/src/util-linux/libmount/src/cache.c

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/* SPDX-License-Identifier: LGPL-2.1-or-later */

/*
 * This file is part of libmount from util-linux project.
 *
 * Copyright (C) 2009-2018 Karel Zak <kzak@redhat.com>
 *
 * libmount is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 */

/**
 * SECTION: cache
 * @title: Cache
 * @short_description: paths and tags (UUID/LABEL) caching
 *
 * The cache is a very simple API for working with tags (LABEL, UUID, ...) and
 * paths. The cache uses libblkid as a backend for TAGs resolution.
 *
 * All returned paths are always canonicalized.
 */
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include <limits.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <blkid.h>

#include "canonicalize.h"
#include "mountP.h"
#include "loopdev.h"
#include "strutils.h"

/*
 * Canonicalized (resolved) paths & tags cache
 */
#define MNT_CACHE_CHUNKSZ 128

#define MNT_CACHE_ISTAG   (1 << 1) /* entry is TAG */
#define MNT_CACHE_ISPATH  (1 << 2) /* entry is path */
#define MNT_CACHE_TAGREAD (1 << 3) /* tag read by mnt_cache_read_tags() */

/* path cache entry */
struct mnt_cache_entry {
  char      *key; /* search key (e.g. uncanonicalized path) */
  char      *value; /* value (e.g. canonicalized path) */
  int     flag;
};

struct libmnt_cache {
  struct mnt_cache_entry  *ents;
  size_t      nents;
  size_t      nallocs;
  int     refcount;
  int     probe_sb_extra; /* extra BLKID_SUBLKS_* flags */

  /* blkid_evaluate_tag() works in two ways:
   *
   * 1/ all tags are evaluated by udev /dev/disk/by-* symlinks,
   *    then the blkid_cache is NULL.
   *
   * 2/ all tags are read from blkid.tab and verified by /dev
   *    scanning, then the blkid_cache is not NULL and then it's
   *    better to reuse the blkid_cache.
   */
  blkid_cache   bc;

  struct libmnt_table *mountinfo;
};

/**
 * mnt_new_cache:
 *
 * Returns: new struct libmnt_cache instance or NULL in case of ENOMEM error.
 */
struct libmnt_cache *mnt_new_cache(void)
{
  struct libmnt_cache *cache = calloc(1, sizeof(*cache));
  if (!cache)
    return NULL;
  DBG(CACHE, ul_debugobj(cache, "alloc"));
  cache->refcount = 1;
  return cache;
}

/**
 * mnt_free_cache:
 * @cache: pointer to struct libmnt_cache instance
 *
 * Deallocates the cache. This function does not care about reference count. Don't
 * use this function directly -- it's better to use mnt_unref_cache().
 */
void mnt_free_cache(struct libmnt_cache *cache)
{
  size_t i;

  if (!cache)
    return;

  DBG(CACHE, ul_debugobj(cache, "free [refcount=%d]", cache->refcount));

  for (i = 0; i < cache->nents; i++) {
    struct mnt_cache_entry *e = &cache->ents[i];
    if (e->value != e->key)
      free(e->value);
    free(e->key);
  }
  free(cache->ents);
  if (cache->bc)
    blkid_put_cache(cache->bc);
  free(cache);
}

/**
 * mnt_ref_cache:
 * @cache: cache pointer
 *
 * Increments reference counter.
 */
void mnt_ref_cache(struct libmnt_cache *cache)
{
  if (cache) {
    cache->refcount++;
    /*DBG(CACHE, ul_debugobj(cache, "ref=%d", cache->refcount));*/
  }
}

/**
 * mnt_unref_cache:
 * @cache: cache pointer
 *
 * De-increments reference counter, on zero the cache is automatically
 * deallocated by mnt_free_cache().
 */
void mnt_unref_cache(struct libmnt_cache *cache)
{
  if (cache) {
    cache->refcount--;
    /*DBG(CACHE, ul_debugobj(cache, "unref=%d", cache->refcount));*/
    if (cache->refcount <= 0) {
      mnt_unref_table(cache->mountinfo);

      mnt_free_cache(cache);
    }
  }
}

/**
 * mnt_cache_set_targets:
 * @cache: cache pointer
 * @mountinfo: table with already canonicalized mountpoints
 *
 * Add to @cache reference to @mountinfo. This can be used to avoid unnecessary paths
 * canonicalization in mnt_resolve_target().
 *
 * Returns: negative number in case of error, or 0 o success.
 */
int mnt_cache_set_targets(struct libmnt_cache *cache,
        struct libmnt_table *mountinfo)
{
  if (!cache)
    return -EINVAL;

  mnt_ref_table(mountinfo);
  mnt_unref_table(cache->mountinfo);
  cache->mountinfo = mountinfo;
  return 0;
}

/**
 * mnt_cache_set_sbprobe:
 * @cache: cache pointer
 * @flags: BLKID_SUBLKS_* flags
 *
 * Add extra flags to the libblkid prober. Don't use if not sure.
 *
 * Returns: negative number in case of error, or 0 o success.
 */
int mnt_cache_set_sbprobe(struct libmnt_cache *cache, int flags)
{
  if (!cache)
    return -EINVAL;

  cache->probe_sb_extra = flags;
  return 0;
}

/* note that the @key could be the same pointer as @value */
static int cache_add_entry(struct libmnt_cache *cache, char *key,
          char *value, int flag)
{
  struct mnt_cache_entry *e;

  assert(cache);
  assert(value);
  assert(key);

  if (cache->nents == cache->nallocs) {
    size_t sz = cache->nallocs + MNT_CACHE_CHUNKSZ;

    e = reallocarray(cache->ents, sz, sizeof(struct mnt_cache_entry));
    if (!e)
      return -ENOMEM;
    cache->ents = e;
    cache->nallocs = sz;
  }

  e = &cache->ents[cache->nents];
  e->key = key;
  e->value = value;
  e->flag = flag;
  cache->nents++;

  DBG(CACHE, ul_debugobj(cache, "add entry [%2zd] (%s): %s: %s",
      cache->nents,
      (flag & MNT_CACHE_ISPATH) ? "path" : "tag",
      value, key));
  return 0;
}

/* add tag to the cache, @devname has to be an allocated string */
static int cache_add_tag(struct libmnt_cache *cache, const char *tagname,
        const char *tagval, char *devname, int flag)
{
  size_t tksz, vlsz;
  char *key;
  int rc;

  assert(cache);
  assert(devname);
  assert(tagname);
  assert(tagval);

  /* add into cache -- cache format for TAGs is
   *  key    = "TAG_NAME\0TAG_VALUE\0"
   *  value  = "/dev/foo"
   */
  tksz = strlen(tagname);
  vlsz = strlen(tagval);

  key = malloc(tksz + vlsz + 2);
  if (!key)
    return -ENOMEM;

  memcpy(key, tagname, tksz + 1);    /* include '\0' */
  memcpy(key + tksz + 1, tagval, vlsz + 1);

  rc = cache_add_entry(cache, key, devname, flag | MNT_CACHE_ISTAG);
  if (!rc)
    return 0;

  free(key);
  return rc;
}


/*
 * Returns cached canonicalized path or NULL.
 */
static const char *cache_find_path(struct libmnt_cache *cache, const char *path)
{
  size_t i;

  if (!cache || !path)
    return NULL;

  for (i = 0; i < cache->nents; i++) {
    struct mnt_cache_entry *e = &cache->ents[i];
    if (!(e->flag & MNT_CACHE_ISPATH))
      continue;
    if (streq_paths(path, e->key))
      return e->value;
  }
  return NULL;
}

/*
 * Returns cached path or NULL.
 */
static const char *cache_find_tag(struct libmnt_cache *cache,
      const char *token, const char *value)
{
  size_t i;
  size_t tksz;

  if (!cache || !token || !value)
    return NULL;

  tksz = strlen(token);

  for (i = 0; i < cache->nents; i++) {
    struct mnt_cache_entry *e = &cache->ents[i];
    if (!(e->flag & MNT_CACHE_ISTAG))
      continue;
    if (strcmp(token, e->key) == 0 &&
        strcmp(value, e->key + tksz + 1) == 0)
      return e->value;
  }
  return NULL;
}

static char *cache_find_tag_value(struct libmnt_cache *cache,
      const char *devname, const char *token)
{
  size_t i;

  assert(cache);
  assert(devname);
  assert(token);

  for (i = 0; i < cache->nents; i++) {
    struct mnt_cache_entry *e = &cache->ents[i];
    if (!(e->flag & MNT_CACHE_ISTAG))
      continue;
    if (strcmp(e->value, devname) == 0 && /* dev name */
        strcmp(token, e->key) == 0) /* tag name */
      return e->key + strlen(token) + 1; /* tag value */
  }

  return NULL;
}

/**
 * mnt_cache_read_tags
 * @cache: pointer to struct libmnt_cache instance
 * @devname: path device
 *
 * Reads @devname LABEL and UUID to the @cache.
 *
 * Returns: 0 if at least one tag was added, 1 if no tag was added or
 *          negative number in case of error.
 */
int mnt_cache_read_tags(struct libmnt_cache *cache, const char *devname)
{
  blkid_probe pr;
  size_t i, ntags = 0;
  int rc;
  const char *tags[] = { "LABEL", "UUID", "TYPE", "PARTUUID", "PARTLABEL" };
  const char *blktags[] = { "LABEL", "UUID", "TYPE", "PART_ENTRY_UUID", "PART_ENTRY_NAME" };

  if (!cache || !devname)
    return -EINVAL;

  DBG(CACHE, ul_debugobj(cache, "tags for %s requested", devname));

  /* check if device is already cached */
  for (i = 0; i < cache->nents; i++) {
    struct mnt_cache_entry *e = &cache->ents[i];
    if (!(e->flag & MNT_CACHE_TAGREAD))
      continue;
    if (strcmp(e->value, devname) == 0)
      /* tags have already been read */
      return 0;
  }

  pr =  blkid_new_probe_from_filename(devname);
  if (!pr)
    return -1;

  blkid_probe_enable_superblocks(pr, 1);
  blkid_probe_set_superblocks_flags(pr,
      BLKID_SUBLKS_LABEL | BLKID_SUBLKS_UUID |
      BLKID_SUBLKS_TYPE | cache->probe_sb_extra);

  blkid_probe_enable_partitions(pr, 1);
  blkid_probe_set_partitions_flags(pr, BLKID_PARTS_ENTRY_DETAILS);

  rc = blkid_do_safeprobe(pr);
  if (rc)
    goto error;

  DBG(CACHE, ul_debugobj(cache, "reading tags for: %s", devname));

  for (i = 0; i < ARRAY_SIZE(tags); i++) {
    const char *data;
    char *dev;

    if (cache_find_tag_value(cache, devname, tags[i])) {
      DBG(CACHE, ul_debugobj(cache,
          "\ntag %s already cached", tags[i]));
      continue;
    }
    if (blkid_probe_lookup_value(pr, blktags[i], &data, NULL))
      continue;
    dev = strdup(devname);
    if (!dev)
      goto error;
    if (cache_add_tag(cache, tags[i], data, dev,
          MNT_CACHE_TAGREAD)) {
      free(dev);
      goto error;
    }
    ntags++;
  }

  DBG(CACHE, ul_debugobj(cache, "\tread %zd tags", ntags));
  blkid_free_probe(pr);
  return ntags ? 0 : 1;
error:
  blkid_free_probe(pr);
  return rc < 0 ? rc : -1;
}

/**
 * mnt_cache_device_has_tag:
 * @cache: paths cache
 * @devname: path to the device
 * @token: tag name (e.g "LABEL")
 * @value: tag value
 *
 * Look up @cache to check if @tag+@value are associated with @devname.
 *
 * Returns: 1 on success or 0.
 */
int mnt_cache_device_has_tag(struct libmnt_cache *cache, const char *devname,
        const char *token, const char *value)
{
  const char *path = cache_find_tag(cache, token, value);

  if (path && devname && strcmp(path, devname) == 0)
    return 1;
  return 0;
}

static int __mnt_cache_find_tag_value(struct libmnt_cache *cache,
    const char *devname, const char *token, char **data)
{
  int rc = 0;

  if (!cache || !devname || !token || !data)
    return -EINVAL;

  rc = mnt_cache_read_tags(cache, devname);
  if (rc)
    return rc;

  *data = cache_find_tag_value(cache, devname, token);
  return *data ? 0 : -1;
}

/**
 * mnt_cache_find_tag_value:
 * @cache: cache for results
 * @devname: device name
 * @token: tag name ("LABEL" or "UUID")
 *
 * Returns: LABEL or UUID for the @devname or NULL in case of error.
 */
char *mnt_cache_find_tag_value(struct libmnt_cache *cache,
    const char *devname, const char *token)
{
  char *data = NULL;

  if (__mnt_cache_find_tag_value(cache, devname, token, &data) == 0)
    return data;
  return NULL;
}

/**
 * mnt_get_fstype:
 * @devname: device name
 * @ambi: returns TRUE if probing result is ambivalent (optional argument)
 * @cache: cache for results or NULL
 *
 * Returns: filesystem type or NULL in case of error. The result has to be
 * deallocated by free() if @cache is NULL.
 */
char *mnt_get_fstype(const char *devname, int *ambi, struct libmnt_cache *cache)
{
  blkid_probe pr;
  const char *data;
  char *type = NULL;
  int rc;

  DBG(CACHE, ul_debugobj(cache, "get %s FS type", devname));

  if (cache) {
    char *val = NULL;
    rc = __mnt_cache_find_tag_value(cache, devname, "TYPE", &val);
    if (ambi)
      *ambi = rc == -2 ? TRUE : FALSE;
    return rc ? NULL : val;
  }

  /*
   * no cache, probe directly
   */
  pr =  blkid_new_probe_from_filename(devname);
  if (!pr)
    return NULL;

  blkid_probe_enable_superblocks(pr, 1);
  blkid_probe_set_superblocks_flags(pr, BLKID_SUBLKS_TYPE);

  rc = blkid_do_safeprobe(pr);

  DBG(CACHE, ul_debugobj(cache, "libblkid rc=%d", rc));

  if (!rc && !blkid_probe_lookup_value(pr, "TYPE", &data, NULL))
    type = strdup(data);

  if (ambi)
    *ambi = rc == -2 ? TRUE : FALSE;

  blkid_free_probe(pr);
  return type;
}

static char *canonicalize_path_and_cache(const char *path,
            struct libmnt_cache *cache)
{
  char *p;
  char *key;
  char *value;

  DBG(CACHE, ul_debugobj(cache, "canonicalize path %s", path));
  p = canonicalize_path(path);

  if (p && cache) {
    value = p;
    key = strcmp(path, p) == 0 ? value : strdup(path);

    if (!key || !value)
      goto error;

    if (cache_add_entry(cache, key, value,
        MNT_CACHE_ISPATH))
      goto error;
  }

  return p;
error:
  if (value != key)
    free(value);
  free(key);
  return NULL;
}

/**
 * mnt_resolve_path:
 * @path: "native" path
 * @cache: cache for results or NULL
 *
 * Converts path:
 *  - to the absolute path
 *  - /dev/dm-N to /dev/mapper/name
 *
 * Returns: absolute path or NULL in case of error. The result has to be
 * deallocated by free() if @cache is NULL.
 */
char *mnt_resolve_path(const char *path, struct libmnt_cache *cache)
{
  char *p = NULL;

  /*DBG(CACHE, ul_debugobj(cache, "resolving path %s", path));*/

  if (!path)
    return NULL;
  if (cache)
    p = (char *) cache_find_path(cache, path);
  if (!p)
    p = canonicalize_path_and_cache(path, cache);

  return p;
}

/**
 * mnt_resolve_target:
 * @path: "native" path, a potential mount point
 * @cache: cache for results or NULL.
 *
 * Like mnt_resolve_path(), unless @cache is not NULL and
 * mnt_cache_set_targets(cache, mountinfo) was called: if @path is found in the
 * cached @mountinfo and the matching entry was provided by the kernel, assume that
 * @path is already canonicalized. By avoiding a call to realpath(2) on
 * known mount points, there is a lower risk of stepping on a stale mount
 * point, which can result in an application freeze. This is also faster in
 * general, as stat(2) on a mount point is slower than on a regular file.
 *
 * Returns: absolute path or NULL in case of error. The result has to be
 * deallocated by free() if @cache is NULL.
 */
char *mnt_resolve_target(const char *path, struct libmnt_cache *cache)
{
  char *p = NULL;

  if (!path)
    return NULL;

  /*DBG(CACHE, ul_debugobj(cache, "resolving target %s", path));*/

  if (!cache || !cache->mountinfo)
    return mnt_resolve_path(path, cache);

  p = (char *) cache_find_path(cache, path);
  if (p)
    return p;

  {
    struct libmnt_iter itr;
    struct libmnt_fs *fs = NULL;

    mnt_reset_iter(&itr, MNT_ITER_BACKWARD);
    while (mnt_table_next_fs(cache->mountinfo, &itr, &fs) == 0) {

      if (!mnt_fs_is_kernel(fs)
           || mnt_fs_is_swaparea(fs)
           || !mnt_fs_streq_target(fs, path))
        continue;

      p = strdup(path);
      if (!p)
        return NULL; /* ENOMEM */

      if (cache_add_entry(cache, p, p, MNT_CACHE_ISPATH)) {
        free(p);
        return NULL;  /* ENOMEM */
      }
      break;
    }
  }

  if (!p)
    p = canonicalize_path_and_cache(path, cache);
  return p;
}

/**
 * mnt_pretty_path:
 * @path: any path
 * @cache: NULL or pointer to the cache
 *
 * Converts path:
 *  - to the absolute path
 *  - /dev/dm-N to /dev/mapper/name
 *  - /dev/loopN to the loop backing filename
 *  - empty path (NULL) to 'none'
 *
 * Returns: newly allocated string with path, result always has to be deallocated
 *          by free().
 */
char *mnt_pretty_path(const char *path, struct libmnt_cache *cache)
{
  char *pretty = mnt_resolve_path(path, cache);

  if (!pretty)
    return strdup("none");

#ifdef __linux__
  /* users assume backing file name rather than /dev/loopN in
   * output if the device has been initialized by mount(8).
   */
  if (strncmp(pretty, "/dev/loop", 9) == 0) {
    struct loopdev_cxt lc;

    if (loopcxt_init(&lc, 0) || loopcxt_set_device(&lc, pretty))
      goto done;

    if (loopcxt_is_autoclear(&lc)) {
      char *tmp = loopcxt_get_backing_file(&lc);
      if (tmp) {
        loopcxt_deinit(&lc);
        if (!cache)
          free(pretty); /* not cached, deallocate */
        return tmp;   /* return backing file */
      }
    }
    loopcxt_deinit(&lc);

  }
#endif

done:
  /* don't return pointer to the cache, allocate a new string */
  return cache ? strdup(pretty) : pretty;
}

/**
 * mnt_resolve_tag:
 * @token: tag name
 * @value: tag value
 * @cache: for results or NULL
 *
 * Returns: device name or NULL in case of error. The result has to be
 * deallocated by free() if @cache is NULL.
 */
char *mnt_resolve_tag(const char *token, const char *value,
          struct libmnt_cache *cache)
{
  char *p = NULL;

  /*DBG(CACHE, ul_debugobj(cache, "resolving tag token=%s value=%s",
        token, value));*/

  if (!token || !value)
    return NULL;

  if (cache)
    p = (char *) cache_find_tag(cache, token, value);

  if (!p) {
    /* returns newly allocated string */
    p = blkid_evaluate_tag(token, value, cache ? &cache->bc : NULL);

    if (p && cache &&
        cache_add_tag(cache, token, value, p, 0))
        goto error;
  }

  return p;
error:
  free(p);
  return NULL;
}



/**
 * mnt_resolve_spec:
 * @spec: path or tag
 * @cache: paths cache
 *
 * Returns: canonicalized path or NULL. The result has to be
 * deallocated by free() if @cache is NULL.
 */
char *mnt_resolve_spec(const char *spec, struct libmnt_cache *cache)
{
  char *cn = NULL;
  char *t = NULL, *v = NULL;

  if (!spec)
    return NULL;

  if (blkid_parse_tag_string(spec, &t, &v) == 0 && mnt_valid_tagname(t))
    cn = mnt_resolve_tag(t, v, cache);
  else
    cn = mnt_resolve_path(spec, cache);

  free(t);
  free(v);
  return cn;
}


#ifdef TEST_PROGRAM

static int test_resolve_path(struct libmnt_test *ts __attribute__((unused)),
           int argc __attribute__((unused)),
           char *argv[] __attribute__((unused)))
{
  char line[BUFSIZ];
  struct libmnt_cache *cache;

  cache = mnt_new_cache();
  if (!cache)
    return -ENOMEM;

  while(fgets(line, sizeof(line), stdin)) {
    size_t sz = strlen(line);
    char *p;

    if (sz > 0 && line[sz - 1] == '\n')
      line[sz - 1] = '\0';

    p = mnt_resolve_path(line, cache);
    printf("%s : %s\n", line, p);
  }
  mnt_unref_cache(cache);
  return 0;
}

static int test_resolve_spec(struct libmnt_test *ts __attribute__((unused)),
           int argc __attribute__((unused)),
           char *argv[] __attribute__((unused)))
{
  char line[BUFSIZ];
  struct libmnt_cache *cache;

  cache = mnt_new_cache();
  if (!cache)
    return -ENOMEM;

  while(fgets(line, sizeof(line), stdin)) {
    size_t sz = strlen(line);
    char *p;

    if (sz > 0 && line[sz - 1] == '\n')
      line[sz - 1] = '\0';

    p = mnt_resolve_spec(line, cache);
    printf("%s : %s\n", line, p);
  }
  mnt_unref_cache(cache);
  return 0;
}

static int test_read_tags(struct libmnt_test *ts __attribute__((unused)),
        int argc __attribute__((unused)),
        char *argv[] __attribute__((unused)))
{
  char line[BUFSIZ];
  struct libmnt_cache *cache;
  size_t i;

  cache = mnt_new_cache();
  if (!cache)
    return -ENOMEM;

  while(fgets(line, sizeof(line), stdin)) {
    size_t sz = strlen(line);
    char *t = NULL, *v = NULL;

    if (sz > 0 && line[sz - 1] == '\n')
      line[sz - 1] = '\0';

    if (!strcmp(line, "quit"))
      break;

    if (*line == '/') {
      if (mnt_cache_read_tags(cache, line) < 0)
        fprintf(stderr, "%s: read tags failed\n", line);

    } else if (blkid_parse_tag_string(line, &t, &v) == 0) {
      const char *cn = NULL;

      if (mnt_valid_tagname(t))
        cn = cache_find_tag(cache, t, v);
      free(t);
      free(v);

      if (cn)
        printf("%s: %s\n", line, cn);
      else
        printf("%s: not cached\n", line);
    }
  }

  for (i = 0; i < cache->nents; i++) {
    struct mnt_cache_entry *e = &cache->ents[i];
    if (!(e->flag & MNT_CACHE_ISTAG))
      continue;

    printf("%15s : %5s : %s\n", e->value, e->key,
        e->key + strlen(e->key) + 1);
  }

  mnt_unref_cache(cache);
  return 0;

}

int main(int argc, char *argv[])
{
  struct libmnt_test ts[] = {
    { "--resolve-path", test_resolve_path, "  resolve paths from stdin" },
    { "--resolve-spec", test_resolve_spec, "  evaluate specs from stdin" },
    { "--read-tags", test_read_tags,       "  read devname or TAG from stdin (\"quit\" to exit)" },
    { NULL }
  };

  return mnt_run_test(ts, argc, argv);
}
#endif

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Created: 2025-08-09 06:31