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Date: Tue, 28 Aug 2018 23:11:12 -0700
From: Peter Hurley <peter@...aki.com>
To: musl@...ts.openwall.com
Cc: Peter Hurley <peter@...aki.com>
Subject: Re: [PATCH] Preserve select() behavior on arm64
Ping?
On Fri, May 25, 2018 at 1:52 PM, Peter Hurley <peter@...aki.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
>
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