On Thu, Mar 01, 2018 at 07:53:44PM -0800, Dan Williams wrote:
The current IS_DAX() helper that checks if a file is in DAX mode serves two purposes. It is a control flow branch condition for DAX vs non-DAX paths and it is a mechanism to perform dead code elimination. The dead code elimination is required in the CONFIG_FS_DAX=n case since there are symbols in fs/dax.c that will be elided. While the dead code elimination can be addressed with nop stubs for the fs/dax.c symbols that does not address the need for a DAX control flow helper where fs/dax.c symbols are not involved.
Moreover, the control flow changes, in some cases, need to be cognizant of whether the DAX file is a typical file or a Device-DAX special file. Introduce IS_DEVDAX() and IS_FSDAX() to simultaneously address the file-type control flow and dead-code elimination use cases. IS_DAX() will be deleted after all sites are converted to use the file-type specific helper.
Note, this change is also a pre-requisite for fixing the definition of the S_DAX inode flag in the CONFIG_FS_DAX=n + CONFIG_DEV_DAX=y case. The flag needs to be defined, non-zero, if either DAX facility is enabled.
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 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 Reviewed-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;
I echo Jan's complaint from the last round that the dead code elimination here is subtle, as compared to:
#if IS_ENABLED(CONFIG_FS_DAX) static inline bool IS_FSDAX(struct inode *inode) { ... } #else # define IS_FSDAX(inode) (false) #endif
But I guess even with that we're relying on dead code elimination higher up in the call stack...
- if ((inode->i_flags & S_DAX) == 0)
return false;- if (S_ISCHR(inode->i_mode))
return false;
I'm curious, do we have character devices with S_DAX set?
I /think/ we're expecting that only block/char devices and files will ever have S_DAX set, so IS_FSDAX is only true for block devices and files. Right?
(A comment here about why S_ISCHR->false here would be helpful.)
--D
- return true;
+}
static inline bool HAS_UNMAPPED_ID(struct inode *inode) { return !uid_valid(inode->i_uid) || !gid_valid(inode->i_gid);
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