[PATCH 2/2] xfs: don't extend the FITRIM range if the rt device does not support discard

[Christoph Hellwig <hch@xxxxxx>]

Fix the newly added discard support to only offer a FITRIM range that
spans the RT device in addition to the main device if the RT device
actually supports discard.  Without this we'll incorrectly accept
a larger range than actually supported and confuse user space if the
RT device does not support discard.  This can easily happen when the
main device is a SSD but the RT device is a hard driver.

Move the code around a bit to keep the max_blocks and granularity
assignments together and to handle the case where only the RT device
supports discard as well.

Fixes: 3ba3ab1f6719 ("xfs: enable FITRIM on the realtime device")
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 fs/xfs/xfs_discard.c | 37 ++++++++++++++++++++++++-------------
 1 file changed, 24 insertions(+), 13 deletions(-)

diff --git a/fs/xfs/xfs_discard.c b/fs/xfs/xfs_discard.c
index 6516afecce0979..46e28499a7d3ce 100644
--- a/fs/xfs/xfs_discard.c
+++ b/fs/xfs/xfs_discard.c
@@ -654,9 +654,9 @@ xfs_ioc_trim(
 	struct xfs_mount		*mp,
 	struct fstrim_range __user	*urange)
 {
-	unsigned int		granularity =
-		bdev_discard_granularity(mp->m_ddev_targp->bt_bdev);
+	struct block_device	*bdev = mp->m_ddev_targp->bt_bdev;
 	struct block_device	*rt_bdev = NULL;
+	unsigned int		granularity = 0;
 	struct fstrim_range	range;
 	xfs_daddr_t		start, end;
 	xfs_extlen_t		minlen;
@@ -666,15 +666,6 @@ xfs_ioc_trim(
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
-	if (mp->m_rtdev_targp &&
-	    bdev_max_discard_sectors(mp->m_rtdev_targp->bt_bdev))
-		rt_bdev = mp->m_rtdev_targp->bt_bdev;
-	if (!bdev_max_discard_sectors(mp->m_ddev_targp->bt_bdev) && !rt_bdev)
-		return -EOPNOTSUPP;
-
-	if (rt_bdev)
-		granularity = max(granularity,
-				  bdev_discard_granularity(rt_bdev));
 
 	/*
 	 * We haven't recovered the log, so we cannot use our bnobt-guided
@@ -683,13 +674,33 @@ xfs_ioc_trim(
 	if (xfs_has_norecovery(mp))
 		return -EROFS;
 
+	if (bdev_max_discard_sectors(bdev)) {
+		max_blocks = mp->m_sb.sb_dblocks;
+		granularity = bdev_discard_granularity(bdev);
+	} else {
+		bdev = NULL;
+	}
+
+	if (mp->m_rtdev_targp) {
+		rt_bdev = mp->m_rtdev_targp->bt_bdev;
+		if (!bdev_max_discard_sectors(rt_bdev)) {
+			if (!bdev)
+				return -EOPNOTSUPP;
+			rt_bdev = NULL;
+		}
+	}
+	if (rt_bdev) {
+		max_blocks += mp->m_sb.sb_rblocks;
+		granularity =
+			max(granularity, bdev_discard_granularity(rt_bdev));
+	}
+
 	if (copy_from_user(&range, urange, sizeof(range)))
 		return -EFAULT;
 
 	range.minlen = max_t(u64, granularity, range.minlen);
 	minlen = XFS_B_TO_FSB(mp, range.minlen);
 
-	max_blocks = mp->m_sb.sb_dblocks + mp->m_sb.sb_rblocks;
 	if (range.start >= XFS_FSB_TO_B(mp, max_blocks) ||
 	    range.minlen > XFS_FSB_TO_B(mp, mp->m_ag_max_usable) ||
 	    range.len < mp->m_sb.sb_blocksize)
@@ -698,7 +709,7 @@ xfs_ioc_trim(
 	start = BTOBB(range.start);
 	end = start + BTOBBT(range.len) - 1;
 
-	if (bdev_max_discard_sectors(mp->m_ddev_targp->bt_bdev)) {
+	if (bdev) {
 		error = xfs_trim_datadev_extents(mp, start, end, minlen,
 				&blocks_trimmed);
 		if (error)
-- 
2.43.0