27a7a9d903
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>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.