[6/9] quota: Fix dquot_transfer for filesystems different from ext4

[Greg KH <gregkh@suse.de>]

2.6.31-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Jan Kara <jack@suse.cz>

commit 05b5d898235401c489c68e1f3bc5706a29ad5713 upstream.

Commit fd8fbfc1 modified the way we find amount of reserved space
belonging to an inode. The amount of reserved space is checked
from dquot_transfer and thus inode_reserved_space gets called
even for filesystems that don't provide get_reserved_space callback
which results in a BUG.

Fix the problem by checking get_reserved_space callback and return 0 if
the filesystem does not provide it.

CC: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 fs/quota/dquot.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -1425,6 +1425,9 @@ static void inode_sub_rsv_space(struct i
 static qsize_t inode_get_rsv_space(struct inode *inode)
 {
 	qsize_t ret;
+
+	if (!inode->i_sb->dq_op->get_reserved_space)
+		return 0;
 	spin_lock(&inode->i_lock);
 	ret = *inode_reserved_space(inode);
 	spin_unlock(&inode->i_lock);