vfs: Provide function to get superblock and wait for it to thaw
In quota code we need to find a superblock corresponding to a device and wait
for superblock to be unfrozen. However this waiting has to happen without
s_umount semaphore because that is required for superblock to thaw. So provide
a function in VFS for this to keep dances with s_umount where they belong.
[AV: implementation switched to saner variant]
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/super.c b/fs/super.c
index 6015c02..6277ec6 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -634,6 +634,28 @@
EXPORT_SYMBOL(get_super);
/**
+ * get_super_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). %NULL is returned if no match
+ * is found.
+ */
+struct super_block *get_super_thawed(struct block_device *bdev)
+{
+ while (1) {
+ struct super_block *s = get_super(bdev);
+ if (!s || s->s_frozen == SB_UNFROZEN)
+ return s;
+ up_read(&s->s_umount);
+ vfs_check_frozen(s, SB_FREEZE_WRITE);
+ put_super(s);
+ }
+}
+EXPORT_SYMBOL(get_super_thawed);
+
+/**
* get_active_super - get an active reference to the superblock of a device
* @bdev: device to get the superblock for
*
