[libc-commits] [libc] [libc] Implement pwait2 using pwait (PR #99781)

[Mikhail R. Gadelha via libc-commits]

https://github.com/mikhailramalho created https://github.com/llvm/llvm-project/pull/99781

This patch implements pwait2 using pwait. The implementation is an approximation of pwait2, since pwait only only supports timeouts in milliseconds, not nanoseconds, as required by pwait2.

>From 17fef7e45874662531e91cca45d9a2df4587bcc8 Mon Sep 17 00:00:00 2001
From: "Mikhail R. Gadelha" <mikhail at igalia.com>
Date: Sat, 20 Jul 2024 16:42:12 -0300
Subject: [PATCH] [libc] Implement pwait2 using pwait

This patch implements pwait2 using pwait. The implementation is an
approximation of pwait2, since pwait only only supports timeouts in
milliseconds, not nanoseconds, as required by pwait2.
---
 libc/src/sys/epoll/linux/epoll_pwait2.cpp | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/libc/src/sys/epoll/linux/epoll_pwait2.cpp b/libc/src/sys/epoll/linux/epoll_pwait2.cpp
index 14b419399fe9b..4123157d29fff 100644
--- a/libc/src/sys/epoll/linux/epoll_pwait2.cpp
+++ b/libc/src/sys/epoll/linux/epoll_pwait2.cpp
@@ -25,10 +25,22 @@ namespace LIBC_NAMESPACE_DECL {
 LLVM_LIBC_FUNCTION(int, epoll_pwait2,
                    (int epfd, struct epoll_event *events, int maxevents,
                     const struct timespec *timeout, const sigset_t *sigmask)) {
+#ifdef SYS_epoll_pwait2
   int ret = LIBC_NAMESPACE::syscall_impl<int>(
       SYS_epoll_pwait2, epfd, reinterpret_cast<long>(events), maxevents,
       reinterpret_cast<long>(timeout), reinterpret_cast<long>(sigmask),
       NSIG / 8);
+#elif defined(SYS_epoll_pwait)
+  // Convert nanoseconds to milliseconds, rounding up if there are remaining
+  // nanoseconds
+  long timeout_ms = static_cast<long>(timeout->tv_sec * 1000 +
+                                      (timeout->tv_nsec + 999999) / 1000000);
+  int ret = LIBC_NAMESPACE::syscall_impl<int>(
+      SYS_epoll_pwait, epfd, reinterpret_cast<long>(events), maxevents,
+      timeout_ms, reinterpret_cast<long>(sigmask), NSIG / 8);
+#else
+#error "epoll_pwait and epoll_pwait2 syscalls not available."
+#endif
 
   // A negative return value indicates an error with the magnitude of the
   // value being the error code.