libmount: improve fs referencing in tables

* Added member 'struct libmnt_table *tab' to libmnt_fs structure.
* Added 'mnt_fs_get_table()'.
* Removed overhead from 'mnt_table_{insert,move,remove}_fs().
* Added check to 'mnt_table_set_iter()' that entry is member of table.

[kzak@redhat.com: - add to libmount.sys
                  - add to docs
                  - cleanup commit message
                  - set fs->tab = NULL before mnt_unref_fs() in mnt_table_remove_fs()]

Signed-off-by: Tim Hildering <hilderingt@posteo.net>
Signed-off-by: Karel Zak <kzak@redhat.com>

5 files changed, 31 insertions, 9 deletions

diff --git a/libmount/src/fs.c b/libmount/src/fs.c
index 9971d6ae3..147398955 100644
--- a/libmount/src/fs.c
+++ b/libmount/src/fs.c
@@ -190,6 +190,7 @@ struct libmnt_fs *mnt_copy_fs(struct libmnt_fs *dest,
 			return NULL;
 	}
 
+	dest->tab	 = NULL;
 	dest->id         = src->id;
 	dest->parent     = src->parent;
 	dest->devno      = src->devno;
@@ -446,6 +447,22 @@ int mnt_fs_streq_srcpath(struct libmnt_fs *fs, const char *path)
 }
 
 /**
+ * mnt_fs_get_table:
+ * @fs: table entry
+ * @tb: table that contains @fs
+ *
+ * Returns: 0 or negative number on error (if @fs or @tb is NULL).
+ */
+int mnt_fs_get_table(struct libmnt_fs *fs, struct libmnt_table **tb)
+{
+	if (!fs || !tb)
+		return -EINVAL;
+
+	*tb = fs->tab;
+	return 0;
+}
+
+/**
  * mnt_fs_streq_target:
  * @fs: fs
  * @path: mount point
diff --git a/libmount/src/libmount.h.in b/libmount/src/libmount.h.in
index fb86aaff9..19535bd7f 100644
--- a/libmount/src/libmount.h.in
+++ b/libmount/src/libmount.h.in
@@ -439,6 +439,7 @@ extern int mnt_fs_set_userdata(struct libmnt_fs *fs, void *data);
 extern const char *mnt_fs_get_source(struct libmnt_fs *fs);
 extern int mnt_fs_set_source(struct libmnt_fs *fs, const char *source);
 extern const char *mnt_fs_get_srcpath(struct libmnt_fs *fs);
+extern int mnt_fs_get_table(struct libmnt_fs *fs, struct libmnt_table **tb);
 
 extern int mnt_fs_get_tag(struct libmnt_fs *fs, const char **name,
 			  const char **value);
diff --git a/libmount/src/libmount.sym b/libmount/src/libmount.sym
index 1d72cf4f7..b92728ff6 100644
--- a/libmount/src/libmount.sym
+++ b/libmount/src/libmount.sym
@@ -344,6 +344,7 @@ MOUNT_2.33 {
 
 MOUNT_2.34 {
 	mnt_context_next_remount;
+	mnt_fs_get_table;
 	mnt_guess_system_root;
 	mnt_table_find_fs;
 	mnt_table_insert_fs;
diff --git a/libmount/src/mountP.h b/libmount/src/mountP.h
index 7887c0a55..11fc28315 100644
--- a/libmount/src/mountP.h
+++ b/libmount/src/mountP.h
@@ -170,6 +170,7 @@ struct libmnt_iter {
  */
 struct libmnt_fs {
 	struct list_head ents;
+	struct libmnt_table *tab;
 
 	int		refcount;	/* reference counter */
 	int		id;		/* mountinfo[1]: ID */
diff --git a/libmount/src/tab.c b/libmount/src/tab.c
index 674dc67e5..6d2fdc0d5 100644
--- a/libmount/src/tab.c
+++ b/libmount/src/tab.c
@@ -443,11 +443,12 @@ int mnt_table_add_fs(struct libmnt_table *tb, struct libmnt_fs *fs)
 	if (!tb || !fs)
 		return -EINVAL;
 
-	if (!list_empty(&fs->ents))
+	if (fs->tab)
 		return -EBUSY;
 
 	mnt_ref_fs(fs);
 	list_add_tail(&fs->ents, &tb->ents);
+	fs->tab = tb;
 	tb->nents++;
 
 	DBG(TAB, ul_debugobj(tb, "add entry: %s %s",
@@ -466,6 +467,7 @@ static int __table_insert_fs(
 	else
 		list_add_tail(&fs->ents, head);
 
+	fs->tab = tb;
 	tb->nents++;
 
 	DBG(TAB, ul_debugobj(tb, "insert entry: %s %s",
@@ -487,7 +489,6 @@ static int __table_insert_fs(
  * This function inncrements reference to @fs. Don't forget to use
  * mnt_unref_fs() after mnt_table_insert_fs() if you want to keep the @fs
  * referenced by the table only.
-
  *
  * Returns: 0 on success or negative number in case of error.
  */
@@ -497,10 +498,10 @@ int mnt_table_insert_fs(struct libmnt_table *tb, int before,
 	if (!tb || !fs)
 		return -EINVAL;
 
-	if (!list_empty(&fs->ents))
+	if (fs->tab)
 		return -EBUSY;
 
-	if (pos && mnt_table_find_fs(tb, pos) < 1)
+	if (pos && pos->tab != tb)
 		return -ENOENT;
 
 	mnt_ref_fs(fs);
@@ -529,10 +530,7 @@ int mnt_table_move_fs(struct libmnt_table *src, struct libmnt_table *dst,
 	if (!src || !dst || !fs)
 		return -EINVAL;
 
-	if (mnt_table_find_fs(src, fs) < 1)
-		return -ENOENT;
-
-	if (pos && mnt_table_find_fs(dst, pos) < 1)
+	if (fs->tab != src || (pos && pos->tab != dst))
 		return -ENOENT;
 
 	/* remove from source */
@@ -557,9 +555,10 @@ int mnt_table_move_fs(struct libmnt_table *src, struct libmnt_table *dst,
  */
 int mnt_table_remove_fs(struct libmnt_table *tb, struct libmnt_fs *fs)
 {
-	if (!tb || !fs || mnt_table_find_fs(tb, fs) < 1)
+	if (!tb || !fs || fs->tab != tb)
 		return -EINVAL;
 
+	fs->tab = NULL;
 	list_del_init(&fs->ents);
 
 	mnt_unref_fs(fs);
@@ -913,6 +912,9 @@ int mnt_table_set_iter(struct libmnt_table *tb, struct libmnt_iter *itr, struct
 	if (!tb || !itr || !fs)
 		return -EINVAL;
 
+	if (fs->tab != tb)
+		return -ENOENT;
+
 	MNT_ITER_INIT(itr, &tb->ents);
 	itr->p = &fs->ents;