src/fd-cache/fd-cache.c

   1 /*
   2  * SPDX-License-Identifier: MIT
   3  *
   4  * Copyright 2019 Francis Deslauriers <francis.deslauriers@efficios.com>
   5  *
   6  * Babeltrace - File descriptor cache
   7  */
   8
   9 #define BT_LOG_OUTPUT_LEVEL (fdc->log_level)
  10 #define BT_LOG_TAG "FD-CACHE"
  11 #include "logging/log.h"
  12
  13 #include <fcntl.h>
  14 #include <sys/stat.h>
  15 #include <sys/types.h>
  16 #include <unistd.h>
  17 #include <glib.h>
  18
  19 #include "common/assert.h"
  20 #include "fd-cache.h"
  21
  22 struct file_key {
  23         uint64_t dev;
  24         uint64_t ino;
  25 };
  26
  27 struct fd_handle_internal {
  28         struct bt_fd_cache_handle fd_handle;
  29         uint64_t ref_count;
  30         struct file_key *key;
  31 };
  32
  33 static
  34 void fd_cache_handle_internal_destroy(
  35                 struct fd_handle_internal *internal_fd)
  36 {
  37         if (!internal_fd) {
  38                 goto end;
  39         }
  40
  41         if (internal_fd->fd_handle.fd >= 0) {
  42                 close(internal_fd->fd_handle.fd);
  43                 internal_fd->fd_handle.fd = -1;
  44         }
  45
  46 end:
  47         g_free(internal_fd);
  48 }
  49
  50 /*
  51  * Using simple hash algorithm found on stackoverflow:
  52  * https://stackoverflow.com/questions/664014/
  53  */
  54 static inline
  55 uint64_t hash_uint64_t(uint64_t x) {
  56         x = (x ^ (x >> 30)) * UINT64_C(0xbf58476d1ce4e5b9);
  57         x = (x ^ (x >> 27)) * UINT64_C(0x94d049bb133111eb);
  58         x = x ^ (x >> 31);
  59         return x;
  60 }
  61
  62 static
  63 guint file_key_hash(gconstpointer v)
  64 {
  65         const struct file_key *fk = v;
  66         return hash_uint64_t(fk->dev) ^ hash_uint64_t(fk->ino);
  67 }
  68
  69 static
  70 gboolean file_key_equal(gconstpointer v1, gconstpointer v2)
  71 {
  72         const struct file_key *fk1 = v1;
  73         const struct file_key *fk2 = v2;
  74
  75         return (fk1->dev == fk2->dev) && (fk1->ino == fk2->ino);
  76 }
  77
  78 static
  79 void file_key_destroy(gpointer data)
  80 {
  81         struct file_key *fk = data;
  82         g_free(fk);
  83 }
  84
  85 int bt_fd_cache_init(struct bt_fd_cache *fdc, int log_level)
  86 {
  87         int ret = 0;
  88
  89         fdc->log_level = log_level;
  90         fdc->cache = g_hash_table_new_full(file_key_hash, file_key_equal,
  91                 file_key_destroy, (GDestroyNotify) fd_cache_handle_internal_destroy);
  92         if (!fdc->cache) {
  93                 ret = -1;
  94         }
  95
  96         return ret;
  97 }
  98
  99 void bt_fd_cache_fini(struct bt_fd_cache *fdc)
 100 {
 101         if (!fdc->cache) {
 102                 goto end;
 103         }
 104
 105         /*
 106          * All handle should have been removed for the hashtable at this point.
 107          */
 108         BT_ASSERT(g_hash_table_size(fdc->cache) == 0);
 109         g_hash_table_destroy(fdc->cache);
 110
 111 end:
 112         return;
 113 }
 114
 115 struct bt_fd_cache_handle *bt_fd_cache_get_handle(struct bt_fd_cache *fdc,
 116                 const char *path)
 117 {
 118         struct fd_handle_internal *fd_internal = NULL;
 119         struct stat statbuf;
 120         struct file_key fk;
 121         int ret, fd = -1;
 122
 123         ret = stat(path, &statbuf);
 124         if (ret < 0) {
 125                 /*
 126                  * This is not necessarily an error as we sometimes try to open
 127                  * files to see if they exist. Log the error as DEBUG severity
 128                  * level.
 129                  */
 130                 BT_LOGD_ERRNO("Failed to stat file", ": path=%s", path);
 131                 goto end;
 132         }
 133
 134         /*
 135          * Use the device number and inode number to uniquely identify a file.
 136          * Even if the file has the same path, it may have been replaced so we
 137          * must open a new FD for it. This replacement of file is more likely
 138          * to happen with a lttng-live source component.
 139          */
 140         fk.dev = statbuf.st_dev;
 141         fk.ino = statbuf.st_ino;
 142
 143         fd_internal = g_hash_table_lookup(fdc->cache, &fk);
 144         if (!fd_internal) {
 145                 struct file_key *file_key;
 146
 147                 fd = open(path, O_RDONLY);
 148                 if (fd < 0) {
 149                         BT_LOGE_ERRNO("Failed to open file", "path=%s", path);
 150                         goto error;
 151                 }
 152
 153                 fd_internal = g_new0(struct fd_handle_internal, 1);
 154                 if (!fd_internal) {
 155                         BT_LOGE_STR("Failed to allocate internal FD handle.");
 156                         goto error;
 157                 }
 158
 159                 file_key = g_new0(struct file_key, 1);
 160                 if (!fd_internal) {
 161                         BT_LOGE_STR("Failed to allocate file key.");
 162                         goto error;
 163                 }
 164
 165                 *file_key = fk;
 166
 167                 fd_internal->fd_handle.fd = fd;
 168                 fd_internal->ref_count = 0;
 169                 fd_internal->key = file_key;
 170
 171                 /* Insert the newly created fd handle. */
 172                 g_hash_table_insert(fdc->cache, fd_internal->key, fd_internal);
 173         }
 174
 175         fd_internal->ref_count++;
 176         goto end;
 177
 178 error:
 179         /*
 180          * Close file descriptor if it was open() and we are currently on error
 181          * path.
 182          */
 183         if (fd != -1) {
 184                 ret = close(fd);
 185                 if (ret) {
 186                         BT_LOGE_ERRNO("Failed to close file descriptor",
 187                                 ": fd=%i, path=%s", fd, path);
 188                 }
 189         }
 190
 191         fd_cache_handle_internal_destroy(fd_internal);
 192         fd_internal = NULL;
 193 end:
 194         return (struct bt_fd_cache_handle *) fd_internal;
 195 }
 196
 197 void bt_fd_cache_put_handle(struct bt_fd_cache *fdc,
 198                 struct bt_fd_cache_handle *handle)
 199 {
 200         struct fd_handle_internal *fd_internal;
 201
 202         if (!handle) {
 203                 goto end;
 204         }
 205
 206         fd_internal = (struct fd_handle_internal *) handle;
 207
 208         BT_ASSERT(fd_internal->ref_count > 0);
 209
 210         if (fd_internal->ref_count > 1) {
 211                 fd_internal->ref_count--;
 212         } else {
 213                 gboolean ret;
 214                 int close_ret;
 215
 216                 close_ret = close(fd_internal->fd_handle.fd);
 217                 if (close_ret == -1) {
 218                         BT_LOGE_ERRNO("Failed to close file descriptor",
 219                                 ": fd=%d", fd_internal->fd_handle.fd);
 220                 }
 221                 ret = g_hash_table_remove(fdc->cache, fd_internal->key);
 222                 BT_ASSERT(ret);
 223         }
 224
 225 end:
 226         return;
 227 }