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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>
This commit is contained in:
Jan Kara 2012-02-10 11:03:00 +01:00 committed by Al Viro
parent 074b85175a
commit 6b6dc836a1
2 changed files with 23 additions and 0 deletions
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22
fs/super.c
View File

@ -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

1
include/linux/fs.h
View File

@ -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 *);