xen: check if device is assigned to guest before reattaching

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=664059

Reattaching pci device back to host without destroying guest or
detaching device from guest would cause host to crash. This patch adds
a check before doing device reattach. If the device is being assigned
to guest, libvirt refuses to reattach device to host. The patch only
works for Xen, for it just checks xenstore to get pci device
information.
Signed-off-by: NYufang Zhang <yuzhang@redhat.com>

AUTHORS

@@ -168,6 +168,7 @@ Patches have also been contributed by:
   Alexander Todorov    <atodorov@otb.bg>
   Richard Laager       <rlaager@wiktel.com>
   Mark Wu              <dwu@redhat.com>
+  Yufang Zhang         <yuzhang@redhat.com>
 
   [....send patches to get your name here....]
 

src/xen/xen_driver.c

@@ -1926,12 +1926,71 @@ out:
     return ret;
 }
 
+static int
+xenUnifiedNodeDeviceAssignedDomainId (virNodeDevicePtr dev)
+{
+    int numdomains;
+    int ret = -1, i;
+    int *ids = NULL;
+    char *bdf = NULL;
+    char *xref = NULL;
+    unsigned int domain, bus, slot, function;
+    virConnectPtr conn = dev->conn;
+    xenUnifiedPrivatePtr priv = conn->privateData;
+
+    /* Get active domains */
+    numdomains = xenUnifiedNumOfDomains(conn);
+    if (numdomains < 0) {
+        return ret;
+    }
+    if (numdomains > 0){
+        if (VIR_ALLOC_N(ids, numdomains) < 0) {
+            virReportOOMError();
+            goto out;
+        }
+        if ((numdomains = xenUnifiedListDomains(conn, &ids[0], numdomains)) < 0) {
+            goto out;
+        }
+    }
+
+    /* Get pci bdf */
+    if (xenUnifiedNodeDeviceGetPciInfo(dev, &domain, &bus, &slot, &function) < 0)
+        goto out;
+
+    if (virAsprintf(&bdf, "%04x:%02x:%02x.%0x",
+                    domain, bus, slot, function) < 0) {
+        virReportOOMError();
+        goto out;
+    }
+
+    xenUnifiedLock(priv);
+    /* Check if bdf is assigned to one of active domains */
+    for (i = 0; i < numdomains; i++ ) {
+        xref = xenStoreDomainGetPCIID(conn, ids[i], bdf);
+        if (xref == NULL) {
+            continue;
+        } else {
+            ret = ids[i];
+            break;
+        }
+    }
+    xenUnifiedUnlock(priv);
+
+    VIR_FREE(xref);
+    VIR_FREE(bdf);
+out:
+    VIR_FREE(ids);
+
+    return ret;
+}
+
 static int
 xenUnifiedNodeDeviceReAttach (virNodeDevicePtr dev)
 {
     pciDevice *pci;
     unsigned domain, bus, slot, function;
     int ret = -1;
+    int domid;
 
     if (xenUnifiedNodeDeviceGetPciInfo(dev, &domain, &bus, &slot, &function) < 0)
         return -1;
@@ -1940,6 +1999,14 @@ xenUnifiedNodeDeviceReAttach (virNodeDevicePtr dev)
     if (!pci)
         return -1;
 
+    /* Check if device is assigned to an active guest */
+    if ((domid = xenUnifiedNodeDeviceAssignedDomainId(dev)) >= 0) {
+        xenUnifiedError(VIR_ERR_INTERNAL_ERROR,
+                        _("Device %s has been assigned to guest %d"),
+                        dev->name, domid);
+        goto out;
+    }
+
     if (pciReAttachDevice(pci, NULL) < 0)
         goto out;