linux-kernel - Re: [PATCH] Rescan the entire target on transport reset when LUN is 0

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Message-ID: <20200908101531-mutt-send-email-mst@kernel.org>
Date:   Tue, 8 Sep 2020 10:15:50 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Matej Genci <matej.genci@...anix.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "stefanha@...hat.com" <stefanha@...hat.com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        Felipe Franciosi <felipe@...anix.com>
Subject: Re: [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@...anix.com>
> Suggested-by: Felipe Franciosi <felipe@...anix.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