From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Message-ID: <1462290096.27137.47.camel@hpe.com>
Subject: Re: [PATCH v2 1/3] ext4: Add alignment check for DAX mount
From: Toshi Kani <toshi.kani@hpe.com>
To: Ross Zwisler <ross.zwisler@linux.intel.com>,
	Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@infradead.org>, dan.j.williams@intel.com,
	david@fromorbit.com, boaz@plexistor.com, tytso@mit.edu,
	adilger.kernel@dilger.ca, micah.parrish@hpe.com,
	linux-nvdimm@ml01.01.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org
Date: Tue, 03 May 2016 09:41:36 -0600
In-Reply-To: <20160503144352.GA27470@linux.intel.com>
References: <1462214578-27122-1-git-send-email-toshi.kani@hpe.com>
	 <1462214578-27122-2-git-send-email-toshi.kani@hpe.com>
	 <20160503084410.GB31363@infradead.org>
	 <20160503090021.GC12748@quack2.suse.cz>
	 <20160503144352.GA27470@linux.intel.com>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-fsdevel.vger.kernel.org>

On Tue, 2016-05-03 at 08:43 -0600, Ross Zwisler wrote:
> On Tue, May 03, 2016 at 11:00:21AM +0200, Jan Kara wrote:
> > 
> > On Tue 03-05-16 01:44:10, Christoph Hellwig wrote:
> > > 
> > > Please come up with a version that doesn't require tons of
> > > boilerplate code in every file system.
> >
> > Well, I was thinking about some helper as well but we could save ~4
> > lines with that and that didn't seem significant to me. Most of the
> > lines is actually reporting appropriate mount error in dmesg and that
> > is fs-dependent so it needs to stay in the filesystem... So what do you
> > have in mind?
>
> I guess if you wanted to reduce the code needed in each filesystem, you
> could avoid having different error messages for each of the failure
> conditions, and just print the error value.  All the error cases caught
> by the current code are unique, so we aren't losing any information.  The
> resulting patch for ext4 would look like this:

I'd prefer to keep the "error: device does not support dax" and "error:
unaligned partition for dax" messages since they clarify the problem as a
user error. The former case is especially common with BTT. The "error: dax
access failed (%d)" message is helpful when we need to look into the case.

If XFS is OK to use the messages similar to ext2/4, then we can do: 

 * Add a new helper function, say bdev_check_dax_mount(), which logs common
error messages with pr_err(), such as:
       "VFS (pmem0): error: device does not support dax"
 * When bdev_check_dax_mount() returns with a negative value:
   - XFS logs an additional message below via xfs_alert() and proceeds
without dax option.
       "XFS (pmem0): Turning DAX off."
   - ext2/4 fails the mount.

Thanks,
-Toshi