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

[Dave Chinner <david@fromorbit.com>]

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