Add a Result to getpgid, and add getpgrp. (#386)

* Add a `Result` to `getpgid`, and add `getpgrp`.

Add a `Result` return type to `getpgid`, as it can fail if there's no
process with the given pid.

And, add a a `getpgrp` function, which is similar to `getpgid`, but
doesn't take a pid argument and always operates on the current process,
which means it doesn't need a `Result` return type.

* Use `getpgid` on platforms which don't have a `getpgrp` syscall.

examples/process.rs

@@ -10,6 +10,13 @@ fn main() -> io::Result<()> {
 
     println!("Pid: {}", getpid().as_raw_nonzero());
     println!("Parent Pid: {}", Pid::as_raw(getppid()));
+    println!("Group Pid: {}", getpgrp().as_raw_nonzero());
+    if let Some(ppid) = getppid() {
+        println!(
+            "Parent Group Pid: {}",
+            getpgid(Some(ppid)).unwrap().as_raw_nonzero()
+        );
+    }
     println!("Uid: {}", getuid().as_raw());
     println!("Gid: {}", getgid().as_raw());
     #[cfg(any(

src/backend/libc/process/syscalls.rs

@@ -3,6 +3,8 @@
 use super::super::c;
 #[cfg(not(any(target_os = "wasi", target_os = "fuchsia")))]
 use super::super::conv::borrowed_fd;
+#[cfg(not(target_os = "wasi"))]
+use super::super::conv::ret_pid_t;
 use super::super::conv::{c_str, ret, ret_c_int, ret_discarded_char_ptr};
 #[cfg(any(target_os = "android", target_os = "linux"))]
 use super::super::conv::{syscall_ret, syscall_ret_u32};
@@ -148,9 +150,20 @@ pub(crate) fn getppid() -> Option<Pid> {
 #[cfg(not(target_os = "wasi"))]
 #[inline]
 #[must_use]
-pub(crate) fn getpgid(pid: Option<Pid>) -> Pid {
+pub(crate) fn getpgid(pid: Option<Pid>) -> io::Result<Pid> {
+    unsafe {
+        let pgid = ret_pid_t(c::getpgid(Pid::as_raw(pid) as _))?;
+        debug_assert_ne!(pgid, 0);
+        Ok(Pid::from_raw_nonzero(RawNonZeroPid::new_unchecked(pgid)))
+    }
+}
+
+#[cfg(not(target_os = "wasi"))]
+#[inline]
+#[must_use]
+pub(crate) fn getpgrp() -> Pid {
     unsafe {
-        let pgid = c::getpgid(Pid::as_raw(pid) as _);
+        let pgid = c::getpgrp();
         debug_assert_ne!(pgid, 0);
         Pid::from_raw_nonzero(RawNonZeroPid::new_unchecked(pgid))
     }

src/backend/linux_raw/process/syscalls.rs

@@ -21,6 +21,7 @@ use crate::process::{
 };
 use core::convert::TryInto;
 use core::mem::MaybeUninit;
+use core::num::NonZeroU32;
 use core::ptr::{null, null_mut};
 use linux_raw_sys::general::{
     __kernel_gid_t, __kernel_pid_t, __kernel_uid_t, membarrier_cmd, membarrier_cmd_flag, rlimit,
@@ -100,11 +101,31 @@ pub(crate) fn getppid() -> Option<Pid> {
 }
 
 #[inline]
-pub(crate) fn getpgid(pid: Option<Pid>) -> Pid {
+pub(crate) fn getpgid(pid: Option<Pid>) -> io::Result<Pid> {
     unsafe {
         let pgid: i32 =
-            ret_usize_infallible(syscall_readonly!(__NR_getpgid, c_uint(Pid::as_raw(pid))))
-                as __kernel_pid_t;
+            ret_usize(syscall_readonly!(__NR_getpgid, c_uint(Pid::as_raw(pid))))? as __kernel_pid_t;
+        Ok(Pid::from_raw_nonzero(NonZeroU32::new_unchecked(
+            pgid as u32,
+        )))
+    }
+}
+
+#[inline]
+pub(crate) fn getpgrp() -> Pid {
+    // Use the `getpgrp` syscall if available.
+    #[cfg(not(any(target_arch = "aarch64", target_arch = "riscv64")))]
+    unsafe {
+        let pgid: i32 = ret_usize_infallible(syscall_readonly!(__NR_getpgrp)) as __kernel_pid_t;
+        debug_assert!(pgid > 0);
+        Pid::from_raw_nonzero(RawNonZeroPid::new_unchecked(pgid as u32))
+    }
+
+    // Otherwise use `getpgrp` and pass it zero.
+    #[cfg(any(target_arch = "aarch64", target_arch = "riscv64"))]
+    unsafe {
+        let pgid: i32 =
+            ret_usize_infallible(syscall_readonly!(__NR_getpgid, c_uint(0))) as __kernel_pid_t;
         debug_assert!(pgid > 0);
         Pid::from_raw_nonzero(RawNonZeroPid::new_unchecked(pgid as u32))
     }

src/process/id.rs

@@ -277,10 +277,24 @@ pub fn getppid() -> Option<Pid> {
 /// [Linux]: https://man7.org/linux/man-pages/man2/getpgid.2.html
 #[inline]
 #[must_use]
-pub fn getpgid(pid: Option<Pid>) -> Pid {
+pub fn getpgid(pid: Option<Pid>) -> io::Result<Pid> {
     backend::process::syscalls::getpgid(pid)
 }
 
+/// `getpgrp()`—Returns the process' group ID.
+///
+/// # References
+///  - [POSIX]
+///  - [Linux]
+///
+/// [POSIX]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/getpgrp.html
+/// [Linux]: https://man7.org/linux/man-pages/man2/getpgrp.2.html
+#[inline]
+#[must_use]
+pub fn getpgrp() -> Pid {
+    backend::process::syscalls::getpgrp()
+}
+
 /// `setsid()`—Create a new session.
 ///
 /// # References

src/process/mod.rs

@@ -39,7 +39,7 @@ pub use exit::{EXIT_FAILURE, EXIT_SUCCESS};
 pub use id::Cpuid;
 #[cfg(not(target_os = "wasi"))]
 pub use id::{
-    getegid, geteuid, getgid, getpgid, getpid, getppid, getuid, setsid, Gid, Pid, RawGid,
+    getegid, geteuid, getgid, getpgid, getpgrp, getpid, getppid, getuid, setsid, Gid, Pid, RawGid,
     RawNonZeroPid, RawPid, RawUid, Uid,
 };
 #[cfg(not(target_os = "wasi"))]

tests/process/id.rs

@@ -67,11 +67,36 @@ fn test_getppid() {
 #[test]
 fn test_getpgid() {
     assert_eq!(process::getpgid(None), process::getpgid(None));
+    assert_eq!(
+        process::getpgid(Some(process::getpid())),
+        process::getpgid(Some(process::getpid()))
+    );
     unsafe {
         assert_eq!(
-            process::getpgid(None).as_raw_nonzero().get() as libc::pid_t,
+            process::getpgid(None).unwrap().as_raw_nonzero().get() as libc::pid_t,
             libc::getpgid(0)
         );
-        assert_eq!(process::getpgid(None).is_init(), libc::getpgid(0) == 1);
+        assert_eq!(
+            process::getpgid(None).unwrap().is_init(),
+            libc::getpgid(0) == 1
+        );
+        assert_eq!(
+            process::getpgid(Some(process::getpid()))
+                .unwrap()
+                .as_raw_nonzero()
+                .get() as libc::pid_t,
+            libc::getpgid(libc::getpid())
+        );
+    }
+}
+
+#[test]
+fn test_getpgrp() {
+    assert_eq!(process::getpgrp(), process::getpgrp());
+    unsafe {
+        assert_eq!(
+            process::getpgrp().as_raw_nonzero().get() as libc::pid_t,
+            libc::getpgrp()
+        );
     }
 }