sd-event: reenable epoll_pwait2()

This reenables epoll_pwait2() use, i.e. undoes the effect of
39f756d3ae4765b8bf017567a12b8a4b358eaaf5.

Instead of just reverting that, this PR will change things so that we
strictly rely on glibc's new epoll_pwait2() wrapper (which was added
earlier this year), and drop our own manual fallback syscall wrapper.
That should nicely side-step any issues with correct syscall wrapping
definitions (which on some arch seem not to be easy, given the sigset_t
size final argument), by making this a glibc problem, not ours.

Given that the only benefit this delivers are time-outs more granular
than msec, it shouldn't really matter that we'll miss out on support
for this on systems with older glibcs.

4 files changed, 9 insertions, 113 deletions

diff --git a/src/basic/missing_syscall.h b/src/basic/missing_syscall.h
index 6ad89da541..98cd037962 100644
--- a/src/basic/missing_syscall.h
+++ b/src/basic/missing_syscall.h
@@ -426,44 +426,6 @@ static inline int missing_close_range(int first_fd, int end_fd, unsigned flags)
 
 /* ======================================================================= */
 
-#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
-
-/* ======================================================================= */
-
 #if !HAVE_MOUNT_SETATTR
 
 #if !HAVE_STRUCT_MOUNT_ATTR
diff --git a/src/basic/missing_syscall_def.h b/src/basic/missing_syscall_def.h
index 67cae7098d..402fdd00dc 100644
--- a/src/basic/missing_syscall_def.h
+++ b/src/basic/missing_syscall_def.h
@@ -246,74 +246,6 @@ assert_cc(__NR_copy_file_range == systemd_NR_copy_file_range);
 #  endif
 #endif
 
-#ifndef __IGNORE_epoll_pwait2
-#  if defined(__aarch64__)
-#    define systemd_NR_epoll_pwait2 441
-#  elif defined(__alpha__)
-#    define systemd_NR_epoll_pwait2 551
-#  elif defined(__arc__) || defined(__tilegx__)
-#    define systemd_NR_epoll_pwait2 441
-#  elif defined(__arm__)
-#    define systemd_NR_epoll_pwait2 441
-#  elif defined(__i386__)
-#    define systemd_NR_epoll_pwait2 441
-#  elif defined(__ia64__)
-#    define systemd_NR_epoll_pwait2 1465
-#  elif defined(__loongarch64)
-#    define systemd_NR_epoll_pwait2 441
-#  elif defined(__m68k__)
-#    define systemd_NR_epoll_pwait2 441
-#  elif defined(_MIPS_SIM)
-#    if _MIPS_SIM == _MIPS_SIM_ABI32
-#      define systemd_NR_epoll_pwait2 4441
-#    elif _MIPS_SIM == _MIPS_SIM_NABI32
-#      define systemd_NR_epoll_pwait2 6441
-#    elif _MIPS_SIM == _MIPS_SIM_ABI64
-#      define systemd_NR_epoll_pwait2 5441
-#    else
-#      error "Unknown MIPS ABI"
-#    endif
-#  elif defined(__hppa__)
-#    define systemd_NR_epoll_pwait2 441
-#  elif defined(__powerpc__)
-#    define systemd_NR_epoll_pwait2 441
-#  elif defined(__riscv)
-#    if __riscv_xlen == 32
-#      define systemd_NR_epoll_pwait2 441
-#    elif __riscv_xlen == 64
-#      define systemd_NR_epoll_pwait2 441
-#    else
-#      error "Unknown RISC-V ABI"
-#    endif
-#  elif defined(__s390__)
-#    define systemd_NR_epoll_pwait2 441
-#  elif defined(__sparc__)
-#    define systemd_NR_epoll_pwait2 441
-#  elif defined(__x86_64__)
-#    if defined(__ILP32__)
-#      define systemd_NR_epoll_pwait2 (441 | /* __X32_SYSCALL_BIT */ 0x40000000)
-#    else
-#      define systemd_NR_epoll_pwait2 441
-#    endif
-#  elif !defined(missing_arch_template)
-#    warning "epoll_pwait2() syscall number is unknown for your architecture"
-#  endif
-
-/* may be an (invalid) negative number due to libseccomp, see PR 13319 */
-#  if defined __NR_epoll_pwait2 && __NR_epoll_pwait2 >= 0
-#    if defined systemd_NR_epoll_pwait2
-assert_cc(__NR_epoll_pwait2 == systemd_NR_epoll_pwait2);
-#    endif
-#  else
-#    if defined __NR_epoll_pwait2
-#      undef __NR_epoll_pwait2
-#    endif
-#    if defined systemd_NR_epoll_pwait2 && systemd_NR_epoll_pwait2 >= 0
-#      define __NR_epoll_pwait2 systemd_NR_epoll_pwait2
-#    endif
-#  endif
-#endif
-
 #ifndef __IGNORE_getrandom
 #  if defined(__aarch64__)
 #    define systemd_NR_getrandom 278
diff --git a/src/basic/missing_syscalls.py b/src/basic/missing_syscalls.py
index 642d4d985d..5ccf02adec 100644
--- a/src/basic/missing_syscalls.py
+++ b/src/basic/missing_syscalls.py
@@ -9,7 +9,6 @@ SYSCALLS = [
     'bpf',
     'close_range',
     'copy_file_range',
-    'epoll_pwait2',
     'getrandom',
     'memfd_create',
     'mount_setattr',
diff --git a/src/libsystemd/sd-event/sd-event.c b/src/libsystemd/sd-event/sd-event.c
index 27908a9abc..fa98c8946e 100644
--- a/src/libsystemd/sd-event/sd-event.c
+++ b/src/libsystemd/sd-event/sd-event.c
@@ -3969,15 +3969,18 @@ static int epoll_wait_usec(
                 usec_t timeout) {
 
         int msec;
-#if 0
+        /* A wrapper that uses epoll_pwait2() if available, and falls back to epoll_wait() if not. */
+
+#if HAVE_EPOLL_PWAIT2
         static bool epoll_pwait2_absent = false;
         int r;
 
-        /* A wrapper that uses epoll_pwait2() if available, and falls back to epoll_wait() if not.
-         *
-         * FIXME: this is temporarily disabled until epoll_pwait2() becomes more widely available.
-         * See https://github.com/systemd/systemd/pull/18973 and
-         * https://github.com/systemd/systemd/issues/19052. */
+        /* epoll_pwait2() was added to Linux 5.11 (2021-02-14) and to glibc in 2.35 (2022-02-03). In contrast
+         * to other syscalls we don't bother with our own fallback syscall wrappers on old libcs, since this
+         * is not that obvious to implement given the libc and kernel definitions differ in the last
+         * argument. Moreover, the only reason to use it is the more accurate time-outs (which is not a
+         * biggie), let's hence rely on glibc's definitions, and fallback to epoll_pwait() when that's
+         * missing. */
 
         if (!epoll_pwait2_absent && timeout != USEC_INFINITY) {
                 r = epoll_pwait2(fd,