tracing_journald/
socket.rs

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1//! socket helpers.
2
3use std::io::{Error, Result};
4use std::mem::{size_of, zeroed};
5use std::os::unix::ffi::OsStrExt;
6use std::os::unix::net::UnixDatagram;
7use std::os::unix::prelude::{AsRawFd, RawFd};
8use std::path::Path;
9use std::ptr;
10
11use libc::*;
12
13const CMSG_BUFSIZE: usize = 64;
14
15#[repr(C)]
16union AlignedBuffer<T: Copy + Clone> {
17    buffer: T,
18    align: cmsghdr,
19}
20
21fn assert_cmsg_bufsize() {
22    let space_one_fd = unsafe { CMSG_SPACE(size_of::<RawFd>() as u32) };
23    assert!(
24        space_one_fd <= CMSG_BUFSIZE as u32,
25        "cmsghdr buffer too small (< {}) to hold a single fd",
26        space_one_fd
27    );
28}
29
30#[cfg(test)]
31#[test]
32fn cmsg_buffer_size_for_one_fd() {
33    assert_cmsg_bufsize()
34}
35
36pub(crate) fn send_one_fd_to<P: AsRef<Path>>(
37    socket: &UnixDatagram,
38    fd: RawFd,
39    path: P,
40) -> Result<usize> {
41    assert_cmsg_bufsize();
42
43    let mut addr: sockaddr_un = unsafe { zeroed() };
44    let path_bytes = path.as_ref().as_os_str().as_bytes();
45    // path_bytes may have at most sun_path + 1 bytes, to account for the trailing NUL byte.
46    if addr.sun_path.len() <= path_bytes.len() {
47        return Err(Error::from_raw_os_error(ENAMETOOLONG));
48    }
49
50    addr.sun_family = AF_UNIX as _;
51    unsafe {
52        std::ptr::copy_nonoverlapping(
53            path_bytes.as_ptr(),
54            addr.sun_path.as_mut_ptr() as *mut u8,
55            path_bytes.len(),
56        )
57    };
58
59    let mut msg: msghdr = unsafe { zeroed() };
60    // Set the target address.
61    msg.msg_name = &mut addr as *mut _ as *mut c_void;
62    msg.msg_namelen = size_of::<sockaddr_un>() as socklen_t;
63
64    // We send no data body with this message.
65    msg.msg_iov = ptr::null_mut();
66    msg.msg_iovlen = 0;
67
68    // Create and fill the control message buffer with our file descriptor
69    let mut cmsg_buffer = AlignedBuffer {
70        buffer: ([0u8; CMSG_BUFSIZE]),
71    };
72    msg.msg_control = unsafe { cmsg_buffer.buffer.as_mut_ptr() as _ };
73    msg.msg_controllen = unsafe { CMSG_SPACE(size_of::<RawFd>() as _) as _ };
74
75    let cmsg: &mut cmsghdr =
76        unsafe { CMSG_FIRSTHDR(&msg).as_mut() }.expect("Control message buffer exhausted");
77
78    cmsg.cmsg_level = SOL_SOCKET;
79    cmsg.cmsg_type = SCM_RIGHTS;
80    cmsg.cmsg_len = unsafe { CMSG_LEN(size_of::<RawFd>() as _) as _ };
81
82    unsafe { ptr::write(CMSG_DATA(cmsg) as *mut RawFd, fd) };
83
84    let result = unsafe { sendmsg(socket.as_raw_fd(), &msg, libc::MSG_NOSIGNAL) };
85
86    if result < 0 {
87        Err(Error::last_os_error())
88    } else {
89        // sendmsg returns the number of bytes written
90        Ok(result as usize)
91    }
92}
tracing_journald/socket.rs

tracing_journald/
socket.rs
