linux-kernel - Re: [PATCH] virtio_blk: decrement index when blockdevice is removed

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Date:	Wed, 06 Apr 2011 11:02:08 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Jens Axboe <jaxboe@...ionio.com>, Takuma Umeya <tumeya@...hat.com>
Cc:	"virtualization\@lists.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	Christoph Hellwig <hch@....de>,
	john cooper <john.cooper@...hat.com>,
	Tejun Heo <tj@...nel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] virtio_blk: decrement index when blockdevice is removed

On Tue, 05 Apr 2011 07:08:12 +0200, Jens Axboe <jaxboe@...ionio.com> wrote:
> On 2011-04-05 06:49, Takuma Umeya wrote:
> > When virtio block device is removed, index does not get decremented. When 
> > another virtio disk is attached it uses the next device letter to the 
> > one that is suppose to be available. 
> > 
> > Signed-off-by: Takuma Umeya <tumeya@...hat.com>
> > 
> > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > index 6ecf89c..730e7af 100644
> > --- a/drivers/block/virtio_blk.c
> > +++ b/drivers/block/virtio_blk.c
> > @@ -489,6 +489,7 @@ static void __devexit virtblk_remove(struct virtio_device *vdev)
> >         mempool_destroy(vblk->pool);
> >         vdev->config->del_vqs(vdev);
> >         kfree(vblk);
> > +       index--;
> >  }
> >  
> >  static const struct virtio_device_id id_table[] = {
> 
> What happens when you delete a device that isn't the last one?

Obviously we should do something cleverer for assigning drives.

It might be a cute if genhd gave us a function to get the next free
index for a given major number, and format it for us, like so:

      /* Return the next available minor for a given @major, at least
       * @spacing after the previous and, and append appropriate letters
       * to @name if it's not NULL.  -ve errno on fail (-ENOSPC?). */
      int disk_next_minor(int major, unsigned spacing, char *name);

A trivial optimization would be to remember the last major and max minor
(resetting that if any disks are removed).

This could clean up other code, too.

Cheers,
Rusty.
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