quota: clean up Q_XQUOTASYNC

Currently Q_XQUOTASYNC calls into the quota_sync method, but XFS does something
entirely different in it than the rest of the filesystems.  xfs_quota which
calls Q_XQUOTASYNC expects an asynchronous data writeout to flush delayed
allocations, while the "VFS" quota support wants to flush changes to the quota
file.

So make Q_XQUOTASYNC call into the writeback code directly and make the
quota_sync method optional as XFS doesn't need in the sense expected by the
rest of the quota code.

GFS2 was using limited XFS-style quota and has a quota_sync method fitting
neither the style used by vfs_quota_sync nor xfs_fs_quota_sync.  I left it
in for now as per discussion with Steve it expects to be called from the
sync path this way.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/linux/quotaops.h b/include/linux/quotaops.h
index a529d86e7e73..69d26bc0f884 100644
--- a/include/linux/quotaops.h
+++ b/include/linux/quotaops.h
@@ -22,7 +22,7 @@ static inline struct quota_info *sb_dqopt(struct super_block *sb)
 void sync_quota_sb(struct super_block *sb, int type);
 static inline void writeout_quota_sb(struct super_block *sb, int type)
 {
-        if (sb->s_qcop->quota_sync)
+        if (sb->s_qcop && sb->s_qcop->quota_sync)
                 sb->s_qcop->quota_sync(sb, type);
 }