src/libstd/sys/unix/process/process_unix.rs - third_party/rust - Git at Google

 // Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.

 use io::{self, Error, ErrorKind};
 use libc::{self, c_int, gid_t, pid_t, uid_t};
 use ptr;

 use sys::cvt;
 use sys::process::process_common::*;

 ////////////////////////////////////////////////////////////////////////////////
 // Command
 ////////////////////////////////////////////////////////////////////////////////

 impl Command {
     pub fn spawn(&mut self, default: Stdio, needs_stdin: bool)
                  -> io::Result<(Process, StdioPipes)> {
         use sys;

         const CLOEXEC_MSG_FOOTER: &'static [u8] = b"NOEX";

         let envp = self.capture_env();

         if self.saw_nul() {
             return Err(io::Error::new(ErrorKind::InvalidInput,
                                       "nul byte found in provided data"));
         }

         let (ours, theirs) = self.setup_io(default, needs_stdin)?;
         let (input, output) = sys::pipe::anon_pipe()?;

         let pid = unsafe {
             match cvt(libc::fork())? {
                 0 => {
                     drop(input);
                     let err = self.do_exec(theirs, envp.as_ref());
                     let errno = err.raw_os_error().unwrap_or(libc::EINVAL) as u32;
                     let bytes = [
                         (errno >> 24) as u8,
                         (errno >> 16) as u8,
                         (errno >>  8) as u8,
                         (errno >>  0) as u8,
                         CLOEXEC_MSG_FOOTER[0], CLOEXEC_MSG_FOOTER[1],
                         CLOEXEC_MSG_FOOTER[2], CLOEXEC_MSG_FOOTER[3]
                     ];
                     // pipe I/O up to PIPE_BUF bytes should be atomic, and then
                     // we want to be sure we *don't* run at_exit destructors as
                     // we're being torn down regardless
                     assert!(output.write(&bytes).is_ok());
                     libc::_exit(1)
                 }
                 n => n,
             }
         };

         let mut p = Process { pid: pid, status: None };
         drop(output);
         let mut bytes = [0; 8];

         // loop to handle EINTR
         loop {
             match input.read(&mut bytes) {
                 Ok(0) => return Ok((p, ours)),
                 Ok(8) => {
                     assert!(combine(CLOEXEC_MSG_FOOTER) == combine(&bytes[4.. 8]),
                             "Validation on the CLOEXEC pipe failed: {:?}", bytes);
                     let errno = combine(&bytes[0.. 4]);
                     assert!(p.wait().is_ok(),
                             "wait() should either return Ok or panic");
                     return Err(Error::from_raw_os_error(errno))
                 }
                 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
                 Err(e) => {
                     assert!(p.wait().is_ok(),
                             "wait() should either return Ok or panic");
                     panic!("the CLOEXEC pipe failed: {:?}", e)
                 },
                 Ok(..) => { // pipe I/O up to PIPE_BUF bytes should be atomic
                     assert!(p.wait().is_ok(),
                             "wait() should either return Ok or panic");
                     panic!("short read on the CLOEXEC pipe")
                 }
             }
         }

         fn combine(arr: &[u8]) -> i32 {
             let a = arr[0] as u32;
             let b = arr[1] as u32;
             let c = arr[2] as u32;
             let d = arr[3] as u32;

             ((a << 24) | (b << 16) | (c << 8) | (d << 0)) as i32
         }
     }

     pub fn exec(&mut self, default: Stdio) -> io::Error {
         let envp = self.capture_env();

         if self.saw_nul() {
             return io::Error::new(ErrorKind::InvalidInput,
                                   "nul byte found in provided data")
         }

         match self.setup_io(default, true) {
             Ok((_, theirs)) => unsafe { self.do_exec(theirs, envp.as_ref()) },
             Err(e) => e,
         }
     }

     // And at this point we've reached a special time in the life of the
     // child. The child must now be considered hamstrung and unable to
     // do anything other than syscalls really. Consider the following
     // scenario:
     //
     //      1. Thread A of process 1 grabs the malloc() mutex
     //      2. Thread B of process 1 forks(), creating thread C
     //      3. Thread C of process 2 then attempts to malloc()
     //      4. The memory of process 2 is the same as the memory of
     //         process 1, so the mutex is locked.
     //
     // This situation looks a lot like deadlock, right? It turns out
     // that this is what pthread_atfork() takes care of, which is
     // presumably implemented across platforms. The first thing that
     // threads to *before* forking is to do things like grab the malloc
     // mutex, and then after the fork they unlock it.
     //
     // Despite this information, libnative's spawn has been witnessed to
     // deadlock on both macOS and FreeBSD. I'm not entirely sure why, but
     // all collected backtraces point at malloc/free traffic in the
     // child spawned process.
     //
     // For this reason, the block of code below should contain 0
     // invocations of either malloc of free (or their related friends).
     //
     // As an example of not having malloc/free traffic, we don't close
     // this file descriptor by dropping the FileDesc (which contains an
     // allocation). Instead we just close it manually. This will never
     // have the drop glue anyway because this code never returns (the
     // child will either exec() or invoke libc::exit)
     unsafe fn do_exec(
         &mut self,
         stdio: ChildPipes,
         maybe_envp: Option<&CStringArray>
     ) -> io::Error {
         use sys::{self, cvt_r};

         macro_rules! t {
             ($e:expr) => (match $e {
                 Ok(e) => e,
                 Err(e) => return e,
             })
         }

         if let Some(fd) = stdio.stdin.fd() {
             t!(cvt_r(|| libc::dup2(fd, libc::STDIN_FILENO)));
         }
         if let Some(fd) = stdio.stdout.fd() {
             t!(cvt_r(|| libc::dup2(fd, libc::STDOUT_FILENO)));
         }
         if let Some(fd) = stdio.stderr.fd() {
             t!(cvt_r(|| libc::dup2(fd, libc::STDERR_FILENO)));
         }

         if cfg!(not(any(target_os = "l4re"))) {
             if let Some(u) = self.get_gid() {
                 t!(cvt(libc::setgid(u as gid_t)));
             }
             if let Some(u) = self.get_uid() {
                 // When dropping privileges from root, the `setgroups` call
                 // will remove any extraneous groups. If we don't call this,
                 // then even though our uid has dropped, we may still have
                 // groups that enable us to do super-user things. This will
                 // fail if we aren't root, so don't bother checking the
                 // return value, this is just done as an optimistic
                 // privilege dropping function.
                 let _ = libc::setgroups(0, ptr::null());

                 t!(cvt(libc::setuid(u as uid_t)));
             }
         }
         if let Some(ref cwd) = *self.get_cwd() {
             t!(cvt(libc::chdir(cwd.as_ptr())));
         }
         if let Some(envp) = maybe_envp {
             *sys::os::environ() = envp.as_ptr();
         }

         // emscripten has no signal support.
         #[cfg(not(any(target_os = "emscripten")))]
         {
             use mem;
             // Reset signal handling so the child process starts in a
             // standardized state. libstd ignores SIGPIPE, and signal-handling
             // libraries often set a mask. Child processes inherit ignored
             // signals and the signal mask from their parent, but most
             // UNIX programs do not reset these things on their own, so we
             // need to clean things up now to avoid confusing the program
             // we're about to run.
             let mut set: libc::sigset_t = mem::uninitialized();
             if cfg!(target_os = "android") {
                 // Implementing sigemptyset allow us to support older Android
                 // versions. See the comment about Android and sig* functions in
                 // process_common.rs
                 libc::memset(&mut set as *mut _ as *mut _,
                              0,
                              mem::size_of::<libc::sigset_t>());
             } else {
                 t!(cvt(libc::sigemptyset(&mut set)));
             }
             t!(cvt(libc::pthread_sigmask(libc::SIG_SETMASK, &set,
                                          ptr::null_mut())));
             let ret = sys::signal(libc::SIGPIPE, libc::SIG_DFL);
             if ret == libc::SIG_ERR {
                 return io::Error::last_os_error()
             }
         }

         for callback in self.get_closures().iter_mut() {
             t!(callback());
         }

         libc::execvp(self.get_argv()[0], self.get_argv().as_ptr());
         io::Error::last_os_error()
     }
 }

 ////////////////////////////////////////////////////////////////////////////////
 // Processes
 ////////////////////////////////////////////////////////////////////////////////

 /// The unique id of the process (this should never be negative).
 pub struct Process {
     pid: pid_t,
     status: Option<ExitStatus>,
 }

 impl Process {
     pub fn id(&self) -> u32 {
         self.pid as u32
     }

     pub fn kill(&mut self) -> io::Result<()> {
         // If we've already waited on this process then the pid can be recycled
         // and used for another process, and we probably shouldn't be killing
         // random processes, so just return an error.
         if self.status.is_some() {
             Err(Error::new(ErrorKind::InvalidInput,
                            "invalid argument: can't kill an exited process"))
         } else {
             cvt(unsafe { libc::kill(self.pid, libc::SIGKILL) }).map(|_| ())
         }
     }

     pub fn wait(&mut self) -> io::Result<ExitStatus> {
         use sys::cvt_r;
         if let Some(status) = self.status {
             return Ok(status)
         }
         let mut status = 0 as c_int;
         cvt_r(|| unsafe { libc::waitpid(self.pid, &mut status, 0) })?;
         self.status = Some(ExitStatus::new(status));
         Ok(ExitStatus::new(status))
     }

     pub fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
         if let Some(status) = self.status {
             return Ok(Some(status))
         }
         let mut status = 0 as c_int;
         let pid = cvt(unsafe {
             libc::waitpid(self.pid, &mut status, libc::WNOHANG)
         })?;
         if pid == 0 {
             Ok(None)
         } else {
             self.status = Some(ExitStatus::new(status));
             Ok(Some(ExitStatus::new(status)))
         }
     }
 }
	// Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT
	// file at the top-level directory of this distribution and at
	// http://rust-lang.org/COPYRIGHT.
	//
	// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
	// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
	// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
	// option. This file may not be copied, modified, or distributed
	// except according to those terms.

	use io::{self, Error, ErrorKind};
	use libc::{self, c_int, gid_t, pid_t, uid_t};
	use ptr;

	use sys::cvt;
	use sys::process::process_common::*;

	////////////////////////////////////////////////////////////////////////////////
	// Command
	////////////////////////////////////////////////////////////////////////////////

	impl Command {
	pub fn spawn(&mut self, default: Stdio, needs_stdin: bool)
	-> io::Result<(Process, StdioPipes)> {
	use sys;

	const CLOEXEC_MSG_FOOTER: &'static [u8] = b"NOEX";

	let envp = self.capture_env();

	if self.saw_nul() {
	return Err(io::Error::new(ErrorKind::InvalidInput,
	"nul byte found in provided data"));
	}

	let (ours, theirs) = self.setup_io(default, needs_stdin)?;
	let (input, output) = sys::pipe::anon_pipe()?;

	let pid = unsafe {
	match cvt(libc::fork())? {
	0 => {
	drop(input);
	let err = self.do_exec(theirs, envp.as_ref());
	let errno = err.raw_os_error().unwrap_or(libc::EINVAL) as u32;
	let bytes = [
	(errno >> 24) as u8,
	(errno >> 16) as u8,
	(errno >> 8) as u8,
	(errno >> 0) as u8,
	CLOEXEC_MSG_FOOTER[0], CLOEXEC_MSG_FOOTER[1],
	CLOEXEC_MSG_FOOTER[2], CLOEXEC_MSG_FOOTER[3]
	];
	// pipe I/O up to PIPE_BUF bytes should be atomic, and then
	// we want to be sure we don't run at_exit destructors as
	// we're being torn down regardless
	assert!(output.write(&bytes).is_ok());
	libc::_exit(1)
	}
	n => n,
	}
	};

	let mut p = Process { pid: pid, status: None };
	drop(output);
	let mut bytes = [0; 8];

	// loop to handle EINTR
	loop {
	match input.read(&mut bytes) {
	Ok(0) => return Ok((p, ours)),
	Ok(8) => {
	assert!(combine(CLOEXEC_MSG_FOOTER) == combine(&bytes[4.. 8]),
	"Validation on the CLOEXEC pipe failed: {:?}", bytes);
	let errno = combine(&bytes[0.. 4]);
	assert!(p.wait().is_ok(),
	"wait() should either return Ok or panic");
	return Err(Error::from_raw_os_error(errno))
	}
	Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
	Err(e) => {
	assert!(p.wait().is_ok(),
	"wait() should either return Ok or panic");
	panic!("the CLOEXEC pipe failed: {:?}", e)
	},
	Ok(..) => { // pipe I/O up to PIPE_BUF bytes should be atomic
	assert!(p.wait().is_ok(),
	"wait() should either return Ok or panic");
	panic!("short read on the CLOEXEC pipe")
	}
	}
	}

	fn combine(arr: &[u8]) -> i32 {
	let a = arr[0] as u32;
	let b = arr[1] as u32;
	let c = arr[2] as u32;
	let d = arr[3] as u32;

	((a << 24) \| (b << 16) \| (c << 8) \| (d << 0)) as i32
	}
	}

	pub fn exec(&mut self, default: Stdio) -> io::Error {
	let envp = self.capture_env();

	if self.saw_nul() {
	return io::Error::new(ErrorKind::InvalidInput,
	"nul byte found in provided data")
	}

	match self.setup_io(default, true) {
	Ok((_, theirs)) => unsafe { self.do_exec(theirs, envp.as_ref()) },
	Err(e) => e,
	}
	}

	// And at this point we've reached a special time in the life of the
	// child. The child must now be considered hamstrung and unable to
	// do anything other than syscalls really. Consider the following
	// scenario:
	//
	// 1. Thread A of process 1 grabs the malloc() mutex
	// 2. Thread B of process 1 forks(), creating thread C
	// 3. Thread C of process 2 then attempts to malloc()
	// 4. The memory of process 2 is the same as the memory of
	// process 1, so the mutex is locked.
	//
	// This situation looks a lot like deadlock, right? It turns out
	// that this is what pthread_atfork() takes care of, which is
	// presumably implemented across platforms. The first thing that
	// threads to before forking is to do things like grab the malloc
	// mutex, and then after the fork they unlock it.
	//
	// Despite this information, libnative's spawn has been witnessed to
	// deadlock on both macOS and FreeBSD. I'm not entirely sure why, but
	// all collected backtraces point at malloc/free traffic in the
	// child spawned process.
	//
	// For this reason, the block of code below should contain 0
	// invocations of either malloc of free (or their related friends).
	//
	// As an example of not having malloc/free traffic, we don't close
	// this file descriptor by dropping the FileDesc (which contains an
	// allocation). Instead we just close it manually. This will never
	// have the drop glue anyway because this code never returns (the
	// child will either exec() or invoke libc::exit)
	unsafe fn do_exec(
	&mut self,
	stdio: ChildPipes,
	maybe_envp: Option<&CStringArray>
	) -> io::Error {
	use sys::{self, cvt_r};

	macro_rules! t {
	($e:expr) => (match $e {
	Ok(e) => e,
	Err(e) => return e,
	})
	}

	if let Some(fd) = stdio.stdin.fd() {
	t!(cvt_r(\|\| libc::dup2(fd, libc::STDIN_FILENO)));
	}
	if let Some(fd) = stdio.stdout.fd() {
	t!(cvt_r(\|\| libc::dup2(fd, libc::STDOUT_FILENO)));
	}
	if let Some(fd) = stdio.stderr.fd() {
	t!(cvt_r(\|\| libc::dup2(fd, libc::STDERR_FILENO)));
	}

	if cfg!(not(any(target_os = "l4re"))) {
	if let Some(u) = self.get_gid() {
	t!(cvt(libc::setgid(u as gid_t)));
	}
	if let Some(u) = self.get_uid() {
	// When dropping privileges from root, the `setgroups` call
	// will remove any extraneous groups. If we don't call this,
	// then even though our uid has dropped, we may still have
	// groups that enable us to do super-user things. This will
	// fail if we aren't root, so don't bother checking the
	// return value, this is just done as an optimistic
	// privilege dropping function.
	let _ = libc::setgroups(0, ptr::null());

	t!(cvt(libc::setuid(u as uid_t)));
	}
	}
	if let Some(ref cwd) = *self.get_cwd() {
	t!(cvt(libc::chdir(cwd.as_ptr())));
	}
	if let Some(envp) = maybe_envp {
	*sys::os::environ() = envp.as_ptr();
	}

	// emscripten has no signal support.
	#[cfg(not(any(target_os = "emscripten")))]
	{
	use mem;
	// Reset signal handling so the child process starts in a
	// standardized state. libstd ignores SIGPIPE, and signal-handling
	// libraries often set a mask. Child processes inherit ignored
	// signals and the signal mask from their parent, but most
	// UNIX programs do not reset these things on their own, so we
	// need to clean things up now to avoid confusing the program
	// we're about to run.
	let mut set: libc::sigset_t = mem::uninitialized();
	if cfg!(target_os = "android") {
	// Implementing sigemptyset allow us to support older Android
	// versions. See the comment about Android and sig* functions in
	// process_common.rs
	libc::memset(&mut set as mut _ as mut _,
	0,
	mem::size_of::<libc::sigset_t>());
	} else {
	t!(cvt(libc::sigemptyset(&mut set)));
	}
	t!(cvt(libc::pthread_sigmask(libc::SIG_SETMASK, &set,
	ptr::null_mut())));
	let ret = sys::signal(libc::SIGPIPE, libc::SIG_DFL);
	if ret == libc::SIG_ERR {
	return io::Error::last_os_error()
	}
	}

	for callback in self.get_closures().iter_mut() {
	t!(callback());
	}

	libc::execvp(self.get_argv()[0], self.get_argv().as_ptr());
	io::Error::last_os_error()
	}
	}

	////////////////////////////////////////////////////////////////////////////////
	// Processes
	////////////////////////////////////////////////////////////////////////////////

	/// The unique id of the process (this should never be negative).
	pub struct Process {
	pid: pid_t,
	status: Option<ExitStatus>,
	}

	impl Process {
	pub fn id(&self) -> u32 {
	self.pid as u32
	}

	pub fn kill(&mut self) -> io::Result<()> {
	// If we've already waited on this process then the pid can be recycled
	// and used for another process, and we probably shouldn't be killing
	// random processes, so just return an error.
	if self.status.is_some() {
	Err(Error::new(ErrorKind::InvalidInput,
	"invalid argument: can't kill an exited process"))
	} else {
	cvt(unsafe { libc::kill(self.pid, libc::SIGKILL) }).map(\|_\| ())
	}
	}

	pub fn wait(&mut self) -> io::Result<ExitStatus> {
	use sys::cvt_r;
	if let Some(status) = self.status {
	return Ok(status)
	}
	let mut status = 0 as c_int;
	cvt_r(\|\| unsafe { libc::waitpid(self.pid, &mut status, 0) })?;
	self.status = Some(ExitStatus::new(status));
	Ok(ExitStatus::new(status))
	}

	pub fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
	if let Some(status) = self.status {
	return Ok(Some(status))
	}
	let mut status = 0 as c_int;
	let pid = cvt(unsafe {
	libc::waitpid(self.pid, &mut status, libc::WNOHANG)
	})?;
	if pid == 0 {
	Ok(None)
	} else {
	self.status = Some(ExitStatus::new(status));
	Ok(Some(ExitStatus::new(status)))
	}
	}
	}