[PATCH] xfs_scrub: fix spacemap scan for internal rt devices

["Darrick J. Wong" <djwong@kernel.org>]

From: Darrick J. Wong <djwong@kernel.org>

The scrub media scan on a filesystem with an internal rt volume still
fails with:

 # xfs_scrub -dTvnx /mnt
 Phase 6: Verify data file integrity.
 Error: dev 7:0 rtgroup 1 fsmap: Invalid argument. (spacemap.c line 162)
 Error: dev 7:0 rtgroup 0 fsmap: Invalid argument. (spacemap.c line 162)
 Info: /mnt: Scrub aborted after phase 6. (xfs_scrub.c line 522)

(this was from xfs/586)

When I tried to add support for internal rt devices in commit
37591ef3f4f14c ("xfs_scrub: support internal RT device"), I forgot that
fsmap reports physical offsets into the underlying block device, and
therefore expects the query keys to reflect that.  Put another way, to
scan a single rtgroup, one must add @rtstart to the fmr_physical field
of the query keys.

This hasn't been reported until now because we inadvertently also
disabled spacemap scans of internal rt volumes until commit
3e4bb144f657b1 ("xfs_scrub: handle media scans of internal rt devices
correctly").

Cc: <linux-xfs@vger.kernel.org> # v6.15.0
Fixes: 37591ef3f4f14c ("xfs_scrub: support internal RT device")
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
---
sorry, I missed this one earlier :(
---
 scrub/spacemap.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/scrub/spacemap.c b/scrub/spacemap.c
index 45ac61d0942ccb..65d716374c9eb3 100644
--- a/scrub/spacemap.c
+++ b/scrub/spacemap.c
@@ -148,6 +148,19 @@ scan_rtg_rmaps(
 	keys[1].fmr_offset = ULLONG_MAX;
 	keys[1].fmr_flags = UINT_MAX;
 
+	/*
+	 * fsmap for an internal rt volume treats physical ranges as offsets
+	 * into the underlying block device.  Shift the query range up by
+	 * @rtstart here to skip the synthetic "internal filesystem" fsmap.
+	 */
+	if (ctx->mnt.fsgeom.rtstart) {
+		uint64_t	offset = ctx->mnt.fsgeom.rtstart *
+					 ctx->mnt.fsgeom.blocksize;
+
+		keys[0].fmr_physical += offset;
+		keys[1].fmr_physical += offset;
+	}
+
 	if (sbx->aborted)
 		return;