On Fri, Dec 03, 2021 at 11:37:10AM +0100, Morten Brørup wrote:

quoted

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


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?

i would not expect many calls that return rte_errno to be made on the
hot path. most of the use of errno / rte_errno is control but it's good
to have considered it. if i start seeing a lot of error handling in hot
paths i ordinarily find a way to get rid of it through various
techniques.