linux-kernel - Re: [PATCH 01/19] dax: remove block device dependencies

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Date:   Mon, 26 Aug 2019 04:51:52 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Vivek Goyal <vgoyal@...hat.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvdimm@...ts.01.org, virtio-fs@...hat.com, miklos@...redi.hu,
        stefanha@...hat.com, dgilbert@...hat.com,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH 01/19] dax: remove block device dependencies

On Wed, Aug 21, 2019 at 01:57:02PM -0400, Vivek Goyal wrote:
> From: Stefan Hajnoczi <stefanha@...hat.com>
> 
> Although struct dax_device itself is not tied to a block device, some
> DAX code assumes there is a block device.  Make block devices optional
> by allowing bdev to be NULL in commonly used DAX APIs.
> 
> When there is no block device:
>  * Skip the partition offset calculation in bdev_dax_pgoff()
>  * Skip the blkdev_issue_zeroout() optimization
> 
> Note that more block device assumptions remain but I haven't reach those
> code paths yet.

I think this should be split into two patches.  For bdev_dax_pgoff
I'd much rather have the partition offset if there is on in the daxdev
somehow so that we can get rid of the block device entirely.

Similarly for dax_range_is_aligned I'd rather have a pure dax way
to offload zeroing rather than this bdev hack.

In the long run I'd really like to make the bdev vs daxdev in iomap a
union instead of having to carry both around.