libmount: add reference counting to libmnt_cache

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

6 files changed, 70 insertions, 30 deletions

diff --git a/libmount/docs/libmount-sections.txt b/libmount/docs/libmount-sections.txt
index 97e0851e5..3ebc4aaf2 100644
--- 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 ef1a64107..cf5c6d430 100644
--- 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 ea13f0d1e..5d5e8fba8 100644
--- 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 29659628d..f4efd9804 100644
--- 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 621821e97..5a7e0def3 100644
--- 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 58edf2f42..a2ad604f7 100644
--- 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;
 }