[libvirt] [PATCH] fix driver lost after detached a node device

[Jincheng Miao]

If nodedev-detach with '--driver', it does not check whether host
currentlly supports vfio passthrough. That will cause the detached
node device failed to bind to vfio driver when iommu is off:
"kernel: vfio-pci: probe of 0000:01:00.0 failed with error -22"

https://bugzilla.redhat.com/show_bug.cgi?id=1046919

So it should check passthrough support before set stub driver.
---
 src/qemu/qemu_driver.c | 33 ++++++++++++++++++++++++---------
 1 file changed, 24 insertions(+), 9 deletions(-)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index ebb77dc..0e0b170 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -10793,6 +10793,8 @@ qemuNodeDeviceDetachFlags(virNodeDevicePtr dev,
     int ret = -1;
     virNodeDeviceDefPtr def = NULL;
     char *xml = NULL;
+    bool supportsPassthroughKVM = qemuHostdevHostSupportsPassthroughLegacy();
+    bool supportsPassthroughVFIO = qemuHostdevHostSupportsPassthroughVFIO();
 
     virCheckFlags(0, -1);
 
@@ -10815,22 +10817,35 @@ qemuNodeDeviceDetachFlags(virNodeDevicePtr dev,
         goto cleanup;
 
     if (!driverName) {
-        /* prefer vfio */
-        if (qemuHostdevHostSupportsPassthroughVFIO())
+        /* decide a driver, prefer vfio */
+        if (supportsPassthroughVFIO)
             driverName = "vfio";
-        else if (qemuHostdevHostSupportsPassthroughLegacy())
+        else if (supportsPassthroughKVM)
             driverName = "kvm";
+        else {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                           _("neither VFIO nor kvm device assignment is "
+                             "currently supported on this system"));
+            goto cleanup;
+        }
     }
 
-    if (!driverName) {
-        virReportError(VIR_ERR_INVALID_ARG, "%s",
-                       _("neither VFIO nor kvm device assignment is "
-                         "currently supported on this system"));
-        goto cleanup;
-    } else if (STREQ(driverName, "vfio")) {
+    if (STREQ(driverName, "vfio")) {
+        if (!supportsPassthroughVFIO) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                           _("VFIO device assignment is currently not "
+                             "supported on this system"));
+            goto cleanup;
+        }
         if (virPCIDeviceSetStubDriver(pci, "vfio-pci") < 0)
             goto cleanup;
     } else if (STREQ(driverName, "kvm")) {
+        if (!supportsPassthroughKVM) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                           _("kvm device assignment is currently not "
+                             "supported on this system"));
+            goto cleanup;
+        }
         if (virPCIDeviceSetStubDriver(pci, "pci-stub") < 0)
             goto cleanup;
     } else {
-- 
1.8.3.1