type_upper = me.fs_type;
+                       for (char &c : fs_type_upper) {
+                               c = toupper(c);
+                       }
+                       me.pruned_due_to_fs_type =
+                               (find(conf_prunefs.begin(), conf_prunefs.end(), fs_type_upper) != conf_prunefs.end());
+                       mount_entries.emplace(make_pair(me.dev_major, me.dev_minor), me);
+                       if (conf_debug_pruning) {
+                               fprintf(stderr,
+                                       " `%s' (%d on %d) is `%s' of `%s' (%u:%u), type `%s' (pruned_fs=%d)\n",
+                                       me.mount_point.c_str(), me.id, me.parent_id, me.root.c_str(), me.source.c_str(),
+                                       me.dev_major, me.dev_minor, me.fs_type.c_str(), me.pruned_due_to_fs_type);
+                       }
+               }
+               fclose(f);
+       }
+
+       // Now propagate pruned status recursively through parent links
+       // (e.g. if /run is tmpfs, then /run/foo should also be pruned).
+       unordered_map<int, mount *> id_to_mount;
+       for (auto &[key, me] : mount_entries) {
+               id_to_mount[me.id] = &me;
+       }
+       unordered_map<int, bool> id_to_pruned_cache;
+       for (auto &[key, me] : mount_entries) {
+               me.to_remove =
+                       find_whether_under_pruned(me.id, id_to_mount, &id_to_pruned_cache);
+               if (conf_debug_pruning && me.to_remove) {
+                       fprintf(stderr, " `%s' is, or is under, a pruned file system; removing\n",
+                               me.mount_point.c_str());
                }
-               mount_entries.emplace(make_pair(me.dev_major, me.dev_minor), me);
        }
-       fclose(f);
+
+       // Now take out those that we won't see due to file system type anyway,
+       // so that we don't inadvertently prefer them to others during bind mount
+       // duplicate detection.
+       for (auto it = mount_entries.begin(); it != mount_entries.end(); ) {
+               if (it->second.to_remove) {
+                       it = mount_entries.erase(it);
+               } else {
+                       ++it;
+               }
+       }
+
        return mount_entries;
 }