qemu: Check remote caps when enabling always-on capabilities

When an always-on migration capability is supposed to be enabled on both
sides of migration, each side can only enable the feature if it is
enabled by the other side.

Thus the source host sends a list of supported migration capabilities in
the migration cookie generated in the Begin phase. The destination host
consumes the list in the Prepare phase and decides what capabilities can
be enabled when starting a QEMU process for incoming migration. Once
done the destination sends the list of supported capabilities back to
the source where it is used during the Perform phase to determine what
capabilities can be automatically enabled.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

src/qemu/qemu_migration.c

@@ -1913,6 +1913,9 @@ qemuMigrationSrcBeginPhase(virQEMUDriverPtr driver,
 
     cookieFlags |= QEMU_MIGRATION_COOKIE_ALLOW_REBOOT;
 
+    if (!(flags & VIR_MIGRATE_OFFLINE))
+        cookieFlags |= QEMU_MIGRATION_COOKIE_CAPS;
+
     if (!(mig = qemuMigrationEatCookie(driver, vm, NULL, 0, 0)))
         goto cleanup;
 
@@ -2205,7 +2208,8 @@ qemuMigrationDstPrepareAny(virQEMUDriverPtr driver,
         }
         cookieFlags = 0;
     } else {
-        cookieFlags = QEMU_MIGRATION_COOKIE_GRAPHICS;
+        cookieFlags = QEMU_MIGRATION_COOKIE_GRAPHICS |
+                      QEMU_MIGRATION_COOKIE_CAPS;
     }
 
     if (flags & VIR_MIGRATE_POSTCOPY &&
@@ -2299,7 +2303,8 @@ qemuMigrationDstPrepareAny(virQEMUDriverPtr driver,
                                        QEMU_MIGRATION_COOKIE_MEMORY_HOTPLUG |
                                        QEMU_MIGRATION_COOKIE_CPU_HOTPLUG |
                                        QEMU_MIGRATION_COOKIE_CPU |
-                                       QEMU_MIGRATION_COOKIE_ALLOW_REBOOT)))
+                                       QEMU_MIGRATION_COOKIE_ALLOW_REBOOT |
+                                       QEMU_MIGRATION_COOKIE_CAPS)))
         goto cleanup;
 
     if (STREQ_NULLABLE(protocol, "rdma") &&
@@ -2378,7 +2383,7 @@ qemuMigrationDstPrepareAny(virQEMUDriverPtr driver,
     }
 
     if (qemuMigrationParamsCheck(driver, vm, QEMU_ASYNC_JOB_MIGRATION_IN,
-                                 migParams) < 0)
+                                 migParams, mig->caps->automatic) < 0)
         goto stopjob;
 
     /* Migrations using TLS need to add the "tls-creds-x509" object and
@@ -3302,7 +3307,9 @@ qemuMigrationSrcRun(virQEMUDriverPtr driver,
     }
 
     mig = qemuMigrationEatCookie(driver, vm, cookiein, cookieinlen,
-                                 cookieFlags | QEMU_MIGRATION_COOKIE_GRAPHICS);
+                                 cookieFlags |
+                                 QEMU_MIGRATION_COOKIE_GRAPHICS |
+                                 QEMU_MIGRATION_COOKIE_CAPS);
     if (!mig)
         goto error;
 
@@ -3310,7 +3317,7 @@ qemuMigrationSrcRun(virQEMUDriverPtr driver,
         VIR_WARN("unable to provide data for graphics client relocation");
 
     if (qemuMigrationParamsCheck(driver, vm, QEMU_ASYNC_JOB_MIGRATION_OUT,
-                                 migParams) < 0)
+                                 migParams, mig->caps->automatic) < 0)
         goto error;
 
     if (flags & VIR_MIGRATE_TLS) {

src/qemu/qemu_migration_params.c

@@ -116,7 +116,9 @@ struct _qemuMigrationParamsFlagMapItem {
 };
 
 /* Migration capabilities which should always be enabled as long as they
- * are supported by QEMU. */
+ * are supported by QEMU. If the capability is supposed to be enabled on both
+ * sides of migration, it won't be enabled unless both sides support it.
+ */
 static const qemuMigrationParamsAlwaysOnItem qemuMigrationParamsAlwaysOn[] = {
     {QEMU_MIGRATION_CAP_PAUSE_BEFORE_SWITCHOVER,
      QEMU_MIGRATION_SOURCE},
@@ -975,7 +977,8 @@ int
 qemuMigrationParamsCheck(virQEMUDriverPtr driver,
                          virDomainObjPtr vm,
                          int asyncJob,
-                         qemuMigrationParamsPtr migParams)
+                         qemuMigrationParamsPtr migParams,
+                         virBitmapPtr remoteCaps)
 {
     qemuDomainObjPrivatePtr priv = vm->privateData;
     qemuMigrationCapability cap;
@@ -1005,6 +1008,21 @@ qemuMigrationParamsCheck(virQEMUDriverPtr driver,
 
         if (qemuMigrationParamsAlwaysOn[i].party & party &&
             qemuMigrationCapsGet(vm, cap)) {
+            if (qemuMigrationParamsAlwaysOn[i].party != party) {
+                bool remote = false;
+
+                if (remoteCaps)
+                    ignore_value(virBitmapGetBit(remoteCaps, cap, &remote));
+
+                if (!remote) {
+                    VIR_DEBUG("Not enabling migration capability '%s'; it is "
+                              "not supported or automatically enabled by the "
+                              "other side of migration",
+                              qemuMigrationCapabilityTypeToString(cap));
+                    continue;
+                }
+            }
+
             VIR_DEBUG("Enabling migration capability '%s'",
                       qemuMigrationCapabilityTypeToString(cap));
             ignore_value(virBitmapSetBit(migParams->caps, cap));

src/qemu/qemu_migration_params.h

@@ -123,7 +123,8 @@ int
 qemuMigrationParamsCheck(virQEMUDriverPtr driver,
                          virDomainObjPtr vm,
                          int asyncJob,
-                         qemuMigrationParamsPtr migParams);
+                         qemuMigrationParamsPtr migParams,
+                         virBitmapPtr remoteCaps);
 
 void
 qemuMigrationParamsReset(virQEMUDriverPtr driver,