[PATCH] btrfs-progs: fix false alert on tree block crossing 64K page boundary

[Qu Wenruo <wqu@suse.com>]

[BUG]
When btrfs-check is executed on even newly created fs, it can report
tree blocks crossing 64K page boundary like this:

  Opening filesystem to check...
  Checking filesystem on /dev/test/test
  UUID: 80d734c8-dcbc-411b-9623-a10bd9e7767f
  [1/7] checking root items
  [2/7] checking extents
  WARNING: tree block [30523392, 30539776) crosses 64K page boudnary, may cause problem for 64K page system
  [3/7] checking free space cache
  [4/7] checking fs roots
  [5/7] checking only csums items (without verifying data)
  [6/7] checking root refs
  [7/7] checking quota groups skipped (not enabled on this FS)
  found 131072 bytes used, no error found
  total csum bytes: 0
  total tree bytes: 131072
  total fs tree bytes: 32768
  total extent tree bytes: 16384
  btree space waste bytes: 125199
  file data blocks allocated: 0
   referenced 0

[CAUSE]
Tree block [30523392, 30539776) is at the last 16K slot of page.
As 30523392 % 65536 = 49152, and 30539776 % 65536 = 0.

The cross boundary check is using exclusive end, which causes false
alerts.

[FIX]
Use inclusive end to do the cross 64K boundary check.

Reported-by: Wang Yugui <wangyugui@e16-tech.com>
Fixes: fc38ae7f4826 ("btrfs-progs: check: detect and warn about tree blocks crossing 64K page boundary")
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 check/mode-common.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/check/mode-common.h b/check/mode-common.h
index 8fdeb7f6be0a..3107b00c48bf 100644
--- a/check/mode-common.h
+++ b/check/mode-common.h
@@ -186,7 +186,7 @@ int get_extent_item_generation(u64 bytenr, u64 *gen_ret);
 static inline void btrfs_check_subpage_eb_alignment(u64 start, u32 len)
 {
 	if (start / BTRFS_MAX_METADATA_BLOCKSIZE !=
-	    (start + len) / BTRFS_MAX_METADATA_BLOCKSIZE)
+	    (start + len - 1) / BTRFS_MAX_METADATA_BLOCKSIZE)
 		warning(
 "tree block [%llu, %llu) crosses 64K page boudnary, may cause problem for 64K page system",
 			start, start + len);
-- 
2.30.1