Re: [PATCH v7 03/15] s390/zcrypt: driver callback to indicate resource in use

[Tony Krowiak]

On 4/23/20 11:33 PM, Halil Pasic wrote:
> On Thu, 16 Apr 2020 11:37:21 +0200
> Cornelia Huck <cohuck@xxxxxxxxxx> wrote:
>
> > On Wed, 15 Apr 2020 13:10:10 -0400
> > Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
> >
> > > On 4/14/20 8:58 AM, Cornelia Huck wrote:
> > > > On Tue,  7 Apr 2020 15:20:03 -0400
> > > > Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
> > > > > +
> > > > > +	if (ap_drv->in_use)
> > > > > +		if (ap_drv->in_use(newapm, ap_perms.aqm))
> > > > Can we log the offending apm somewhere, preferably with additional info
> > > > that allows the admin to figure out why an error was returned?
> > > One of the things on my TODO list is to add logging to the vfio_ap
> > > module which will track all significant activity within the device
> > > driver. I plan to do that with a patch or set of patches specifically
> > > put together for that purpose. Having said that, the best place to
> > > log this would be in the in_use callback in the vfio_ap device driver
> > > (see next patch) where the APQNs that are in use can be identified.
> > > For now, I will log a message to the dmesg log indicating which
> > > APQNs are in use by the matrix mdev.
> > Sounds reasonable. My main issue was what an admin was supposed to do
> > until logging was in place :)
> Logging may not be the right answer here. Imagine somebody wants to build
> a nice web-tool for managing this stuff at scale -- e.g. something HMC. I
> don't think the solution is to let this tool parse the kernel messages
> and try to relate that to its own transactions.

I don't believe there is no right or wrong answer here; I simply don't
see the relevance of discussing a tool in this context. We are talking
about a sysfs attribute interface here, so - correct me if I'm
mistaken - our options for notifying the user that a queue is in use are
limited to the return code from the sysfs interface and logging. I would
expect that a tool would have to do something similar to the callback
implemented in the vfio_ap device driver and check the APQNs
removed against the APQNs assigned to the mdevs to determine which
is in use.

> But I do agree, having a way to report why "won't do" to the end user is
> important for usability.
>
> Regards,
> Halil
>
> > > >   
> > > > > +			rc = -EADDRINUSE;
> > > > > +
> > > > > +	module_put(drv->owner);
> > > > > +
> > > > > +	return rc;
> > > > > +}