RE: [PATCH v5] introduce vfio-user protocol specification

[Thanos Makatos]

> -----Original Message-----
> From: Qemu-devel <qemu-devel-
> bounces+thanos.makatos=nutanix.com@nongnu.org> On Behalf Of John
> Levon
> Sent: 02 November 2020 11:41
> To: Thanos Makatos <thanos.makatos@nutanix.com>
> Cc: benjamin.walker@intel.com; Elena Ufimtseva
> <elena.ufimtseva@oracle.com>; jag.raman@oracle.com;
> james.r.harris@intel.com; Swapnil Ingle <swapnil.ingle@nutanix.com>;
> john.g.johnson@oracle.com; yuvalkashtan@gmail.com;
> konrad.wilk@oracle.com; tina.zhang@intel.com; qemu-devel@nongnu.org;
> dgilbert@redhat.com; Marc-André Lureau
> <marcandre.lureau@redhat.com>; ismael@linux.com;
> alex.williamson@redhat.com; Stefan Hajnoczi <stefanha@redhat.com>;
> Felipe Franciosi <felipe@nutanix.com>; xiuchun.lu@intel.com;
> tomassetti.andrea@gmail.com; changpeng.liu@intel.com; Raphael Norwitz
> <raphael.norwitz@nutanix.com>; Kanth.Ghatraju@oracle.com
> Subject: Re: [PATCH v5] introduce vfio-user protocol specification
> 
> On Mon, Nov 02, 2020 at 11:29:23AM +0000, Thanos Makatos wrote:
> 
> > >
> +==============+========+=================================
> > > ==================+
> > > > | version      | object | ``{"major": <number>, "minor": <number>}``
> |
> > > > |              |        |                                               
> > > >     |
> > > > |              |        | Version supported by the sender, e.g. "0.1".  
> > > >     |
> > >
> > > It seems quite unlikely but this should specify it's strings not floating 
> > > point
> > > values maybe?
> > >
> > > Definitely applies to max_fds too.
> >
> > major and minor are JSON numbers and specifically integers.
> 
> It is debatable as to whether there is such a thing as a JSON integer :)

AFAIK there isn't.

> 
> > The rationale behind this is to simplify parsing. Is specifying that
> > major/minor/max_fds should be an interger sufficient to clear any
> vagueness
> > here?
> 
> I suppose that's OK as long as we never want a 0.1.1 or whatever. I'm not
> sure
> it simplifies parsing, but maybe it does.

Now that you mention it, why preclude 0.1.1? IIUC the whole point of not
stating the version as a float is to simply have this flexibility in the future.
You're right in your earlier suggestion to explicitly state major/minor as
strings.

> 
> > > > Versioning and Feature Support
> > > > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > > > Upon accepting a connection, the server must send a
> VFIO_USER_VERSION
> > > message
> > > > proposing a protocol version and a set of capabilities. The client
> compares
> > > > these with the versions and capabilities it supports and sends a
> > > > VFIO_USER_VERSION reply according to the following rules.
> > >
> > > I'm curious if there was a specific reason it's this way around, when it
> seems
> > > more natural for the client to propose first, and the server to reply?
> >
> > I'm not aware of any specific reason.
> 
> So can we switch it now so the initial setup is a send/recv too?

I'm fine with that but would first like to hear back from John in case he 
objects.