Re: [RFC v2 03/20] y2038: linux: Provide __clock_settime64 implementation

[Lukasz Majewski <lukma at denx dot de>]

Hi Arnd,

> On Thu, Jun 27, 2019 at 6:17 PM Lukasz Majewski <lukma@denx.de> wrote:
> 
> > >
> > > Ok, so you redirect both __clock_settime64 to __clock_settime
> > > and __NR_settime64 to __NR_settime, in order to get back to the
> > > same definition that you have today on 64-bit.
> > >
> > > Sorry for taking so long to understand that.  
> >
> > Not only you had a hard time to understand it.  
> 
> Here is how I had imagined it would be done in a way that I find
> easier to understand:
> 
> #if __WORDSIZE == 32 /* yes, all of them including rv32 and x32 */
> __clock_settime64 (clockid_t clock_id, const struct __timespec64 *tp)
> {
>    int ret;
> 
>    /* Make sure the time cvalue is OK.  */
>    if (tp->tv_nsec < 0 || tp->tv_nsec >= 1000000000)
>     {
>        __set_errno (EINVAL);
>        return -1;
>      }
> #ifdef __NR_clock_settime64
>  ret = INLINE_SYSCALL_CALL (clock_settime64, clock_id, tp);
> #endif
> 
> #ifndef __ASSUME_TIME64_SYSCALLS
>   if (ret == 0 || errno != ENOSYS)
>     return ret;
> 
>   if (! in_time_t_range (tp->tv_sec))
>     {
>       __set_errno (EOVERFLOW);
>       return -1;
>     }
> 
>   struct timespec ts32;
>   valid_timespec64_to_timespec (tp, &ts32);
>   ret = INLINE_SYSCALL_CALL (clock_settime, clock_id, &ts32);
> #endif
> 
>   return ret;
> }
> #endif
> 
> This should be functionally identical to what you have, but avoid
> some of the complexity, especially once linux-5.1 becomes the
> minimum version.

The semantics for __ASSUME_TIME64_SYSCALLS is under the discussion for
some time [1].

Also the __clock_settime64() implementation from [2] takes into
account some corner cases (like support for all archs since 3.2
kernel, x32, legacy systems, etc). The implementation from [2] IMHO
seems to be more concise and fits into the 64 bit conversion paradigm
for glibc [3].

However, this is only my opinion and we shall wait for other community
members to express their opinions.

> 
>       Arnd


Note:

[1] - https://patchwork.ozlabs.org/patch/1117100/
[2] - https://patchwork.ozlabs.org/patch/1107235/
[3] - 
https://www.gnu.org/software/libc/manual/html_mono/libc.html
"D.2.1 64-bit time symbol handling in the GNU C Library"



Best regards,

Lukasz Majewski

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