From b72e04cb7e417d9e1c973223747ab3a27abda8b4 Mon Sep 17 00:00:00 2001
From: Fam Zheng <famz@redhat.com>
Date: Wed, 14 Jun 2017 15:37:01 +0200
Subject: virtio-scsi: Reject scsi-cd if data plane enabled [RHEL only]

RH-Author: Fam Zheng <famz@redhat.com>
Message-id: <20170614153701.14757-1-famz@redhat.com>
Patchwork-id: 75613
O-Subject: [RHV-7.4 qemu-kvm-rhev PATCH v3] virtio-scsi: Reject scsi-cd if data plane enabled [RHEL only]
Bugzilla: 1378816
RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Max Reitz <mreitz@redhat.com>

We need a fix for RHEL 7.4 and 7.3.z, but unfortunately upstream isn't
ready. If it were, the changes will be too invasive. To have an idea:

https://lists.gnu.org/archive/html/qemu-devel/2017-05/msg05400.html

is an incomplete attempt to fix part of the issue, and the remaining
work unfortunately involve even more complex changes.

As a band-aid, this partially reverts the effect of ef8875b
(virtio-scsi: Remove op blocker for dataplane, since v2.7). We cannot
simply revert that commit as a whole because we already shipped it in
qemu-kvm-rhev 7.3, since when, block jobs has been possible.  We should
only block what has been broken.  Also, faithfully reverting the above
commit means adding back the removed op blocker, but that is not enough,
because it still crashes when inserting media into an initially empty
scsi-cd.

All in all, scsi-cd on virtio-scsi-dataplane has basically been unusable
unless the scsi-cd never enters an empty state, so, disable it
altogether.  Otherwise it would be much more difficult to avoid
crashing.

Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
---
 hw/scsi/virtio-scsi.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index 34a968ecfb..7f6da33a8a 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -896,6 +896,15 @@ static void virtio_scsi_hotplug(HotplugHandler *hotplug_dev, DeviceState *dev,
     AioContext *old_context;
     int ret;
 
+    /* XXX: Remove this check once block backend is capable of handling
+     * AioContext change upon eject/insert.
+     * s->ctx is NULL if ioeventfd is off, s->ctx is qemu_get_aio_context() if
+     * data plane is not used, both cases are safe for scsi-cd. */
+    if (s->ctx && s->ctx != qemu_get_aio_context() &&
+        object_dynamic_cast(OBJECT(dev), "scsi-cd")) {
+        error_setg(errp, "scsi-cd is not supported by data plane");
+        return;
+    }
     if (s->ctx && !s->dataplane_fenced) {
         if (blk_op_is_blocked(sd->conf.blk, BLOCK_OP_TYPE_DATAPLANE, errp)) {
             return;
-- 
2.31.1

