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Re: [PATCH 1/2] qapi/run-state: Add a new shutdown cause 'migration-comp

From: Kunkun Jiang
Subject: Re: [PATCH 1/2] qapi/run-state: Add a new shutdown cause 'migration-completed'
Date: Mon, 5 Jul 2021 21:22:43 +0800
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1

Hi Daniel,

On 2021/7/5 20:48, Daniel P. Berrangé wrote:
On Mon, Jul 05, 2021 at 08:36:52PM +0800, Kunkun Jiang wrote:
In the current version, the source QEMU process does not automatic
exit after a successful migration. Additional action is required,
such as sending { "execute": "quit" } or ctrl+c. For simplify, add
a new shutdown cause 'migration-completed' to exit the source QEMU
process after a successful migration.
IIUC, 'STATUS_COMPLETED' state is entered on the source host
once it has finished sending all VM state, and thus does not
guarantee that the target host has successfully received and
loaded all VM state.
Thanks for your reply.

If the target host doesn't successfully receive and load all VM state,
we can send { "execute": "cont" } to resume the soruce in time to
ensure that VM will not lost?
Typically a mgmt app will need to directly confirm that the
target host QEMU has succesfully started running, before it
will tell the source QEMU to quit.
'a mgmt app', such as libvirt?

Kunkun Jiang
So, AFAICT, this automatic exit after STATUS_COMPLETED is
not safe and could lead to total loss of the running VM in
error scenarios.

Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
  migration/migration.c | 1 +
  qapi/run-state.json   | 4 +++-
  2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/migration/migration.c b/migration/migration.c
index 4228635d18..16782c93c2 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -3539,6 +3539,7 @@ static void migration_iteration_finish(MigrationState *s)
+        qemu_system_shutdown_request(SHUTDOWN_CAUSE_MIGRATION_COMPLETED);
diff --git a/qapi/run-state.json b/qapi/run-state.json
index 43d66d700f..66aaef4e2b 100644
--- a/qapi/run-state.json
+++ b/qapi/run-state.json
@@ -86,12 +86,14 @@
  #                   ignores --no-reboot. This is useful for sanitizing
  #                   hypercalls on s390 that are used during kexec/kdump/boot
+# @migration-completed: Reaction to the successful migration
  { 'enum': 'ShutdownCause',
    # Beware, shutdown_caused_by_guest() depends on enumeration order
    'data': [ 'none', 'host-error', 'host-qmp-quit', 'host-qmp-system-reset',
              'host-signal', 'host-ui', 'guest-shutdown', 'guest-reset',
-            'guest-panic', 'subsystem-reset'] }
+            'guest-panic', 'subsystem-reset', 'migration-completed'] }
  # @StatusInfo:


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