serialport/posix/
poll.rs

1#![allow(non_camel_case_types, dead_code)]
2
3use std::io;
4use std::os::unix::io::RawFd;
5use std::slice;
6use std::time::Duration;
7
8use nix::libc::c_int;
9use nix::poll::{PollFd, PollFlags};
10#[cfg(target_os = "linux")]
11use nix::sys::signal::SigSet;
12#[cfg(any(target_os = "linux", test))]
13use nix::sys::time::TimeSpec;
14
15pub fn wait_read_fd(fd: RawFd, timeout: Duration) -> io::Result<()> {
16    wait_fd(fd, PollFlags::POLLIN, timeout)
17}
18
19pub fn wait_write_fd(fd: RawFd, timeout: Duration) -> io::Result<()> {
20    wait_fd(fd, PollFlags::POLLOUT, timeout)
21}
22
23fn wait_fd(fd: RawFd, events: PollFlags, timeout: Duration) -> io::Result<()> {
24    use nix::errno::Errno::{EIO, EPIPE};
25
26    let mut fd = PollFd::new(fd, events);
27
28    let wait = match poll_clamped(&mut fd, timeout) {
29        Ok(r) => r,
30        Err(e) => return Err(io::Error::from(crate::Error::from(e))),
31    };
32    // All errors generated by poll or ppoll are already caught by the nix wrapper around libc, so
33    // here we only need to check if there's at least 1 event
34    if wait != 1 {
35        return Err(io::Error::new(
36            io::ErrorKind::TimedOut,
37            "Operation timed out",
38        ));
39    }
40
41    // Check the result of ppoll() by looking at the revents field
42    match fd.revents() {
43        Some(e) if e == events => return Ok(()),
44        // If there was a hangout or invalid request
45        Some(e) if e.contains(PollFlags::POLLHUP) || e.contains(PollFlags::POLLNVAL) => {
46            return Err(io::Error::new(io::ErrorKind::BrokenPipe, EPIPE.desc()));
47        }
48        Some(_) | None => (),
49    }
50
51    Err(io::Error::new(io::ErrorKind::Other, EIO.desc()))
52}
53
54/// Poll with a duration clamped to the maximum value representable by the `TimeSpec` used by
55/// `ppoll`.
56#[cfg(target_os = "linux")]
57fn poll_clamped(fd: &mut PollFd, timeout: Duration) -> nix::Result<c_int> {
58    let spec = clamped_time_spec(timeout);
59    nix::poll::ppoll(slice::from_mut(fd), Some(spec), Some(SigSet::empty()))
60}
61
62#[cfg(any(target_os = "linux", test))]
63// The type time_t is deprecaten on musl. The nix crate internally uses this type and makes an
64// exeption for the deprecation for musl. And so do we.
65//
66// See https://github.com/rust-lang/libc/issues/1848 which is referenced from every exemption used
67// in nix.
68#[cfg_attr(target_env = "musl", allow(deprecated))]
69fn clamped_time_spec(duration: Duration) -> TimeSpec {
70    use nix::libc::c_long;
71    use nix::sys::time::time_t;
72
73    // We need to clamp manually as TimeSpec::from_duration translates durations with more than
74    // i64::MAX seconds to negative timespans. This happens due to casting to i64 and is still the
75    // case as of nix 0.29.
76    let secs_limit = time_t::MAX as u64;
77    let secs = duration.as_secs();
78    if secs <= secs_limit {
79        TimeSpec::new(secs as time_t, duration.subsec_nanos() as c_long)
80    } else {
81        TimeSpec::new(time_t::MAX, 999_999_999)
82    }
83}
84
85// Poll with a duration clamped to the maximum millisecond value representable by the `c_int` used
86// by `poll`.
87#[cfg(not(target_os = "linux"))]
88fn poll_clamped(fd: &mut PollFd, timeout: Duration) -> nix::Result<c_int> {
89    let millis = clamped_millis_c_int(timeout);
90    nix::poll::poll(slice::from_mut(fd), millis)
91}
92
93#[cfg(any(not(target_os = "linux"), test))]
94fn clamped_millis_c_int(duration: Duration) -> c_int {
95    let secs_limit = (c_int::MAX as u64) / 1000;
96    let secs = duration.as_secs();
97
98    if secs <= secs_limit {
99        secs as c_int * 1000 + duration.subsec_millis() as c_int
100    } else {
101        c_int::MAX
102    }
103}
104
105#[cfg(test)]
106mod tests {
107    use super::*;
108    use crate::tests::timeout::MONOTONIC_DURATIONS;
109
110    #[test]
111    fn clamped_millis_c_int_is_monotonic() {
112        let mut last = clamped_millis_c_int(Duration::ZERO);
113
114        for (i, d) in MONOTONIC_DURATIONS.iter().enumerate() {
115            let next = clamped_millis_c_int(*d);
116            assert!(
117                next >= last,
118                "{next} >= {last} failed for {d:?} at index {i}"
119            );
120            last = next;
121        }
122    }
123
124    #[test]
125    fn clamped_millis_c_int_zero_is_zero() {
126        assert_eq!(0, clamped_millis_c_int(Duration::ZERO));
127    }
128
129    #[test]
130    fn clamped_time_spec_is_monotonic() {
131        let mut last = clamped_time_spec(Duration::ZERO);
132
133        for (i, d) in MONOTONIC_DURATIONS.iter().enumerate() {
134            let next = clamped_time_spec(*d);
135            assert!(
136                next >= last,
137                "{next} >= {last} failed for {d:?} at index {i}"
138            );
139            last = next;
140        }
141    }
142
143    #[test]
144    fn clamped_time_spec_zero_is_zero() {
145        let spec = clamped_time_spec(Duration::ZERO);
146        assert_eq!(0, spec.tv_sec());
147        assert_eq!(0, spec.tv_nsec());
148    }
149}
serialport/posix/poll.rs

serialport/posix/
poll.rs
