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

 // Copyright 2016 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 env::{split_paths};
 use ffi::OsStr;
 use os::unix::ffi::OsStrExt;
 use fmt;
 use io::{self, Error, ErrorKind};
 use path::{Path, PathBuf};
 use sys::fd::FileDesc;
 use sys::fs::{File, OpenOptions};
 use sys::pipe::{self, AnonPipe};
 use sys::{cvt, syscall};
 use sys_common::process::{CommandEnv, DefaultEnvKey};

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

 pub struct Command {
     // Currently we try hard to ensure that the call to `.exec()` doesn't
     // actually allocate any memory. While many platforms try to ensure that
     // memory allocation works after a fork in a multithreaded process, it's
     // been observed to be buggy and somewhat unreliable, so we do our best to
     // just not do it at all!
     //
     // Along those lines, the `argv` and `envp` raw pointers here are exactly
     // what's gonna get passed to `execvp`. The `argv` array starts with the
     // `program` and ends with a NULL, and the `envp` pointer, if present, is
     // also null-terminated.
     //
     // Right now we don't support removing arguments, so there's no much fancy
     // support there, but we support adding and removing environment variables,
     // so a side table is used to track where in the `envp` array each key is
     // located. Whenever we add a key we update it in place if it's already
     // present, and whenever we remove a key we update the locations of all
     // other keys.
     program: String,
     args: Vec<String>,
     env: CommandEnv<DefaultEnvKey>,

     cwd: Option<String>,
     uid: Option<u32>,
     gid: Option<u32>,
     saw_nul: bool,
     closures: Vec<Box<FnMut() -> io::Result<()> + Send + Sync>>,
     stdin: Option<Stdio>,
     stdout: Option<Stdio>,
     stderr: Option<Stdio>,
 }

 // passed back to std::process with the pipes connected to the child, if any
 // were requested
 pub struct StdioPipes {
     pub stdin: Option<AnonPipe>,
     pub stdout: Option<AnonPipe>,
     pub stderr: Option<AnonPipe>,
 }

 // passed to do_exec() with configuration of what the child stdio should look
 // like
 struct ChildPipes {
     stdin: ChildStdio,
     stdout: ChildStdio,
     stderr: ChildStdio,
 }

 enum ChildStdio {
     Inherit,
     Explicit(usize),
     Owned(FileDesc),
 }

 pub enum Stdio {
     Inherit,
     Null,
     MakePipe,
     Fd(FileDesc),
 }

 impl Command {
     pub fn new(program: &OsStr) -> Command {
         Command {
             program: program.to_str().unwrap().to_owned(),
             args: Vec::new(),
             env: Default::default(),
             cwd: None,
             uid: None,
             gid: None,
             saw_nul: false,
             closures: Vec::new(),
             stdin: None,
             stdout: None,
             stderr: None,
         }
     }

     pub fn arg(&mut self, arg: &OsStr) {
         self.args.push(arg.to_str().unwrap().to_owned());
     }

     pub fn env_mut(&mut self) -> &mut CommandEnv<DefaultEnvKey> {
         &mut self.env
     }

     pub fn cwd(&mut self, dir: &OsStr) {
         self.cwd = Some(dir.to_str().unwrap().to_owned());
     }
     pub fn uid(&mut self, id: u32) {
         self.uid = Some(id);
     }
     pub fn gid(&mut self, id: u32) {
         self.gid = Some(id);
     }

     pub fn before_exec(&mut self,
                        f: Box<FnMut() -> io::Result<()> + Send + Sync>) {
         self.closures.push(f);
     }

     pub fn stdin(&mut self, stdin: Stdio) {
         self.stdin = Some(stdin);
     }
     pub fn stdout(&mut self, stdout: Stdio) {
         self.stdout = Some(stdout);
     }
     pub fn stderr(&mut self, stderr: Stdio) {
         self.stderr = Some(stderr);
     }

     pub fn spawn(&mut self, default: Stdio, needs_stdin: bool)
                  -> io::Result<(Process, StdioPipes)> {
          const CLOEXEC_MSG_FOOTER: &'static [u8] = b"NOEX";

          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) = pipe::anon_pipe()?;

          let pid = unsafe {
              match cvt(syscall::clone(0))? {
                  0 => {
                      drop(input);
                      let err = self.do_exec(theirs);
                      let errno = err.raw_os_error().unwrap_or(syscall::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());
                      let _ = syscall::exit(1);
                      panic!("failed to exit");
                  }
                  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 {
         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) },
             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 syscall::exit)
     unsafe fn do_exec(&mut self, stdio: ChildPipes) -> io::Error {
         macro_rules! t {
             ($e:expr) => (match $e {
                 Ok(e) => e,
                 Err(e) => return e,
             })
         }

         if let Some(fd) = stdio.stderr.fd() {
             t!(cvt(syscall::dup2(fd, 2, &[])));
             let mut flags = t!(cvt(syscall::fcntl(2, syscall::F_GETFD, 0)));
             flags &= ! syscall::O_CLOEXEC;
             t!(cvt(syscall::fcntl(2, syscall::F_SETFD, flags)));
         }
         if let Some(fd) = stdio.stdout.fd() {
             t!(cvt(syscall::dup2(fd, 1, &[])));
             let mut flags = t!(cvt(syscall::fcntl(1, syscall::F_GETFD, 0)));
             flags &= ! syscall::O_CLOEXEC;
             t!(cvt(syscall::fcntl(1, syscall::F_SETFD, flags)));
         }
         if let Some(fd) = stdio.stdin.fd() {
             t!(cvt(syscall::dup2(fd, 0, &[])));
             let mut flags = t!(cvt(syscall::fcntl(0, syscall::F_GETFD, 0)));
             flags &= ! syscall::O_CLOEXEC;
             t!(cvt(syscall::fcntl(0, syscall::F_SETFD, flags)));
         }

         if let Some(g) = self.gid {
             t!(cvt(syscall::setregid(g as usize, g as usize)));
         }
         if let Some(u) = self.uid {
             t!(cvt(syscall::setreuid(u as usize, u as usize)));
         }
         if let Some(ref cwd) = self.cwd {
             t!(cvt(syscall::chdir(cwd)));
         }

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

         let mut args: Vec<[usize; 2]> = Vec::new();
         args.push([self.program.as_ptr() as usize, self.program.len()]);
         for arg in self.args.iter() {
             args.push([arg.as_ptr() as usize, arg.len()]);
         }

         self.env.apply();

         let program = if self.program.contains(':') || self.program.contains('/') {
             Some(PathBuf::from(&self.program))
         } else if let Ok(path_env) = ::env::var("PATH") {
             let mut program = None;
             for mut path in split_paths(&path_env) {
                 path.push(&self.program);
                 if path.exists() {
                     program = Some(path);
                     break;
                 }
             }
             program
         } else {
             None
         };

         if let Some(program) = program {
             if let Err(err) = syscall::execve(program.as_os_str().as_bytes(), &args) {
                 io::Error::from_raw_os_error(err.errno as i32)
             } else {
                 panic!("return from exec without err");
             }
         } else {
             io::Error::from_raw_os_error(syscall::ENOENT)
         }
     }


     fn setup_io(&self, default: Stdio, needs_stdin: bool)
                 -> io::Result<(StdioPipes, ChildPipes)> {
         let null = Stdio::Null;
         let default_stdin = if needs_stdin {&default} else {&null};
         let stdin = self.stdin.as_ref().unwrap_or(default_stdin);
         let stdout = self.stdout.as_ref().unwrap_or(&default);
         let stderr = self.stderr.as_ref().unwrap_or(&default);
         let (their_stdin, our_stdin) = stdin.to_child_stdio(true)?;
         let (their_stdout, our_stdout) = stdout.to_child_stdio(false)?;
         let (their_stderr, our_stderr) = stderr.to_child_stdio(false)?;
         let ours = StdioPipes {
             stdin: our_stdin,
             stdout: our_stdout,
             stderr: our_stderr,
         };
         let theirs = ChildPipes {
             stdin: their_stdin,
             stdout: their_stdout,
             stderr: their_stderr,
         };
         Ok((ours, theirs))
     }
 }

 impl Stdio {
     fn to_child_stdio(&self, readable: bool)
                       -> io::Result<(ChildStdio, Option<AnonPipe>)> {
         match *self {
             Stdio::Inherit => Ok((ChildStdio::Inherit, None)),

             // Make sure that the source descriptors are not an stdio
             // descriptor, otherwise the order which we set the child's
             // descriptors may blow away a descriptor which we are hoping to
             // save. For example, suppose we want the child's stderr to be the
             // parent's stdout, and the child's stdout to be the parent's
             // stderr. No matter which we dup first, the second will get
             // overwritten prematurely.
             Stdio::Fd(ref fd) => {
                 if fd.raw() <= 2 {
                     Ok((ChildStdio::Owned(fd.duplicate()?), None))
                 } else {
                     Ok((ChildStdio::Explicit(fd.raw()), None))
                 }
             }

             Stdio::MakePipe => {
                 let (reader, writer) = pipe::anon_pipe()?;
                 let (ours, theirs) = if readable {
                     (writer, reader)
                 } else {
                     (reader, writer)
                 };
                 Ok((ChildStdio::Owned(theirs.into_fd()), Some(ours)))
             }

             Stdio::Null => {
                 let mut opts = OpenOptions::new();
                 opts.read(readable);
                 opts.write(!readable);
                 let fd = File::open(Path::new("null:"), &opts)?;
                 Ok((ChildStdio::Owned(fd.into_fd()), None))
             }
         }
     }
 }

 impl From<AnonPipe> for Stdio {
     fn from(pipe: AnonPipe) -> Stdio {
         Stdio::Fd(pipe.into_fd())
     }
 }

 impl From<File> for Stdio {
     fn from(file: File) -> Stdio {
         Stdio::Fd(file.into_fd())
     }
 }

 impl ChildStdio {
     fn fd(&self) -> Option<usize> {
         match *self {
             ChildStdio::Inherit => None,
             ChildStdio::Explicit(fd) => Some(fd),
             ChildStdio::Owned(ref fd) => Some(fd.raw()),
         }
     }
 }

 impl fmt::Debug for Command {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(f, "{:?}", self.program)?;
         for arg in &self.args {
             write!(f, " {:?}", arg)?;
         }
         Ok(())
     }
 }

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

 /// Unix exit statuses
 #[derive(PartialEq, Eq, Clone, Copy, Debug)]
 pub struct ExitStatus(i32);

 impl ExitStatus {
     fn exited(&self) -> bool {
         self.0 & 0x7F == 0
     }

     pub fn success(&self) -> bool {
         self.code() == Some(0)
     }

     pub fn code(&self) -> Option<i32> {
         if self.exited() {
             Some((self.0 >> 8) & 0xFF)
         } else {
             None
         }
     }

     pub fn signal(&self) -> Option<i32> {
         if !self.exited() {
             Some(self.0 & 0x7F)
         } else {
             None
         }
     }
 }

 impl From<i32> for ExitStatus {
     fn from(a: i32) -> ExitStatus {
         ExitStatus(a)
     }
 }

 impl fmt::Display for ExitStatus {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         if let Some(code) = self.code() {
             write!(f, "exit code: {}", code)
         } else {
             let signal = self.signal().unwrap();
             write!(f, "signal: {}", signal)
         }
     }
 }

 /// The unique id of the process (this should never be negative).
 pub struct Process {
     pid: usize,
     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(syscall::kill(self.pid, syscall::SIGKILL))?;
             Ok(())
         }
     }

     pub fn wait(&mut self) -> io::Result<ExitStatus> {
         if let Some(status) = self.status {
             return Ok(status)
         }
         let mut status = 0;
         cvt(syscall::waitpid(self.pid, &mut status, 0))?;
         self.status = Some(ExitStatus(status as i32));
         Ok(ExitStatus(status as i32))
     }

     pub fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
         if let Some(status) = self.status {
             return Ok(Some(status))
         }
         let mut status = 0;
         let pid = cvt(syscall::waitpid(self.pid, &mut status, syscall::WNOHANG))?;
         if pid == 0 {
             Ok(None)
         } else {
             self.status = Some(ExitStatus(status as i32));
             Ok(Some(ExitStatus(status as i32)))
         }
     }
 }
	// Copyright 2016 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 env::{split_paths};
	use ffi::OsStr;
	use os::unix::ffi::OsStrExt;
	use fmt;
	use io::{self, Error, ErrorKind};
	use path::{Path, PathBuf};
	use sys::fd::FileDesc;
	use sys::fs::{File, OpenOptions};
	use sys::pipe::{self, AnonPipe};
	use sys::{cvt, syscall};
	use sys_common::process::{CommandEnv, DefaultEnvKey};

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

	pub struct Command {
	// Currently we try hard to ensure that the call to `.exec()` doesn't
	// actually allocate any memory. While many platforms try to ensure that
	// memory allocation works after a fork in a multithreaded process, it's
	// been observed to be buggy and somewhat unreliable, so we do our best to
	// just not do it at all!
	//
	// Along those lines, the `argv` and `envp` raw pointers here are exactly
	// what's gonna get passed to `execvp`. The `argv` array starts with the
	// `program` and ends with a NULL, and the `envp` pointer, if present, is
	// also null-terminated.
	//
	// Right now we don't support removing arguments, so there's no much fancy
	// support there, but we support adding and removing environment variables,
	// so a side table is used to track where in the `envp` array each key is
	// located. Whenever we add a key we update it in place if it's already
	// present, and whenever we remove a key we update the locations of all
	// other keys.
	program: String,
	args: Vec<String>,
	env: CommandEnv<DefaultEnvKey>,

	cwd: Option<String>,
	uid: Option<u32>,
	gid: Option<u32>,
	saw_nul: bool,
	closures: Vec<Box<FnMut() -> io::Result<()> + Send + Sync>>,
	stdin: Option<Stdio>,
	stdout: Option<Stdio>,
	stderr: Option<Stdio>,
	}

	// passed back to std::process with the pipes connected to the child, if any
	// were requested
	pub struct StdioPipes {
	pub stdin: Option<AnonPipe>,
	pub stdout: Option<AnonPipe>,
	pub stderr: Option<AnonPipe>,
	}

	// passed to do_exec() with configuration of what the child stdio should look
	// like
	struct ChildPipes {
	stdin: ChildStdio,
	stdout: ChildStdio,
	stderr: ChildStdio,
	}

	enum ChildStdio {
	Inherit,
	Explicit(usize),
	Owned(FileDesc),
	}

	pub enum Stdio {
	Inherit,
	Null,
	MakePipe,
	Fd(FileDesc),
	}

	impl Command {
	pub fn new(program: &OsStr) -> Command {
	Command {
	program: program.to_str().unwrap().to_owned(),
	args: Vec::new(),
	env: Default::default(),
	cwd: None,
	uid: None,
	gid: None,
	saw_nul: false,
	closures: Vec::new(),
	stdin: None,
	stdout: None,
	stderr: None,
	}
	}

	pub fn arg(&mut self, arg: &OsStr) {
	self.args.push(arg.to_str().unwrap().to_owned());
	}

	pub fn env_mut(&mut self) -> &mut CommandEnv<DefaultEnvKey> {
	&mut self.env
	}

	pub fn cwd(&mut self, dir: &OsStr) {
	self.cwd = Some(dir.to_str().unwrap().to_owned());
	}
	pub fn uid(&mut self, id: u32) {
	self.uid = Some(id);
	}
	pub fn gid(&mut self, id: u32) {
	self.gid = Some(id);
	}

	pub fn before_exec(&mut self,
	f: Box<FnMut() -> io::Result<()> + Send + Sync>) {
	self.closures.push(f);
	}

	pub fn stdin(&mut self, stdin: Stdio) {
	self.stdin = Some(stdin);
	}
	pub fn stdout(&mut self, stdout: Stdio) {
	self.stdout = Some(stdout);
	}
	pub fn stderr(&mut self, stderr: Stdio) {
	self.stderr = Some(stderr);
	}

	pub fn spawn(&mut self, default: Stdio, needs_stdin: bool)
	-> io::Result<(Process, StdioPipes)> {
	const CLOEXEC_MSG_FOOTER: &'static [u8] = b"NOEX";

	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) = pipe::anon_pipe()?;

	let pid = unsafe {
	match cvt(syscall::clone(0))? {
	0 => {
	drop(input);
	let err = self.do_exec(theirs);
	let errno = err.raw_os_error().unwrap_or(syscall::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());
	let _ = syscall::exit(1);
	panic!("failed to exit");
	}
	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 {
	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) },
	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 syscall::exit)
	unsafe fn do_exec(&mut self, stdio: ChildPipes) -> io::Error {
	macro_rules! t {
	($e:expr) => (match $e {
	Ok(e) => e,
	Err(e) => return e,
	})
	}

	if let Some(fd) = stdio.stderr.fd() {
	t!(cvt(syscall::dup2(fd, 2, &[])));
	let mut flags = t!(cvt(syscall::fcntl(2, syscall::F_GETFD, 0)));
	flags &= ! syscall::O_CLOEXEC;
	t!(cvt(syscall::fcntl(2, syscall::F_SETFD, flags)));
	}
	if let Some(fd) = stdio.stdout.fd() {
	t!(cvt(syscall::dup2(fd, 1, &[])));
	let mut flags = t!(cvt(syscall::fcntl(1, syscall::F_GETFD, 0)));
	flags &= ! syscall::O_CLOEXEC;
	t!(cvt(syscall::fcntl(1, syscall::F_SETFD, flags)));
	}
	if let Some(fd) = stdio.stdin.fd() {
	t!(cvt(syscall::dup2(fd, 0, &[])));
	let mut flags = t!(cvt(syscall::fcntl(0, syscall::F_GETFD, 0)));
	flags &= ! syscall::O_CLOEXEC;
	t!(cvt(syscall::fcntl(0, syscall::F_SETFD, flags)));
	}

	if let Some(g) = self.gid {
	t!(cvt(syscall::setregid(g as usize, g as usize)));
	}
	if let Some(u) = self.uid {
	t!(cvt(syscall::setreuid(u as usize, u as usize)));
	}
	if let Some(ref cwd) = self.cwd {
	t!(cvt(syscall::chdir(cwd)));
	}

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

	let mut args: Vec<[usize; 2]> = Vec::new();
	args.push([self.program.as_ptr() as usize, self.program.len()]);
	for arg in self.args.iter() {
	args.push([arg.as_ptr() as usize, arg.len()]);
	}

	self.env.apply();

	let program = if self.program.contains(':') \|\| self.program.contains('/') {
	Some(PathBuf::from(&self.program))
	} else if let Ok(path_env) = ::env::var("PATH") {
	let mut program = None;
	for mut path in split_paths(&path_env) {
	path.push(&self.program);
	if path.exists() {
	program = Some(path);
	break;
	}
	}
	program
	} else {
	None
	};

	if let Some(program) = program {
	if let Err(err) = syscall::execve(program.as_os_str().as_bytes(), &args) {
	io::Error::from_raw_os_error(err.errno as i32)
	} else {
	panic!("return from exec without err");
	}
	} else {
	io::Error::from_raw_os_error(syscall::ENOENT)
	}
	}


	fn setup_io(&self, default: Stdio, needs_stdin: bool)
	-> io::Result<(StdioPipes, ChildPipes)> {
	let null = Stdio::Null;
	let default_stdin = if needs_stdin {&default} else {&null};
	let stdin = self.stdin.as_ref().unwrap_or(default_stdin);
	let stdout = self.stdout.as_ref().unwrap_or(&default);
	let stderr = self.stderr.as_ref().unwrap_or(&default);
	let (their_stdin, our_stdin) = stdin.to_child_stdio(true)?;
	let (their_stdout, our_stdout) = stdout.to_child_stdio(false)?;
	let (their_stderr, our_stderr) = stderr.to_child_stdio(false)?;
	let ours = StdioPipes {
	stdin: our_stdin,
	stdout: our_stdout,
	stderr: our_stderr,
	};
	let theirs = ChildPipes {
	stdin: their_stdin,
	stdout: their_stdout,
	stderr: their_stderr,
	};
	Ok((ours, theirs))
	}
	}

	impl Stdio {
	fn to_child_stdio(&self, readable: bool)
	-> io::Result<(ChildStdio, Option<AnonPipe>)> {
	match *self {
	Stdio::Inherit => Ok((ChildStdio::Inherit, None)),

	// Make sure that the source descriptors are not an stdio
	// descriptor, otherwise the order which we set the child's
	// descriptors may blow away a descriptor which we are hoping to
	// save. For example, suppose we want the child's stderr to be the
	// parent's stdout, and the child's stdout to be the parent's
	// stderr. No matter which we dup first, the second will get
	// overwritten prematurely.
	Stdio::Fd(ref fd) => {
	if fd.raw() <= 2 {
	Ok((ChildStdio::Owned(fd.duplicate()?), None))
	} else {
	Ok((ChildStdio::Explicit(fd.raw()), None))
	}
	}

	Stdio::MakePipe => {
	let (reader, writer) = pipe::anon_pipe()?;
	let (ours, theirs) = if readable {
	(writer, reader)
	} else {
	(reader, writer)
	};
	Ok((ChildStdio::Owned(theirs.into_fd()), Some(ours)))
	}

	Stdio::Null => {
	let mut opts = OpenOptions::new();
	opts.read(readable);
	opts.write(!readable);
	let fd = File::open(Path::new("null:"), &opts)?;
	Ok((ChildStdio::Owned(fd.into_fd()), None))
	}
	}
	}
	}

	impl From<AnonPipe> for Stdio {
	fn from(pipe: AnonPipe) -> Stdio {
	Stdio::Fd(pipe.into_fd())
	}
	}

	impl From<File> for Stdio {
	fn from(file: File) -> Stdio {
	Stdio::Fd(file.into_fd())
	}
	}

	impl ChildStdio {
	fn fd(&self) -> Option<usize> {
	match *self {
	ChildStdio::Inherit => None,
	ChildStdio::Explicit(fd) => Some(fd),
	ChildStdio::Owned(ref fd) => Some(fd.raw()),
	}
	}
	}

	impl fmt::Debug for Command {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
	write!(f, "{:?}", self.program)?;
	for arg in &self.args {
	write!(f, " {:?}", arg)?;
	}
	Ok(())
	}
	}

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

	/// Unix exit statuses
	#[derive(PartialEq, Eq, Clone, Copy, Debug)]
	pub struct ExitStatus(i32);

	impl ExitStatus {
	fn exited(&self) -> bool {
	self.0 & 0x7F == 0
	}

	pub fn success(&self) -> bool {
	self.code() == Some(0)
	}

	pub fn code(&self) -> Option<i32> {
	if self.exited() {
	Some((self.0 >> 8) & 0xFF)
	} else {
	None
	}
	}

	pub fn signal(&self) -> Option<i32> {
	if !self.exited() {
	Some(self.0 & 0x7F)
	} else {
	None
	}
	}
	}

	impl From<i32> for ExitStatus {
	fn from(a: i32) -> ExitStatus {
	ExitStatus(a)
	}
	}

	impl fmt::Display for ExitStatus {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
	if let Some(code) = self.code() {
	write!(f, "exit code: {}", code)
	} else {
	let signal = self.signal().unwrap();
	write!(f, "signal: {}", signal)
	}
	}
	}

	/// The unique id of the process (this should never be negative).
	pub struct Process {
	pid: usize,
	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(syscall::kill(self.pid, syscall::SIGKILL))?;
	Ok(())
	}
	}

	pub fn wait(&mut self) -> io::Result<ExitStatus> {
	if let Some(status) = self.status {
	return Ok(status)
	}
	let mut status = 0;
	cvt(syscall::waitpid(self.pid, &mut status, 0))?;
	self.status = Some(ExitStatus(status as i32));
	Ok(ExitStatus(status as i32))
	}

	pub fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
	if let Some(status) = self.status {
	return Ok(Some(status))
	}
	let mut status = 0;
	let pid = cvt(syscall::waitpid(self.pid, &mut status, syscall::WNOHANG))?;
	if pid == 0 {
	Ok(None)
	} else {
	self.status = Some(ExitStatus(status as i32));
	Ok(Some(ExitStatus(status as i32)))
	}
	}
	}