Re: [RFT][PATCH v2 1/9] vfio: Make vfio_unpin_pages() return void

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, Jul 07, 2022 at 10:12:41AM -0700, Nicolin Chen wrote:
> On Thu, Jul 07, 2022 at 08:42:28AM +0000, Tian, Kevin wrote:
> > External email: Use caution opening links or attachments
> > 
> > 
> > > From: Nicolin Chen <nicolinc@nvidia.com>
> > > Sent: Wednesday, July 6, 2022 2:28 PM
> > >
> > > There's only one caller that checks its return value with a WARN_ON_ONCE,
> > > while all other callers do not check return value at all. So simplify the
> > > API to return void by embedding similar WARN_ON_ONCEs.
> > 
> > While this change keeps the similar effect as before it leads to different
> > policy for same type of errors between pin and unpin paths:
> 
> I think it's because of the policy that an undo function should not
> fail. Meanwhile, indulging faulty inputs isn't good either.
> 
> > e.g.
> > 
> > vfio_unpin_pages():
> >         if (WARN_ON_ONCE(!user_pfn || !npage || !vfio_assert_device_open(device)))
> >                 return;
> > 
> > vfio_pin_pages():
> >         if (!user_pfn || !phys_pfn || !npage ||
> >             !vfio_assert_device_open(device))
> >                 return -EINVAL;
> > 
> > It sounds a bit weird when reading related code...
> 
> Any better way to handle this?

They should all be WARN_ON's, that is the standard pattern to assert
that function arguments must be correctly formed.

I would also drop the tests that obviously will oops on their on
anyone, like NULL pointer checks. This is a semi-performance path.

Jason