RE: [PATCH v1] gpudev: return EINVAL if invalid input pointer for free and unregister

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Morten Brørup [mailto:mb@smartsharesystems.com]
> Sent: Thursday, 2 December 2021 14.56
> 
> > From: Ananyev, Konstantin [mailto:konstantin.ananyev@intel.com]
> > Sent: Thursday, 2 December 2021 14.01
> >
> > > > From: Thomas Monjalon [mailto:thomas@monjalon.net]
> > > > Sent: Thursday, 2 December 2021 08.19
> > > >
> > > > 01/12/2021 22:37, Tyler Retzlaff:
> > > > > On Wed, Nov 24, 2021 at 06:04:56PM +0000, Bruce Richardson
> wrote:
> > > > > >   if (ret < 0 && rte_errno == EAGAIN)
> > > > >
> > > > > i only urge that this be explicit as opposed to a range i.e.
> ret
> > == -
> > > > 1
> > > > > preferred over ret < 0
> > > >
> > > > I don't understand why you think it is important to limit return
> > value
> > > > to -1.
> > > > Why "if (ret == -1)" is better than "if (ret < 0)" ?
> > >
> > > Speaking for myself:
> > >
> > > For clarity. It leaves no doubt that "it failed" is represented by
> > the return value -1, and that the function does not return errno
> values
> > such as
> > > -EINVAL.
> > >
> >
> > But why '< 0' gives you less clarity?
> > Negative value means failure - seems perfectly clear to me.
> 
> I disagree: Negative value does not mean failure. Only -1 means
> failure.
> 
> There is no -2 return value. There is no -EINVAL return value.
> 
> Testing for (ret < 0) might confuse someone to think that other values
> than -1 could be returned as indication of failure, which is not the
> case when following the convention where the functions set errno and
> return -1 in case of failure.
> 
> It would be different if following a convention where the functions
> return -errno in case of failure. In this case, testing (ret < 0) would
> be appropriate.
> 
> So explicitly testing (ret == -1) clarifies which of the two
> conventions are relevant.
> 

I tested it on Godbolt, and (ret < 0) produces slightly smaller code than (ret == -1) on x86-64:

https://godbolt.org/z/3xME3jxq8

A binary test (Error or Data) uses 1 byte less, and a tristate test (Error, Zero or Data) uses 3 byte less.

Although there is no measurable performance difference for a single instance of this kind of test, we should consider that this kind of test appears many times in the code, so the saved bytes might add up to something slightly significant in the instruction cache.

My opinion is not so strong anymore... perhaps we should prefer performance over code readability, also in this case?