[PATCH 3/5] xfs: silence sparse warning when checking version number

Dave Chinner
2024-04-02T21:35:48Z

From: Dave Chinner <dchinner@redhat.com>

Scrub checks the superblock version number against the known good
feature bits that can be set in the version mask. It calculates
the version mask to compare like so:

vernum_mask = cpu_to_be16(~XFS_SB_VERSION_OKBITS |
XFS_SB_VERSION_NUMBITS |
XFS_SB_VERSION_ALIGNBIT |
XFS_SB_VERSION_DALIGNBIT |
XFS_SB_VERSION_SHAREDBIT |
XFS_SB_VERSION_LOGV2BIT |
XFS_SB_VERSION_SECTORBIT |
XFS_SB_VERSION_EXTFLGBIT |
XFS_SB_VERSION_DIRV2BIT);

This generates a sparse warning:

fs/xfs/scrub/agheader.c:168:23: warning: cast truncates bits from constant value (ffff3f8f becomes 3f8f)

This is because '~XFS_SB_VERSION_OKBITS' is considered a 32 bit
constant, even though it's value is always under 16 bits.

This is a kinda silly thing to do, because:

/*
* Supported feature bit list is just all bits in the versionnum field because
* we've used them all up and understand them all. Except, of course, for the
* shared superblock bit, which nobody knows what it does and so is unsupported.
*/
#define XFS_SB_VERSION_OKBITS \
((XFS_SB_VERSION_NUMBITS | XFS_SB_VERSION_ALLFBITS) & \
~XFS_SB_VERSION_SHAREDBIT)

#define XFS_SB_VERSION_NUMBITS 0x000f
#define XFS_SB_VERSION_ALLFBITS 0xfff0
#define XFS_SB_VERSION_SHAREDBIT 0x0200

XFS_SB_VERSION_OKBITS has a value of 0xfdff, and so
~XFS_SB_VERSION_OKBITS == XFS_SB_VERSION_SHAREDBIT. The calculated
mask already sets XFS_SB_VERSION_SHAREDBIT, so starting with
~XFS_SB_VERSION_OKBITS is completely redundant....

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
fs/xfs/scrub/agheader.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/xfs/scrub/agheader.c b/fs/xfs/scrub/agheader.c
index e954f07679dd..d6a1a9fc63c9 100644
--- a/fs/xfs/scrub/agheader.c
+++ b/fs/xfs/scrub/agheader.c
@@ -165,8 +165,7 @@ xchk_superblock(
xchk_block_set_corrupt(sc, bp);

/* Check sb_versionnum bits that are set at mkfs time. */
- vernum_mask = cpu_to_be16(~XFS_SB_VERSION_OKBITS |
- XFS_SB_VERSION_NUMBITS |
+ vernum_mask = cpu_to_be16(XFS_SB_VERSION_NUMBITS |
XFS_SB_VERSION_ALIGNBIT |
XFS_SB_VERSION_DALIGNBIT |
XFS_SB_VERSION_SHAREDBIT |
--
2.43.0