std/sys/pal/unix/process/
process_unix.rs

1#[cfg(target_os = "vxworks")]
2use libc::RTP_ID as pid_t;
3#[cfg(not(target_os = "vxworks"))]
4use libc::{c_int, pid_t};
5#[cfg(not(any(
6    target_os = "vxworks",
7    target_os = "l4re",
8    target_os = "tvos",
9    target_os = "watchos",
10)))]
11use libc::{gid_t, uid_t};
12
13use crate::io::{self, Error, ErrorKind};
14use crate::num::NonZero;
15use crate::sys::cvt;
16#[cfg(target_os = "linux")]
17use crate::sys::pal::unix::linux::pidfd::PidFd;
18use crate::sys::process::process_common::*;
19use crate::{fmt, mem, sys};
20
21cfg_if::cfg_if! {
22    if #[cfg(target_os = "nto")] {
23        use crate::thread;
24        use libc::{c_char, posix_spawn_file_actions_t, posix_spawnattr_t};
25        use crate::time::Duration;
26        use crate::sync::LazyLock;
27        // Get smallest amount of time we can sleep.
28        // Return a common value if it cannot be determined.
29        fn get_clock_resolution() -> Duration {
30            static MIN_DELAY: LazyLock<Duration, fn() -> Duration> = LazyLock::new(|| {
31                let mut mindelay = libc::timespec { tv_sec: 0, tv_nsec: 0 };
32                if unsafe { libc::clock_getres(libc::CLOCK_MONOTONIC, &mut mindelay) } == 0
33                {
34                    Duration::from_nanos(mindelay.tv_nsec as u64)
35                } else {
36                    Duration::from_millis(1)
37                }
38            });
39            *MIN_DELAY
40        }
41        // Arbitrary minimum sleep duration for retrying fork/spawn
42        const MIN_FORKSPAWN_SLEEP: Duration = Duration::from_nanos(1);
43        // Maximum duration of sleeping before giving up and returning an error
44        const MAX_FORKSPAWN_SLEEP: Duration = Duration::from_millis(1000);
45    }
46}
47
48////////////////////////////////////////////////////////////////////////////////
49// Command
50////////////////////////////////////////////////////////////////////////////////
51
52impl Command {
53    pub fn spawn(
54        &mut self,
55        default: Stdio,
56        needs_stdin: bool,
57    ) -> io::Result<(Process, StdioPipes)> {
58        const CLOEXEC_MSG_FOOTER: [u8; 4] = *b"NOEX";
59
60        let envp = self.capture_env();
61
62        if self.saw_nul() {
63            return Err(io::const_error!(
64                ErrorKind::InvalidInput,
65                "nul byte found in provided data",
66            ));
67        }
68
69        let (ours, theirs) = self.setup_io(default, needs_stdin)?;
70
71        if let Some(ret) = self.posix_spawn(&theirs, envp.as_ref())? {
72            return Ok((ret, ours));
73        }
74
75        #[cfg(target_os = "linux")]
76        let (input, output) = sys::net::Socket::new_pair(libc::AF_UNIX, libc::SOCK_SEQPACKET)?;
77
78        #[cfg(not(target_os = "linux"))]
79        let (input, output) = sys::pipe::anon_pipe()?;
80
81        // Whatever happens after the fork is almost for sure going to touch or
82        // look at the environment in one way or another (PATH in `execvp` or
83        // accessing the `environ` pointer ourselves). Make sure no other thread
84        // is accessing the environment when we do the fork itself.
85        //
86        // Note that as soon as we're done with the fork there's no need to hold
87        // a lock any more because the parent won't do anything and the child is
88        // in its own process. Thus the parent drops the lock guard immediately.
89        // The child calls `mem::forget` to leak the lock, which is crucial because
90        // releasing a lock is not async-signal-safe.
91        let env_lock = sys::os::env_read_lock();
92        let pid = unsafe { self.do_fork()? };
93
94        if pid == 0 {
95            crate::panic::always_abort();
96            mem::forget(env_lock); // avoid non-async-signal-safe unlocking
97            drop(input);
98            #[cfg(target_os = "linux")]
99            if self.get_create_pidfd() {
100                self.send_pidfd(&output);
101            }
102            let Err(err) = unsafe { self.do_exec(theirs, envp.as_ref()) };
103            let errno = err.raw_os_error().unwrap_or(libc::EINVAL) as u32;
104            let errno = errno.to_be_bytes();
105            let bytes = [
106                errno[0],
107                errno[1],
108                errno[2],
109                errno[3],
110                CLOEXEC_MSG_FOOTER[0],
111                CLOEXEC_MSG_FOOTER[1],
112                CLOEXEC_MSG_FOOTER[2],
113                CLOEXEC_MSG_FOOTER[3],
114            ];
115            // pipe I/O up to PIPE_BUF bytes should be atomic, and then
116            // we want to be sure we *don't* run at_exit destructors as
117            // we're being torn down regardless
118            rtassert!(output.write(&bytes).is_ok());
119            unsafe { libc::_exit(1) }
120        }
121
122        drop(env_lock);
123        drop(output);
124
125        #[cfg(target_os = "linux")]
126        let pidfd = if self.get_create_pidfd() { self.recv_pidfd(&input) } else { -1 };
127
128        #[cfg(not(target_os = "linux"))]
129        let pidfd = -1;
130
131        // Safety: We obtained the pidfd (on Linux) using SOCK_SEQPACKET, so it's valid.
132        let mut p = unsafe { Process::new(pid, pidfd) };
133        let mut bytes = [0; 8];
134
135        // loop to handle EINTR
136        loop {
137            match input.read(&mut bytes) {
138                Ok(0) => return Ok((p, ours)),
139                Ok(8) => {
140                    let (errno, footer) = bytes.split_at(4);
141                    assert_eq!(
142                        CLOEXEC_MSG_FOOTER, footer,
143                        "Validation on the CLOEXEC pipe failed: {:?}",
144                        bytes
145                    );
146                    let errno = i32::from_be_bytes(errno.try_into().unwrap());
147                    assert!(p.wait().is_ok(), "wait() should either return Ok or panic");
148                    return Err(Error::from_raw_os_error(errno));
149                }
150                Err(ref e) if e.is_interrupted() => {}
151                Err(e) => {
152                    assert!(p.wait().is_ok(), "wait() should either return Ok or panic");
153                    panic!("the CLOEXEC pipe failed: {e:?}")
154                }
155                Ok(..) => {
156                    // pipe I/O up to PIPE_BUF bytes should be atomic
157                    // similarly SOCK_SEQPACKET messages should arrive whole
158                    assert!(p.wait().is_ok(), "wait() should either return Ok or panic");
159                    panic!("short read on the CLOEXEC pipe")
160                }
161            }
162        }
163    }
164
165    pub fn output(&mut self) -> io::Result<(ExitStatus, Vec<u8>, Vec<u8>)> {
166        let (proc, pipes) = self.spawn(Stdio::MakePipe, false)?;
167        crate::sys_common::process::wait_with_output(proc, pipes)
168    }
169
170    // WatchOS and TVOS headers mark the `fork`/`exec*` functions with
171    // `__WATCHOS_PROHIBITED __TVOS_PROHIBITED`, and indicate that the
172    // `posix_spawn*` functions should be used instead. It isn't entirely clear
173    // what `PROHIBITED` means here (e.g. if calls to these functions are
174    // allowed to exist in dead code), but it sounds bad, so we go out of our
175    // way to avoid that all-together.
176    #[cfg(any(target_os = "tvos", target_os = "watchos"))]
177    const ERR_APPLE_TV_WATCH_NO_FORK_EXEC: Error = io::const_error!(
178        ErrorKind::Unsupported,
179        "`fork`+`exec`-based process spawning is not supported on this target",
180    );
181
182    #[cfg(any(target_os = "tvos", target_os = "watchos"))]
183    unsafe fn do_fork(&mut self) -> Result<pid_t, io::Error> {
184        return Err(Self::ERR_APPLE_TV_WATCH_NO_FORK_EXEC);
185    }
186
187    // Attempts to fork the process. If successful, returns Ok((0, -1))
188    // in the child, and Ok((child_pid, -1)) in the parent.
189    #[cfg(not(any(target_os = "watchos", target_os = "tvos", target_os = "nto")))]
190    unsafe fn do_fork(&mut self) -> Result<pid_t, io::Error> {
191        cvt(libc::fork())
192    }
193
194    // On QNX Neutrino, fork can fail with EBADF in case "another thread might have opened
195    // or closed a file descriptor while the fork() was occurring".
196    // Documentation says "... or try calling fork() again". This is what we do here.
197    // See also https://www.qnx.com/developers/docs/7.1/#com.qnx.doc.neutrino.lib_ref/topic/f/fork.html
198    #[cfg(target_os = "nto")]
199    unsafe fn do_fork(&mut self) -> Result<pid_t, io::Error> {
200        use crate::sys::os::errno;
201
202        let mut delay = MIN_FORKSPAWN_SLEEP;
203
204        loop {
205            let r = libc::fork();
206            if r == -1 as libc::pid_t && errno() as libc::c_int == libc::EBADF {
207                if delay < get_clock_resolution() {
208                    // We cannot sleep this short (it would be longer).
209                    // Yield instead.
210                    thread::yield_now();
211                } else if delay < MAX_FORKSPAWN_SLEEP {
212                    thread::sleep(delay);
213                } else {
214                    return Err(io::const_error!(
215                        ErrorKind::WouldBlock,
216                        "forking returned EBADF too often",
217                    ));
218                }
219                delay *= 2;
220                continue;
221            } else {
222                return cvt(r);
223            }
224        }
225    }
226
227    pub fn exec(&mut self, default: Stdio) -> io::Error {
228        let envp = self.capture_env();
229
230        if self.saw_nul() {
231            return io::const_error!(ErrorKind::InvalidInput, "nul byte found in provided data",);
232        }
233
234        match self.setup_io(default, true) {
235            Ok((_, theirs)) => {
236                unsafe {
237                    // Similar to when forking, we want to ensure that access to
238                    // the environment is synchronized, so make sure to grab the
239                    // environment lock before we try to exec.
240                    let _lock = sys::os::env_read_lock();
241
242                    let Err(e) = self.do_exec(theirs, envp.as_ref());
243                    e
244                }
245            }
246            Err(e) => e,
247        }
248    }
249
250    // And at this point we've reached a special time in the life of the
251    // child. The child must now be considered hamstrung and unable to
252    // do anything other than syscalls really. Consider the following
253    // scenario:
254    //
255    //      1. Thread A of process 1 grabs the malloc() mutex
256    //      2. Thread B of process 1 forks(), creating thread C
257    //      3. Thread C of process 2 then attempts to malloc()
258    //      4. The memory of process 2 is the same as the memory of
259    //         process 1, so the mutex is locked.
260    //
261    // This situation looks a lot like deadlock, right? It turns out
262    // that this is what pthread_atfork() takes care of, which is
263    // presumably implemented across platforms. The first thing that
264    // threads to *before* forking is to do things like grab the malloc
265    // mutex, and then after the fork they unlock it.
266    //
267    // Despite this information, libnative's spawn has been witnessed to
268    // deadlock on both macOS and FreeBSD. I'm not entirely sure why, but
269    // all collected backtraces point at malloc/free traffic in the
270    // child spawned process.
271    //
272    // For this reason, the block of code below should contain 0
273    // invocations of either malloc of free (or their related friends).
274    //
275    // As an example of not having malloc/free traffic, we don't close
276    // this file descriptor by dropping the FileDesc (which contains an
277    // allocation). Instead we just close it manually. This will never
278    // have the drop glue anyway because this code never returns (the
279    // child will either exec() or invoke libc::exit)
280    #[cfg(not(any(target_os = "tvos", target_os = "watchos")))]
281    unsafe fn do_exec(
282        &mut self,
283        stdio: ChildPipes,
284        maybe_envp: Option<&CStringArray>,
285    ) -> Result<!, io::Error> {
286        use crate::sys::{self, cvt_r};
287
288        if let Some(fd) = stdio.stdin.fd() {
289            cvt_r(|| libc::dup2(fd, libc::STDIN_FILENO))?;
290        }
291        if let Some(fd) = stdio.stdout.fd() {
292            cvt_r(|| libc::dup2(fd, libc::STDOUT_FILENO))?;
293        }
294        if let Some(fd) = stdio.stderr.fd() {
295            cvt_r(|| libc::dup2(fd, libc::STDERR_FILENO))?;
296        }
297
298        #[cfg(not(target_os = "l4re"))]
299        {
300            if let Some(_g) = self.get_groups() {
301                //FIXME: Redox kernel does not support setgroups yet
302                #[cfg(not(target_os = "redox"))]
303                cvt(libc::setgroups(_g.len().try_into().unwrap(), _g.as_ptr()))?;
304            }
305            if let Some(u) = self.get_gid() {
306                cvt(libc::setgid(u as gid_t))?;
307            }
308            if let Some(u) = self.get_uid() {
309                // When dropping privileges from root, the `setgroups` call
310                // will remove any extraneous groups. We only drop groups
311                // if we have CAP_SETGID and we weren't given an explicit
312                // set of groups. If we don't call this, then even though our
313                // uid has dropped, we may still have groups that enable us to
314                // do super-user things.
315                //FIXME: Redox kernel does not support setgroups yet
316                #[cfg(not(target_os = "redox"))]
317                if self.get_groups().is_none() {
318                    let res = cvt(libc::setgroups(0, crate::ptr::null()));
319                    if let Err(e) = res {
320                        // Here we ignore the case of not having CAP_SETGID.
321                        // An alternative would be to require CAP_SETGID (in
322                        // addition to CAP_SETUID) for setting the UID.
323                        if e.raw_os_error() != Some(libc::EPERM) {
324                            return Err(e.into());
325                        }
326                    }
327                }
328                cvt(libc::setuid(u as uid_t))?;
329            }
330        }
331        if let Some(cwd) = self.get_cwd() {
332            cvt(libc::chdir(cwd.as_ptr()))?;
333        }
334
335        if let Some(pgroup) = self.get_pgroup() {
336            cvt(libc::setpgid(0, pgroup))?;
337        }
338
339        // emscripten has no signal support.
340        #[cfg(not(target_os = "emscripten"))]
341        {
342            // Inherit the signal mask from the parent rather than resetting it (i.e. do not call
343            // pthread_sigmask).
344
345            // If -Zon-broken-pipe is used, don't reset SIGPIPE to SIG_DFL.
346            // If -Zon-broken-pipe is not used, reset SIGPIPE to SIG_DFL for backward compatibility.
347            //
348            // -Zon-broken-pipe is an opportunity to change the default here.
349            if !crate::sys::pal::on_broken_pipe_flag_used() {
350                #[cfg(target_os = "android")] // see issue #88585
351                {
352                    let mut action: libc::sigaction = mem::zeroed();
353                    action.sa_sigaction = libc::SIG_DFL;
354                    cvt(libc::sigaction(libc::SIGPIPE, &action, crate::ptr::null_mut()))?;
355                }
356                #[cfg(not(target_os = "android"))]
357                {
358                    let ret = sys::signal(libc::SIGPIPE, libc::SIG_DFL);
359                    if ret == libc::SIG_ERR {
360                        return Err(io::Error::last_os_error());
361                    }
362                }
363                #[cfg(target_os = "hurd")]
364                {
365                    let ret = sys::signal(libc::SIGLOST, libc::SIG_DFL);
366                    if ret == libc::SIG_ERR {
367                        return Err(io::Error::last_os_error());
368                    }
369                }
370            }
371        }
372
373        for callback in self.get_closures().iter_mut() {
374            callback()?;
375        }
376
377        // Although we're performing an exec here we may also return with an
378        // error from this function (without actually exec'ing) in which case we
379        // want to be sure to restore the global environment back to what it
380        // once was, ensuring that our temporary override, when free'd, doesn't
381        // corrupt our process's environment.
382        let mut _reset = None;
383        if let Some(envp) = maybe_envp {
384            struct Reset(*const *const libc::c_char);
385
386            impl Drop for Reset {
387                fn drop(&mut self) {
388                    unsafe {
389                        *sys::os::environ() = self.0;
390                    }
391                }
392            }
393
394            _reset = Some(Reset(*sys::os::environ()));
395            *sys::os::environ() = envp.as_ptr();
396        }
397
398        libc::execvp(self.get_program_cstr().as_ptr(), self.get_argv().as_ptr());
399        Err(io::Error::last_os_error())
400    }
401
402    #[cfg(any(target_os = "tvos", target_os = "watchos"))]
403    unsafe fn do_exec(
404        &mut self,
405        _stdio: ChildPipes,
406        _maybe_envp: Option<&CStringArray>,
407    ) -> Result<!, io::Error> {
408        return Err(Self::ERR_APPLE_TV_WATCH_NO_FORK_EXEC);
409    }
410
411    #[cfg(not(any(
412        target_os = "freebsd",
413        all(target_os = "linux", target_env = "gnu"),
414        all(target_os = "linux", target_env = "musl"),
415        target_os = "nto",
416        target_vendor = "apple",
417    )))]
418    fn posix_spawn(
419        &mut self,
420        _: &ChildPipes,
421        _: Option<&CStringArray>,
422    ) -> io::Result<Option<Process>> {
423        Ok(None)
424    }
425
426    // Only support platforms for which posix_spawn() can return ENOENT
427    // directly.
428    #[cfg(any(
429        target_os = "freebsd",
430        all(target_os = "linux", target_env = "gnu"),
431        all(target_os = "linux", target_env = "musl"),
432        target_os = "nto",
433        target_vendor = "apple",
434    ))]
435    fn posix_spawn(
436        &mut self,
437        stdio: &ChildPipes,
438        envp: Option<&CStringArray>,
439    ) -> io::Result<Option<Process>> {
440        #[cfg(target_os = "linux")]
441        use core::sync::atomic::{AtomicU8, Ordering};
442
443        use crate::mem::MaybeUninit;
444        use crate::sys::{self, cvt_nz, on_broken_pipe_flag_used};
445
446        if self.get_gid().is_some()
447            || self.get_uid().is_some()
448            || (self.env_saw_path() && !self.program_is_path())
449            || !self.get_closures().is_empty()
450            || self.get_groups().is_some()
451        {
452            return Ok(None);
453        }
454
455        cfg_if::cfg_if! {
456            if #[cfg(target_os = "linux")] {
457                use crate::sys::weak::weak;
458
459                weak! {
460                    fn pidfd_spawnp(
461                        *mut libc::c_int,
462                        *const libc::c_char,
463                        *const libc::posix_spawn_file_actions_t,
464                        *const libc::posix_spawnattr_t,
465                        *const *mut libc::c_char,
466                        *const *mut libc::c_char
467                    ) -> libc::c_int
468                }
469
470                weak! { fn pidfd_getpid(libc::c_int) -> libc::c_int }
471
472                static PIDFD_SUPPORTED: AtomicU8 = AtomicU8::new(0);
473                const UNKNOWN: u8 = 0;
474                const SPAWN: u8 = 1;
475                // Obtaining a pidfd via the fork+exec path might work
476                const FORK_EXEC: u8 = 2;
477                // Neither pidfd_spawn nor fork/exec will get us a pidfd.
478                // Instead we'll just posix_spawn if the other preconditions are met.
479                const NO: u8 = 3;
480
481                if self.get_create_pidfd() {
482                    let mut support = PIDFD_SUPPORTED.load(Ordering::Relaxed);
483                    if support == FORK_EXEC {
484                        return Ok(None);
485                    }
486                    if support == UNKNOWN {
487                        support = NO;
488                        let our_pid = crate::process::id();
489                        let pidfd = cvt(unsafe { libc::syscall(libc::SYS_pidfd_open, our_pid, 0) } as c_int);
490                        match pidfd {
491                            Ok(pidfd) => {
492                                support = FORK_EXEC;
493                                if let Some(Ok(pid)) = pidfd_getpid.get().map(|f| cvt(unsafe { f(pidfd) } as i32)) {
494                                    if pidfd_spawnp.get().is_some() && pid as u32 == our_pid {
495                                        support = SPAWN
496                                    }
497                                }
498                                unsafe { libc::close(pidfd) };
499                            }
500                            Err(e) if e.raw_os_error() == Some(libc::EMFILE) => {
501                                // We're temporarily(?) out of file descriptors.  In this case obtaining a pidfd would also fail
502                                // Don't update the support flag so we can probe again later.
503                                return Err(e)
504                            }
505                            _ => {}
506                        }
507                        PIDFD_SUPPORTED.store(support, Ordering::Relaxed);
508                        if support == FORK_EXEC {
509                            return Ok(None);
510                        }
511                    }
512                    core::assert_matches::debug_assert_matches!(support, SPAWN | NO);
513                }
514            } else {
515                if self.get_create_pidfd() {
516                    unreachable!("only implemented on linux")
517                }
518            }
519        }
520
521        // Only glibc 2.24+ posix_spawn() supports returning ENOENT directly.
522        #[cfg(all(target_os = "linux", target_env = "gnu"))]
523        {
524            if let Some(version) = sys::os::glibc_version() {
525                if version < (2, 24) {
526                    return Ok(None);
527                }
528            } else {
529                return Ok(None);
530            }
531        }
532
533        // On QNX Neutrino, posix_spawnp can fail with EBADF in case "another thread might have opened
534        // or closed a file descriptor while the posix_spawn() was occurring".
535        // Documentation says "... or try calling posix_spawn() again". This is what we do here.
536        // See also http://www.qnx.com/developers/docs/7.1/#com.qnx.doc.neutrino.lib_ref/topic/p/posix_spawn.html
537        #[cfg(target_os = "nto")]
538        unsafe fn retrying_libc_posix_spawnp(
539            pid: *mut pid_t,
540            file: *const c_char,
541            file_actions: *const posix_spawn_file_actions_t,
542            attrp: *const posix_spawnattr_t,
543            argv: *const *mut c_char,
544            envp: *const *mut c_char,
545        ) -> io::Result<i32> {
546            let mut delay = MIN_FORKSPAWN_SLEEP;
547            loop {
548                match libc::posix_spawnp(pid, file, file_actions, attrp, argv, envp) {
549                    libc::EBADF => {
550                        if delay < get_clock_resolution() {
551                            // We cannot sleep this short (it would be longer).
552                            // Yield instead.
553                            thread::yield_now();
554                        } else if delay < MAX_FORKSPAWN_SLEEP {
555                            thread::sleep(delay);
556                        } else {
557                            return Err(io::const_error!(
558                                ErrorKind::WouldBlock,
559                                "posix_spawnp returned EBADF too often",
560                            ));
561                        }
562                        delay *= 2;
563                        continue;
564                    }
565                    r => {
566                        return Ok(r);
567                    }
568                }
569            }
570        }
571
572        type PosixSpawnAddChdirFn = unsafe extern "C" fn(
573            *mut libc::posix_spawn_file_actions_t,
574            *const libc::c_char,
575        ) -> libc::c_int;
576
577        /// Get the function pointer for adding a chdir action to a
578        /// `posix_spawn_file_actions_t`, if available, assuming a dynamic libc.
579        ///
580        /// Some platforms can set a new working directory for a spawned process in the
581        /// `posix_spawn` path. This function looks up the function pointer for adding
582        /// such an action to a `posix_spawn_file_actions_t` struct.
583        #[cfg(not(all(target_os = "linux", target_env = "musl")))]
584        fn get_posix_spawn_addchdir() -> Option<PosixSpawnAddChdirFn> {
585            use crate::sys::weak::weak;
586
587            weak! {
588                fn posix_spawn_file_actions_addchdir_np(
589                    *mut libc::posix_spawn_file_actions_t,
590                    *const libc::c_char
591                ) -> libc::c_int
592            }
593
594            posix_spawn_file_actions_addchdir_np.get()
595        }
596
597        /// Get the function pointer for adding a chdir action to a
598        /// `posix_spawn_file_actions_t`, if available, on platforms where the function
599        /// is known to exist.
600        ///
601        /// Weak symbol lookup doesn't work with statically linked libcs, so in cases
602        /// where static linking is possible we need to either check for the presence
603        /// of the symbol at compile time or know about it upfront.
604        #[cfg(all(target_os = "linux", target_env = "musl"))]
605        fn get_posix_spawn_addchdir() -> Option<PosixSpawnAddChdirFn> {
606            // Our minimum required musl supports this function, so we can just use it.
607            Some(libc::posix_spawn_file_actions_addchdir_np)
608        }
609
610        let addchdir = match self.get_cwd() {
611            Some(cwd) => {
612                if cfg!(target_vendor = "apple") {
613                    // There is a bug in macOS where a relative executable
614                    // path like "../myprogram" will cause `posix_spawn` to
615                    // successfully launch the program, but erroneously return
616                    // ENOENT when used with posix_spawn_file_actions_addchdir_np
617                    // which was introduced in macOS 10.15.
618                    if self.get_program_kind() == ProgramKind::Relative {
619                        return Ok(None);
620                    }
621                }
622                // Check for the availability of the posix_spawn addchdir
623                // function now. If it isn't available, bail and use the
624                // fork/exec path.
625                match get_posix_spawn_addchdir() {
626                    Some(f) => Some((f, cwd)),
627                    None => return Ok(None),
628                }
629            }
630            None => None,
631        };
632
633        let pgroup = self.get_pgroup();
634
635        struct PosixSpawnFileActions<'a>(&'a mut MaybeUninit<libc::posix_spawn_file_actions_t>);
636
637        impl Drop for PosixSpawnFileActions<'_> {
638            fn drop(&mut self) {
639                unsafe {
640                    libc::posix_spawn_file_actions_destroy(self.0.as_mut_ptr());
641                }
642            }
643        }
644
645        struct PosixSpawnattr<'a>(&'a mut MaybeUninit<libc::posix_spawnattr_t>);
646
647        impl Drop for PosixSpawnattr<'_> {
648            fn drop(&mut self) {
649                unsafe {
650                    libc::posix_spawnattr_destroy(self.0.as_mut_ptr());
651                }
652            }
653        }
654
655        unsafe {
656            let mut attrs = MaybeUninit::uninit();
657            cvt_nz(libc::posix_spawnattr_init(attrs.as_mut_ptr()))?;
658            let attrs = PosixSpawnattr(&mut attrs);
659
660            let mut flags = 0;
661
662            let mut file_actions = MaybeUninit::uninit();
663            cvt_nz(libc::posix_spawn_file_actions_init(file_actions.as_mut_ptr()))?;
664            let file_actions = PosixSpawnFileActions(&mut file_actions);
665
666            if let Some(fd) = stdio.stdin.fd() {
667                cvt_nz(libc::posix_spawn_file_actions_adddup2(
668                    file_actions.0.as_mut_ptr(),
669                    fd,
670                    libc::STDIN_FILENO,
671                ))?;
672            }
673            if let Some(fd) = stdio.stdout.fd() {
674                cvt_nz(libc::posix_spawn_file_actions_adddup2(
675                    file_actions.0.as_mut_ptr(),
676                    fd,
677                    libc::STDOUT_FILENO,
678                ))?;
679            }
680            if let Some(fd) = stdio.stderr.fd() {
681                cvt_nz(libc::posix_spawn_file_actions_adddup2(
682                    file_actions.0.as_mut_ptr(),
683                    fd,
684                    libc::STDERR_FILENO,
685                ))?;
686            }
687            if let Some((f, cwd)) = addchdir {
688                cvt_nz(f(file_actions.0.as_mut_ptr(), cwd.as_ptr()))?;
689            }
690
691            if let Some(pgroup) = pgroup {
692                flags |= libc::POSIX_SPAWN_SETPGROUP;
693                cvt_nz(libc::posix_spawnattr_setpgroup(attrs.0.as_mut_ptr(), pgroup))?;
694            }
695
696            // Inherit the signal mask from this process rather than resetting it (i.e. do not call
697            // posix_spawnattr_setsigmask).
698
699            // If -Zon-broken-pipe is used, don't reset SIGPIPE to SIG_DFL.
700            // If -Zon-broken-pipe is not used, reset SIGPIPE to SIG_DFL for backward compatibility.
701            //
702            // -Zon-broken-pipe is an opportunity to change the default here.
703            if !on_broken_pipe_flag_used() {
704                let mut default_set = MaybeUninit::<libc::sigset_t>::uninit();
705                cvt(sigemptyset(default_set.as_mut_ptr()))?;
706                cvt(sigaddset(default_set.as_mut_ptr(), libc::SIGPIPE))?;
707                #[cfg(target_os = "hurd")]
708                {
709                    cvt(sigaddset(default_set.as_mut_ptr(), libc::SIGLOST))?;
710                }
711                cvt_nz(libc::posix_spawnattr_setsigdefault(
712                    attrs.0.as_mut_ptr(),
713                    default_set.as_ptr(),
714                ))?;
715                flags |= libc::POSIX_SPAWN_SETSIGDEF;
716            }
717
718            cvt_nz(libc::posix_spawnattr_setflags(attrs.0.as_mut_ptr(), flags as _))?;
719
720            // Make sure we synchronize access to the global `environ` resource
721            let _env_lock = sys::os::env_read_lock();
722            let envp = envp.map(|c| c.as_ptr()).unwrap_or_else(|| *sys::os::environ() as *const _);
723
724            #[cfg(not(target_os = "nto"))]
725            let spawn_fn = libc::posix_spawnp;
726            #[cfg(target_os = "nto")]
727            let spawn_fn = retrying_libc_posix_spawnp;
728
729            #[cfg(target_os = "linux")]
730            if self.get_create_pidfd() && PIDFD_SUPPORTED.load(Ordering::Relaxed) == SPAWN {
731                let mut pidfd: libc::c_int = -1;
732                let spawn_res = pidfd_spawnp.get().unwrap()(
733                    &mut pidfd,
734                    self.get_program_cstr().as_ptr(),
735                    file_actions.0.as_ptr(),
736                    attrs.0.as_ptr(),
737                    self.get_argv().as_ptr() as *const _,
738                    envp as *const _,
739                );
740
741                let spawn_res = cvt_nz(spawn_res);
742                if let Err(ref e) = spawn_res
743                    && e.raw_os_error() == Some(libc::ENOSYS)
744                {
745                    PIDFD_SUPPORTED.store(FORK_EXEC, Ordering::Relaxed);
746                    return Ok(None);
747                }
748                spawn_res?;
749
750                let pid = match cvt(pidfd_getpid.get().unwrap()(pidfd)) {
751                    Ok(pid) => pid,
752                    Err(e) => {
753                        // The child has been spawned and we are holding its pidfd.
754                        // But we cannot obtain its pid even though pidfd_getpid support was verified earlier.
755                        // This might happen if libc can't open procfs because the file descriptor limit has been reached.
756                        libc::close(pidfd);
757                        return Err(Error::new(
758                            e.kind(),
759                            "pidfd_spawnp succeeded but the child's PID could not be obtained",
760                        ));
761                    }
762                };
763
764                return Ok(Some(Process::new(pid, pidfd)));
765            }
766
767            // Safety: -1 indicates we don't have a pidfd.
768            let mut p = Process::new(0, -1);
769
770            let spawn_res = spawn_fn(
771                &mut p.pid,
772                self.get_program_cstr().as_ptr(),
773                file_actions.0.as_ptr(),
774                attrs.0.as_ptr(),
775                self.get_argv().as_ptr() as *const _,
776                envp as *const _,
777            );
778
779            #[cfg(target_os = "nto")]
780            let spawn_res = spawn_res?;
781
782            cvt_nz(spawn_res)?;
783            Ok(Some(p))
784        }
785    }
786
787    #[cfg(target_os = "linux")]
788    fn send_pidfd(&self, sock: &crate::sys::net::Socket) {
789        use libc::{CMSG_DATA, CMSG_FIRSTHDR, CMSG_LEN, CMSG_SPACE, SCM_RIGHTS, SOL_SOCKET};
790
791        use crate::io::IoSlice;
792        use crate::os::fd::RawFd;
793        use crate::sys::cvt_r;
794
795        unsafe {
796            let child_pid = libc::getpid();
797            // pidfd_open sets CLOEXEC by default
798            let pidfd = libc::syscall(libc::SYS_pidfd_open, child_pid, 0);
799
800            let fds: [c_int; 1] = [pidfd as RawFd];
801
802            const SCM_MSG_LEN: usize = mem::size_of::<[c_int; 1]>();
803
804            #[repr(C)]
805            union Cmsg {
806                buf: [u8; unsafe { CMSG_SPACE(SCM_MSG_LEN as u32) as usize }],
807                _align: libc::cmsghdr,
808            }
809
810            let mut cmsg: Cmsg = mem::zeroed();
811
812            // 0-length message to send through the socket so we can pass along the fd
813            let mut iov = [IoSlice::new(b"")];
814            let mut msg: libc::msghdr = mem::zeroed();
815
816            msg.msg_iov = (&raw mut iov) as *mut _;
817            msg.msg_iovlen = 1;
818
819            // only attach cmsg if we successfully acquired the pidfd
820            if pidfd >= 0 {
821                msg.msg_controllen = mem::size_of_val(&cmsg.buf) as _;
822                msg.msg_control = (&raw mut cmsg.buf) as *mut _;
823
824                let hdr = CMSG_FIRSTHDR((&raw mut msg) as *mut _);
825                (*hdr).cmsg_level = SOL_SOCKET;
826                (*hdr).cmsg_type = SCM_RIGHTS;
827                (*hdr).cmsg_len = CMSG_LEN(SCM_MSG_LEN as _) as _;
828                let data = CMSG_DATA(hdr);
829                crate::ptr::copy_nonoverlapping(
830                    fds.as_ptr().cast::<u8>(),
831                    data as *mut _,
832                    SCM_MSG_LEN,
833                );
834            }
835
836            // we send the 0-length message even if we failed to acquire the pidfd
837            // so we get a consistent SEQPACKET order
838            match cvt_r(|| libc::sendmsg(sock.as_raw(), &msg, 0)) {
839                Ok(0) => {}
840                other => rtabort!("failed to communicate with parent process. {:?}", other),
841            }
842        }
843    }
844
845    #[cfg(target_os = "linux")]
846    fn recv_pidfd(&self, sock: &crate::sys::net::Socket) -> pid_t {
847        use libc::{CMSG_DATA, CMSG_FIRSTHDR, CMSG_LEN, CMSG_SPACE, SCM_RIGHTS, SOL_SOCKET};
848
849        use crate::io::IoSliceMut;
850        use crate::sys::cvt_r;
851
852        unsafe {
853            const SCM_MSG_LEN: usize = mem::size_of::<[c_int; 1]>();
854
855            #[repr(C)]
856            union Cmsg {
857                _buf: [u8; unsafe { CMSG_SPACE(SCM_MSG_LEN as u32) as usize }],
858                _align: libc::cmsghdr,
859            }
860            let mut cmsg: Cmsg = mem::zeroed();
861            // 0-length read to get the fd
862            let mut iov = [IoSliceMut::new(&mut [])];
863
864            let mut msg: libc::msghdr = mem::zeroed();
865
866            msg.msg_iov = (&raw mut iov) as *mut _;
867            msg.msg_iovlen = 1;
868            msg.msg_controllen = mem::size_of::<Cmsg>() as _;
869            msg.msg_control = (&raw mut cmsg) as *mut _;
870
871            match cvt_r(|| libc::recvmsg(sock.as_raw(), &mut msg, libc::MSG_CMSG_CLOEXEC)) {
872                Err(_) => return -1,
873                Ok(_) => {}
874            }
875
876            let hdr = CMSG_FIRSTHDR((&raw mut msg) as *mut _);
877            if hdr.is_null()
878                || (*hdr).cmsg_level != SOL_SOCKET
879                || (*hdr).cmsg_type != SCM_RIGHTS
880                || (*hdr).cmsg_len != CMSG_LEN(SCM_MSG_LEN as _) as _
881            {
882                return -1;
883            }
884            let data = CMSG_DATA(hdr);
885
886            let mut fds = [-1 as c_int];
887
888            crate::ptr::copy_nonoverlapping(
889                data as *const _,
890                fds.as_mut_ptr().cast::<u8>(),
891                SCM_MSG_LEN,
892            );
893
894            fds[0]
895        }
896    }
897}
898
899////////////////////////////////////////////////////////////////////////////////
900// Processes
901////////////////////////////////////////////////////////////////////////////////
902
903/// The unique ID of the process (this should never be negative).
904pub struct Process {
905    pid: pid_t,
906    status: Option<ExitStatus>,
907    // On Linux, stores the pidfd created for this child.
908    // This is None if the user did not request pidfd creation,
909    // or if the pidfd could not be created for some reason
910    // (e.g. the `pidfd_open` syscall was not available).
911    #[cfg(target_os = "linux")]
912    pidfd: Option<PidFd>,
913}
914
915impl Process {
916    #[cfg(target_os = "linux")]
917    /// # Safety
918    ///
919    /// `pidfd` must either be -1 (representing no file descriptor) or a valid, exclusively owned file
920    /// descriptor (See [I/O Safety]).
921    ///
922    /// [I/O Safety]: crate::io#io-safety
923    unsafe fn new(pid: pid_t, pidfd: pid_t) -> Self {
924        use crate::os::unix::io::FromRawFd;
925        use crate::sys_common::FromInner;
926        // Safety: If `pidfd` is nonnegative, we assume it's valid and otherwise unowned.
927        let pidfd = (pidfd >= 0).then(|| PidFd::from_inner(sys::fd::FileDesc::from_raw_fd(pidfd)));
928        Process { pid, status: None, pidfd }
929    }
930
931    #[cfg(not(target_os = "linux"))]
932    unsafe fn new(pid: pid_t, _pidfd: pid_t) -> Self {
933        Process { pid, status: None }
934    }
935
936    pub fn id(&self) -> u32 {
937        self.pid as u32
938    }
939
940    pub fn kill(&mut self) -> io::Result<()> {
941        // If we've already waited on this process then the pid can be recycled
942        // and used for another process, and we probably shouldn't be killing
943        // random processes, so return Ok because the process has exited already.
944        if self.status.is_some() {
945            return Ok(());
946        }
947        #[cfg(target_os = "linux")]
948        if let Some(pid_fd) = self.pidfd.as_ref() {
949            // pidfd_send_signal predates pidfd_open. so if we were able to get an fd then sending signals will work too
950            return pid_fd.kill();
951        }
952        cvt(unsafe { libc::kill(self.pid, libc::SIGKILL) }).map(drop)
953    }
954
955    pub fn wait(&mut self) -> io::Result<ExitStatus> {
956        use crate::sys::cvt_r;
957        if let Some(status) = self.status {
958            return Ok(status);
959        }
960        #[cfg(target_os = "linux")]
961        if let Some(pid_fd) = self.pidfd.as_ref() {
962            let status = pid_fd.wait()?;
963            self.status = Some(status);
964            return Ok(status);
965        }
966        let mut status = 0 as c_int;
967        cvt_r(|| unsafe { libc::waitpid(self.pid, &mut status, 0) })?;
968        self.status = Some(ExitStatus::new(status));
969        Ok(ExitStatus::new(status))
970    }
971
972    pub fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
973        if let Some(status) = self.status {
974            return Ok(Some(status));
975        }
976        #[cfg(target_os = "linux")]
977        if let Some(pid_fd) = self.pidfd.as_ref() {
978            let status = pid_fd.try_wait()?;
979            if let Some(status) = status {
980                self.status = Some(status)
981            }
982            return Ok(status);
983        }
984        let mut status = 0 as c_int;
985        let pid = cvt(unsafe { libc::waitpid(self.pid, &mut status, libc::WNOHANG) })?;
986        if pid == 0 {
987            Ok(None)
988        } else {
989            self.status = Some(ExitStatus::new(status));
990            Ok(Some(ExitStatus::new(status)))
991        }
992    }
993}
994
995/// Unix exit statuses
996//
997// This is not actually an "exit status" in Unix terminology.  Rather, it is a "wait status".
998// See the discussion in comments and doc comments for `std::process::ExitStatus`.
999#[derive(PartialEq, Eq, Clone, Copy, Default)]
1000pub struct ExitStatus(c_int);
1001
1002impl fmt::Debug for ExitStatus {
1003    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1004        f.debug_tuple("unix_wait_status").field(&self.0).finish()
1005    }
1006}
1007
1008impl ExitStatus {
1009    pub fn new(status: c_int) -> ExitStatus {
1010        ExitStatus(status)
1011    }
1012
1013    #[cfg(target_os = "linux")]
1014    pub fn from_waitid_siginfo(siginfo: libc::siginfo_t) -> ExitStatus {
1015        let status = unsafe { siginfo.si_status() };
1016
1017        match siginfo.si_code {
1018            libc::CLD_EXITED => ExitStatus((status & 0xff) << 8),
1019            libc::CLD_KILLED => ExitStatus(status),
1020            libc::CLD_DUMPED => ExitStatus(status | 0x80),
1021            libc::CLD_CONTINUED => ExitStatus(0xffff),
1022            libc::CLD_STOPPED | libc::CLD_TRAPPED => ExitStatus(((status & 0xff) << 8) | 0x7f),
1023            _ => unreachable!("waitid() should only return the above codes"),
1024        }
1025    }
1026
1027    fn exited(&self) -> bool {
1028        libc::WIFEXITED(self.0)
1029    }
1030
1031    pub fn exit_ok(&self) -> Result<(), ExitStatusError> {
1032        // This assumes that WIFEXITED(status) && WEXITSTATUS==0 corresponds to status==0. This is
1033        // true on all actual versions of Unix, is widely assumed, and is specified in SuS
1034        // https://pubs.opengroup.org/onlinepubs/9699919799/functions/wait.html. If it is not
1035        // true for a platform pretending to be Unix, the tests (our doctests, and also
1036        // process_unix/tests.rs) will spot it. `ExitStatusError::code` assumes this too.
1037        match NonZero::try_from(self.0) {
1038            /* was nonzero */ Ok(failure) => Err(ExitStatusError(failure)),
1039            /* was zero, couldn't convert */ Err(_) => Ok(()),
1040        }
1041    }
1042
1043    pub fn code(&self) -> Option<i32> {
1044        self.exited().then(|| libc::WEXITSTATUS(self.0))
1045    }
1046
1047    pub fn signal(&self) -> Option<i32> {
1048        libc::WIFSIGNALED(self.0).then(|| libc::WTERMSIG(self.0))
1049    }
1050
1051    pub fn core_dumped(&self) -> bool {
1052        libc::WIFSIGNALED(self.0) && libc::WCOREDUMP(self.0)
1053    }
1054
1055    pub fn stopped_signal(&self) -> Option<i32> {
1056        libc::WIFSTOPPED(self.0).then(|| libc::WSTOPSIG(self.0))
1057    }
1058
1059    pub fn continued(&self) -> bool {
1060        libc::WIFCONTINUED(self.0)
1061    }
1062
1063    pub fn into_raw(&self) -> c_int {
1064        self.0
1065    }
1066}
1067
1068/// Converts a raw `c_int` to a type-safe `ExitStatus` by wrapping it without copying.
1069impl From<c_int> for ExitStatus {
1070    fn from(a: c_int) -> ExitStatus {
1071        ExitStatus(a)
1072    }
1073}
1074
1075/// Converts a signal number to a readable, searchable name.
1076///
1077/// This string should be displayed right after the signal number.
1078/// If a signal is unrecognized, it returns the empty string, so that
1079/// you just get the number like "0". If it is recognized, you'll get
1080/// something like "9 (SIGKILL)".
1081fn signal_string(signal: i32) -> &'static str {
1082    match signal {
1083        libc::SIGHUP => " (SIGHUP)",
1084        libc::SIGINT => " (SIGINT)",
1085        libc::SIGQUIT => " (SIGQUIT)",
1086        libc::SIGILL => " (SIGILL)",
1087        libc::SIGTRAP => " (SIGTRAP)",
1088        libc::SIGABRT => " (SIGABRT)",
1089        #[cfg(not(target_os = "l4re"))]
1090        libc::SIGBUS => " (SIGBUS)",
1091        libc::SIGFPE => " (SIGFPE)",
1092        libc::SIGKILL => " (SIGKILL)",
1093        #[cfg(not(target_os = "l4re"))]
1094        libc::SIGUSR1 => " (SIGUSR1)",
1095        libc::SIGSEGV => " (SIGSEGV)",
1096        #[cfg(not(target_os = "l4re"))]
1097        libc::SIGUSR2 => " (SIGUSR2)",
1098        libc::SIGPIPE => " (SIGPIPE)",
1099        libc::SIGALRM => " (SIGALRM)",
1100        libc::SIGTERM => " (SIGTERM)",
1101        #[cfg(not(target_os = "l4re"))]
1102        libc::SIGCHLD => " (SIGCHLD)",
1103        #[cfg(not(target_os = "l4re"))]
1104        libc::SIGCONT => " (SIGCONT)",
1105        #[cfg(not(target_os = "l4re"))]
1106        libc::SIGSTOP => " (SIGSTOP)",
1107        #[cfg(not(target_os = "l4re"))]
1108        libc::SIGTSTP => " (SIGTSTP)",
1109        #[cfg(not(target_os = "l4re"))]
1110        libc::SIGTTIN => " (SIGTTIN)",
1111        #[cfg(not(target_os = "l4re"))]
1112        libc::SIGTTOU => " (SIGTTOU)",
1113        #[cfg(not(target_os = "l4re"))]
1114        libc::SIGURG => " (SIGURG)",
1115        #[cfg(not(target_os = "l4re"))]
1116        libc::SIGXCPU => " (SIGXCPU)",
1117        #[cfg(not(any(target_os = "l4re", target_os = "rtems")))]
1118        libc::SIGXFSZ => " (SIGXFSZ)",
1119        #[cfg(not(any(target_os = "l4re", target_os = "rtems")))]
1120        libc::SIGVTALRM => " (SIGVTALRM)",
1121        #[cfg(not(target_os = "l4re"))]
1122        libc::SIGPROF => " (SIGPROF)",
1123        #[cfg(not(any(target_os = "l4re", target_os = "rtems")))]
1124        libc::SIGWINCH => " (SIGWINCH)",
1125        #[cfg(not(any(target_os = "haiku", target_os = "l4re")))]
1126        libc::SIGIO => " (SIGIO)",
1127        #[cfg(target_os = "haiku")]
1128        libc::SIGPOLL => " (SIGPOLL)",
1129        #[cfg(not(target_os = "l4re"))]
1130        libc::SIGSYS => " (SIGSYS)",
1131        // For information on Linux signals, run `man 7 signal`
1132        #[cfg(all(
1133            target_os = "linux",
1134            any(
1135                target_arch = "x86_64",
1136                target_arch = "x86",
1137                target_arch = "arm",
1138                target_arch = "aarch64"
1139            )
1140        ))]
1141        libc::SIGSTKFLT => " (SIGSTKFLT)",
1142        #[cfg(any(target_os = "linux", target_os = "nto"))]
1143        libc::SIGPWR => " (SIGPWR)",
1144        #[cfg(any(
1145            target_os = "freebsd",
1146            target_os = "netbsd",
1147            target_os = "openbsd",
1148            target_os = "dragonfly",
1149            target_os = "nto",
1150            target_vendor = "apple",
1151        ))]
1152        libc::SIGEMT => " (SIGEMT)",
1153        #[cfg(any(
1154            target_os = "freebsd",
1155            target_os = "netbsd",
1156            target_os = "openbsd",
1157            target_os = "dragonfly",
1158            target_vendor = "apple",
1159        ))]
1160        libc::SIGINFO => " (SIGINFO)",
1161        #[cfg(target_os = "hurd")]
1162        libc::SIGLOST => " (SIGLOST)",
1163        #[cfg(target_os = "freebsd")]
1164        libc::SIGTHR => " (SIGTHR)",
1165        #[cfg(target_os = "freebsd")]
1166        libc::SIGLIBRT => " (SIGLIBRT)",
1167        _ => "",
1168    }
1169}
1170
1171impl fmt::Display for ExitStatus {
1172    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1173        if let Some(code) = self.code() {
1174            write!(f, "exit status: {code}")
1175        } else if let Some(signal) = self.signal() {
1176            let signal_string = signal_string(signal);
1177            if self.core_dumped() {
1178                write!(f, "signal: {signal}{signal_string} (core dumped)")
1179            } else {
1180                write!(f, "signal: {signal}{signal_string}")
1181            }
1182        } else if let Some(signal) = self.stopped_signal() {
1183            let signal_string = signal_string(signal);
1184            write!(f, "stopped (not terminated) by signal: {signal}{signal_string}")
1185        } else if self.continued() {
1186            write!(f, "continued (WIFCONTINUED)")
1187        } else {
1188            write!(f, "unrecognised wait status: {} {:#x}", self.0, self.0)
1189        }
1190    }
1191}
1192
1193#[derive(PartialEq, Eq, Clone, Copy)]
1194pub struct ExitStatusError(NonZero<c_int>);
1195
1196impl Into<ExitStatus> for ExitStatusError {
1197    fn into(self) -> ExitStatus {
1198        ExitStatus(self.0.into())
1199    }
1200}
1201
1202impl fmt::Debug for ExitStatusError {
1203    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1204        f.debug_tuple("unix_wait_status").field(&self.0).finish()
1205    }
1206}
1207
1208impl ExitStatusError {
1209    pub fn code(self) -> Option<NonZero<i32>> {
1210        ExitStatus(self.0.into()).code().map(|st| st.try_into().unwrap())
1211    }
1212}
1213
1214#[cfg(target_os = "linux")]
1215mod linux_child_ext {
1216
1217    use crate::os::linux::process as os;
1218    use crate::sys::pal::unix::ErrorKind;
1219    use crate::sys::pal::unix::linux::pidfd as imp;
1220    use crate::sys_common::FromInner;
1221    use crate::{io, mem};
1222
1223    #[unstable(feature = "linux_pidfd", issue = "82971")]
1224    impl crate::os::linux::process::ChildExt for crate::process::Child {
1225        fn pidfd(&self) -> io::Result<&os::PidFd> {
1226            self.handle
1227                .pidfd
1228                .as_ref()
1229                // SAFETY: The os type is a transparent wrapper, therefore we can transmute references
1230                .map(|fd| unsafe { mem::transmute::<&imp::PidFd, &os::PidFd>(fd) })
1231                .ok_or_else(|| io::Error::new(ErrorKind::Uncategorized, "No pidfd was created."))
1232        }
1233
1234        fn into_pidfd(mut self) -> Result<os::PidFd, Self> {
1235            self.handle
1236                .pidfd
1237                .take()
1238                .map(|fd| <os::PidFd as FromInner<imp::PidFd>>::from_inner(fd))
1239                .ok_or_else(|| self)
1240        }
1241    }
1242}
1243
1244#[cfg(test)]
1245#[path = "process_unix/tests.rs"]
1246mod tests;
1247
1248// See [`process_unsupported_wait_status::compare_with_linux`];
1249#[cfg(all(test, target_os = "linux"))]
1250#[path = "process_unsupported/wait_status.rs"]
1251mod process_unsupported_wait_status;