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SubjectRe: [PATCH v4 02/12] dax: introduce IS_DEVDAX() and IS_FSDAX()
On Mon 26-02-18 20:20:05, Dan Williams wrote:
> The current IS_DAX() helper that checks the S_DAX inode flag is
> ambiguous, and currently has the broken assumption that the S_DAX flag

I don't think S_DAX flag is really ambiguous. It is just that in
CONFIG_FS_DAX=n + CONFIG_DEV_DAX=y case, the compiler is not able to figure
out some calls behind IS_DAX() are dead code and so the kernel won't
compile / link. Or is there any other problem I'm missing?

If I'm indeed right, then please tell this in the changelog and don't talk
about abstract ambiguity of S_DAX flag.

As much as I'd prefer to solve link-time problems with stubs instead of
relying on dead-code elimination, I can live with split macros so once the
changelog is settled, feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

Honza

> is only non-zero in the CONFIG_FS_DAX=y case. In preparation for
> defining S_DAX to non-zero in the CONFIG_FS_DAX=n + CONFIG_DEV_DAX=y
> case, introduce two explicit helpers to replace IS_DAX().
>
> Cc: "Theodore Ts'o" <tytso@mit.edu>
> Cc: Andreas Dilger <adilger.kernel@dilger.ca>
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
> Cc: linux-xfs@vger.kernel.org (supporter:XFS FILESYSTEM)
> Cc: Matthew Wilcox <mawilcox@microsoft.com>
> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> Cc: <stable@vger.kernel.org>
> Fixes: dee410792419 ("/dev/dax, core: file operations and dax-mmap")
> Reported-by: Jan Kara <jack@suse.cz>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
> include/linux/fs.h | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 79c413985305..bd0c46880572 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1909,6 +1909,28 @@ static inline bool sb_rdonly(const struct super_block *sb) { return sb->s_flags
> #define IS_WHITEOUT(inode) (S_ISCHR(inode->i_mode) && \
> (inode)->i_rdev == WHITEOUT_DEV)
>
> +static inline bool IS_DEVDAX(struct inode *inode)
> +{
> + if (!IS_ENABLED(CONFIG_DEV_DAX))
> + return false;
> + if ((inode->i_flags & S_DAX) == 0)
> + return false;
> + if (!S_ISCHR(inode->i_mode))
> + return false;
> + return true;
> +}
> +
> +static inline bool IS_FSDAX(struct inode *inode)
> +{
> + if (!IS_ENABLED(CONFIG_FS_DAX))
> + return false;
> + if ((inode->i_flags & S_DAX) == 0)
> + return false;
> + if (S_ISCHR(inode->i_mode))
> + return false;
> + return true;
> +}
> +
> static inline bool HAS_UNMAPPED_ID(struct inode *inode)
> {
> return !uid_valid(inode->i_uid) || !gid_valid(inode->i_gid);
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR

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