libmount: add reference counting to libmnt_cache

Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/libmount/docs/libmount-sections.txt b/libmount/docs/libmount-sections.txt
index 97e0851e500c1810f9e8dbe4d7399ab69e25693b..3ebc4aaf2e5a2916305b2a7bf57f72a38e6bf200 100644 (file)
--- a/libmount/docs/libmount-sections.txt
+++ b/libmount/docs/libmount-sections.txt
@@ -3,6 +3,8 @@
 libmnt_cache
 mnt_new_cache
 mnt_free_cache
+mnt_ref_cache
+mnt_unref_cache
 mnt_cache_device_has_tag
 mnt_cache_find_tag_value
 mnt_cache_read_tags

diff --git a/libmount/src/cache.c b/libmount/src/cache.c
index ef1a64107a609f957c7618b828e94306eec7a1be..cf5c6d430229be64e7dfb80392046edb7be7bb1a 100644 (file)
--- a/libmount/src/cache.c
+++ b/libmount/src/cache.c
@@ -48,6 +48,7 @@ struct libmnt_cache {
        struct mnt_cache_entry  *ents;
        size_t                  nents;
        size_t                  nallocs;
+       int                     refcount;
 
        /* blkid_evaluate_tag() works in two ways:
         *
@@ -72,6 +73,7 @@ struct libmnt_cache *mnt_new_cache(void)
        if (!cache)
                return NULL;
        DBG(CACHE, mnt_debug_h(cache, "alloc"));
+       cache->refcount = 1;
        return cache;
 }
 
@@ -89,6 +91,7 @@ void mnt_free_cache(struct libmnt_cache *cache)
                return;
 
        DBG(CACHE, mnt_debug_h(cache, "free"));
+       WARN_REFCOUNT(CACHE, cache, cache->refcount);
 
        for (i = 0; i < cache->nents; i++) {
                struct mnt_cache_entry *e = &cache->ents[i];
@@ -102,6 +105,38 @@ void mnt_free_cache(struct libmnt_cache *cache)
        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, mnt_debug_h(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, mnt_debug_h(cache, "unref=%d", cache->refcount));*/
+               if (cache->refcount <= 0)
+                       mnt_free_cache(cache);
+       }
+}
+
+
 /* 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)
@@ -620,7 +655,7 @@ int test_resolve_path(struct libmnt_test *ts, int argc, char *argv[])
                p = mnt_resolve_path(line, cache);
                printf("%s : %s\n", line, p);
        }
-       mnt_free_cache(cache);
+       mnt_unref_cache(cache);
        return 0;
 }
 
@@ -643,7 +678,7 @@ int test_resolve_spec(struct libmnt_test *ts, int argc, char *argv[])
                p = mnt_resolve_spec(line, cache);
                printf("%s : %s\n", line, p);
        }
-       mnt_free_cache(cache);
+       mnt_unref_cache(cache);
        return 0;
 }
 
@@ -695,7 +730,7 @@ int test_read_tags(struct libmnt_test *ts, int argc, char *argv[])
                                e->key + strlen(e->key) + 1);
        }
 
-       mnt_free_cache(cache);
+       mnt_unref_cache(cache);
        return 0;
 
 }

diff --git a/libmount/src/context.c b/libmount/src/context.c
index ea13f0d1e4a13f7e0ef5f5b889f27cc04d1f45b9..5d5e8fba8dc82b38d309ebee07fae95d3137463f 100644 (file)
--- a/libmount/src/context.c
+++ b/libmount/src/context.c
@@ -91,8 +91,8 @@ void mnt_free_context(struct libmnt_context *cxt)
 
        if (!(cxt->flags & MNT_FL_EXTERN_FSTAB))
                mnt_free_table(cxt->fstab);
-       if (!(cxt->flags & MNT_FL_EXTERN_CACHE))
-               mnt_free_cache(cxt->cache);
+
+       mnt_unref_cache(cxt->cache);
 
        mnt_context_clear_loopdev(cxt);
        mnt_free_lock(cxt->lock);
@@ -925,8 +925,6 @@ int mnt_context_set_fstab(struct libmnt_context *cxt, struct libmnt_table *tb)
  */
 int mnt_context_get_fstab(struct libmnt_context *cxt, struct libmnt_table **tb)
 {
-       struct libmnt_cache *cache;
-
        assert(cxt);
        if (!cxt)
                return -EINVAL;
@@ -944,11 +942,9 @@ int mnt_context_get_fstab(struct libmnt_context *cxt, struct libmnt_table **tb)
                        return rc;
        }
 
-       cache = mnt_context_get_cache(cxt);
-
        /*  never touch an external fstab */
        if (!(cxt->flags & MNT_FL_EXTERN_FSTAB))
-               mnt_table_set_cache(cxt->fstab, cache);
+               mnt_table_set_cache(cxt->fstab, mnt_context_get_cache(cxt));
 
        if (tb)
                *tb = cxt->fstab;
@@ -967,8 +963,6 @@ int mnt_context_get_fstab(struct libmnt_context *cxt, struct libmnt_table **tb)
  */
 int mnt_context_get_mtab(struct libmnt_context *cxt, struct libmnt_table **tb)
 {
-       struct libmnt_cache *cache;
-
        assert(cxt);
        if (!cxt)
                return -EINVAL;
@@ -991,8 +985,7 @@ int mnt_context_get_mtab(struct libmnt_context *cxt, struct libmnt_table **tb)
                        return rc;
        }
 
-       cache = mnt_context_get_cache(cxt);
-       mnt_table_set_cache(cxt->mtab, cache);
+       mnt_table_set_cache(cxt->mtab, mnt_context_get_cache(cxt));
 
        if (tb)
                *tb = cxt->mtab;
@@ -1048,7 +1041,6 @@ int mnt_context_set_tabfilter(struct libmnt_context *cxt,
 int mnt_context_get_table(struct libmnt_context *cxt,
                          const char *filename, struct libmnt_table **tb)
 {
-       struct libmnt_cache *cache;
        int rc;
 
        assert(cxt);
@@ -1069,10 +1061,7 @@ int mnt_context_get_table(struct libmnt_context *cxt,
                return rc;
        }
 
-       cache = mnt_context_get_cache(cxt);
-       if (cache)
-               mnt_table_set_cache(*tb, cache);
-
+       mnt_table_set_cache(*tb, mnt_context_get_cache(cxt));
        return 0;
 }
 
@@ -1106,23 +1095,25 @@ int mnt_context_set_tables_errcb(struct libmnt_context *cxt,
  * @cxt: mount context
  * @cache: cache instance or nULL
  *
- * The mount context maintains a private struct libmnt_cache by default.  This function
- * allows to overwrite the private cache with an external instance. Note that
- * the external instance is not deallocated by mnt_free_context().
+ * The mount context maintains a private struct libmnt_cache by default. This
+ * function allows to overwrite the private cache with an external instance.
+ * This function increments cache reference counter.
  *
  * If the @cache argument is NULL, then the current private cache instance is
  * reset.
  *
+ * The old cache instance reference counter is de-incremented.
+ *
  * Returns: 0 on success, negative number in case of error.
  */
 int mnt_context_set_cache(struct libmnt_context *cxt, struct libmnt_cache *cache)
 {
        if (!cxt)
                return -EINVAL;
-       if (!(cxt->flags & MNT_FL_EXTERN_CACHE))
-               mnt_free_cache(cxt->cache);
 
-       set_flag(cxt, MNT_FL_EXTERN_CACHE, cache != NULL);
+       mnt_ref_cache(cache);                   /* new */
+       mnt_unref_cache(cxt->cache);            /* old */
+
        cxt->cache = cache;
        return 0;
 }
@@ -1145,7 +1136,6 @@ struct libmnt_cache *mnt_context_get_cache(struct libmnt_context *cxt)
                cxt->cache = mnt_new_cache();
                if (!cxt->cache)
                        return NULL;
-               cxt->flags &= ~MNT_FL_EXTERN_CACHE;
        }
        return cxt->cache;
 }

diff --git a/libmount/src/libmount.h.in b/libmount/src/libmount.h.in
index 29659628dd9eba062fc5052504ac2a6148d2f859..f4efd980435679e804a3d689289f1d9d88ddb0a9 100644 (file)
--- a/libmount/src/libmount.h.in
+++ b/libmount/src/libmount.h.in
@@ -216,6 +216,9 @@ extern struct libmnt_cache *mnt_new_cache(void)
                        __ul_attribute__((warn_unused_result));
 extern void mnt_free_cache(struct libmnt_cache *cache);
 
+extern void mnt_ref_cache(struct libmnt_cache *cache);
+extern void mnt_unref_cache(struct libmnt_cache *cache);
+
 extern int mnt_cache_read_tags(struct libmnt_cache *cache, const char *devname);
 
 extern int mnt_cache_device_has_tag(struct libmnt_cache *cache,

diff --git a/libmount/src/libmount.sym b/libmount/src/libmount.sym
index 621821e9779469b4787bca67987e1292bf1a4941..5a7e0def3f92a28a8831eedde232e7ecd2d7c6ec 100644 (file)
--- a/libmount/src/libmount.sym
+++ b/libmount/src/libmount.sym
@@ -265,6 +265,7 @@ global:
        mnt_fs_append_comment;
        mnt_fs_get_comment;
        mnt_fs_set_comment;
+       mnt_ref_cache;
        mnt_ref_fs;
        mnt_table_append_intro_comment;
        mnt_table_append_trailing_comment;
@@ -281,5 +282,6 @@ global:
        mnt_table_set_userdata;
        mnt_table_with_comments;
        mnt_table_write_file;
+       mnt_unref_cache;
        mnt_unref_fs;
 } MOUNT_2.23;

diff --git a/libmount/src/tab.c b/libmount/src/tab.c
index 58edf2f4261449e1dc649ba48e7837b36f1e0a85..a2ad604f792024ab89df4038fab32c2833c5939d 100644 (file)
--- a/libmount/src/tab.c
+++ b/libmount/src/tab.c
@@ -109,6 +109,7 @@ void mnt_free_table(struct libmnt_table *tb)
                return;
 
        mnt_reset_table(tb);
+       mnt_unref_cache(tb->cache);
 
        DBG(TAB, mnt_debug_h(tb, "free"));
        free(tb->comm_intro);
@@ -338,6 +339,10 @@ int mnt_table_append_trailing_comment(struct libmnt_table *tb, const char *comm)
  * same cache between more threads -- currently the cache does not provide any
  * locking method.
  *
+ * This function increments cache refrence counter. It's recomented to use
+ * mnt_unref_cache() after mnt_table_set_cache() if you want to keep the cache
+ * referenced by @tb only.
+ *
  * See also mnt_new_cache().
  *
  * Returns: 0 on success or negative number in case of error.
@@ -347,6 +352,9 @@ int mnt_table_set_cache(struct libmnt_table *tb, struct libmnt_cache *mpc)
        assert(tb);
        if (!tb)
                return -EINVAL;
+
+       mnt_ref_cache(mpc);                     /* new */
+       mnt_unref_cache(tb->cache);             /* old */
        tb->cache = mpc;
        return 0;
 }
@@ -1456,6 +1464,7 @@ int test_find(struct libmnt_test *ts, int argc, char *argv[], int dr)
        if (!mpc)
                goto done;
        mnt_table_set_cache(tb, mpc);
+       mnt_unref_cache(mpc);
 
        if (strcasecmp(find, "source") == 0)
                fs = mnt_table_find_source(tb, what, dr);
@@ -1470,7 +1479,6 @@ int test_find(struct libmnt_test *ts, int argc, char *argv[], int dr)
        }
 done:
        mnt_free_table(tb);
-       mnt_free_cache(mpc);
        return rc;
 }
 
@@ -1498,6 +1506,7 @@ int test_find_pair(struct libmnt_test *ts, int argc, char *argv[])
        if (!mpc)
                goto done;
        mnt_table_set_cache(tb, mpc);
+       mnt_unref_cache(mpc);
 
        fs = mnt_table_find_pair(tb, argv[2], argv[3], MNT_ITER_FORWARD);
        if (!fs)
@@ -1507,7 +1516,6 @@ int test_find_pair(struct libmnt_test *ts, int argc, char *argv[])
        rc = 0;
 done:
        mnt_free_table(tb);
-       mnt_free_cache(mpc);
        return rc;
 }
 
@@ -1525,6 +1533,7 @@ int test_find_mountpoint(struct libmnt_test *ts, int argc, char *argv[])
        if (!mpc)
                goto done;
        mnt_table_set_cache(tb, mpc);
+       mnt_unref_cache(mpc);
 
        fs = mnt_table_find_mountpoint(tb, argv[1], MNT_ITER_BACKWARD);
        if (!fs)
@@ -1534,7 +1543,6 @@ int test_find_mountpoint(struct libmnt_test *ts, int argc, char *argv[])
        rc = 0;
 done:
        mnt_free_table(tb);
-       mnt_free_cache(mpc);
        return rc;
 }
 
@@ -1564,6 +1572,7 @@ static int test_is_mounted(struct libmnt_test *ts, int argc, char *argv[])
        if (!mpc)
                goto done;
        mnt_table_set_cache(tb, mpc);
+       mnt_unref_cache(mpc);
 
        while(mnt_table_next_fs(fstab, itr, &fs) == 0) {
                if (mnt_table_is_fs_mounted(tb, fs))
@@ -1580,7 +1589,6 @@ static int test_is_mounted(struct libmnt_test *ts, int argc, char *argv[])
 done:
        mnt_free_table(tb);
        mnt_free_table(fstab);
-       mnt_free_cache(mpc);
        mnt_free_iter(itr);
        return rc;
 }