Define eventfd on NetBSD

Like FreeBSD but unlike OpenBSD, NetBSD supports eventfd since version
10 (September 2021, see http://netbsd.org/changes/changes-10.0.html).

I don't know enough about NetBSD to know whether all systems running
10 can be expected to have eventfd, but it's probably fine. Our GitHub
actions CI only tests NetBSD 10.1.

Ref: https://man.netbsd.org/eventfd.2
Ref: https://github.com/NetBSD/src/blob/d04b0c735abc997743bb3faa74464524cbe7becd/sys/sys/eventfd.h

(backport <#4830>)
(cherry picked from commit 3e82c57)

Author: krobelus

libc-test/build.rs

@@ -1365,6 +1365,7 @@ fn test_netbsd(target: &str) {
         "mqueue.h",
         "netinet/dccp.h",
         "sys/event.h",
+        (!netbsd9, "sys/eventfd.h"),
         "sys/quota.h",
         "sys/reboot.h",
         "sys/shm.h",
@@ -1411,6 +1412,7 @@ fn test_netbsd(target: &str) {
             "sighandler_t" => true,
             // Incomplete type in C
             "cpuset_t" => true,
+            "eventfd_t" if netbsd9 => true,
             _ => false,
         }
     });
@@ -1474,6 +1476,8 @@ fn test_netbsd(target: &str) {
             // FIXME(netbsd): Look into setting `_POSIX_C_SOURCE` to enable this
             "qsort_r" => true,
 
+            "eventfd" | "eventfd_read" | "eventfd_write" if netbsd9 => true,
+
             _ => false,
         }
     });

src/unix/bsd/netbsdlike/netbsd/mod.rs

@@ -7,6 +7,7 @@ use crate::{
 };
 
 pub type blksize_t = i32;
+pub type eventfd_t = u64;
 pub type fsblkcnt_t = u64;
 pub type fsfilcnt_t = u64;
 pub type idtype_t = c_int;
@@ -1743,6 +1744,11 @@ pub const RTA_TAG: c_int = 0x100;
 pub const RTAX_TAG: c_int = 8;
 pub const RTAX_MAX: c_int = 9;
 
+// For eventfd
+pub const EFD_SEMAPHORE: c_int = crate::O_RDWR;
+pub const EFD_NONBLOCK: c_int = crate::O_NONBLOCK;
+pub const EFD_CLOEXEC: c_int = crate::O_CLOEXEC;
+
 // sys/timerfd.h
 pub const TFD_CLOEXEC: i32 = crate::O_CLOEXEC;
 pub const TFD_NONBLOCK: i32 = crate::O_NONBLOCK;
@@ -2198,6 +2204,10 @@ extern "C" {
     pub fn getmntinfo(mntbufp: *mut *mut crate::statvfs, flags: c_int) -> c_int;
     pub fn getvfsstat(buf: *mut crate::statvfs, bufsize: size_t, flags: c_int) -> c_int;
 
+    pub fn eventfd(val: c_uint, flags: c_int) -> c_int;
+    pub fn eventfd_read(efd: c_int, valp: *mut eventfd_t) -> c_int;
+    pub fn eventfd_write(efd: c_int, val: eventfd_t) -> c_int;
+
     // Added in `NetBSD` 10.0
     pub fn timerfd_create(clockid: crate::clockid_t, flags: c_int) -> c_int;
     pub fn timerfd_gettime(fd: c_int, curr_value: *mut crate::itimerspec) -> c_int;