linux-kernel - Re: [PATCH] virtio-scsi: hotplug suppot for virtio-scsi

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Message-ID: <4FF157CD.7090001@redhat.com>
Date:	Mon, 02 Jul 2012 10:11:57 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	mc@...ux.vnet.ibm.com
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>,
	stefanha@...ux.vnet.ibm.com, linuxram@...ibm.com,
	Anthony Liguori <anthony@...emonkey.ws>,
	senwang@...ux.vnet.ibm.com, zwanp@...ibm.com,
	"James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org
Subject: Re: [PATCH] virtio-scsi: hotplug suppot for virtio-scsi

Il 02/07/2012 09:20, mc@...ux.vnet.ibm.com ha scritto:
>>> +static void virtscsi_handle_event(struct work_struct *work)
>>> +{
>>> +    struct virtio_scsi_event_node *event_node =
>>> +        container_of(work, struct virtio_scsi_event_node, work);
>>> +    struct virtio_scsi *vscsi = event_node->vscsi;
>>> +    struct virtio_scsi_event *event = &event_node->event;
>>> +
>>> +    switch (event->event) {
>>> +    case VIRTIO_SCSI_T_TRANSPORT_RESET:
>>> +        virtscsi_handle_transport_reset(vscsi, event);
>>> +        break;
>>
>> Please handle VIRTIO_SCSI_T_NO_EVENT too here, and mask out
>> VIRTIO_SCSI_T_EVENTS_MISSED even if you do not handle it by triggering a
>> full rescan.
>>
> Paolo, what's the appropriate action to response VIRTIO_SCSI_T_NO_EVENT
> event? An error message?

No, just do nothing.

> I also have some confusion on VIRTIO_SCSI_T_EVENTS_MISSED:
> Should VIRTIO_SCSI_T_EVENTS_MISSED always be used with other event flag?

Yes.

> For instanse:
> (VIRTIO_SCSI_T_EVENTS_MISSED|VIRTIO_SCSI_T_TRANSPORT_RESET) is used to
> report hotplug event dropped when a buffer available.

The idea in the spec was that QEMU would report VIRTIO_SCSI_T_NO_EVENT |
VIRTIO_SCSI_T_EVENTS_MISSED as soon as a buffer becomes available, but
technically this is indeed possible.  So you need to handle
VIRTIO_SCSI_T_EVENTS_MISSED first, and the other bits separately.

Paolo
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