linux-kernel - Re: [PATCH v2 12/30] dax: remove block device dependencies

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Message-ID: <CAPcyv4i_-ri=w0jYJ4WjK4QD9E8pMzkGQNdMbt9H_nawDqYD3A@mail.gmail.com>
Date:   Wed, 15 May 2019 17:21:51 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Vivek Goyal <vgoyal@...hat.com>
Cc:     linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        KVM list <kvm@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Steven Whitehouse <swhiteho@...hat.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>
Subject: Re: [PATCH v2 12/30] dax: remove block device dependencies

On Wed, May 15, 2019 at 12:28 PM Vivek Goyal <vgoyal@...hat.com> 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.
>

Is there a generic object that non-block-based filesystems reference
for physical storage as a bdev stand-in? I assume "sector_t" is still
the common type for addressing filesystem capacity?

It just seems to me that we should stop pretending that the
filesystem-dax facility requires block devices and try to move this
functionality to generically use a dax device across all interfaces.