linux-ext4 - Re: [PATCH V4 7/8] fs/ext4: Introduce DAX inode flag

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Date:   Sun, 24 May 2020 21:39:10 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        "Theodore Y. Ts'o" <tytso@....edu>,
        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>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4 7/8] fs/ext4: Introduce DAX inode flag

On Fri, May 22, 2020 at 01:48:48PM +0200, Jan Kara wrote:
> On Thu 21-05-20 12:13:12, 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>
> 
> ...
> 
> > @@ -303,6 +318,16 @@ static int ext4_ioctl_setflags(struct inode *inode,
> >  	unsigned int jflag;
> >  	struct super_block *sb = inode->i_sb;
> >  
> > +	if (ext4_test_inode_flag(inode, EXT4_INODE_DAX)) {
> > +		if (ext4_test_inode_flag(inode, EXT4_INODE_VERITY) ||
> > +		    ext4_test_inode_flag(inode, EXT4_INODE_ENCRYPT) ||
> > +		    ext4_test_inode_state(inode,
> > +					  EXT4_STATE_VERITY_IN_PROGRESS)) {
> > +			err = -EOPNOTSUPP;
> > +			goto flags_out;
> > +		}
> > +	}
> 
> The way this check is implemented wouldn't IMO do what we need... It
> doesn't check the flags that are being set but just the current inode
> state. I think it should rather be:

Sorry, I got confused by the flags when I wrote this.

> 
> 	if ((flags ^ oldflags) & EXT4_INODE_DAX_FL) {
> 		...
> 	}
> 
> And perhaps move this to a place in ext4_ioctl_setflags() where we check
> other similar conflicts.

Sure.  It seems like a ext4_setflags_prepare() helper would be in order.  I'll
see what I can do.

> 
> And then we should check conflicts with the journal flag as well, as I
> mentioned in reply to the first patch. There it is more complicated by the
> fact that we should disallow setting of both EXT4_INODE_DAX_FL and
> EXT4_JOURNAL_DATA_FL at the same time so the checks will be somewhat more
> complicated.

I'm confused by jflag.  Why is EXT4_JOURNAL_DATA_FL stored in jflag?

Ira

> 
> 								Honza
> 
> > +
> >  	/* Is it quota file? Do not allow user to mess with it */
> >  	if (ext4_is_quota_file(inode))
> >  		goto flags_out;
> -- 
> Jan Kara <jack@...e.com>
> SUSE Labs, CR