Re: [PATCH] migration: check magic value for deciding the mapping of channels

["Daniel P. Berrangé" <berrange@redhat.com>]

On Thu, Nov 03, 2022 at 02:50:25PM +0530, manish.mishra wrote:
> 
> On 01/11/22 9:15 pm, Daniel P. Berrangé wrote:
> > On Tue, Nov 01, 2022 at 09:10:14PM +0530, manish.mishra wrote:
> > > On 01/11/22 8:21 pm, Daniel P. Berrangé wrote:
> > > > On Tue, Nov 01, 2022 at 02:30:29PM +0000, manish.mishra wrote:
> > > > > diff --git a/migration/migration.c b/migration/migration.c
> > > > > index 739bb683f3..f4b6f278a9 100644
> > > > > --- a/migration/migration.c
> > > > > +++ b/migration/migration.c
> > > > > @@ -733,31 +733,40 @@ void migration_ioc_process_incoming(QIOChannel *ioc, Error **errp)
> > > > >    {
> > > > >        MigrationIncomingState *mis = migration_incoming_get_current();
> > > > >        Error *local_err = NULL;
> > > > > -    bool start_migration;
> > > > >        QEMUFile *f;
> > > > > +    bool default_channel = true;
> > > > > +    uint32_t channel_magic = 0;
> > > > > +    int ret = 0;
> > > > > -    if (!mis->from_src_file) {
> > > > > -        /* The first connection (multifd may have multiple) */
> > > > > +    if (migrate_use_multifd() && !migration_in_postcopy()) {
> > > > > +        ret = qio_channel_read_peek_all(ioc, (void *)&channel_magic,
> > > > > +                                        sizeof(channel_magic), &local_err);
> > > > > +
> > > > > +        if (ret != 1) {
> > > > > +            error_propagate(errp, local_err);
> > > > > +            return;
> > > > > +        }
> > > > ....and thus this will fail for TLS channels AFAICT.
> > > Yes, thanks for quick review Daniel. You pointed this earlier too, sorry missed it, will put another check !migrate_use_tls() in V2.
> > But we need this problem fixed with TLS too, so just excluding it
> > isn't right. IMHO we need to modify the migration code so we can
> > read the magic earlier, instead of peeking.
> > 
> > 
> > With regards,
> > Daniel
> 
> Hi Daniel, I was trying tls migrations. What i see is that tls session
> creation does handshake. So if we read ahead in ioc_process_incoming
> for default channel. Because client sends magic only after multiFD
> channels are setup, which too requires tls handshake.

By the time we get to migrate_ioc_process_incoming, the TLS handshake
has already been performed.

migration_channel_process_incoming
    -> migration_ioc_process_incoming

vs

migration_channel_process_incoming
    -> migration_tls_channel_process_incoming
        -> migration_tls_incoming_handshake
	     -> migration_channel_process_incoming
	         ->  migration_ioc_process_incoming


With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|