linux-ext4 - Re: [PATCH v2 1/2] fs, xfs: perform dax

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Message-ID: <CAPcyv4i2rS0sAxiJSVxFSHirsycaYofuxp3yPxeyB8xzsryx3g@mail.gmail.com>
Date:   Tue, 29 Aug 2017 14:35:27 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Christoph Hellwig <hch@....de>
Cc:     linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Jan Kara <jack@...e.cz>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        linux-xfs@...r.kernel.org, linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] fs, xfs: perform dax_device lookup at mount

On Tue, Aug 29, 2017 at 2:31 PM, Dan Williams <dan.j.williams@...el.com> wrote:
> On Tue, Aug 29, 2017 at 2:26 PM, Christoph Hellwig <hch@....de> wrote:
>> Call me nitpicky, but..
>>
>> First this really should be three patches, one for the DAX code, one
>> for the VFS code and one for XFS.  The DAX and XFS bits looks fine to
>> me:
>>
>> Reviewed-by: Christoph Hellwig <hch@....de>
>>
>> But I'm a little worried about stuffing more DAX knowledge into the
>> block mount_bdev helper.  For now it's probably ok as everything
>> else would involve a lot of refactoring and/or duplication, but
>> I'm generally not too happy about it.
>
> I think this is why we ended up with calling dax_get_by_host() in
> ->iomap_begin() because the mount_bdev() touches I started with back
> when this was first introduced were not very palatable. I agree with
> the direction to move to mount_dax() in the future. I can respin this
> into three patches and a TODO comment about how we want to kill the
> dax knowledge in mount_bdev() going forward.

Actually, why not just do this directly in xfs_fs_mount()? I think I
can refactor this to not touch mount_bdev() and put all the details in
the per-fs mount/umount paths.