linux-kernel - Re: [PATCH 2/2] init, mount: export the name_to_dev

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Date:	Tue, 25 May 2010 11:11:33 -0500
From:	Will Drewry <wad@...omium.org>
To:	Alasdair G Kergon <agk@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Will Drewry <wad@...omium.org>, linux-kernel@...r.kernel.org,
	Al Viro <viro@...iv.linux.org.uk>,
	Nick Piggin <npiggin@...e.de>, Tejun Heo <tj@...nel.org>,
	Scott James Remnant <scott@...ntu.com>,
	Vegard Nossum <vegard.nossum@...il.com>,
	Harald Hoyer <harald@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>, snitzer@...hat.com
Subject: Re: [PATCH 2/2] init, mount: export the name_to_dev_t symbol

On Tue, May 25, 2010 at 11:05 AM, Alasdair G Kergon <agk@...hat.com> wrote:
> On Tue, May 25, 2010 at 11:55:35AM -0400, Christoph Hellwig wrote:
>> NACK.  It's really a hack for the boot code, there's no offical name to
>> dev_t mapping.
>> What are you trying to use it for?
>
> Device-mapper contains a subset of that code, so he's proposing we
> use it here:
>
> @@ -434,17 +435,13 @@ static int __table_get_device(struct dm_
>        int r;
>        dev_t uninitialized_var(dev);
>        struct dm_dev_internal *dd;
> -       unsigned int major, minor;
>
>        BUG_ON(!t);
>
> -       if (sscanf(path, "%u:%u", &major, &minor) == 2) {
> -               /* Extract the major/minor numbers */
> -               dev = MKDEV(major, minor);
> -               if (MAJOR(dev) != major || MINOR(dev) != minor)
> -                       return -EOVERFLOW;
> -       } else {
> -               /* convert the path to a device */
> +       /* lookup by major:minor or registered device name */
> +       dev = name_to_dev_t(path);
> +       if (!dev) {
> +               /* convert the path to a device by finding its inode */
>                struct block_device *bdev = lookup_bdev(path);
>
>                if (IS_ERR(bdev))

In addition to getting rid of the code duplication, I'd like device-mapper
to be able to resolve slave devices at boot-time to accommodate a
do_mounts_dm.c equivalent to do_mounts_md.c:

  https://patchwork.kernel.org/patch/101024/

(which I neglected to mail to the other init-related maintainers - sorry!
 I'll correct that when I mail out the next revision.)

thanks!
will
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