Re: [PATCH v10 03/10] admin: introduce group administration commands

[Max Gurtovoy <mgurtovoy@nvidia.com>]

On 03/03/2023 15:19, Michael S. Tsirkin wrote:
> On Fri, Mar 03, 2023 at 08:17:03AM -0500, Stefan Hajnoczi wrote:
> > On Thu, Mar 02, 2023 at 07:01:56PM -0500, Michael S. Tsirkin wrote:
> > > On Thu, Mar 02, 2023 at 03:19:12PM -0500, Stefan Hajnoczi wrote:
> > > > On Thu, Mar 02, 2023 at 06:40:29PM +0000, Parav Pandit wrote:
> > > > > > From: Michael S. Tsirkin <mst@redhat.com>
> > > > > > Sent: Thursday, March 2, 2023 8:05 AM
> > > > >
> > > > > > +When \field{status} is VIRTIO_ADMIN_STATUS_OK, \field{status_qialifier}
> > > > > > +is reserved and set to zero by the device.
> > > > > > +
> > > > > s/status_qialifier/status_qualifier
> > > > > Missed from v10 of Feb.
> > > > >
> > > > > > +When \field{status} is VIRTIO_ADMIN_STATUS_EINVAL, the following table
> > > > > > +describes possible \field{status_qialifier} values:
> > > > > s/status_qialifier/status_qualifier
> > > > >
> > > > > Can you please add other useful error codes in addition to the EINVAL?
> > > > > Few that we are needed EAGAIN, ENOMEM, EBUSY, ENODEV.
> > > >
> > > > Please define a unique constant for each error condition that can occur
> > > > instead of sharing catch-all errno constants between multiple error
> > > > conditions. If a driver wants to squash them together into an errno,
> > > > that's fine, but I think doing this at the hardware interface level is
> > > > just propagating the mistakes of errnos.
> > > >
> > > > Only status_qualifier is needed and the vague status field can be
> > > > dropped. It's not clear to me why adding EAGAIN, ENOMEM, EBUSY, and
> > > > ENODEV is useful. They have no meaning to the driver, only the
> > > > status_qualifier really indicates what is going on.
> > >
> > > At a high level at the moment we have only two cases:
> > > - ok
> > > - invalid input supplied by driver
> > >
> > > maybe we will have more reasons for a failure - remains to
> > > be seen.
> > >
> > >
> > >
> > >
> > >
> > > > I'm sure you guys have discussed this previously, but please provide
> > > > rationale in the spec because it looks weird to someone with fresh eyes.
> > > >
> > > > Stefan
> > >
> > > Really most drivers just want to propagate errno to userspace.
> > > All the detailed reporting is for sure well intentional but
> > > in the end it is at best printed into log - end to end
> > > people just end up with a switch statement
> > > converting these to errno codes.
> > > So we are passing them from device and this way there will be
> > > some uniformity.
> >
> > Please clarify the rationale in the spec. I don't agree with it, as
> > explained in my earlier email, but as long as its documented, people can
> > try to follow it.
> >
> > Stefan
>
> It's 2:2 for now, you are with Parav, me and Cornelia like it :)
> Or I will try to document it better.
I don't understand this status_qualifier as well and it wasn't included 
in my original patch set.
I vote for "status" that describe generic status codes and 
"command_specific_error" that should be inspected by the driver only if 
"status" is set to "VIRTIO_ADMIN_STATUS_COMMAND_SPECIFIC_ERR".
We discussed this so many times before (and already agreed IIRC) and 
adding this new qualifiers mechanism sounds not right to me and not 
intuitive for device and driver developers.

I suggest:

1. VIRTIO_ADMIN_STATUS_Q_INVALID_OPCODE
2. VIRTIO_ADMIN_STATUS_Q_INVALID_FIELD
3. VIRTIO_ADMIN_STATUS_Q_INVALID_GROUP
4. VIRTIO_ADMIN_STATUS_Q_INVALID_MEMBER
5. VIRTIO_ADMIN_STATUS_COMMAND_SPECIFIC_ERR (for more info read the 
command_specific_error field).



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