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

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Message-ID: <20200520205509.GA17615@magnolia>
Date:   Wed, 20 May 2020 13:55:09 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     Andreas Dilger <adilger@...ger.ca>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
        Eric Biggers <ebiggers@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>, Jeff Moyer <jmoyer@...hat.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Li Xi <lixi@....com>
Subject: Re: [PATCH V3 7/8] fs/ext4: Introduce DAX inode flag

On Wed, May 20, 2020 at 01:02:42PM -0700, Ira Weiny wrote:
> On Wed, May 20, 2020 at 01:26:44PM -0600, Andreas Dilger wrote:
> > On May 19, 2020, at 11:57 PM, ira.weiny@...el.com wrote:
> > > 
> > > From: Ira Weiny <ira.weiny@...el.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@...el.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 */
> 
> Sure NP but is that new?  I'm building off of 5.7-rc4.
> 
> Just curious if I completely missed something.

Yeah, you missed that ... for some reason the kernel ext4 driver is
missing flags that are in e2fsprogs.  (huh??)

I would say you could probably just take over the flag because the 2010s
called and they don't want next3 back.  I guess that leaves 0x02000000
as the sole unclaimed bit, but this seriously needs some cleaning.

--D

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