qemu: Report all supported machine types in capabilities

Some machine types are only reported as canonical names for other
machine types, which make it a bit harder to find what machine types are
supported by a specific QEMU binary. Ideally, one would just use
/capabilities/guest/arch[@name='...']/machine/text() XPath to get a list
of all supported machine types, but it doesn't work right now.

For example, we report

    <machine canonical='pc-i440fx-2.3' maxCpus='255'>pc</machine>

in guest capabilities, but the corresponding

    <machine maxCpus='255'>pc-i440fx-2.3</machine>

is missing.

This is a result of QMP probing. With "-machine ?" parsing QEMU sends
us two lines:

pc                   Standard PC (i440FX + PIIX, 1996) (alias of pc-i440fx-2.3)
pc-i440fx-2.3        Standard PC (i440FX + PIIX, 1996) (default)

while query-machines QMP command reports both in the same entry:

{"name": "pc-i440fx-2.3", "is-default": true, "cpu-max": 255, "alias": "pc"}

Let's make sure we always report separate <machine/> for both the
canonical name and its alias and using the canonical name as the default
machine type (i.e., inserting it before its alias) in case is-default is
true.

https://bugzilla.redhat.com/show_bug.cgi?id=1229666

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>

src/qemu/qemu_capabilities.c

@@ -2229,6 +2229,44 @@ int virQEMUCapsGetMachineTypesCaps(virQEMUCapsPtr qemuCaps,
         mach->maxCpus = qemuCaps->machineMaxCpus[i];
     }
 
+    /* Make sure all canonical machine types also have their own entry so that
+     * /capabilities/guest/arch[@name='...']/machine/text() XPath selects all
+     * supported machine types.
+     */
+    i = 0;
+    while (i < *nmachines) {
+        size_t j;
+        bool found = false;
+        virCapsGuestMachinePtr machine = (*machines)[i];
+
+        if (!machine->canonical) {
+            i++;
+            continue;
+        }
+
+        for (j = 0; j < *nmachines; j++) {
+            if (STREQ(machine->canonical, (*machines)[j]->name)) {
+                found = true;
+                break;
+            }
+        }
+
+        if (!found) {
+            virCapsGuestMachinePtr mach;
+            if (VIR_ALLOC(mach) < 0)
+                goto error;
+            if (VIR_INSERT_ELEMENT_COPY(*machines, i, *nmachines, mach) < 0) {
+                VIR_FREE(mach);
+                goto error;
+            }
+            if (VIR_STRDUP(mach->name, machine->canonical) < 0)
+                goto error;
+            mach->maxCpus = machine->maxCpus;
+            i++;
+        }
+        i++;
+    }
+
     return 0;
 
  error: