[v6] dax: introduce IS_DEVDAX() and IS_FSDAX()
diff mbox

Message ID 152001757529.22146.17936438768625217740.stgit@dwillia2-desk3.amr.corp.intel.com
State New
Headers show

Commit Message

Dan Williams March 2, 2018, 7:06 p.m. UTC
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>
---
Changes since v5:
* add comments to clarify the S_ISCHR() checks (Darrick)

 include/linux/fs.h |   24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)


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Comments

Darrick J. Wong March 2, 2018, 7:58 p.m. UTC | #1
On Fri, Mar 02, 2018 at 11:06:36AM -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>
> ---
> Changes since v5:
> * add comments to clarify the S_ISCHR() checks (Darrick)

Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> 
>  include/linux/fs.h |   24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 79c413985305..751975b8b29b 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1909,6 +1909,30 @@ 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;
> +	/* regular files with S_DAX are filesystem-dax instances */
> +	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;
> +	/* character devices with S_DAX are device-dax instances */
> +	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);
> 
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Patch
diff mbox

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 79c413985305..751975b8b29b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1909,6 +1909,30 @@  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;
+	/* regular files with S_DAX are filesystem-dax instances */
+	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;
+	/* character devices with S_DAX are device-dax instances */
+	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);