feat: pidfd_send_signal

Author: JonathanWoollett-Light

CHANGELOG.md

@@ -15,6 +15,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
   ([#1868](https://github.com/nix-rust/nix/pull/1868))
 - Added `pid_open` on Linux.
   ([#1868](https://github.com/nix-rust/nix/pull/1868))
+- Added `pidfd_send_signal` on Linux.
+  ([#1868](https://github.com/nix-rust/nix/pull/1868))
 
 ### Changed
 

src/sys/mod.rs

@@ -227,6 +227,6 @@ feature! {
     pub mod timer;
 }
 
-#[cfg(all(target_os = "linux", feature = "process"))]
+#[cfg(all(target_os = "linux", feature = "signal", feature = "process"))]
 /// pidfd related functionality
 pub mod pidfd;

src/sys/pidfd.rs

@@ -1,4 +1,5 @@
 use crate::errno::Errno;
+use crate::sys::signal::Signal;
 use crate::unistd::Pid;
 use crate::Result;
 use std::convert::TryFrom;
@@ -74,3 +75,44 @@ 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: AsRawFd>(
+    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_raw_fd(),
+            sig as i32,
+            info,
+        )
+    } {
+        -1 => Err(Errno::last()),
+        0 => Ok(()),
+        _ => unreachable!(),
+    }
+}