Re: [Qemu-devel] [PATCH 0/2] migration/channel errors and cancelling

[Peter Xu <peterx@redhat.com>]

On Fri, Dec 15, 2017 at 05:16:53PM +0000, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> Hi,
>   Where a channel fails asynchronously during connect, call
> back through the migration code so it can clean up.
>   In particular this causes the transition of a 'cancelling' state
> to 'cancelled' in the case of:
> 
>     migrate -d tcp:deadhost:port
>      <host tries to connect>
>     migrate_cancel
> 
> previously the status would get stuck in cancelling because
> the final cleanup didn't happen.
> 
>   This is the second part of the fix for:
> https://bugzilla.redhat.com/show_bug.cgi?id=1525899

IIUC this series tries to deliver the connection error a long way
until migrate_fd_connect() to handle it. But, haven't we already have
a function migrate_fd_error() to do that (which is faster, and
simpler)?

void migrate_fd_error(MigrationState *s, const Error *error)
{
    trace_migrate_fd_error(error_get_pretty(error));
    assert(s->to_dst_file == NULL);
    migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
                      MIGRATION_STATUS_FAILED);
    migrate_set_error(s, error);
    notifier_list_notify(&migration_state_notifiers, s);
    block_cleanup_parameters(s);
}

I think it's not handling the case when cancelling.  If we let it to
handle the cancelling case well, would it be a simpler fix?

Moreover, I think this is another good example that migration is not
handling the cleanup "cleanly" in general... I really hope we can do
this better in 2.12.  I'll see whether I can give it a shot, but in
all cases it'll be after the merging of existing patches since there
are already quite a lot of dangling patches.

Thanks,

-- 
Peter Xu