[Qemu-devel] Re: [PATCH 10/22] migration: Refactor and simplify error checking in migrate_fd_put_ready

[Juan Quintela <quintela@redhat.com>]

Yoshiaki Tamura <tamura.yoshiaki@lab.ntt.co.jp> wrote:
> 2011/2/23 Juan Quintela <quintela@redhat.com>:
>>
>> Signed-off-by: Juan Quintela <quintela@redhat.com>
>> ---
>>  migration.c |   20 +++++++++-----------
>>  1 files changed, 9 insertions(+), 11 deletions(-)
>>
>> diff --git a/migration.c b/migration.c
>> index f015e02..641df9f 100644
>> --- a/migration.c
>> +++ b/migration.c
>> @@ -361,28 +361,26 @@ static void migrate_fd_put_ready(void *opaque)
>>
>>     DPRINTF("iterate\n");
>>     if (qemu_savevm_state_iterate(s->mon, s->file) == 1) {
>> -        int state;
>>         int old_vm_running = vm_running;
>>
>>         DPRINTF("done iterating\n");
>>         vm_stop(VMSTOP_MIGRATE);
>>
>> -        if ((qemu_savevm_state_complete(s->mon, s->file)) < 0) {
>> -            if (old_vm_running) {
>> -                vm_start();
>> -            }
>> -            state = MIG_STATE_ERROR;
>> +        if (qemu_savevm_state_complete(s->mon, s->file) < 0) {
>> +            migrate_fd_error(s);
>>         } else {
>> -            state = MIG_STATE_COMPLETED;
>> +            if (migrate_fd_cleanup(s) < 0) {
>> +                migrate_fd_error(s);
>> +            } else {
>> +                s->state = MIG_STATE_COMPLETED;
>> +                notifier_list_notify(&migration_state_notifiers);
>> +            }
>>         }
>> -        if (migrate_fd_cleanup(s) < 0) {
>> +        if (s->get_status(s) != MIG_STATE_COMPLETED) {
>>             if (old_vm_running) {
>>                 vm_start();
>>             }
>
> This part, although it's not fair to ask you, but calling
> vm_start when != MIG_STATE_COMPLETED terrifies me because just
> failing migrate_fd_cleanup (mostly calling qemu_fclose) may cause
> split brain between src/dst.  Although I haven't encountered this
> situation, just having stopped VMs on both sides is safer.

I see your pain. I am not happy at all, but this was integrated by
Anthony to fix this bug:

commit 41ef56e61153d7bd27d34a634633bb51b1c5988d
Author: Anthony Liguori <aliguori@us.ibm.com>
Date:   Wed Jun 2 14:55:25 2010 -0500

    migration: respect exit status with exec:

 This fixes https://bugs.launchpad.net/qemu/+bug/391879


I think that it fixes that bug, but it makes me un-easy to restart vm if
there is a failure in migrate_fd_cleanup().  As I didn't wanted to
change behaviour with this series, I left it as it was.

Next on ToDo list is to do something sensible with errors, just now we
are not very good at handling them.

Later, Juan.