vhost-scsi: log event queue write descriptors

Log write descriptors for the event queue, leveraging vhost_get_vq_desc()
to retrieve the array of write descriptors to obtain the log buffer.

There is only one path for event queue.

Suggested-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Message-Id: <20250403063028.16045-9-dongli.zhang@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Author: Dongli Zhang

drivers/vhost/scsi.c

@@ -571,6 +571,8 @@ vhost_scsi_do_evt_work(struct vhost_scsi *vs, struct vhost_scsi_evt *evt)
 	struct vhost_virtqueue *vq = &vs->vqs[VHOST_SCSI_VQ_EVT].vq;
 	struct virtio_scsi_event *event = &evt->event;
 	struct virtio_scsi_event __user *eventp;
+	struct vhost_log *vq_log;
+	unsigned int log_num;
 	unsigned out, in;
 	int head, ret;
 
@@ -581,9 +583,19 @@ vhost_scsi_do_evt_work(struct vhost_scsi *vs, struct vhost_scsi_evt *evt)
 
 again:
 	vhost_disable_notify(&vs->dev, vq);
+
+	vq_log = unlikely(vhost_has_feature(vq, VHOST_F_LOG_ALL)) ?
+		vq->log : NULL;
+
+	/*
+	 * Reset 'log_num' since vhost_get_vq_desc() may reset it only
+	 * after certain condition checks.
+	 */
+	log_num = 0;
+
 	head = vhost_get_vq_desc(vq, vq->iov,
 			ARRAY_SIZE(vq->iov), &out, &in,
-			NULL, NULL);
+			vq_log, &log_num);
 	if (head < 0) {
 		vs->vs_events_missed = true;
 		return;
@@ -613,6 +625,8 @@ vhost_scsi_do_evt_work(struct vhost_scsi *vs, struct vhost_scsi_evt *evt)
 		vhost_add_used_and_signal(&vs->dev, vq, head, 0);
 	else
 		vq_err(vq, "Faulted on vhost_scsi_send_event\n");
+
+	vhost_scsi_log_write(vq, vq_log, log_num);
 }
 
 static void vhost_scsi_complete_events(struct vhost_scsi *vs, bool drop)