nix/sys/
eventfd.rs

1use crate::errno::Errno;
2use crate::{unistd, Result};
3use std::os::unix::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, OwnedFd, RawFd};
4
5libc_bitflags! {
6    /// Eventfd flags.
7    pub struct EfdFlags: libc::c_int {
8        /// Set the close-on-exec (`FD_CLOEXEC`) flag on the new event file descriptor.
9        EFD_CLOEXEC; // Since Linux 2.6.27/FreeBSD 13.0
10        /// Set the `O_NONBLOCK` file status flag on the new event file description.
11        EFD_NONBLOCK; // Since Linux 2.6.27/FreeBSD 13.0
12        /// Provide semaphore-like semantics for reads from the new event file
13        /// descriptor.
14        EFD_SEMAPHORE; // Since Linux 2.6.30/FreeBSD 13.0
15    }
16}
17
18#[deprecated(
19    since = "0.28.0",
20    note = "Use EventFd::from_value_and_flags() instead"
21)]
22#[allow(missing_docs)]
23pub fn eventfd(initval: libc::c_uint, flags: EfdFlags) -> Result<OwnedFd> {
24    let res = unsafe { libc::eventfd(initval, flags.bits()) };
25
26    Errno::result(res).map(|r| unsafe { OwnedFd::from_raw_fd(r) })
27}
28
29/// An eventfd file descriptor.
30#[derive(Debug)]
31#[repr(transparent)]
32pub struct EventFd(OwnedFd);
33
34impl EventFd {
35    /// [`EventFd::from_value_and_flags`] with `init_val = 0` and `flags = EfdFlags::empty()`.
36    pub fn new() -> Result<Self> {
37        Self::from_value_and_flags(0, EfdFlags::empty())
38    }
39
40    /// Constructs [`EventFd`] with the given `init_val` and `flags`.
41    ///
42    /// Wrapper around [`libc::eventfd`].
43    pub fn from_value_and_flags(
44        init_val: u32,
45        flags: EfdFlags,
46    ) -> Result<Self> {
47        let res = unsafe { libc::eventfd(init_val, flags.bits()) };
48        Errno::result(res).map(|r| Self(unsafe { OwnedFd::from_raw_fd(r) }))
49    }
50
51    /// [`EventFd::from_value_and_flags`] with `init_val = 0` and given `flags`.
52    pub fn from_flags(flags: EfdFlags) -> Result<Self> {
53        Self::from_value_and_flags(0, flags)
54    }
55
56    /// [`EventFd::from_value_and_flags`] with given `init_val` and `flags = EfdFlags::empty()`.
57    pub fn from_value(init_val: u32) -> Result<Self> {
58        Self::from_value_and_flags(init_val, EfdFlags::empty())
59    }
60
61    /// Constructs an `EventFd` wrapping an existing `OwnedFd`.
62    ///
63    /// # Safety
64    ///
65    /// `OwnedFd` is a valid eventfd.
66    pub unsafe fn from_owned_fd(fd: OwnedFd) -> Self {
67        Self(fd)
68    }
69
70    /// Enqueues `value` triggers, i.e., adds the integer value supplied in `value`
71    /// to the counter.
72    ///
73    /// The next `value` calls to `poll`, `select` or `epoll` will return immediately.
74    ///
75    /// [`EventFd::write`] with `value`.
76    pub fn write(&self, value: u64) -> Result<usize> {
77        unistd::write(&self.0, &value.to_ne_bytes())
78    }
79
80    /// Reads the value from the file descriptor.
81    ///
82    /// * If [`EFD_SEMAPHORE`](EfdFlags::EFD_SEMAPHORE) was not specified and
83    ///   the eventfd counter has a nonzero value, then this function returns
84    ///   an `u64` containing that value, and the counter's value is reset to
85    ///   zero.
86    ///
87    /// * If [`EFD_SEMAPHORE`](EfdFlags::EFD_SEMAPHORE) was specified and the
88    ///   eventfd counter has a nonzero value, then this function returns an
89    ///   `u64` containing the value 1, and the counter's value is decremented
90    ///   by 1.
91    ///
92    /// * If the eventfd counter is zero at the time of this call, then the
93    ///   call either blocks until the counter becomes nonzero (at which time,
94    ///   this function proceeds as described above) or fails with the error
95    ///   `EAGAIN` if the file descriptor has been made nonblocking with
96    ///   [`EFD_NONBLOCK`](EfdFlags::EFD_NONBLOCK).
97    pub fn read(&self) -> Result<u64> {
98        let mut arr = [0; std::mem::size_of::<u64>()];
99        unistd::read(&self.0, &mut arr)?;
100        Ok(u64::from_ne_bytes(arr))
101    }
102}
103impl AsFd for EventFd {
104    fn as_fd(&self) -> BorrowedFd {
105        self.0.as_fd()
106    }
107}
108impl AsRawFd for EventFd {
109    fn as_raw_fd(&self) -> RawFd {
110        self.0.as_raw_fd()
111    }
112}
113
114impl From<EventFd> for OwnedFd {
115    fn from(value: EventFd) -> Self {
116        value.0
117    }
118}
nix/sys/eventfd.rs

nix/sys/
eventfd.rs
