On Wed, Apr 03, 2024 at 08:28:30AM +1100, Dave Chinner wrote: > From: Dave Chinner <dchinner@xxxxxxxxxx> > > 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@xxxxxxxxxx> What a tongue twister! Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx> --D > --- > 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 > >
