[libvirt] [PATCH] qemu: Fix mdev checking for VFIO support

[Erik Skultety]

Commit a4a39d90 added a check that checks for VFIO support with mediated
devices. The problem is that the hostdev preparing functions behave like
a fallthrough if device of that specific type doesn't exist. However,
the check for VFIO support was independent of the existence of a mdev
device which caused the guest to fail to start with any device to be
directly assigned if VFIO was disabled/unavailable in the kernel.
The proposed change first ensures that it makes sense to check for VFIO
support in the first place, and only then performs the VFIO support check
itself.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1441291

Signed-off-by: Erik Skultety <eskultet at redhat.com>
---
 src/qemu/qemu_hostdev.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/qemu/qemu_hostdev.c b/src/qemu/qemu_hostdev.c
index 685bf5b59..9b5504832 100644
--- a/src/qemu/qemu_hostdev.c
+++ b/src/qemu/qemu_hostdev.c
@@ -330,11 +330,19 @@ qemuHostdevPrepareMediatedDevices(virQEMUDriverPtr driver,
                                   int nhostdevs)
 {
     virHostdevManagerPtr hostdev_mgr = driver->hostdevMgr;
+    bool supportsVFIO = qemuHostdevHostSupportsPassthroughVFIO();
+    size_t i;
 
-    if (!qemuHostdevHostSupportsPassthroughVFIO()) {
-        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
-                       _("host doesn't support VFIO PCI interface"));
-        return -1;
+    for (i = 0; i < nhostdevs; i++) {
+        if (hostdevs[i]->mode == VIR_DOMAIN_HOSTDEV_MODE_SUBSYS &&
+            hostdevs[i]->source.subsys.type == VIR_DOMAIN_HOSTDEV_SUBSYS_TYPE_MDEV) {
+            if (!supportsVFIO) {
+                virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                               _("host doesn't support VFIO PCI interface"));
+                return -1;
+            }
+            break;
+        }
     }
 
     return virHostdevPrepareMediatedDevices(hostdev_mgr, QEMU_DRIVER_NAME,
-- 
2.12.2