linux-kernel - Re: [PATCH 4/4] virtio_blk: use disk_name_format() to support mass of disks naming

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Message-ID: <20120402072009.GF30360@redhat.com>
Date:	Mon, 2 Apr 2012 10:20:09 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Ren Mingxin <renmx@...fujitsu.com>
Cc:	Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	Rusty Russell <rusty@...tcorp.com.au>,
	LKML <linux-kernel@...r.kernel.org>,
	SCSI <linux-scsi@...r.kernel.org>, KVM <kvm@...r.kernel.org>,
	VIRTUAL <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH 4/4] virtio_blk: use disk_name_format() to support mass
 of disks naming

On Mon, Apr 02, 2012 at 09:19:05AM +0800, Ren Mingxin wrote:
>  On 03/30/2012 11:28 PM, Tejun Heo wrote:
> >On Fri, Mar 30, 2012 at 08:26:06AM -0700, Tejun Heo wrote:
> >>On Fri, Mar 30, 2012 at 05:53:52PM +0800, Ren Mingxin wrote:
> >>>  The current virtblk's naming algorithm only supports 263  disks.
> >>>If there are mass of virtblks(exceeding 263), there will be disks
> >>>with the same name.
> >>>
> >>>By renaming "sd_format_disk_name()" to "disk_name_format()"
> >>>and moving it into block core, virtio_blk can use this function to
> >>>support mass of disks.
> >>>
> >>>Signed-off-by: Ren Mingxin<renmx@...fujitsu.com>
> >>I guess it's already way too late but why couldn't they have been
> >>named vdD-P where both D and P are integers denoting disk number and
> >>partition number?  [sh]dX's were created when there weren't supposed
> >>to be too many disks, so we had to come up with the horrible alphabet
> >>based numbering scheme but vd is new enough.  I mean, naming is one
> >>thing but who wants to figure out which sequence is or guess what
> >>comes next vdzz9?  :(
> >>
> >>If we're gonna move it to block layer, let's add big blinking red
> >>comment saying "don't ever use it for any new driver".
> >And also let's make that clear in the function name - say,
> >format_legacy_disk_name() or something.
> 
> So, to legacy disks [sh]d, we'd name them as [sh]d[a-z]{1,}. To new devices
> like vd, we'd name them as vd<index>(vd<index>p<partno> as partitions)?

Pleae don't rename virtio disks, it is way too late for that:
virtio block driver was merged around 2007, it is not new by
any measure, and there are many systems out there using
the current naming scheme.

> And how about the rssd in the patch 3 then?

Probably same. Renaming existing devices will break setups.
I think the idea is to avoid using the
legacy naming in new drivers *that will be added from now on*.

> Besides, does anybody have comments?
> Looking forward to your replies ;-)
> 
> -- 
> Thanks,
> Ren
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