Re: [PULL 22/33] migration: remove the QEMUFileOps 'get_buffer' callback

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

On Wed, Jun 22, 2022 at 03:34:52PM -0400, Peter Xu wrote:
> On Wed, Jun 22, 2022 at 07:39:06PM +0100, Dr. David Alan Gilbert (git) wrote:
> > diff --git a/migration/qemu-file.c b/migration/qemu-file.c
> > index 74f919de67..e206b05550 100644
> > --- a/migration/qemu-file.c
> > +++ b/migration/qemu-file.c
> > @@ -377,8 +377,22 @@ static ssize_t qemu_fill_buffer(QEMUFile *f)
> >          return 0;
> >      }
> >  
> > -    len = f->ops->get_buffer(f->ioc, f->buf + pending, f->total_transferred,
> > -                             IO_BUF_SIZE - pending, &local_error);
> > +    do {
> > +        len = qio_channel_read(f->ioc,
> > +                               (char *)f->buf + pending,
> > +                               IO_BUF_SIZE - pending,
> > +                               &local_error);
> > +        if (len == QIO_CHANNEL_ERR_BLOCK) {
> > +            if (qemu_in_coroutine()) {
> > +                qio_channel_yield(f->ioc, G_IO_IN);
> > +            } else {
> > +                qio_channel_wait(f->ioc, G_IO_IN);
> > +            }
> > +        } else if (len < 0) {
> > +            len = EIO;
> 
> This should be -EIO.
> 
> > +        }
> > +    } while (len == QIO_CHANNEL_ERR_BLOCK);
> 
> It's failing only with the new TLS test I added for postcopy somehow (at
> least /x86_64/migration/postcopy/recovery/tls).. I also verified after the
> change it'll work again.

Assuming you can still reproduce the pre-existing flaw, can you capture
a stack trace when it hangs.   I'm wondering if it is a sign that the
migration is not converging when using TLS under certain load conditions,
because the test waits forever for converge.

Also what scenario are you running in ? Bare metal or a VM, and what
host arch ? Wondering if the machine is at all slow, or for example
missing AES hardware acceleration or some such thing.

With regards,
Daniel
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