Rollup of 3 pull requests

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

@@ -67,8 +67,10 @@ impl PidFd {
     /// Waits for the child to exit completely, returning the status that it exited with.
     ///
     /// Unlike [`Child::wait`] it does not ensure that the stdin handle is closed.
-    /// Additionally it will not return an `ExitStatus` if the child
-    /// has already been reaped. Instead an error will be returned.
+    ///
+    /// Additionally on kernels prior to 6.15 only the first attempt to
+    /// reap a child will return an ExitStatus, further attempts
+    /// will return an Error.
     ///
     /// [`Child::wait`]: process::Child::wait
     pub fn wait(&self) -> Result<ExitStatus> {
@@ -77,8 +79,8 @@ impl PidFd {
 
     /// Attempts to collect the exit status of the child if it has already exited.
     ///
-    /// Unlike [`Child::try_wait`] this method will return an Error
-    /// if the child has already been reaped.
+    /// On kernels prior to 6.15, and unlike [`Child::try_wait`], only the first attempt
+    /// to reap a child will return an ExitStatus, further attempts will return an Error.
     ///
     /// [`Child::try_wait`]: process::Child::try_wait
     pub fn try_wait(&self) -> Result<Option<ExitStatus>> {

library/std/src/os/unix/io/mod.rs

@@ -92,9 +92,137 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
+use crate::io::{self, Stderr, StderrLock, Stdin, StdinLock, Stdout, StdoutLock, Write};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use crate::os::fd::*;
+#[allow(unused_imports)] // not used on all targets
+use crate::sys::cvt;
 
 // Tests for this module
 #[cfg(test)]
 mod tests;
+
+#[unstable(feature = "stdio_swap", issue = "150667", reason = "recently added")]
+pub trait StdioExt: crate::sealed::Sealed {
+    /// Redirects the stdio file descriptor to point to the file description underpinning `fd`.
+    ///
+    /// Rust std::io write buffers (if any) are flushed, but other runtimes
+    /// (e.g. C stdio) or libraries that acquire a clone of the file descriptor
+    /// will not be aware of this change.
+    ///
+    /// # Platform-specific behavior
+    ///
+    /// This is [currently] implemented using
+    ///
+    /// - `fd_renumber` on wasip1
+    /// - `dup2` on most unixes
+    ///
+    /// [currently]: crate::io#platform-specific-behavior
+    ///
+    /// ```
+    /// #![feature(stdio_swap)]
+    /// use std::io::{self, Read, Write};
+    /// use std::os::unix::io::StdioExt;
+    ///
+    /// fn main() -> io::Result<()> {
+    ///    let (reader, mut writer) = io::pipe()?;
+    ///    let mut stdin = io::stdin();
+    ///    stdin.set_fd(reader)?;
+    ///    writer.write_all(b"Hello, world!")?;
+    ///    let mut buffer = vec![0; 13];
+    ///    assert_eq!(stdin.read(&mut buffer)?, 13);
+    ///    assert_eq!(&buffer, b"Hello, world!");
+    ///    Ok(())
+    /// }
+    /// ```
+    fn set_fd<T: Into<OwnedFd>>(&mut self, fd: T) -> io::Result<()>;
+
+    /// Redirects the stdio file descriptor and returns a new `OwnedFd`
+    /// backed by the previous file description.
+    ///
+    /// See [`set_fd()`] for details.
+    ///
+    /// [`set_fd()`]: StdioExt::set_fd
+    fn replace_fd<T: Into<OwnedFd>>(&mut self, replace_with: T) -> io::Result<OwnedFd>;
+
+    /// Redirects the stdio file descriptor to the null device (`/dev/null`)
+    /// and returns a new `OwnedFd` backed by the previous file description.
+    ///
+    /// Programs that communicate structured data via stdio can use this early in `main()` to
+    /// extract the fds, treat them as other IO types (`File`, `UnixStream`, etc),
+    /// apply custom buffering or avoid interference from stdio use later in the program.
+    ///
+    /// See [`set_fd()`] for additional details.
+    ///
+    /// [`set_fd()`]: StdioExt::set_fd
+    fn take_fd(&mut self) -> io::Result<OwnedFd>;
+}
+
+macro io_ext_impl($stdio_ty:ty, $stdio_lock_ty:ty, $writer:literal) {
+    #[unstable(feature = "stdio_swap", issue = "150667", reason = "recently added")]
+    impl StdioExt for $stdio_ty {
+        fn set_fd<T: Into<OwnedFd>>(&mut self, fd: T) -> io::Result<()> {
+            self.lock().set_fd(fd)
+        }
+
+        fn take_fd(&mut self) -> io::Result<OwnedFd> {
+            self.lock().take_fd()
+        }
+
+        fn replace_fd<T: Into<OwnedFd>>(&mut self, replace_with: T) -> io::Result<OwnedFd> {
+            self.lock().replace_fd(replace_with)
+        }
+    }
+
+    #[unstable(feature = "stdio_swap", issue = "150667", reason = "recently added")]
+    impl StdioExt for $stdio_lock_ty {
+        fn set_fd<T: Into<OwnedFd>>(&mut self, fd: T) -> io::Result<()> {
+            #[cfg($writer)]
+            self.flush()?;
+            replace_stdio_fd(self.as_fd(), fd.into())
+        }
+
+        fn take_fd(&mut self) -> io::Result<OwnedFd> {
+            let null = null_fd()?;
+            let cloned = self.as_fd().try_clone_to_owned()?;
+            self.set_fd(null)?;
+            Ok(cloned)
+        }
+
+        fn replace_fd<T: Into<OwnedFd>>(&mut self, replace_with: T) -> io::Result<OwnedFd> {
+            let cloned = self.as_fd().try_clone_to_owned()?;
+            self.set_fd(replace_with)?;
+            Ok(cloned)
+        }
+    }
+}
+
+io_ext_impl!(Stdout, StdoutLock<'_>, true);
+io_ext_impl!(Stdin, StdinLock<'_>, false);
+io_ext_impl!(Stderr, StderrLock<'_>, true);
+
+fn null_fd() -> io::Result<OwnedFd> {
+    let null_dev = crate::fs::OpenOptions::new().read(true).write(true).open("/dev/null")?;
+    Ok(null_dev.into())
+}
+
+/// Replaces the underlying file descriptor with the one from `other`.
+/// Does not set CLOEXEC.
+fn replace_stdio_fd(this: BorrowedFd<'_>, other: OwnedFd) -> io::Result<()> {
+    cfg_select! {
+        all(target_os = "wasi", target_env = "p1") => {
+            cvt(unsafe { libc::__wasilibc_fd_renumber(other.as_raw_fd(), this.as_raw_fd()) }).map(|_| ())
+        }
+        not(any(
+            target_arch = "wasm32",
+            target_os = "hermit",
+            target_os = "trusty",
+            target_os = "motor"
+        )) => {
+            cvt(unsafe {libc::dup2(other.as_raw_fd(), this.as_raw_fd())}).map(|_| ())
+        }
+        _ => {
+            Err(io::Error::UNSUPPORTED_PLATFORM)
+        }
+    }
+}

library/std/src/sys/pal/unix/linux/pidfd.rs

@@ -1,7 +1,8 @@
 use crate::io;
-use crate::os::fd::{AsRawFd, FromRawFd, RawFd};
+use crate::os::fd::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
 use crate::sys::fd::FileDesc;
 use crate::sys::process::ExitStatus;
+use crate::sys::weak::weak;
 use crate::sys::{AsInner, FromInner, IntoInner, cvt};
 
 #[cfg(test)]
@@ -15,6 +16,69 @@ impl PidFd {
         self.send_signal(libc::SIGKILL)
     }
 
+    pub(crate) fn current_process() -> io::Result<PidFd> {
+        let pid = crate::process::id();
+        let pidfd = cvt(unsafe { libc::syscall(libc::SYS_pidfd_open, pid, 0) })?;
+        Ok(unsafe { PidFd::from_raw_fd(pidfd as RawFd) })
+    }
+
+    pub(crate) fn pid(&self) -> io::Result<u32> {
+        // since kernel 6.13
+        // https://lore.kernel.org/all/[email protected]/
+        let mut pidfd_info: libc::pidfd_info = unsafe { crate::mem::zeroed() };
+        pidfd_info.mask = libc::PIDFD_INFO_PID as u64;
+        match cvt(unsafe { libc::ioctl(self.0.as_raw_fd(), libc::PIDFD_GET_INFO, &mut pidfd_info) })
+        {
+            Ok(_) => {}
+            Err(e) if e.raw_os_error() == Some(libc::EINVAL) => {
+                // kernel doesn't support that ioctl, try the glibc helper that looks at procfs
+                weak!(
+                    fn pidfd_getpid(pidfd: RawFd) -> libc::pid_t;
+                );
+                if let Some(pidfd_getpid) = pidfd_getpid.get() {
+                    let pid: libc::c_int = cvt(unsafe { pidfd_getpid(self.0.as_raw_fd()) })?;
+                    return Ok(pid as u32);
+                }
+                return Err(e);
+            }
+            Err(e) => return Err(e),
+        }
+
+        Ok(pidfd_info.pid)
+    }
+
+    fn exit_for_reaped_child(&self) -> io::Result<ExitStatus> {
+        // since kernel 6.15
+        // https://lore.kernel.org/linux-fsdevel/20250305-work-pidfs-kill_on_last_close-v3-0-c8c3d8361705@kernel.org/T/
+        let mut pidfd_info: libc::pidfd_info = unsafe { crate::mem::zeroed() };
+        pidfd_info.mask = libc::PIDFD_INFO_EXIT as u64;
+        cvt(unsafe { libc::ioctl(self.0.as_raw_fd(), libc::PIDFD_GET_INFO, &mut pidfd_info) })?;
+        Ok(ExitStatus::new(pidfd_info.exit_code))
+    }
+
+    fn waitid(&self, options: libc::c_int) -> io::Result<Option<ExitStatus>> {
+        let mut siginfo: libc::siginfo_t = unsafe { crate::mem::zeroed() };
+        let r = cvt(unsafe {
+            libc::waitid(libc::P_PIDFD, self.0.as_raw_fd() as u32, &mut siginfo, options)
+        });
+        match r {
+            Err(waitid_err) if waitid_err.raw_os_error() == Some(libc::ECHILD) => {
+                // already reaped
+                match self.exit_for_reaped_child() {
+                    Ok(exit_status) => return Ok(Some(exit_status)),
+                    Err(_) => return Err(waitid_err),
+                }
+            }
+            Err(e) => return Err(e),
+            Ok(_) => {}
+        }
+        if unsafe { siginfo.si_pid() } == 0 {
+            Ok(None)
+        } else {
+            Ok(Some(ExitStatus::from_waitid_siginfo(siginfo)))
+        }
+    }
+
     pub(crate) fn send_signal(&self, signal: i32) -> io::Result<()> {
         cvt(unsafe {
             libc::syscall(
@@ -29,29 +93,15 @@ impl PidFd {
     }
 
     pub fn wait(&self) -> io::Result<ExitStatus> {
-        let mut siginfo: libc::siginfo_t = unsafe { crate::mem::zeroed() };
-        cvt(unsafe {
-            libc::waitid(libc::P_PIDFD, self.0.as_raw_fd() as u32, &mut siginfo, libc::WEXITED)
-        })?;
-        Ok(ExitStatus::from_waitid_siginfo(siginfo))
+        let r = self.waitid(libc::WEXITED)?;
+        match r {
+            Some(exit_status) => Ok(exit_status),
+            None => unreachable!("waitid with WEXITED should not return None"),
+        }
     }
 
     pub fn try_wait(&self) -> io::Result<Option<ExitStatus>> {
-        let mut siginfo: libc::siginfo_t = unsafe { crate::mem::zeroed() };
-
-        cvt(unsafe {
-            libc::waitid(
-                libc::P_PIDFD,
-                self.0.as_raw_fd() as u32,
-                &mut siginfo,
-                libc::WEXITED | libc::WNOHANG,
-            )
-        })?;
-        if unsafe { siginfo.si_pid() } == 0 {
-            Ok(None)
-        } else {
-            Ok(Some(ExitStatus::from_waitid_siginfo(siginfo)))
-        }
+        self.waitid(libc::WEXITED | libc::WNOHANG)
     }
 }
 
@@ -78,3 +128,9 @@ impl FromRawFd for PidFd {
         Self(FileDesc::from_raw_fd(fd))
     }
 }
+
+impl IntoRawFd for PidFd {
+    fn into_raw_fd(self) -> RawFd {
+        self.0.into_raw_fd()
+    }
+}

library/std/src/sys/pal/unix/linux/pidfd/tests.rs

@@ -1,8 +1,11 @@
+use super::PidFd as InternalPidFd;
 use crate::assert_matches::assert_matches;
-use crate::os::fd::{AsRawFd, RawFd};
+use crate::io::ErrorKind;
+use crate::os::fd::AsRawFd;
 use crate::os::linux::process::{ChildExt, CommandExt as _};
 use crate::os::unix::process::{CommandExt as _, ExitStatusExt};
 use crate::process::Command;
+use crate::sys::AsInner;
 
 #[test]
 fn test_command_pidfd() {
@@ -48,11 +51,22 @@ fn test_command_pidfd() {
     let mut cmd = Command::new("false");
     let mut child = unsafe { cmd.pre_exec(|| Ok(())) }.create_pidfd(true).spawn().unwrap();
 
-    assert!(child.id() > 0 && child.id() < -1i32 as u32);
+    let id = child.id();
+
+    assert!(id > 0 && id < -1i32 as u32, "spawning with pidfd still returns a sane pid");
 
     if pidfd_open_available {
         assert!(child.pidfd().is_ok())
     }
+
+    if let Ok(pidfd) = child.pidfd() {
+        match pidfd.as_inner().pid() {
+            Ok(pid) => assert_eq!(pid, id),
+            Err(e) if e.kind() == ErrorKind::InvalidInput => { /* older kernel */ }
+            Err(e) => panic!("unexpected error getting pid from pidfd: {}", e),
+        }
+    }
+
     child.wait().expect("error waiting on child");
 }
 
@@ -77,23 +91,21 @@ fn test_pidfd() {
     assert_eq!(status.signal(), Some(libc::SIGKILL));
 
     // Trying to wait again for a reaped child is safe since there's no pid-recycling race.
-    // But doing so will return an error.
+    // But doing so may return an error.
     let res = fd.wait();
-    assert_matches!(res, Err(e) if e.raw_os_error() == Some(libc::ECHILD));
+    match res {
+        // older kernels
+        Err(e) if e.raw_os_error() == Some(libc::ECHILD) => {}
+        // 6.15+
+        Ok(exit) if exit.signal() == Some(libc::SIGKILL) => {}
+        other => panic!("expected ECHILD error, got {:?}", other),
+    }
 
     // Ditto for additional attempts to kill an already-dead child.
     let res = fd.kill();
     assert_matches!(res, Err(e) if e.raw_os_error() == Some(libc::ESRCH));
 }
 
 fn probe_pidfd_support() -> bool {
-    // pidfds require the pidfd_open syscall
-    let our_pid = crate::process::id();
-    let pidfd = unsafe { libc::syscall(libc::SYS_pidfd_open, our_pid, 0) };
-    if pidfd >= 0 {
-        unsafe { libc::close(pidfd as RawFd) };
-        true
-    } else {
-        false
-    }
+    InternalPidFd::current_process().is_ok()
 }