Re: [musl] C23 implications for C libraries

["罗勇刚(Yonggang Luo)" <luoyonggang@gmail.com>]

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On Sun, Nov 20, 2022 at 2:32 AM Rich Felker <dalias@libc.org> wrote:
>
> On Sat, Nov 19, 2022 at 04:46:22AM +0800, 罗勇刚(Yonggang Luo) wrote:
> > There is a concept called CLOCK_MONOTONIC_RAW  (since Linux 2.6.28;
> > Linux-specific),
> > May C2x provide TIME_MONOTONIC_RAW in future or can we just implement
> >  TIME_MONOTONIC with
> > CLOCK_MONOTONIC_RAW  on Linux? When implement mesa vulkan driver, it's
ask
> > for CLOCK_MONOTONIC_RAW   at
> >
> >
https://gitlab.freedesktop.org/mesa/mesa/-/blob/c6c5949ff70a47c47795fe9161a7514173b5be24/src/vulkan/runtime/vk_device.c#L557
> >
> > May intention is using C2x timespec_get to replace function
> > vk_clock_gettime but it's lack of  TIME_MONOTONIC_RAW, so I don't know
> > what's the best way
>
> The code there is already doing exactly what it should do in the case
> where CLOCK_MONOTONIC_RAW is not defined so I'm not sure what you're
> trying to achieve.
>
> On a system where CLOCK_MONOTONIC_RAW is defined, the caller may have
> (for likely-nonsensical reasons) chosen to pass CLOCK_MONOTONIC_RAW,
> and they're handling the case where the kernel is too old to have that
> extension clock by substituting CLOCK_MONOTONIC instead.

That's the issue, when you access `CLOCK_MONOTONIC_RAW`, it's have to be
defined, suppose we have
standardized TIME_MONOTONIC_RAW, then we have no need get the time with,
```
#ifndef CLOCK_MONOTONIC_RAW
 // The code
#endif
```
but with
```
if (timespec_get(ts, TIME_MONOTONIC_RAW) != 0) {
}
```




>
> If CLOCK_MONOTONIC_RAW is not defined, then most certainly the caller
> did not pass it (since there's no such thing) and thus there is no
> need for any fallback code.
>
> No action is needed at all here.
>
> Rich



--
         此致
礼
罗勇刚
Yours
    sincerely,
Yonggang Luo

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