src/libstd/sys/unix/pipe.rs

   1 use crate::io::{self, IoSlice, IoSliceMut};
   2 use crate::mem;
   3 use crate::sync::atomic::{AtomicBool, Ordering};
   4 use crate::sys::fd::FileDesc;
   5 use crate::sys::{cvt, cvt_r};
   6
   7 use libc::c_int;
   8
   9 ////////////////////////////////////////////////////////////////////////////////
  10 // Anonymous pipes
  11 ////////////////////////////////////////////////////////////////////////////////
  12
  13 pub struct AnonPipe(FileDesc);
  14
  15 pub fn anon_pipe() -> io::Result<(AnonPipe, AnonPipe)> {
  16     syscall! { fn pipe2(fds: *mut c_int, flags: c_int) -> c_int }
  17     static INVALID: AtomicBool = AtomicBool::new(false);
  18
  19     let mut fds = [0; 2];
  20
  21     // Unfortunately the only known way right now to create atomically set the
  22     // CLOEXEC flag is to use the `pipe2` syscall on Linux. This was added in
  23     // 2.6.27, however, and because we support 2.6.18 we must detect this
  24     // support dynamically.
  25     if cfg!(any(
  26         target_os = "dragonfly",
  27         target_os = "freebsd",
  28         target_os = "linux",
  29         target_os = "netbsd",
  30         target_os = "openbsd",
  31         target_os = "redox"
  32     )) && !INVALID.load(Ordering::SeqCst)
  33     {
  34         // Note that despite calling a glibc function here we may still
  35         // get ENOSYS. Glibc has `pipe2` since 2.9 and doesn't try to
  36         // emulate on older kernels, so if you happen to be running on
  37         // an older kernel you may see `pipe2` as a symbol but still not
  38         // see the syscall.
  39         match cvt(unsafe { pipe2(fds.as_mut_ptr(), libc::O_CLOEXEC) }) {
  40             Ok(_) => {
  41                 return Ok((AnonPipe(FileDesc::new(fds[0])), AnonPipe(FileDesc::new(fds[1]))));
  42             }
  43             Err(ref e) if e.raw_os_error() == Some(libc::ENOSYS) => {
  44                 INVALID.store(true, Ordering::SeqCst);
  45             }
  46             Err(e) => return Err(e),
  47         }
  48     }
  49     cvt(unsafe { libc::pipe(fds.as_mut_ptr()) })?;
  50
  51     let fd0 = FileDesc::new(fds[0]);
  52     let fd1 = FileDesc::new(fds[1]);
  53     fd0.set_cloexec()?;
  54     fd1.set_cloexec()?;
  55     Ok((AnonPipe(fd0), AnonPipe(fd1)))
  56 }
  57
  58 impl AnonPipe {
  59     pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
  60         self.0.read(buf)
  61     }
  62
  63     pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
  64         self.0.read_vectored(bufs)
  65     }
  66
  67     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
  68         self.0.write(buf)
  69     }
  70
  71     pub fn write_vectored(&self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
  72         self.0.write_vectored(bufs)
  73     }
  74
  75     pub fn fd(&self) -> &FileDesc {
  76         &self.0
  77     }
  78     pub fn into_fd(self) -> FileDesc {
  79         self.0
  80     }
  81 }
  82
  83 pub fn read2(p1: AnonPipe, v1: &mut Vec<u8>, p2: AnonPipe, v2: &mut Vec<u8>) -> io::Result<()> {
  84     // Set both pipes into nonblocking mode as we're gonna be reading from both
  85     // in the `select` loop below, and we wouldn't want one to block the other!
  86     let p1 = p1.into_fd();
  87     let p2 = p2.into_fd();
  88     p1.set_nonblocking(true)?;
  89     p2.set_nonblocking(true)?;
  90
  91     let mut fds: [libc::pollfd; 2] = unsafe { mem::zeroed() };
  92     fds[0].fd = p1.raw();
  93     fds[0].events = libc::POLLIN;
  94     fds[1].fd = p2.raw();
  95     fds[1].events = libc::POLLIN;
  96     loop {
  97         // wait for either pipe to become readable using `poll`
  98         cvt_r(|| unsafe { libc::poll(fds.as_mut_ptr(), 2, -1) })?;
  99
 100         if fds[0].revents != 0 && read(&p1, v1)? {
 101             p2.set_nonblocking(false)?;
 102             return p2.read_to_end(v2).map(drop);
 103         }
 104         if fds[1].revents != 0 && read(&p2, v2)? {
 105             p1.set_nonblocking(false)?;
 106             return p1.read_to_end(v1).map(drop);
 107         }
 108     }
 109
 110     // Read as much as we can from each pipe, ignoring EWOULDBLOCK or
 111     // EAGAIN. If we hit EOF, then this will happen because the underlying
 112     // reader will return Ok(0), in which case we'll see `Ok` ourselves. In
 113     // this case we flip the other fd back into blocking mode and read
 114     // whatever's leftover on that file descriptor.
 115     fn read(fd: &FileDesc, dst: &mut Vec<u8>) -> Result<bool, io::Error> {
 116         match fd.read_to_end(dst) {
 117             Ok(_) => Ok(true),
 118             Err(e) => {
 119                 if e.raw_os_error() == Some(libc::EWOULDBLOCK)
 120                     || e.raw_os_error() == Some(libc::EAGAIN)
 121                 {
 122                     Ok(false)
 123                 } else {
 124                     Err(e)
 125                 }
 126             }
 127         }
 128     }
 129 }