feat: pidfd_send_signal

Author: JonathanWoollett-Light

changelog/1868.added.md

@@ -1,2 +1,3 @@
 - Added `pidfd_getfd` on Linux.
-- Added `pid_open` on Linux.
+- Added `pid_open` on Linux.
+- Added `pidfd_send_signal` on Linux.

src/sys/mod.rs

@@ -224,5 +224,5 @@ feature! {
     pub mod timer;
 }
 
-#[cfg(all(target_os = "linux", feature = "process"))]
+#[cfg(all(target_os = "linux", feature = "signal", feature = "process"))]
 pub mod pidfd;

src/sys/pidfd.rs

@@ -1,6 +1,7 @@
 //! pidfd related functionality
 
 use crate::errno::Errno;
+use crate::sys::signal::Signal;
 use crate::unistd::Pid;
 use crate::Result;
 use std::convert::TryFrom;
@@ -70,3 +71,45 @@ pub fn pid_open(pid: Pid, nonblock: bool) -> Result<OwnedFd> {
         _ => unreachable!(),
     }
 }
+
+/// Sends the signal `sig` to the target process referred to by `pid`, a PID file descriptor that
+/// refers to a process.
+///
+/// If the info argument is some [`libc::siginfo_t`] buffer, that buffer should be populated as
+/// described in [rt_sigqueueinfo(2)](https://man7.org/linux/man-pages/man2/rt_sigqueueinfo.2.html).
+///
+/// If the info argument is `None`, this is equivalent to specifying a pointer to a `siginfo_t`
+/// buffer whose fields match the values that are implicitly supplied when a signal is sent using
+/// [`crate::sys::signal::kill`]:
+///
+/// -  `si_signo` is set to the signal number;
+/// -  `si_errno` is set to 0;
+/// -  `si_code` is set to SI_USER;
+/// -  `si_pid` is set to the caller's PID; and
+/// -  `si_uid` is set to the caller's real user ID.
+///
+/// The calling process must either be in the same PID namespace as the process referred to by
+/// pidfd, or be in an ancestor of that namespace.
+pub fn pidfd_send_signal<Fd: AsFd>(
+    pid: Fd,
+    sig: Signal,
+    info: Option<libc::siginfo_t>,
+) -> Result<()> {
+    let info = match info {
+        Some(i) => &i,
+        None => std::ptr::null(),
+    };
+    match unsafe {
+        libc::syscall(
+            libc::SYS_pidfd_send_signal,
+            pid.as_fd().as_raw_fd(),
+            sig as i32,
+            info,
+            0u32,
+        )
+    } {
+        -1 => Err(Errno::last()),
+        0 => Ok(()),
+        _ => unreachable!(),
+    }
+}

test/sys/mod.rs

@@ -57,3 +57,6 @@ mod test_pthread;
 mod test_ptrace;
 #[cfg(any(target_os = "android", target_os = "linux"))]
 mod test_timerfd;
+
+#[cfg(all(target_os = "linux", feature = "signal", feature = "process"))]
+pub mod test_pidfd;

test/sys/test_pidfd.rs

@@ -0,0 +1,28 @@
+use nix::{
+    sys::{
+        pidfd::{pid_open, pidfd_send_signal},
+        signal::Signal,
+        signalfd::SigSet,
+        wait::waitpid,
+    },
+    unistd::{fork, ForkResult},
+};
+
+#[test]
+fn test_pidfd_send_signal() {
+    match unsafe { fork().unwrap() } {
+        ForkResult::Parent { child } => {
+            // Send SIGUSR1
+            let pid_fd = pid_open(child, false).unwrap();
+            pidfd_send_signal(pid_fd, Signal::SIGUSR1, None).unwrap();
+            // Wait for child to exit.
+            waitpid(child, None).unwrap();
+        }
+        ForkResult::Child => {
+            // Wait for SIGUSR1
+            let mut mask = SigSet::empty();
+            mask.add(Signal::SIGUSR1);
+            assert_eq!(mask.wait().unwrap(), Signal::SIGUSR1);
+        }
+    }
+}