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From: ira.weiny@intel.com
To: linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org,
	"Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Ira Weiny <ira.weiny@intel.com>,
	Dave Chinner <dchinner@redhat.com>, Jan Kara <jack@suse.cz>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Dan Williams <dan.j.williams@intel.com>,
	Dave Chinner <david@fromorbit.com>,
	Christoph Hellwig <hch@lst.de>,
	"Theodore Y. Ts'o" <tytso@mit.edu>,
	Jeff Moyer <jmoyer@redhat.com>,
	linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-api@vger.kernel.org
Subject: [PATCH V11 03/11] fs/stat: Define DAX statx attribute
Date: Mon, 27 Apr 2020 17:21:34 -0700
Message-ID: <20200428002142.404144-4-ira.weiny@intel.com> (raw)
In-Reply-To: <20200428002142.404144-1-ira.weiny@intel.com>

From: Ira Weiny <ira.weiny@intel.com>

In order for users to determine if a file is currently operating in DAX
state (effective DAX).  Define a statx attribute value and set that
attribute if the effective DAX flag is set.

To go along with this we propose the following addition to the statx man
page:

STATX_ATTR_DAX

	The file is in the DAX (cpu direct access) state.  DAX state
	attempts to minimize software cache effects for both I/O and
	memory mappings of this file.  It requires a file system which
	has been configured to support DAX.

	DAX generally assumes all accesses are via cpu load / store
	instructions which can minimize overhead for small accesses, but
	may adversely affect cpu utilization for large transfers.

	File I/O is done directly to/from user-space buffers and memory
	mapped I/O may be performed with direct memory mappings that
	bypass kernel page cache.

	While the DAX property tends to result in data being transferred
	synchronously, it does not give the same guarantees of O_SYNC
	where data and the necessary metadata are transferred together.

	A DAX file may support being mapped with the MAP_SYNC flag,
	which enables a program to use CPU cache flush instructions to
	persist CPU store operations without an explicit fsync(2).  See
	mmap(2) for more information.

Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>

---
Changes from V2:
	Update man page text with comments from Darrick, Jan, Dan, and
	Dave.
---
 fs/stat.c                 | 3 +++
 include/uapi/linux/stat.h | 1 +
 2 files changed, 4 insertions(+)

diff --git a/fs/stat.c b/fs/stat.c
index 030008796479..894699c74dde 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -79,6 +79,9 @@ int vfs_getattr_nosec(const struct path *path, struct kstat *stat,
 	if (IS_AUTOMOUNT(inode))
 		stat->attributes |= STATX_ATTR_AUTOMOUNT;
 
+	if (IS_DAX(inode))
+		stat->attributes |= STATX_ATTR_DAX;
+
 	if (inode->i_op->getattr)
 		return inode->i_op->getattr(path, stat, request_mask,
 					    query_flags);
diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
index ad80a5c885d5..e5f9d5517f6b 100644
--- a/include/uapi/linux/stat.h
+++ b/include/uapi/linux/stat.h
@@ -169,6 +169,7 @@ struct statx {
 #define STATX_ATTR_ENCRYPTED		0x00000800 /* [I] File requires key to decrypt in fs */
 #define STATX_ATTR_AUTOMOUNT		0x00001000 /* Dir: Automount trigger */
 #define STATX_ATTR_VERITY		0x00100000 /* [I] Verity protected file */
+#define STATX_ATTR_DAX			0x00002000 /* [I] File is DAX */
 
 
 #endif /* _UAPI_LINUX_STAT_H */
-- 
2.25.1


  parent reply index

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-28  0:21 [PATCH V11 00/11] XFS - Enable per-file/per-directory DAX operations V11 ira.weiny
2020-04-28  0:21 ` [PATCH V11 01/11] fs/xfs: Remove unnecessary initialization of i_rwsem ira.weiny
2020-04-28  0:21 ` [PATCH V11 02/11] fs: Remove unneeded IS_DAX() check in io_is_direct() ira.weiny
2020-04-28  0:21 ` ira.weiny [this message]
2020-04-28  0:21 ` [PATCH V11 04/11] Documentation/dax: Update Usage section ira.weiny
2020-04-28 20:27   ` Darrick J. Wong
2020-04-28 20:53     ` Ira Weiny
2020-04-28 21:12       ` Darrick J. Wong
2020-04-28 22:21   ` [PATCH V11.1] " ira.weiny
2020-04-29  2:21     ` Randy Dunlap
2020-04-29  4:30       ` Ira Weiny
2020-04-29  4:33     ` [PATCH V11.2] " ira.weiny
2020-04-29  5:47       ` Randy Dunlap
2020-04-28  0:21 ` [PATCH V11 05/11] fs/xfs: Change XFS_MOUNT_DAX to XFS_MOUNT_DAX_ALWAYS ira.weiny
2020-04-28  0:21 ` [PATCH V11 06/11] fs/xfs: Make DAX mount option a tri-state ira.weiny
2020-04-28 20:08   ` Darrick J. Wong
2020-04-28  0:21 ` [PATCH V11 07/11] fs/xfs: Create function xfs_inode_should_enable_dax() ira.weiny
2020-04-28  0:21 ` [PATCH V11 08/11] fs/xfs: Combine xfs_diflags_to_linux() and xfs_diflags_to_iflags() ira.weiny
2020-04-28  0:21 ` [PATCH V11 09/11] fs: Lift XFS_IDONTCACHE to the VFS layer ira.weiny
2020-04-28 20:06   ` Darrick J. Wong
2020-04-28  0:21 ` [PATCH V11 10/11] fs: Introduce DCACHE_DONTCACHE ira.weiny
2020-04-28 13:04   ` Jan Kara
2020-04-28 20:09   ` Darrick J. Wong
2020-04-28  0:21 ` [PATCH V11 11/11] fs/xfs: Update xfs_ioctl_setattr_dax_invalidate() ira.weiny
2020-04-28 20:11   ` Darrick J. Wong
2020-06-02 17:23     ` Darrick J. Wong
2020-06-02 23:15       ` Ira Weiny
2020-06-03 10:10       ` Jan Kara
2020-06-03 17:03         ` Darrick J. Wong

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