fs: Provide function to get superblock with exclusive s_umount
Quota code will need a variant of get_super_thawed() that returns
superblock with s_umount held in exclusive mode to serialize quota on
and quota off operations. Provide this functionality.
Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/super.c b/fs/super.c
index c183835..f7f7242 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -558,6 +558,13 @@ void drop_super(struct super_block *sb)
EXPORT_SYMBOL(drop_super);
+void drop_super_exclusive(struct super_block *sb)
+{
+ up_write(&sb->s_umount);
+ put_super(sb);
+}
+EXPORT_SYMBOL(drop_super_exclusive);
+
/**
* iterate_supers - call function for all active superblocks
* @f: function to call
@@ -628,15 +635,7 @@ void iterate_supers_type(struct file_system_type *type,
EXPORT_SYMBOL(iterate_supers_type);
-/**
- * get_super - get the superblock of a device
- * @bdev: device to get the superblock for
- *
- * Scans the superblock list and finds the superblock of the file system
- * mounted on the device given. %NULL is returned if no match is found.
- */
-
-struct super_block *get_super(struct block_device *bdev)
+static struct super_block *__get_super(struct block_device *bdev, bool excl)
{
struct super_block *sb;
@@ -651,11 +650,17 @@ struct super_block *get_super(struct block_device *bdev)
if (sb->s_bdev == bdev) {
sb->s_count++;
spin_unlock(&sb_lock);
- down_read(&sb->s_umount);
+ if (!excl)
+ down_read(&sb->s_umount);
+ else
+ down_write(&sb->s_umount);
/* still alive? */
if (sb->s_root && (sb->s_flags & MS_BORN))
return sb;
- up_read(&sb->s_umount);
+ if (!excl)
+ up_read(&sb->s_umount);
+ else
+ up_write(&sb->s_umount);
/* nope, got unmounted */
spin_lock(&sb_lock);
__put_super(sb);
@@ -666,8 +671,36 @@ struct super_block *get_super(struct block_device *bdev)
return NULL;
}
+/**
+ * get_super - get the superblock of a device
+ * @bdev: device to get the superblock for
+ *
+ * Scans the superblock list and finds the superblock of the file system
+ * mounted on the device given. %NULL is returned if no match is found.
+ */
+struct super_block *get_super(struct block_device *bdev)
+{
+ return __get_super(bdev, false);
+}
EXPORT_SYMBOL(get_super);
+static struct super_block *__get_super_thawed(struct block_device *bdev,
+ bool excl)
+{
+ while (1) {
+ struct super_block *s = __get_super(bdev, excl);
+ if (!s || s->s_writers.frozen == SB_UNFROZEN)
+ return s;
+ if (!excl)
+ up_read(&s->s_umount);
+ else
+ up_write(&s->s_umount);
+ wait_event(s->s_writers.wait_unfrozen,
+ s->s_writers.frozen == SB_UNFROZEN);
+ put_super(s);
+ }
+}
+
/**
* get_super_thawed - get thawed superblock of a device
* @bdev: device to get the superblock for
@@ -679,19 +712,26 @@ EXPORT_SYMBOL(get_super);
*/
struct super_block *get_super_thawed(struct block_device *bdev)
{
- while (1) {
- struct super_block *s = get_super(bdev);
- if (!s || s->s_writers.frozen == SB_UNFROZEN)
- return s;
- up_read(&s->s_umount);
- wait_event(s->s_writers.wait_unfrozen,
- s->s_writers.frozen == SB_UNFROZEN);
- put_super(s);
- }
+ return __get_super_thawed(bdev, false);
}
EXPORT_SYMBOL(get_super_thawed);
/**
+ * get_super_exclusive_thawed - get thawed superblock of a device
+ * @bdev: device to get the superblock for
+ *
+ * Scans the superblock list and finds the superblock of the file system
+ * mounted on the device. The superblock is returned once it is thawed
+ * (or immediately if it was not frozen) and s_umount semaphore is held
+ * in exclusive mode. %NULL is returned if no match is found.
+ */
+struct super_block *get_super_exclusive_thawed(struct block_device *bdev)
+{
+ return __get_super_thawed(bdev, true);
+}
+EXPORT_SYMBOL(get_super_exclusive_thawed);
+
+/**
* get_active_super - get an active reference to the superblock of a device
* @bdev: device to get the superblock for
*