Re: [Qemu-devel] [PATCH v6 1/2] virtio-crypto: Add virtio crypto device specification

[Zeng, Xin]

On Tuesday, August 9, 2016 6:58 PM Michael S. Tsirkin Wrote:
> -----Original Message-----
> From: Michael S. Tsirkin [mailto:address@hidden
> Sent: Tuesday, August 9, 2016 6:58 PM
> To: Zeng, Xin <address@hidden>
> Cc: Gonglei (Arei) <address@hidden>; address@hidden;
> address@hidden; Huangpeng (Peter)
> <address@hidden>; Luonengjun <address@hidden>;
> address@hidden; address@hidden;
> address@hidden; Jani Kokkonen <address@hidden>;
> address@hidden; address@hidden; Keating, Brian A
> <address@hidden>; Ma, Liang J <address@hidden>; Griffin,
> John <address@hidden>; Hanweidong (Randy)
> <address@hidden>; Huangweidong (C)
> <address@hidden>
> Subject: Re: [PATCH v6 1/2] virtio-crypto: Add virtio crypto device
> specification
> 
> On Mon, Aug 08, 2016 at 06:27:15AM +0000, Zeng, Xin wrote:
> > On Thu, Friday, August 05, 2016 3:56 AM, Michael S. Tsirkin wrote:
> > > -----Original Message-----
> > > From: Michael S. Tsirkin [mailto:address@hidden
> > > Sent: Friday, August 05, 2016 3:56 AM
> > > To: Gonglei (Arei)
> > > Cc: Zeng, Xin; address@hidden; address@hidden;
> > > Huangpeng (Peter); Luonengjun; address@hidden;
> > > address@hidden; address@hidden; Jani Kokkonen;
> > > address@hidden; address@hidden; Keating, Brian A;
> Ma,
> > > Liang J; Griffin, John; Hanweidong (Randy); Huangweidong (C)
> > > Subject: Re: [PATCH v6 1/2] virtio-crypto: Add virtio crypto device
> > > specification
> > >
> > > On Thu, Aug 04, 2016 at 11:24:26AM +0000, Gonglei (Arei) wrote:
> > > > > > +The first driver-read-only field, \field{version} specifies the
> > > > > > +virtio crypto's version, which is reserved for back-compatibility
> > > > > > +in future.It's currently defined for the version field:
> > > > > > +
> > > > > > +\begin{lstlisting}
> > > > > > +#define VIRTIO_CRYPTO_VERSION_1  (1)
> > > > >
> > > > > Suggest to remove this macro,
> > > > > Do you think a version which is composed of major version and minor
> > > > > version is better?
> > > > >
> > > >
> > > > I think we should tell the developer how to set the value of version
> > > > field, but I have no idea about which value or form is better, so I
> > > > used 1 as the first version. What's your opinion?
> > >
> > > My opinion is that you should drop this completely. We do feature bits,
> not
> > > version numbers in virtio. We do not want each device doing its own
> thing for
> > > compatibility.
> > >
> >
> > But as I mentioned before,  considering the bug fix case, if each backend
> device
> > release need a feature bit meaning "some bugs are fixed", are the feature
> bits
> > enough?
> 
> It depends on whether the bug is very entrenched and important. In most
> cases, for minor bugs, it's better to just fix the bug in the driver or
> the hypervisor and be done with it.  For cases where
> that's not feasible because many drivers relied on a specific bug,
> and the bug is very important, we can always add more
> if we run out of feature bits.
> 
> > Physical devices usually have a revision ID to mark its version,
> 
> Because compatibility is one way (new devices usually need
> new drivers).
> 

Yes, that's also why I propose to put version(revision) field into device 
configuration read-only filed instead of feature bits field.

> > could we have a
> > revision Id field for each virtio device to distinguish the the virtio 
> > devices
> which
> > have the same feature sets but have different version?
> 
> ccw has version negotiation. It was only changed once at the 0.9->1.0
> transition so far, it's not used for bug fixes.  We could discuss adding
> this to pci and mmio as well, but if yes this should be discussed
> separately.
> 

Ok, that's good, I do think this is needed. I can initiate this discussion in 
another separated mail loop. 

> So far no argument made here was crypto specific, so
> let's not put this in the crypto device.
> 

Sure,  It is indeed not crypto device specific,  but probably all virtio  
devices needs. We can drop it from crypto device spec.
Thanks!

> 
> > > --
> > > MST