Re: [Qemu-devel] [PATCH v3 11/29] vhost+postcopy: Transmit 'listen' to client

[Peter Xu <peterx@redhat.com>]

On Mon, Mar 05, 2018 at 05:42:42PM +0000, Dr. David Alan Gilbert wrote:
> * Peter Xu (peterx@redhat.com) wrote:
> > On Fri, Feb 16, 2018 at 01:16:07PM +0000, Dr. David Alan Gilbert (git) wrote:
> > 
> > [...]
> > 
> > >  typedef struct VuVirtqElement {
> > > diff --git a/docs/interop/vhost-user.txt b/docs/interop/vhost-user.txt
> > > index 621543e654..bdec9ec0e8 100644
> > > --- a/docs/interop/vhost-user.txt
> > > +++ b/docs/interop/vhost-user.txt
> > > @@ -682,6 +682,12 @@ Master message types
> > >        the slave must open a userfaultfd for later use.
> > >        Note that at this stage the migration is still in precopy mode.
> > >  
> > > + * VHOST_USER_POSTCOPY_LISTEN
> > > +      Id: 27
> > > +      Master payload: N/A
> > > +
> > > +      Master advises slave that a transition to postcopy mode has happened.
> > 
> > Could we add something to explain why this listen needs to be
> > broadcasted to clients?  Since I failed to find it out quickly
> > myself. :(
> 
> I've changed this to:
> 
>  * VHOST_USER_POSTCOPY_LISTEN
>       Id: 29
>       Master payload: N/A
> 
>       Master advises slave that a transition to postcopy mode has happened.
>       The slave must ensure that shared memory is registered with userfaultfd
>       to cause faulting of non-present pages.

But shouldn't this be assured by the SET_MEM_TABLE call?

Sorry for being not that familiar with vhost-user protocol... but
what's the correct order of these commands?

  POSTCOPY_ADVISE
  POSTCOPY_LISTEN
  SET_MEM_TABLE

?  Thanks,

> 
>       This is always sent sometime after a VHOST_USER_POSTCOPY_ADVISE, and
>       thus only when VHOST_USER_PROTOCOL_F_PAGEFAULT is supported.
> 
> Dave
> 
> > -- 
> > Peter Xu
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

-- 
Peter Xu