qemu: fix switchover-ack regression for old qemu

When enabling switchover-ack on qemu from libvirt, the .party value
was set to both source and target; however, qemuMigrationParamsCheck()
only takes that into account to validate that the remote side of the
migration supports the flag if it is marked optional or auto/always on.

In the case of switchover-ack, when enabled on only the dst and not
the src, the migration will fail if the src qemu does not support
switchover-ack, as the dst qemu will issue a switchover-ack msg:
qemu/migration/savevm.c ->
  loadvm_process_command ->
    migrate_send_rp_switchover_ack(mis) ->
      migrate_send_rp_message(mis, MIG_RP_MSG_SWITCHOVER_ACK, 0, NULL)

Since the src qemu doesn't understand messages with header_type ==
MIG_RP_MSG_SWITCHOVER_ACK, qemu will kill the migration with error:
  qemu-kvm: RP: Received invalid message 0x0007 length 0x0000
  qemu-kvm: Unable to write to socket: Bad file descriptor

Looking at the original commit [1] for optional migration capabilities,
it seems that the spirit of optional handling was to enhance a given
existing capability where possible. Given that switchover-ack
exclusively depends on return-path, adding it as optional to that cap
feels right.

[1] 61e34b08568 ("qemu: Add support for optional migration capabilities")

Fixes: 1cc7737f69e ("qemu: add support for qemu switchover-ack")
Signed-off-by: Jon Kohler <jon@nutanix.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Avihai Horon <avihaih@nvidia.com>
Cc: Jiri Denemark <jdenemar@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: YangHang Liu <yanghliu@redhat.com>
Reviewed-by: Jiri Denemark <jdenemar@redhat.com>

diff --git a/src/qemu/qemu_migration_params.c b/src/qemu/qemu_migration_params.c
index 9593b6ba65dc9c8e9936ec63f08aa97c1af42eb9..98822012cc99a7a3511fdd86fb701900fdae0fdf 100644 (file)
--- a/src/qemu/qemu_migration_params.c
+++ b/src/qemu/qemu_migration_params.c
@@ -210,17 +210,13 @@ static const qemuMigrationParamsFlagMapItem qemuMigrationParamsFlagMap[] = {
     {.match = QEMU_MIGRATION_FLAG_FORBIDDEN,
      .flag = VIR_MIGRATE_TUNNELLED,
      .cap = QEMU_MIGRATION_CAP_RETURN_PATH,
+     .optional = QEMU_MIGRATION_CAP_SWITCHOVER_ACK,
      .party = QEMU_MIGRATION_SOURCE | QEMU_MIGRATION_DESTINATION},
 
     {.match = QEMU_MIGRATION_FLAG_REQUIRED,
      .flag = VIR_MIGRATE_ZEROCOPY,
      .cap = QEMU_MIGRATION_CAP_ZERO_COPY_SEND,
      .party = QEMU_MIGRATION_SOURCE},
-
-    {.match = QEMU_MIGRATION_FLAG_FORBIDDEN,
-     .flag = VIR_MIGRATE_TUNNELLED,
-     .cap = QEMU_MIGRATION_CAP_SWITCHOVER_ACK,
-     .party = QEMU_MIGRATION_SOURCE | QEMU_MIGRATION_DESTINATION},
 };
 
 /* Translation from VIR_MIGRATE_PARAM_* typed parameters to