git.sesse.net Git - plocate/blob - io_uring_engine.cpp

   1 #include <errno.h>
   2 #include <stdio.h>
   3 #include <stdlib.h>
   4 #include <string.h>
   5 #ifndef WITHOUT_URING
   6 #include <liburing.h>
   7 #endif
   8 #include "io_uring_engine.h"
   9
  10 #include <functional>
  11 #include <iosfwd>
  12 #include <string>
  13 #include <unistd.h>
  14 #include <utility>
  15
  16 using namespace std;
  17
  18 IOUringEngine::IOUringEngine(size_t slop_bytes)
  19         : slop_bytes(slop_bytes)
  20 {
  21 #ifdef WITHOUT_URING
  22         int ret = -1;
  23 #else
  24         int ret = io_uring_queue_init(queue_depth, &ring, 0);
  25 #endif
  26         using_uring = (ret >= 0);
  27 }
  28
  29 void IOUringEngine::submit_read(int fd, size_t len, off_t offset, function<void(string_view)> cb)
  30 {
  31         if (!using_uring) {
  32                 // Synchronous read.
  33                 string s;
  34                 s.resize(len + slop_bytes);
  35                 complete_pread(fd, &s[0], len, offset);
  36                 cb(string_view(s.data(), len));
  37                 return;
  38         }
  39
  40 #ifndef WITHOUT_URING
  41         if (pending_reads < queue_depth) {
  42                 io_uring_sqe *sqe = io_uring_get_sqe(&ring);
  43                 if (sqe == nullptr) {
  44                         fprintf(stderr, "io_uring_get_sqe: %s\n", strerror(errno));
  45                         exit(1);
  46                 }
  47                 submit_read_internal(sqe, fd, len, offset, move(cb));
  48         } else {
  49                 queued_reads.push(QueuedRead{ fd, len, offset, move(cb) });
  50         }
  51 #endif
  52 }
  53
  54 #ifndef WITHOUT_URING
  55 void IOUringEngine::submit_read_internal(io_uring_sqe *sqe, int fd, size_t len, off_t offset, function<void(string_view)> cb)
  56 {
  57         void *buf;
  58         if (posix_memalign(&buf, /*alignment=*/4096, len + slop_bytes)) {
  59                 fprintf(stderr, "Couldn't allocate %zu bytes: %s\n", len, strerror(errno));
  60                 exit(1);
  61         }
  62         PendingRead *pending = new PendingRead{ buf, len, move(cb), fd, offset, { buf, len } };
  63
  64         io_uring_prep_readv(sqe, fd, &pending->iov, 1, offset);
  65         io_uring_sqe_set_data(sqe, pending);
  66         ++pending_reads;
  67 }
  68 #endif
  69
  70 void IOUringEngine::finish()
  71 {
  72         if (!using_uring) {
  73                 return;
  74         }
  75
  76 #ifndef WITHOUT_URING
  77         bool anything_to_submit = true;
  78         while (pending_reads > 0) {
  79                 io_uring_cqe *cqe;
  80                 if (io_uring_peek_cqe(&ring, &cqe) != 0) {
  81                         if (anything_to_submit) {
  82                                 // Nothing ready, so submit whatever is pending and then do a blocking wait.
  83                                 int ret = io_uring_submit_and_wait(&ring, 1);
  84                                 if (ret < 0) {
  85                                         fprintf(stderr, "io_uring_submit(queued): %s\n", strerror(-ret));
  86                                         exit(1);
  87                                 }
  88                                 anything_to_submit = false;
  89                         } else {
  90                                 int ret = io_uring_wait_cqe(&ring, &cqe);
  91                                 if (ret < 0) {
  92                                         fprintf(stderr, "io_uring_wait_cqe: %s\n", strerror(-ret));
  93                                         exit(1);
  94                                 }
  95                         }
  96                 }
  97
  98                 unsigned head;
  99                 io_uring_for_each_cqe(&ring, head, cqe)
 100                 {
 101                         PendingRead *pending = reinterpret_cast<PendingRead *>(cqe->user_data);
 102                         if (cqe->res <= 0) {
 103                                 fprintf(stderr, "async read failed: %s\n", strerror(-cqe->res));
 104                                 exit(1);
 105                         }
 106
 107                         if (size_t(cqe->res) < pending->iov.iov_len) {
 108                                 // Incomplete read, so resubmit it.
 109                                 pending->iov.iov_base = (char *)pending->iov.iov_base + cqe->res;
 110                                 pending->iov.iov_len -= cqe->res;
 111                                 pending->offset += cqe->res;
 112                                 io_uring_cqe_seen(&ring, cqe);
 113
 114                                 io_uring_sqe *sqe = io_uring_get_sqe(&ring);
 115                                 if (sqe == nullptr) {
 116                                         fprintf(stderr, "No free SQE for resubmit; this shouldn't happen.\n");
 117                                         exit(1);
 118                                 }
 119                                 io_uring_prep_readv(sqe, pending->fd, &pending->iov, 1, pending->offset);
 120                                 io_uring_sqe_set_data(sqe, pending);
 121                                 anything_to_submit = true;
 122                         } else {
 123                                 io_uring_cqe_seen(&ring, cqe);
 124                                 --pending_reads;
 125
 126                                 size_t old_pending_reads = pending_reads;
 127                                 pending->cb(string_view(reinterpret_cast<char *>(pending->buf), pending->len));
 128                                 free(pending->buf);
 129                                 delete pending;
 130
 131                                 if (pending_reads != old_pending_reads) {
 132                                         // A new read was made in the callback (and not queued),
 133                                         // so we need to re-submit.
 134                                         anything_to_submit = true;
 135                                 }
 136                         }
 137                 }
 138
 139                 // See if there are any queued reads we can submit now.
 140                 while (!queued_reads.empty() && pending_reads < queue_depth) {
 141                         io_uring_sqe *sqe = io_uring_get_sqe(&ring);
 142                         if (sqe == nullptr) {
 143                                 fprintf(stderr, "io_uring_get_sqe: %s\n", strerror(errno));
 144                                 exit(1);
 145                         }
 146                         QueuedRead &qr = queued_reads.front();
 147                         submit_read_internal(sqe, qr.fd, qr.len, qr.offset, move(qr.cb));
 148                         queued_reads.pop();
 149                         anything_to_submit = true;
 150                 }
 151         }
 152 #endif
 153 }
 154
 155 void complete_pread(int fd, void *ptr, size_t len, off_t offset)
 156 {
 157         while (len > 0) {
 158                 ssize_t ret = pread(fd, ptr, len, offset);
 159                 if (ret == -1 && errno == EINTR) {
 160                         continue;
 161                 }
 162                 if (ret <= 0) {
 163                         perror("pread");
 164                         exit(1);
 165                 }
 166                 ptr = reinterpret_cast<char *>(ptr) + ret;
 167                 len -= ret;
 168                 offset -= ret;
 169         }
 170 }