xfs: Fix missing interval for missing_owner in xfs fsmap

In the fsmap query of xfs, there is an interval missing problem:
[root@fedora ~]# xfs_io -c 'fsmap -vvvv' /mnt
EXT: DEV BLOCK-RANGE OWNER FILE-OFFSET AG AG-OFFSET TOTAL
0: 253:16 [0..7]: static fs metadata 0 (0..7) 8
1: 253:16 [8..23]: per-AG metadata 0 (8..23) 16
2: 253:16 [24..39]: inode btree 0 (24..39) 16
3: 253:16 [40..47]: per-AG metadata 0 (40..47) 8
4: 253:16 [48..55]: refcount btree 0 (48..55) 8
5: 253:16 [56..103]: per-AG metadata 0 (56..103) 48
6: 253:16 [104..127]: free space 0 (104..127) 24
......

BUG:
[root@fedora ~]# xfs_io -c 'fsmap -vvvv -d 104 107' /mnt
[root@fedora ~]#
Normally, we should be able to get [104, 107), but we got nothing.

The problem is caused by shifting. The query for the problem-triggered
scenario is for the missing_owner interval (e.g. freespace in rmapbt/
unknown space in bnobt), which is obtained by subtraction (gap). For this
scenario, the interval is obtained by info->last. However, rec_daddr is
calculated based on the start_block recorded in key[1], which is converted
by calling XFS_BB_TO_FSBT. Then if rec_daddr does not exceed
info->next_daddr, which means keys[1].fmr_physical >> (mp)->m_blkbb_log
<= info->next_daddr, no records will be displayed. In the above example,
104 >> (mp)->m_blkbb_log = 12 and 107 >> (mp)->m_blkbb_log = 12, so the two
are reduced to 0 and the gap is ignored:

before calculate ----------------> after shifting
104(st) 107(ed) 12(st/ed)
|---------| |
sector size block size

Resolve this issue by introducing the "end_daddr" field in
xfs_getfsmap_info. This records |key[1].fmr_physical + key[1].length| at
the granularity of sector. If the current query is the last, the rec_daddr
is end_daddr to prevent missing interval problems caused by shifting. We
only need to focus on the last query, because xfs disks are internally
aligned with disk blocksize that are powers of two and minimum 512, so
there is no problem with shifting in previous queries.

After applying this patch, the above problem have been solved:
[root@fedora ~]# xfs_io -c 'fsmap -vvvv -d 104 107' /mnt
EXT: DEV BLOCK-RANGE OWNER FILE-OFFSET AG AG-OFFSET TOTAL
0: 253:16 [104..106]: free space 0 (104..106) 3

Fixes: e89c041338ed ("xfs: implement the GETFSMAP ioctl")
Signed-off-by: Zizhi Wo <[e-mail]>
Reviewed-by: Darrick J. Wong <[e-mail]>
[djwong: limit the range of end_addr correctly]
Signed-off-by: Darrick J. Wong <[e-mail]>
Signed-off-by: Chandan Babu R <[e-mail]>

fs/xfs/xfs_fsmap.c

···
 	xfs_daddr_t		next_daddr;	/* next daddr we expect */
 	/* daddr of low fsmap key when we're using the rtbitmap */
 	xfs_daddr_t		low_daddr;
+	xfs_daddr_t		end_daddr;	/* daddr of high fsmap key */
 	u64			missing_owner;	/* owner of holes */
 	u32			dev;		/* device id */
 	/*
···
 	int			(*fn)(struct xfs_trans *tp,
 				      const struct xfs_fsmap *keys,
 				      struct xfs_getfsmap_info *info);
+	sector_t		nr_sectors;
 };
 
 /* Compare two getfsmap device handlers. */
···
 			info->next_daddr = rec_daddr;
 		return 0;
 	}
+
+	/*
+	 * For an info->last query, we're looking for a gap between the last
+	 * mapping emitted and the high key specified by userspace.  If the
+	 * user's query spans less than 1 fsblock, then info->high and
+	 * info->low will have the same rm_startblock, which causes rec_daddr
+	 * and next_daddr to be the same.  Therefore, use the end_daddr that
+	 * we calculated from userspace's high key to synthesize the record.
+	 * Note that if the btree query found a mapping, there won't be a gap.
+	 */
+	if (info->last && info->end_daddr != XFS_BUF_DADDR_NULL)
+		rec_daddr = info->end_daddr;
 
 	/* Are we just counting mappings? */
 	if (info->head->fmh_count == 0) {
···
 
 	/* Set up our device handlers. */
 	memset(handlers, 0, sizeof(handlers));
+	handlers[0].nr_sectors = XFS_FSB_TO_BB(mp, mp->m_sb.sb_dblocks);
 	handlers[0].dev = new_encode_dev(mp->m_ddev_targp->bt_dev);
 	if (use_rmap)
 		handlers[0].fn = xfs_getfsmap_datadev_rmapbt;
 	else
 		handlers[0].fn = xfs_getfsmap_datadev_bnobt;
 	if (mp->m_logdev_targp != mp->m_ddev_targp) {
+		handlers[1].nr_sectors = XFS_FSB_TO_BB(mp,
+						       mp->m_sb.sb_logblocks);
 		handlers[1].dev = new_encode_dev(mp->m_logdev_targp->bt_dev);
 		handlers[1].fn = xfs_getfsmap_logdev;
 	}
 #ifdef CONFIG_XFS_RT
 	if (mp->m_rtdev_targp) {
+		handlers[2].nr_sectors = XFS_FSB_TO_BB(mp, mp->m_sb.sb_rblocks);
 		handlers[2].dev = new_encode_dev(mp->m_rtdev_targp->bt_dev);
 		handlers[2].fn = xfs_getfsmap_rtdev_rtbitmap;
 	}
···
 
 	info.next_daddr = head->fmh_keys[0].fmr_physical +
 			  head->fmh_keys[0].fmr_length;
+	info.end_daddr = XFS_BUF_DADDR_NULL;
 	info.fsmap_recs = fsmap_recs;
 	info.head = head;
 
···
 		 * low key, zero out the low key so that we get
 		 * everything from the beginning.
 		 */
-		if (handlers[i].dev == head->fmh_keys[1].fmr_device)
+		if (handlers[i].dev == head->fmh_keys[1].fmr_device) {
 			dkeys[1] = head->fmh_keys[1];
+			info.end_daddr = min(handlers[i].nr_sectors - 1,
+					     dkeys[1].fmr_physical);
+		}
 		if (handlers[i].dev > head->fmh_keys[0].fmr_device)
 			memset(&dkeys[0], 0, sizeof(struct xfs_fsmap));