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

From: Jan Kara <jack@suse.cz>
To: Ira Weiny <ira.weiny@intel.com>
Cc: Jan Kara <jack@suse.cz>,
	linux-ext4@vger.kernel.org,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	"Theodore Y. Ts'o" <tytso@mit.edu>,
	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@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH V4 7/8] fs/ext4: Introduce DAX inode flag
Date: Mon, 25 May 2020 09:28:44 +0200	[thread overview]
Message-ID: <20200525072844.GH14199@quack2.suse.cz> (raw)
In-Reply-To: <20200525043910.GA319107@iweiny-DESK2.sc.intel.com>

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@suse.com>
SUSE Labs, CR