linux-kernel - RE: new driver for drivers/virt/?

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Message-ID: <f78390c7af0e47c3ab54de1024ef0ba6@US-EXCH13-2.na.uis.unisys.com>
Date:	Wed, 18 May 2016 22:24:45 +0000
From:	"Sell, Timothy C" <Timothy.Sell@...sys.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	"mingo@...nel.org" <mingo@...nel.org>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
	"timur@...escale.com" <timur@...escale.com>,
	"galak@...nel.crashing.org" <galak@...nel.crashing.org>,
	"Kershner, David A" <David.Kershner@...sys.com>,
	"corbet@....net" <corbet@....net>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"Arfvidson, Erik" <Erik.Arfvidson@...sys.com>,
	"hofrat@...dl.org" <hofrat@...dl.org>,
	"dzickus@...hat.com" <dzickus@...hat.com>,
	"Curtin, Alexander Paul" <Alexander.Curtin@...sys.com>,
	"janani.rvchndrn@...il.com" <janani.rvchndrn@...il.com>,
	"sudipm.mukherjee@...il.com" <sudipm.mukherjee@...il.com>,
	"prarit@...hat.com" <prarit@...hat.com>,
	"Binder, David Anthony" <David.Binder@...sys.com>,
	"nhorman@...hat.com" <nhorman@...hat.com>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"driverdev-devel@...uxdriverproject.org" 
	<driverdev-devel@...uxdriverproject.org>,
	*S-Par-Maintainer <SParMaintainer@...sys.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	"Jes Sorensen" <Jes.Sorensen@...hat.com>
Subject: RE: new driver for drivers/virt/?

> -----Original Message-----
> From: Thomas Gleixner [mailto:tglx@...utronix.de]
> Sent: Wednesday, May 18, 2016 6:12 PM
> To: Sell, Timothy C
> Cc: mingo@...nel.org; dave.hansen@...ux.intel.com;
> timur@...escale.com; galak@...nel.crashing.org; Kershner, David A;
> corbet@....net; mingo@...hat.com; hpa@...or.com; Arfvidson, Erik;
> hofrat@...dl.org; dzickus@...hat.com; Curtin, Alexander Paul;
> janani.rvchndrn@...il.com; sudipm.mukherjee@...il.com;
> prarit@...hat.com; Binder, David Anthony; nhorman@...hat.com;
> dan.j.williams@...el.com; linux-kernel@...r.kernel.org; linux-
> doc@...r.kernel.org; driverdev-devel@...uxdriverproject.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
>