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 6015c02296b7ad2adba75c7946b8fb4762a62265..6277ec6cb60a65e71b2c590260c67a057a1748ca 100644 (file)
--- a/fs/super.c
+++ b/fs/super.c
@@ -633,6 +633,28 @@ rescan:
 
 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

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 386da09f229dfad8ff8ef5600c8045f221ae862f..69cd5bb640f5f6f0e4dd13431c34c6f8c760f42b 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2496,6 +2496,7 @@ extern void get_filesystem(struct file_system_type *fs);
 extern void put_filesystem(struct file_system_type *fs);
 extern struct file_system_type *get_fs_type(const char *name);
 extern struct super_block *get_super(struct block_device *);
+extern struct super_block *get_super_thawed(struct block_device *);
 extern struct super_block *get_active_super(struct block_device *bdev);
 extern void drop_super(struct super_block *sb);
 extern void iterate_supers(void (*)(struct super_block *, void *), void *);