Re: [PATCH V3 7/8] fs/ext4: Introduce DAX inode flag

From: Andreas Dilger <adilger@dilger.ca>
To: ira.weiny@intel.com
Cc: Ext4 Developers List <linux-ext4@vger.kernel.org>,
	"Theodore Y. Ts'o" <tytso@mit.edu>, Jan Kara <jack@suse.cz>,
	Eric Biggers <ebiggers@kernel.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Dan Williams <dan.j.williams@intel.com>,
	Dave Chinner <david@fromorbit.com>,
	Christoph Hellwig <hch@lst.de>, Jeff Moyer <jmoyer@redhat.com>,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Li Xi <lixi@ddn.com>
Subject: Re: [PATCH V3 7/8] fs/ext4: Introduce DAX inode flag
Date: Wed, 20 May 2020 13:26:44 -0600	[thread overview]
Message-ID: <34ECB1DE-9F2F-4365-BBBC-DFACF703E7D4@dilger.ca> (raw)
In-Reply-To: <20200520055753.3733520-8-ira.weiny@intel.com>

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On May 19, 2020, at 11:57 PM, ira.weiny@intel.com wrote:
> 
> From: Ira Weiny <ira.weiny@intel.com>
> 
> Add a flag to preserve FS_XFLAG_DAX in the ext4 inode.
> 
> Set the flag to be user visible and changeable.  Set the flag to be
> inherited.  Allow applications to change the flag at any time with the
> exception of if VERITY or ENCRYPT is set.
> 
> Disallow setting VERITY or ENCRYPT if DAX is set.
> 
> Finally, on regular files, flag the inode to not be cached to facilitate
> changing S_DAX on the next creation of the inode.
> 
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> 
> ---
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 6235440e4c39..467c30a789b6 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -415,13 +415,16 @@ struct flex_groups {
> #define EXT4_VERITY_FL			0x00100000 /* Verity protected inode */
> #define EXT4_EA_INODE_FL	        0x00200000 /* Inode used for large EA */
> /* 0x00400000 was formerly EXT4_EOFBLOCKS_FL */
> +
> +#define EXT4_DAX_FL			0x01000000 /* Inode is DAX */
> +
> #define EXT4_INLINE_DATA_FL		0x10000000 /* Inode has inline data. */
> #define EXT4_PROJINHERIT_FL		0x20000000 /* Create with parents projid */
> #define EXT4_CASEFOLD_FL		0x40000000 /* Casefolded file */
> #define EXT4_RESERVED_FL		0x80000000 /* reserved for ext4 lib */

Hi Ira,
This flag value conflicts with the reserved flag in e2fsprogs for snapshots:

#define EXT4_SNAPFILE_FL                0x01000000  /* Inode is a snapshot */

Please change EXT4_DAX_FL and FS_DAX_FL to use 0x02000000, which is not used
for anything in either case.

Cheers, Andreas

> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index 379a612f8f1d..7c5f6eb51e2d 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -262,6 +262,7 @@ struct fsxattr {
> #define FS_EA_INODE_FL			0x00200000 /* Inode used for large EA */
> #define FS_EOFBLOCKS_FL			0x00400000 /* Reserved for ext4 */
> #define FS_NOCOW_FL			0x00800000 /* Do not cow file */
> +#define FS_DAX_FL			0x01000000 /* Inode is DAX */
> #define FS_INLINE_DATA_FL		0x10000000 /* Reserved for ext4 */
> #define FS_PROJINHERIT_FL		0x20000000 /* Create with parents projid */
> #define FS_CASEFOLD_FL			0x40000000 /* Folder is case insensitive */
> --
> 2.25.1
> 

Cheers, Andreas

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