Rollup merge of #93858 - krallin:process-process_group, r=dtolnay

Add a `process_group` method to UNIX `CommandExt`

- Tracking issue: #93857
- RFC: rust-lang/rfcs#3228

Add a `process_group` method to `std::os::unix::process::CommandExt` that
allows setting the process group id (i.e. calling `setpgid`) in the child, thus
enabling users to set process groups while leveraging the `posix_spawn` fast
path.

library/std/src/os/unix/process.rs

@@ -149,6 +149,11 @@ pub trait CommandExt: Sealed {
     fn arg0<S>(&mut self, arg: S) -> &mut process::Command
     where
         S: AsRef<OsStr>;
+
+    /// Sets the process group ID of the child process. Translates to a `setpgid` call in the child
+    /// process.
+    #[unstable(feature = "process_set_process_group", issue = "93857")]
+    fn process_group(&mut self, pgroup: i32) -> &mut process::Command;
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -201,6 +206,11 @@ impl CommandExt for process::Command {
         self.as_inner_mut().set_arg_0(arg.as_ref());
         self
     }
+
+    fn process_group(&mut self, pgroup: i32) -> &mut process::Command {
+        self.as_inner_mut().pgroup(pgroup);
+        self
+    }
 }
 
 /// Unix-specific extensions to [`process::ExitStatus`] and

library/std/src/sys/unix/process/process_common.rs

@@ -18,7 +18,7 @@ use crate::sys_common::IntoInner;
 #[cfg(not(target_os = "fuchsia"))]
 use crate::sys::fs::OpenOptions;
 
-use libc::{c_char, c_int, gid_t, uid_t, EXIT_FAILURE, EXIT_SUCCESS};
+use libc::{c_char, c_int, gid_t, pid_t, uid_t, EXIT_FAILURE, EXIT_SUCCESS};
 
 cfg_if::cfg_if! {
     if #[cfg(target_os = "fuchsia")] {
@@ -82,6 +82,7 @@ pub struct Command {
     stderr: Option<Stdio>,
     #[cfg(target_os = "linux")]
     create_pidfd: bool,
+    pgroup: Option<pid_t>,
 }
 
 // Create a new type for argv, so that we can make it `Send` and `Sync`
@@ -145,6 +146,7 @@ impl Command {
             stdin: None,
             stdout: None,
             stderr: None,
+            pgroup: None,
         }
     }
 
@@ -167,6 +169,7 @@ impl Command {
             stdout: None,
             stderr: None,
             create_pidfd: false,
+            pgroup: None,
         }
     }
 
@@ -202,6 +205,9 @@ impl Command {
     pub fn groups(&mut self, groups: &[gid_t]) {
         self.groups = Some(Box::from(groups));
     }
+    pub fn pgroup(&mut self, pgroup: pid_t) {
+        self.pgroup = Some(pgroup);
+    }
 
     #[cfg(target_os = "linux")]
     pub fn create_pidfd(&mut self, val: bool) {
@@ -265,6 +271,10 @@ impl Command {
     pub fn get_groups(&self) -> Option<&[gid_t]> {
         self.groups.as_deref()
     }
+    #[allow(dead_code)]
+    pub fn get_pgroup(&self) -> Option<pid_t> {
+        self.pgroup
+    }
 
     pub fn get_closures(&mut self) -> &mut Vec<Box<dyn FnMut() -> io::Result<()> + Send + Sync>> {
         &mut self.closures

library/std/src/sys/unix/process/process_common/tests.rs

@@ -67,3 +67,58 @@ fn test_process_mask() {
         t!(cat.wait());
     }
 }
+
+#[test]
+#[cfg_attr(
+    any(
+        // See test_process_mask
+        target_os = "macos",
+        target_arch = "arm",
+        target_arch = "aarch64",
+        target_arch = "riscv64",
+    ),
+    ignore
+)]
+fn test_process_group_posix_spawn() {
+    unsafe {
+        // Spawn a cat subprocess that's just going to hang since there is no I/O.
+        let mut cmd = Command::new(OsStr::new("cat"));
+        cmd.pgroup(0);
+        cmd.stdin(Stdio::MakePipe);
+        cmd.stdout(Stdio::MakePipe);
+        let (mut cat, _pipes) = t!(cmd.spawn(Stdio::Null, true));
+
+        // Check that we can kill its process group, which means there *is* one.
+        t!(cvt(libc::kill(-(cat.id() as libc::pid_t), libc::SIGINT)));
+
+        t!(cat.wait());
+    }
+}
+
+#[test]
+#[cfg_attr(
+    any(
+        // See test_process_mask
+        target_os = "macos",
+        target_arch = "arm",
+        target_arch = "aarch64",
+        target_arch = "riscv64",
+    ),
+    ignore
+)]
+fn test_process_group_no_posix_spawn() {
+    unsafe {
+        // Same as above, create hang-y cat. This time, force using the non-posix_spawnp path.
+        let mut cmd = Command::new(OsStr::new("cat"));
+        cmd.pgroup(0);
+        cmd.pre_exec(Box::new(|| Ok(()))); // pre_exec forces fork + exec
+        cmd.stdin(Stdio::MakePipe);
+        cmd.stdout(Stdio::MakePipe);
+        let (mut cat, _pipes) = t!(cmd.spawn(Stdio::Null, true));
+
+        // Check that we can kill its process group, which means there *is* one.
+        t!(cvt(libc::kill(-(cat.id() as libc::pid_t), libc::SIGINT)));
+
+        t!(cat.wait());
+    }
+}

library/std/src/sys/unix/process/process_unix.rs

@@ -320,6 +320,10 @@ impl Command {
             cvt(libc::chdir(cwd.as_ptr()))?;
         }
 
+        if let Some(pgroup) = self.get_pgroup() {
+            cvt(libc::setpgid(0, pgroup))?;
+        }
+
         // emscripten has no signal support.
         #[cfg(not(target_os = "emscripten"))]
         {
@@ -459,6 +463,8 @@ impl Command {
             None => None,
         };
 
+        let pgroup = self.get_pgroup();
+
         // Safety: -1 indicates we don't have a pidfd.
         let mut p = unsafe { Process::new(0, -1) };
 
@@ -487,6 +493,8 @@ impl Command {
             cvt_nz(libc::posix_spawnattr_init(attrs.as_mut_ptr()))?;
             let attrs = PosixSpawnattr(&mut attrs);
 
+            let mut flags = 0;
+
             let mut file_actions = MaybeUninit::uninit();
             cvt_nz(libc::posix_spawn_file_actions_init(file_actions.as_mut_ptr()))?;
             let file_actions = PosixSpawnFileActions(&mut file_actions);
@@ -516,13 +524,18 @@ impl Command {
                 cvt_nz(f(file_actions.0.as_mut_ptr(), cwd.as_ptr()))?;
             }
 
+            if let Some(pgroup) = pgroup {
+                flags |= libc::POSIX_SPAWN_SETPGROUP;
+                cvt_nz(libc::posix_spawnattr_setpgroup(attrs.0.as_mut_ptr(), pgroup))?;
+            }
+
             let mut set = MaybeUninit::<libc::sigset_t>::uninit();
             cvt(sigemptyset(set.as_mut_ptr()))?;
             cvt_nz(libc::posix_spawnattr_setsigmask(attrs.0.as_mut_ptr(), set.as_ptr()))?;
             cvt(sigaddset(set.as_mut_ptr(), libc::SIGPIPE))?;
             cvt_nz(libc::posix_spawnattr_setsigdefault(attrs.0.as_mut_ptr(), set.as_ptr()))?;
 
-            let flags = libc::POSIX_SPAWN_SETSIGDEF | libc::POSIX_SPAWN_SETSIGMASK;
+            flags |= libc::POSIX_SPAWN_SETSIGDEF | libc::POSIX_SPAWN_SETSIGMASK;
             cvt_nz(libc::posix_spawnattr_setflags(attrs.0.as_mut_ptr(), flags as _))?;
 
             // Make sure we synchronize access to the global `environ` resource