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

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Date:   Wed, 15 Jan 2020 12:17:40 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Vivek Goyal <vgoyal@...hat.com>
Cc:     Jan Kara <jack@...e.cz>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Christoph Hellwig <hch@...radead.org>,
        Dave Chinner <david@...morbit.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        virtio-fs@...hat.com, Stefan Hajnoczi <stefanha@...hat.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Jeff Moyer <jmoyer@...hat.com>
Subject: Re: [PATCH 01/19] dax: remove block device dependencies

On Wed, Jan 15, 2020 at 11:56 AM Vivek Goyal <vgoyal@...hat.com> wrote:
[..]
> > Even the Red Hat
> > installation guide example shows mounting on pmem0 directly. [1]
>
> Below that example it also says.
>
> "When creating partitions on a pmem device to be used for direct access,
> partitions must be aligned on page boundaries. On the Intel 64 and AMD64
> architecture, at least 4KiB alignment for the start and end of the
> partition, but 2MiB is the preferred alignment. By default, the parted
> tool aligns partitions on 1MiB boundaries. For the first partition,
> specify 2MiB as the start of the partition. If the size of the partition
> is a multiple of 2MiB, all other partitions are also aligned."
>
> So documentation is clearly saying dax will work with partitions as well.
> And some user might decide to just do that.

Yes, of course but my point is that it was ambiguous.

I'm going to take a look at how hard it would be to develop a kpartx
fallback in udev. If that can live across the driver transition then
maybe this can be a non-event for end users that already have that
udev update deployed.