[PATCH v2] xfs: preserve default grace interval during quotacheck

["Darrick J. Wong" <darrick.wong@oracle.com>]

From: Darrick J. Wong <darrick.wong@oracle.com>

When quotacheck runs, it zeroes all the timer fields in every dquot.
Unfortunately, it also does this to the root dquot, which erases any
preconfigured grace intervals and warning limits that the administrator
may have set.  Worse yet, the incore copies of those variables remain
set.  This cache coherence problem manifests itself as the grace
interval mysteriously being reset back to the defaults at the /next/
mount.

Fix it by not resetting the root disk dquot's timer and warning fields.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
v2: just use a branch
---
 fs/xfs/xfs_qm.c |   20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
index 0ce334c51d73..ee175617630e 100644
--- a/fs/xfs/xfs_qm.c
+++ b/fs/xfs/xfs_qm.c
@@ -889,12 +889,20 @@ xfs_qm_reset_dqcounts(
 		ddq->d_bcount = 0;
 		ddq->d_icount = 0;
 		ddq->d_rtbcount = 0;
-		ddq->d_btimer = 0;
-		ddq->d_itimer = 0;
-		ddq->d_rtbtimer = 0;
-		ddq->d_bwarns = 0;
-		ddq->d_iwarns = 0;
-		ddq->d_rtbwarns = 0;
+
+		/*
+		 * dquot id 0 stores the default grace period and the maximum
+		 * warning limit that were set by the administrator, so we
+		 * should not reset them.
+		 */
+		if (ddq->d_id != 0) {
+			ddq->d_btimer = 0;
+			ddq->d_itimer = 0;
+			ddq->d_rtbtimer = 0;
+			ddq->d_bwarns = 0;
+			ddq->d_iwarns = 0;
+			ddq->d_rtbwarns = 0;
+		}
 
 		if (xfs_sb_version_hascrc(&mp->m_sb)) {
 			xfs_update_cksum((char *)&dqb[j],