Add signalfd support

1 files changed, 219 insertions, 0 deletions

diff --git a/src/sys/signalfd.rs b/src/sys/signalfd.rs
new file mode 100644
index 00000000..66eaa04e
--- /dev/null
+++ b/src/sys/signalfd.rs
@@ -0,0 +1,219 @@
+//! Interface for the `signalfd` syscall.
+//!
+//! # Signal discarding
+//! When a signal can't be delivered to a process (or thread), it will become a pending signal.
+//! Failure to deliver could happen if the signal is blocked by every thread in the process or if
+//! the signal handler is still handling a previous signal.
+//!
+//! If a signal is sent to a process (or thread) that already has a pending signal of the same
+//! type, it will be discarded. This means that if signals of the same type are received faster than
+//! they are processed, some of those signals will be dropped. Because of this limitation,
+//! `signalfd` in itself cannot be used for reliable communication between processes or threads.
+//!
+//! Once the signal is unblocked, or the signal handler is finished, and a signal is still pending
+//! (ie. not consumed from a signalfd) it will be delivered to the signal handler.
+//!
+//! Please note that signal discarding is not specific to `signalfd`, but also happens with regular
+//! signal handlers.
+use libc::{c_int, pid_t, uid_t};
+use {Error, Result};
+use unistd;
+use errno::Errno;
+use sys::signal::signal::siginfo as signal_siginfo;
+pub use sys::signal::{self, SigSet};
+
+use std::os::unix::io::{RawFd, AsRawFd};
+use std::mem;
+
+mod ffi {
+    use libc::c_int;
+    use sys::signal::sigset_t;
+
+    extern {
+        pub fn signalfd(fd: c_int, mask: *const sigset_t, flags: c_int) -> c_int;
+    }
+}
+
+bitflags!{
+    flags SfdFlags: c_int {
+        const SFD_NONBLOCK  = 0o00004000, // O_NONBLOCK
+        const SFD_CLOEXEC   = 0o02000000, // O_CLOEXEC
+    }
+}
+
+pub const CREATE_NEW_FD: RawFd = -1;
+
+/// Creates a new file descriptor for reading signals.
+///
+/// **Important:** please read the module level documentation about signal discarding before using
+/// this function!
+///
+/// The `mask` parameter specifies the set of signals that can be accepted via this file descriptor.
+///
+/// A signal must be blocked on every thread in a process, otherwise it won't be visible from
+/// signalfd (the default handler will be invoked instead).
+///
+/// See [the signalfd man page for more information](http://man7.org/linux/man-pages/man2/signalfd.2.html)
+pub fn signalfd(fd: RawFd, mask: &SigSet, flags: SfdFlags) -> Result<RawFd> {
+    unsafe {
+        match ffi::signalfd(fd as c_int, mask.as_ref(), flags.bits()) {
+            -1 => Err(Error::Sys(Errno::last())),
+            res => Ok(res as RawFd),
+        }
+    }
+}
+
+/// A helper struct for creating, reading and closing a `signalfd` instance.
+///
+/// **Important:** please read the module level documentation about signal discarding before using
+/// this struct!
+///
+/// # Examples
+///
+/// ```
+/// use nix::sys::signalfd::*;
+///
+/// let mut mask = SigSet::empty();
+/// mask.add(signal::SIGUSR1).unwrap();
+///
+/// // Block the signal, otherwise the default handler will be invoked instead.
+/// mask.thread_block().unwrap();
+///
+/// // Signals are queued up on the file descriptor
+/// let mut sfd = SignalFd::with_flags(&mask, SFD_NONBLOCK).unwrap();
+///
+/// match sfd.read_signal() {
+///     // we caught a signal
+///     Ok(Some(sig)) => (),
+///
+///     // there were no signals waiting (only happens when the SFD_NONBLOCK flag is set,
+///     // otherwise the read_signal call blocks)
+///     Ok(None) => (),
+///
+///     Err(err) => (), // some error happend
+/// }
+/// ```
+#[derive(Debug)]
+pub struct SignalFd(RawFd);
+
+impl SignalFd {
+    pub fn new(mask: &SigSet) -> Result<SignalFd> {
+        Self::with_flags(mask, SfdFlags::empty())
+    }
+
+    pub fn with_flags(mask: &SigSet, flags: SfdFlags) -> Result<SignalFd> {
+        let fd = try!(signalfd(CREATE_NEW_FD, mask, flags));
+
+        Ok(SignalFd(fd))
+    }
+
+    pub fn set_mask(&mut self, mask: &SigSet) -> Result<()> {
+        signalfd(self.0, mask, SfdFlags::empty()).map(|_| ())
+    }
+
+    pub fn read_signal(&mut self) -> Result<Option<siginfo>> {
+        let mut buffer: [u8; SIGINFO_SIZE] = unsafe { mem::uninitialized() };
+
+        match unistd::read(self.0, &mut buffer) {
+            Ok(SIGINFO_SIZE) => Ok(Some(unsafe { mem::transmute_copy(&buffer) })),
+            Ok(_) => unreachable!("partial read on signalfd"),
+            Err(Error::Sys(Errno::EAGAIN)) => Ok(None),
+            Err(error) => Err(error)
+        }
+    }
+}
+
+impl Drop for SignalFd {
+    fn drop(&mut self) {
+        let _ = unistd::close(self.0);
+    }
+}
+
+impl AsRawFd for SignalFd {
+    fn as_raw_fd(&self) -> RawFd {
+        self.0
+    }
+}
+
+impl Iterator for SignalFd {
+    type Item = siginfo;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match self.read_signal() {
+            Ok(Some(sig)) => Some(sig),
+            Ok(None) => None,
+            Err(..) => None,
+        }
+    }
+}
+
+pub const SIGINFO_SIZE: usize = 128;
+pub const SIGINFO_PADDING: usize = 48;
+
+#[derive(Debug, Clone, PartialEq)]
+#[repr(C, packed)]
+pub struct siginfo {
+    pub ssi_signo: u32,
+    pub ssi_errno: i32,
+    pub ssi_code: i32,
+    pub ssi_pid: u32,
+    pub ssi_uid: u32,
+    pub ssi_fd: i32,
+    pub ssi_tid: u32,
+    pub ssi_band: u32,
+    pub ssi_overrun: u32,
+    pub ssi_trapno: u32,
+    pub ssi_status: i32,
+    pub ssi_int: i32,
+    pub ssi_ptr: u64,
+    pub ssi_utime: u64,
+    pub ssi_stime: u64,
+    pub ssi_addr: u64,
+}
+
+impl Into<signal_siginfo> for siginfo {
+    fn into(self) -> signal_siginfo {
+        signal_siginfo {
+            si_signo: self.ssi_signo as c_int,
+            si_errno: self.ssi_errno as c_int,
+            si_code: self.ssi_code as c_int,
+            pid: self.ssi_pid as pid_t,
+            uid: self.ssi_uid as uid_t,
+            status: self.ssi_status as c_int,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::mem;
+
+    #[test]
+    fn check_siginfo_size() {
+        assert_eq!(mem::size_of::<siginfo>() + SIGINFO_PADDING, SIGINFO_SIZE);
+    }
+
+    #[test]
+    fn create_signalfd() {
+        let mask = SigSet::empty();
+        let fd = SignalFd::new(&mask);
+        assert!(fd.is_ok());
+    }
+
+    #[test]
+    fn create_signalfd_with_opts() {
+        let mask = SigSet::empty();
+        let fd = SignalFd::with_flags(&mask, SFD_CLOEXEC | SFD_NONBLOCK);
+        assert!(fd.is_ok());
+    }
+
+    #[test]
+    fn read_empty_signalfd() {
+        let mask = SigSet::empty();
+        let mut fd = SignalFd::with_flags(&mask, SFD_NONBLOCK).unwrap();
+
+        let res = fd.read_signal();
+        assert_eq!(res, Ok(None));
+    }
+}