missing_syscall: add epoll_pwait2() wrapper

src/basic/missing_syscall.h

@@ -5,6 +5,11 @@
 
 #include <errno.h>
 #include <fcntl.h>
+#if HAVE_LINUX_TIME_TYPES_H
+/* This header defines __kernel_timespec for us, but is only available since Linux 5.1, hence conditionally
+ * include this. */
+#include <linux/time_types.h>
+#endif
 #include <signal.h>
 #include <sys/syscall.h>
 #include <sys/types.h>
@@ -382,3 +387,41 @@ static inline int missing_close_range(int first_fd, int end_fd, unsigned flags)
 
 #  define close_range missing_close_range
 #endif
+
+/* ======================================================================= */
+
+#if !HAVE_EPOLL_PWAIT2
+
+/* Defined to be equivalent to the kernel's _NSIG_WORDS, i.e. the size of the array of longs that is
+ * encapsulated by sigset_t. */
+#define KERNEL_NSIG_WORDS (64 / (sizeof(long) * 8))
+#define KERNEL_NSIG_BYTES (KERNEL_NSIG_WORDS * sizeof(long))
+
+struct epoll_event;
+
+static inline int missing_epoll_pwait2(
+                int fd,
+                struct epoll_event *events,
+                int maxevents,
+                const struct timespec *timeout,
+                const sigset_t *sigset) {
+
+#  if defined(__NR_epoll_pwait2) && HAVE_LINUX_TIME_TYPES_H
+        if (timeout) {
+                /* Convert from userspace timespec to kernel timespec */
+                struct __kernel_timespec ts = {
+                        .tv_sec = timeout->tv_sec,
+                        .tv_nsec = timeout->tv_nsec,
+                };
+
+                return syscall(__NR_epoll_pwait2, fd, events, maxevents, &ts, sigset, sigset ? KERNEL_NSIG_BYTES : 0);
+        } else
+                return syscall(__NR_epoll_pwait2, fd, events, maxevents, NULL, sigset, sigset ? KERNEL_NSIG_BYTES : 0);
+#  else
+        errno = ENOSYS;
+        return -1;
+#  endif
+}
+
+#  define epoll_pwait2 missing_epoll_pwait2
+#endif