Re: [PATCH] Preserve select() behavior on arm64

[Peter Hurley <peter@meraki.com>]

Ping?

On Fri, May 25, 2018 at 1:52 PM, Peter Hurley <peter@meraki.com> wrote:
> On Linux, all the select-related syscalls update the timeout value to
> indicate how much elapsed time the syscall consumed, and many programs
> expect this behavior when running on Linux.
>
> Newer archs like arm64 have deprecated the select syscall because the
> pselect syscall is a superset implementation of the select syscall.
>
> A complication of implementing select() with the pselect syscall is
> that the timeouts are specified in different units; select() accepts
> a struct timeval ptr whereas the pselect syscall takes a struct
> timespec ptr. These are trivial convertible; struct timeval is
> specified in seconds + microseconds and struct timespec is in
> seconds + nanoseconds.
>
> For kernel configurations without select syscall available, update the
> caller's struct timeval argument after the pselect syscall.
> ---
>  src/select/select.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/src/select/select.c b/src/select/select.c
> index 7b5f6dcf7a53..45d4cb7a3d0a 100644
> --- a/src/select/select.c
> +++ b/src/select/select.c
> @@ -12,15 +12,16 @@ int select(int n, fd_set *restrict rfds, fd_set *restrict wfds, fd_set *restrict
>  #else
>         syscall_arg_t data[2] = { 0, _NSIG/8 };
>         struct timespec ts;
> +       int result;
>         if (tv) {
> -               if (tv->tv_sec < 0 || tv->tv_usec < 0)
> -                       return __syscall_ret(-EINVAL);
> -               time_t extra_secs = tv->tv_usec / 1000000;
> -               ts.tv_nsec = tv->tv_usec % 1000000 * 1000;
> -               const time_t max_time = (1ULL<<8*sizeof(time_t)-1)-1;
> -               ts.tv_sec = extra_secs > max_time - tv->tv_sec ?
> -                       max_time : tv->tv_sec + extra_secs;
> +               ts->tv_sec = tv->tv_sec;
> +               ts->tv_nsec = tv->usec * 1000;
>         }
> -       return syscall_cp(SYS_pselect6, n, rfds, wfds, efds, tv ? &ts : 0, data);
> +       result = syscall_cp(SYS_pselect6, n, rfds, wfds, efds, tv ? &ts : 0, data);
> +       if (tv) {
> +               tv->tv_sec = ts->tv_sec;
> +               tv->tv_usec = ts->tv_nsec / 1000;
> +       }
> +       return result;
>  #endif
>  }
> --
> 2.14.2
>