Linux Virtualization - Sep 2020 - [PATCH] Rescan the entire target on transport reset when LUN is 0

On Fri, Aug 28, 2020 at 12:21:35PM +0000, Matej Genci
wrote:
> VirtIO 1.0 spec says
>     The removed and rescan events ... when sent for LUN 0, they MAY
>     apply to the entire target so the driver can ask the initiator
>     to rescan the target to detect this.
> 
> This change introduces the behaviour described above by scanning the
> entire scsi target when LUN is set to 0. This is both a functional and a
> performance fix. It aligns the driver with the spec and allows control
> planes to hotplug targets with large numbers of LUNs without having to
> request a RESCAN for each one of them.
> 
> Signed-off-by: Matej Genci <matej at nutanix.com>
> Suggested-by: Felipe Franciosi <felipe at nutanix.com>
Stefan, Paolo, could you review this pls?
> ---
>  drivers/scsi/virtio_scsi.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
> index bfec84aacd90..a4b9bc7b4b4a 100644
> --- a/drivers/scsi/virtio_scsi.c
> +++ b/drivers/scsi/virtio_scsi.c
> @@ -284,7 +284,12 @@ static void virtscsi_handle_transport_reset(struct
virtio_scsi *vscsi,
>  
>  	switch (virtio32_to_cpu(vscsi->vdev, event->reason)) {
>  	case VIRTIO_SCSI_EVT_RESET_RESCAN:
> -		scsi_add_device(shost, 0, target, lun);
> +		if (lun == 0) {
> +			scsi_scan_target(&shost->shost_gendev, 0, target,
> +					 SCAN_WILD_CARD, SCSI_SCAN_INITIAL);
> +		} else {
> +			scsi_add_device(shost, 0, target, lun);
> +		}
>  		break;
>  	case VIRTIO_SCSI_EVT_RESET_REMOVED:
>  		sdev = scsi_device_lookup(shost, 0, target, lun);
> -- 
> 2.20.1