From: Morten Brørup [mailto:mb@smartsharesystems.com]
Sent: Thursday, 2 December 2021 14.56

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From: Ananyev, Konstantin [mailto:konstantin.ananyev@intel.com]
Sent: Thursday, 2 December 2021 14.01

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From: Thomas Monjalon [mailto:thomas@monjalon.net]
Sent: Thursday, 2 December 2021 08.19

01/12/2021 22:37, Tyler Retzlaff:

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On Wed, Nov 24, 2021 at 06:04:56PM +0000, Bruce Richardson

wrote:

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  if (ret < 0 && rte_errno == EAGAIN)

i only urge that this be explicit as opposed to a range i.e.

ret

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== -

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1

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preferred over ret < 0

I don't understand why you think it is important to limit return

value

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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

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such as

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-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?