[Qemu-devel] Re: [PATCH] virtio-blk: assign a default serial number if none provided

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jun 01, 2010 at 08:48:54PM -0500, Ryan Harper wrote:
> This patch applies on-top of John's virtio-blk serial patches.
> 
> Generate default serial numbers for virtio drives based on DriveInfo.unit which is
> incremented for each additional virtio-blk device.  This provides a
> per-virtio-blk number to use in the default string: QM%05d that is used in
> hw/ide/core.c.  The resulting serial number looks like: QM00001, etc.
> 
> Signed-off-by: Ryan Harper <ryanh@us.ibm.com>


I think that there's a problem with this approach in that hot plug A,
hot plug B, hot unplug A is not the same as hot plug B.
So you might get guest boot failures and no easy way to
figure out why. For guests that need S/N, I think they
really must be persistent.

> ---
>  hw/virtio-blk.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c
> index 98c62f2..e5c6e7c 100644
> --- a/hw/virtio-blk.c
> +++ b/hw/virtio-blk.c
> @@ -518,6 +518,9 @@ VirtIODevice *virtio_blk_init(DeviceState *dev, BlockConf *conf)
>      bdrv_guess_geometry(s->bs, &cylinders, &heads, &secs);
>  
>      strncpy(s->sn, drive_get_serial(s->bs), sizeof (s->sn));
> +    if (strlen(s->sn) == 0) {
> +        snprintf(s->sn, sizeof(s->sn), "QM%05d", conf->dinfo->unit);
> +    }
>  
>      s->vq = virtio_add_queue(&s->vdev, 128, virtio_blk_handle_output);
>  
> -- 
> 1.6.3.3
> 
> 
> -- 
> Ryan Harper
> Software Engineer; Linux Technology Center
> IBM Corp., Austin, Tx
> ryanh@us.ibm.com