xfs: Directory's data fork extent counter can never overflow

The maximum file size that can be represented by the data fork extent counter
in the worst case occurs when all extents are 1 block in length and each block
is 1KB in size.

With XFS_MAX_EXTCNT_DATA_FORK_SMALL representing maximum extent count and with
1KB sized blocks, a file can reach upto,
(2^31) * 1KB = 2TB

This is much larger than the theoretical maximum size of a directory
i.e. XFS_DIR2_SPACE_SIZE * 3 = ~96GB.

Since a directory's inode can never overflow its data fork extent counter,
this commit removes all the overflow checks associated with
it. xfs_dinode_verify() now performs a rough check to verify if a diretory's
data fork is larger than 96GB.

Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandan.babu@oracle.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
index 82b404c99b80..43de892d0305 100644
--- a/fs/xfs/libxfs/xfs_format.h
+++ b/fs/xfs/libxfs/xfs_format.h
@@ -915,6 +915,19 @@ enum xfs_dinode_fmt {
  *
  * Rounding up 47 to the nearest multiple of bits-per-byte results in 48. Hence
  * 2^48 was chosen as the maximum data fork extent count.
+ *
+ * The maximum file size that can be represented by the data fork extent counter
+ * in the worst case occurs when all extents are 1 block in length and each
+ * block is 1KB in size.
+ *
+ * With XFS_MAX_EXTCNT_DATA_FORK_SMALL representing maximum extent count and
+ * with 1KB sized blocks, a file can reach upto,
+ * 1KB * (2^31) = 2TB
+ *
+ * This is much larger than the theoretical maximum size of a directory
+ * i.e. XFS_DIR2_SPACE_SIZE * XFS_DIR2_MAX_SPACES = ~96GB.
+ *
+ * Hence, a directory inode can never overflow its data fork extent counter.
  */
 #define XFS_MAX_EXTCNT_DATA_FORK_LARGE	((xfs_extnum_t)((1ULL << 48) - 1))
 #define XFS_MAX_EXTCNT_ATTR_FORK_LARGE	((xfs_extnum_t)((1ULL << 32) - 1))