Add getpgid (#380)

* Add getpgid

src/backend/libc/process/syscalls.rs

@@ -145,6 +145,17 @@ pub(crate) fn getppid() -> Option<Pid> {
     }
 }
 
+#[cfg(not(target_os = "wasi"))]
+#[inline]
+#[must_use]
+pub(crate) fn getpgid(pid: Option<Pid>) -> Pid {
+    unsafe {
+        let pgid = c::getpgid(Pid::as_raw(pid) as _);
+        debug_assert_ne!(pgid, 0);
+        Pid::from_raw_nonzero(RawNonZeroPid::new_unchecked(pgid))
+    }
+}
+
 #[cfg(any(
     target_os = "android",
     target_os = "dragonfly",

src/backend/linux_raw/process/syscalls.rs

@@ -99,6 +99,17 @@ pub(crate) fn getppid() -> Option<Pid> {
     }
 }
 
+#[inline]
+pub(crate) fn getpgid(pid: Option<Pid>) -> Pid {
+    unsafe {
+        let pgid: i32 =
+            ret_usize_infallible(syscall_readonly!(__NR_getpgid, c_uint(Pid::as_raw(pid))))
+                as __kernel_pid_t;
+        debug_assert!(pgid > 0);
+        Pid::from_raw_nonzero(RawNonZeroPid::new_unchecked(pgid as u32))
+    }
+}
+
 #[inline]
 pub(crate) fn getgid() -> Gid {
     #[cfg(any(target_arch = "x86", target_arch = "sparc", target_arch = "arm"))]

src/process/id.rs

@@ -267,6 +267,20 @@ pub fn getppid() -> Option<Pid> {
     backend::process::syscalls::getppid()
 }
 
+/// `getpgid(pid)`—Returns the process group ID of the given process.
+///
+/// # References
+///  - [POSIX]
+///  - [Linux]
+///
+/// [POSIX]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/getpgid.html
+/// [Linux]: https://man7.org/linux/man-pages/man2/getpgid.2.html
+#[inline]
+#[must_use]
+pub fn getpgid(pid: Option<Pid>) -> Pid {
+    backend::process::syscalls::getpgid(pid)
+}
+
 /// `setsid()`—Create a new session.
 ///
 /// # References

src/process/mod.rs

@@ -39,8 +39,8 @@ pub use exit::{EXIT_FAILURE, EXIT_SUCCESS};
 pub use id::Cpuid;
 #[cfg(not(target_os = "wasi"))]
 pub use id::{
-    getegid, geteuid, getgid, getpid, getppid, getuid, setsid, Gid, Pid, RawGid, RawNonZeroPid,
-    RawPid, RawUid, Uid,
+    getegid, geteuid, getgid, getpgid, getpid, getppid, getuid, setsid, Gid, Pid, RawGid,
+    RawNonZeroPid, RawPid, RawUid, Uid,
 };
 #[cfg(not(target_os = "wasi"))]
 pub use kill::{kill_current_process_group, kill_process, kill_process_group, Signal};

tests/process/id.rs

@@ -63,3 +63,15 @@ fn test_getppid() {
         }
     }
 }
+
+#[test]
+fn test_getpgid() {
+    assert_eq!(process::getpgid(None), process::getpgid(None));
+    unsafe {
+        assert_eq!(
+            process::getpgid(None).as_raw_nonzero().get() as libc::pid_t,
+            libc::getpgid(0)
+        );
+        assert_eq!(process::getpgid(None).is_init(), libc::getpgid(0) == 1);
+    }
+}