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

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Message-ID: <20200525072844.GH14199@quack2.suse.cz>
Date:   Mon, 25 May 2020 09:28:44 +0200
From:   Jan Kara <jack@...e.cz>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     Jan Kara <jack@...e.cz>, 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 Sun 24-05-20 21:39:10, Ira Weiny wrote:
> On Fri, May 22, 2020 at 01:48:48PM +0200, Jan Kara wrote:
> > 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?

It isn't just EXT4_JOURNAL_DATA_FL. It is:

	jflag = flags & EXT4_JOURNAL_DATA_FL;

so it is EXT4_JOURNAL_DATA_FL if it should be set by the current ioctl and 0
otherwise. But I agree that since we mostly do

	(jflag ^ oldflags) & EXT4_JOURNAL_DATA_FL

jflags is mostly useless as we could do just

	(flags ^ oldflags) & EXT4_JOURNAL_DATA_FL

I guess it's mostly a relict from the past...

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR