[PATCH] Preserve select() behavior on arm64

[Peter Hurley <peter@meraki.com>]

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