[RFC PATCH] vfio-ccw: Permit missing IRQs

[Eric Farman <farman@linux.ibm.com>]

Commit 690e29b91102 ("vfio-ccw: Refactor ccw irq handler") changed
one of the checks for the IRQ notifier registration from saying
"the host needs to recognize the only IRQ that exists" to saying
"the host needs to recognize ANY IRQ that exists."

And this worked fine, because the subsequent change to support the
CRW IRQ notifier doesn't get into this code when running on an older
kernel, thanks to a guard by a capability region. The later addition
of the REQ(uest) IRQ by commit b2f96f9e4f5f ("vfio-ccw: Connect the
device request notifier") broke this assumption because there is no
matching capability region. Thus, running new QEMU on an older
kernel fails with:

  vfio: unexpected number of irqs 2

Let's simply remove the check (and the less-than-helpful message),
and make the VFIO_DEVICE_GET_IRQ_INFO ioctl request for the IRQ
being processed. If it returns with EINVAL, we can treat it as
an unfortunate mismatch but not a fatal error for the guest.

Fixes: 690e29b91102 ("vfio-ccw: Refactor ccw irq handler")
Fixes: b2f96f9e4f5f ("vfio-ccw: Connect the device request notifier")
Signed-off-by: Eric Farman <farman@linux.ibm.com>
---
 hw/vfio/ccw.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/hw/vfio/ccw.c b/hw/vfio/ccw.c
index b2df708e4b..cfbfc3d1a2 100644
--- a/hw/vfio/ccw.c
+++ b/hw/vfio/ccw.c
@@ -411,20 +411,19 @@ static void vfio_ccw_register_irq_notifier(VFIOCCWDevice *vcdev,
         return;
     }
 
-    if (vdev->num_irqs < irq + 1) {
-        error_setg(errp, "vfio: unexpected number of irqs %u",
-                   vdev->num_irqs);
-        return;
-    }
-
     argsz = sizeof(*irq_info);
     irq_info = g_malloc0(argsz);
     irq_info->index = irq;
     irq_info->argsz = argsz;
     if (ioctl(vdev->fd, VFIO_DEVICE_GET_IRQ_INFO,
               irq_info) < 0 || irq_info->count < 1) {
-        error_setg_errno(errp, errno, "vfio: Error getting irq info");
-        goto out_free_info;
+        if (errno == EINVAL) {
+            warn_report("Unable to get information about IRQ %u", irq);
+            goto out_free_info;
+        } else {
+            error_setg_errno(errp, errno, "vfio: Error getting irq info");
+            goto out_free_info;
+        }
     }
 
     if (event_notifier_init(notifier, 0)) {
-- 
2.25.1