xfs: fix logdev fsmap query result filtering

The external log device fsmap backend doesn't have an rmapbt to query,
so it's wasteful to spend time initializing the rmap_irec objects.
Worse yet, the log could (someday) be longer than 2^32 fsblocks, so
using the rmap irec structure will result in integer overflows.

Fix this mess by computing the start address that we want from keys[0]
directly, and use the daddr-based record filtering algorithm that we
also use for rtbitmap queries.

Fixes: e89c041 ("xfs: implement the GETFSMAP ioctl")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

Author: Darrick J. Wong

fs/xfs/xfs_fsmap.c

@@ -437,36 +437,22 @@ xfs_getfsmap_logdev(
 	struct xfs_mount		*mp = tp->t_mountp;
 	struct xfs_rmap_irec		rmap;
 	xfs_daddr_t			rec_daddr, len_daddr;
-	xfs_fsblock_t			start_fsb;
-	int				error;
+	xfs_fsblock_t			start_fsb, end_fsb;
+	uint64_t			eofs;
 
-	/* Set up search keys */
+	eofs = XFS_FSB_TO_BB(mp, mp->m_sb.sb_logblocks);
+	if (keys[0].fmr_physical >= eofs)
+		return 0;
 	start_fsb = XFS_BB_TO_FSBT(mp,
 				keys[0].fmr_physical + keys[0].fmr_length);
-	info->low.rm_startblock = XFS_BB_TO_FSBT(mp, keys[0].fmr_physical);
-	info->low.rm_offset = XFS_BB_TO_FSBT(mp, keys[0].fmr_offset);
-	error = xfs_fsmap_owner_to_rmap(&info->low, keys);
-	if (error)
-		return error;
-	info->low.rm_blockcount = 0;
-	xfs_getfsmap_set_irec_flags(&info->low, &keys[0]);
+	end_fsb = XFS_BB_TO_FSB(mp, min(eofs - 1, keys[1].fmr_physical));
 
 	/* Adjust the low key if we are continuing from where we left off. */
 	if (keys[0].fmr_length > 0)
 		info->low_daddr = XFS_FSB_TO_BB(mp, start_fsb);
 
-	error = xfs_fsmap_owner_to_rmap(&info->high, keys + 1);
-	if (error)
-		return error;
-	info->high.rm_startblock = -1U;
-	info->high.rm_owner = ULLONG_MAX;
-	info->high.rm_offset = ULLONG_MAX;
-	info->high.rm_blockcount = 0;
-	info->high.rm_flags = XFS_RMAP_KEY_FLAGS | XFS_RMAP_REC_FLAGS;
-	info->missing_owner = XFS_FMR_OWN_FREE;
-
-	trace_xfs_fsmap_low_key(mp, info->dev, NULLAGNUMBER, &info->low);
-	trace_xfs_fsmap_high_key(mp, info->dev, NULLAGNUMBER, &info->high);
+	trace_xfs_fsmap_low_key_linear(mp, info->dev, start_fsb);
+	trace_xfs_fsmap_high_key_linear(mp, info->dev, end_fsb);
 
 	if (start_fsb > 0)
 		return 0;