new driver for drivers/virt/?

[Sell, Timothy C]

> -----Original Message-----
> From: Thomas Gleixner [mailto:tglx at linutronix.de]
> Sent: Wednesday, May 18, 2016 6:12 PM
> To: Sell, Timothy C
> Cc: mingo at kernel.org; dave.hansen at linux.intel.com;
> timur at freescale.com; galak at kernel.crashing.org; Kershner, David A;
> corbet at lwn.net; mingo at redhat.com; hpa at zytor.com; Arfvidson, Erik;
> hofrat at osadl.org; dzickus at redhat.com; Curtin, Alexander Paul;
> janani.rvchndrn at gmail.com; sudipm.mukherjee at gmail.com;
> prarit at redhat.com; Binder, David Anthony; nhorman at redhat.com;
> dan.j.williams at intel.com; linux-kernel at vger.kernel.org; linux-
> doc at vger.kernel.org; driverdev-devel at linuxdriverproject.org; *S-Par-
> Maintainer; Greg KH; Jes Sorensen
> Subject: Re: new driver for drivers/virt/?
> 
> On Wed, 18 May 2016, Sell, Timothy C wrote:
> > We have a bus driver currently in drivers/staging/unisys/visorbus/ that
> > we are trying to get out of staging and into the kernel proper.  Since
> > "visorbus" is a driver to host a virtual bus presented to a Linux guest
> > in a hypervisor environment (refer to
> > drivers/staging/unisys/Documentation/overview.txt for more details),
> > Greg KH and Jes Sorensen have suggested the possibility that drivers/virt/
> > might be a good place for visorbus.  But right now, we see that the only
> > driver under drivers/virt/ is the Freescale hypervisor environment, which
> > made us wonder whether this was really the correct place.
> >
> > Would you have any guidance for us?
> > Our intent is to push our visorbus out of staging immediately following
> > the current merge window.
> 
> What's the problem with Gregs and Jes suggestion? I don't see any.
> 

That's good; glad you agree with them.  We just wanted to double-check
with those of you listed as maintainers of drivers/virt/.  Thanks.

> There is bigger fish to fry than the final place of this driver. I had just a
> peek at the staging code and there is enough stuff which wants to be
> cleaned
> up before moving anywhere. I don't have time to do a proper review now,
> but
> here are a few hints upfront:
> 
> 1) Locking:
> 
>    visordriver_callback_lock:
> 
>       That should be a mutex, not a semaphore
> 
>    periodic_work->lock:
> 
>       Why is this a rw_lock if it's only locked with write_lock? And what's
>       the purpose of this lock at all?
> 
> 2) Memory barriers:
> 
>    Completely undocumented wmb()s without corresponding rmb()s to do
> obscure
>    protection of that periodic work stuff.
> 
> 3) periodic_work:
> 
>    That set of functions is obscure. Especially visor_periodic_work_stop()
>    makes me shudder. See also #2.
> 
>    That work->lock does not inspire my confidence further.
> 
> 4) Exports:
> 
>    A gazillion of exports which are just wrappers around another set of
>    exports
> 
> 5) Function comments:
> 
>    Try to mimic kerneldoc comments, i.e. start with: /**
>    but do not implement any of the kerneldoc requirements.
> 

We'll take a look at these.  Thanks.

Tim Sell

> I'll try do find a time slot for a proper review of that thing, but don't
> expect that to happen in the next days.
> 
> Thanks,
> 
> 	tglx
>