qemu: fix alias name for <interface type='hostdev'>

Starting with commit f8e712fe, if you start a domain that has an
<interface type='hostdev' (or that has <interface type='network'>
where the network is a pool of devices for hostdev assignment), when
you later try to add *another* interface (of any kind) with hotplug,
the function qemuAssignDeviceNetAlias() fails as soon as it sees a
"hostdevN" alias in the list of interfaces), causing the attach to
fail.

This is because (starting with f8e712fe) the device alias names are
assigned during the new function qemuProcessPrepareDomain(), which is
called *before* networkAllocateActualDevice() (which is called from
qemuProcessPrepareHost(), which is called from
qemuProcessLaunch()). Prior to that commit,
networkAllocateActualDevice() was called first.

The problem with this is that the alias for interfaces that are really
a hostdev (<interface type='hostdev'>) is of the form "hostdevN" (just
like other hostdevs), while other interfaces are "netN". But if you
don't know that the interface is going to be a hostdev at the time you
assign the alias name, you can't name it differently. (As far as I've
seen so far, the change in name by itself wouldn't have been a problem
(other than just an outwardly noticeable change in behavior) except
for the abovementioned failure to attach/detach new interfaces.

Rather than take the chance that there may be other not-yet-revealed
problems associated with changing the alias name, this patch changes
the way that aliases are assigned to restore the old behavior.

Old: In the past, assigning an alias to an interface was skipped if it
was seen that the interface was type='hostdev' - we knew that the
hostdev part of the interface was also in the list of hostdevs (that's
part of what happens in networkAllocateActualDevice()) and it would be
assigned when all the other hostdev aliases were assigned.

New: When assigning an alias to an interface, we haven't yet called
networkAllocateActualDevice() to construct the hostdev part of the
interface, so we can't just wait for the loop that creates aliases for
all the hostdevs (there's nothing on that list for this device
yet!). Instead we handle it immediately in the loop creating interface
aliases, by calling the new function networkGetActualType() to
determine if it is going to be hostdev, and if so calling
qemuAssignDeviceHostdevAlias() instead.

Some adjustments have to be made to both
qemuAssignDeviceHostdevAlias() and to qemuAssignDeviceNetAlias() to
accommodate this. In both of them, an error return from
qemuDomainDeviceAliasIndex() is no longer considered an error; instead
it's just ignored (because it almost certainly means that the alias
string for the device was "net" when we expected "hostdev" or vice
versa). in qemuAssignDeviceHostdevAlias() we have to look at all
interface aliases for hostdevN in addition to looking at all hostdev
aliases (this wasn't necessary in the past, because both the interface
entry and the hostdev entry for the device already pointed at the
device info; no longer the case since the hostdev entry hasn't yet
been setup).

Fortunately the buggy behavior hasn't yet been in any official release
of libvirt.

src/qemu/qemu_alias.c

@@ -27,6 +27,7 @@
 #include "viralloc.h"
 #include "virlog.h"
 #include "virstring.h"
+#include "network/bridge_driver.h"
 
 #define VIR_FROM_THIS VIR_FROM_QEMU
 
@@ -293,14 +294,22 @@ qemuAssignDeviceHostdevAlias(virDomainDefPtr def,
 {
     if (idx == -1) {
         size_t i;
+
         idx = 0;
         for (i = 0; i < def->nhostdevs; i++) {
             int thisidx;
-            if ((thisidx = qemuDomainDeviceAliasIndex(def->hostdevs[i]->info, "hostdev")) < 0) {
-                virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                               _("Unable to determine device index for hostdev device"));
-                return -1;
-            }
+
+            if ((thisidx = qemuDomainDeviceAliasIndex(def->hostdevs[i]->info, "hostdev")) < 0)
+                continue; /* error just means the alias wasn't "hostdevN", but something else */
+            if (thisidx >= idx)
+                idx = thisidx + 1;
+        }
+        /* network interfaces can also have a hostdevN alias */
+        for (i = 0; i < def->nnets; i++) {
+            int thisidx;
+
+            if ((thisidx = qemuDomainDeviceAliasIndex(&def->nets[i]->info, "hostdev")) < 0)
+                continue;
             if (thisidx >= idx)
                 idx = thisidx + 1;
         }
@@ -318,22 +327,23 @@ qemuAssignDeviceNetAlias(virDomainDefPtr def,
                          virDomainNetDefPtr net,
                          int idx)
 {
+
+    /* <interface type='hostdev'> uses "hostdevN" as the alias
+     * We must use "-1" as the index because the caller doesn't know
+     * that we're now looking for a unique hostdevN rather than netN
+     */
+    if (networkGetActualType(net) == VIR_DOMAIN_NET_TYPE_HOSTDEV)
+        return qemuAssignDeviceHostdevAlias(def, &net->info.alias, -1);
+
     if (idx == -1) {
         size_t i;
+
         idx = 0;
         for (i = 0; i < def->nnets; i++) {
             int thisidx;
 
-            if (virDomainNetGetActualType(def->nets[i])
-                == VIR_DOMAIN_NET_TYPE_HOSTDEV) {
-                /* type='hostdev' interfaces have a hostdev%d alias */
-               continue;
-            }
-            if ((thisidx = qemuDomainDeviceAliasIndex(&def->nets[i]->info, "net")) < 0) {
-                virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                               _("Unable to determine device index for network device"));
-                return -1;
-            }
+            if ((thisidx = qemuDomainDeviceAliasIndex(&def->nets[i]->info, "net")) < 0)
+                continue; /* failure could be due to "hostdevN" */
             if (thisidx >= idx)
                 idx = thisidx + 1;
         }
@@ -392,14 +402,8 @@ qemuAssignDeviceAliases(virDomainDefPtr def, virQEMUCapsPtr qemuCaps)
             return -1;
     }
     for (i = 0; i < def->nnets; i++) {
-        /* type='hostdev' interfaces are also on the hostdevs list,
-         * and will have their alias assigned with other hostdevs.
-         */
-        if (virDomainNetGetActualType(def->nets[i])
-            != VIR_DOMAIN_NET_TYPE_HOSTDEV &&
-            qemuAssignDeviceNetAlias(def, def->nets[i], i) < 0) {
+        if (qemuAssignDeviceNetAlias(def, def->nets[i], -1) < 0)
             return -1;
-        }
     }
 
     if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_DEVICE))
@@ -414,7 +418,13 @@ qemuAssignDeviceAliases(virDomainDefPtr def, virQEMUCapsPtr qemuCaps)
             return -1;
     }
     for (i = 0; i < def->nhostdevs; i++) {
-        if (qemuAssignDeviceHostdevAlias(def, &def->hostdevs[i]->info->alias, i) < 0)
+        /* we can't start assigning at 0, since netdevs may have used
+         * up some hostdevN entries already. Also if the HostdevDef is
+         * linked to a NetDef, they will share an info and the alias
+         * will already be set, so don't try to set it again.
+         */
+        if (!def->hostdevs[i]->info->alias &&
+            qemuAssignDeviceHostdevAlias(def, &def->hostdevs[i]->info->alias, -1) < 0)
             return -1;
     }
     for (i = 0; i < def->nredirdevs; i++) {