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qemu: fix switchover-ack regression for old qemu

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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] 61e34b0856 ("qemu: Add support for optional migration capabilities")

Fixes: 1cc7737f69 ("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>
This commit is contained in:
Jon Kohler 2024-06-27 11:11:56 -07:00 committed by Jiri Denemark
parent 5a68c4306e
commit 76e2dae01a
1 changed files with 1 additions and 5 deletions
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6
src/qemu/qemu_migration_params.c
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@ -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