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journald: use unconnected socket (#1758)
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Lets journald subscribers survive a journald restart.

Closes #1745

## Motivation

Currently the journald subscriber immediately connects to the journald
socket.  As such I understand it'd not survive a full restart of
journald.

## Solution

Do not connect the client socket immediately; instead pass the socket
pathname every time we send a message.  This is also what upstream does.
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swsnr authored and hawkw committed Dec 19, 2021
1 parent bd0bcc2 commit 89de8f7
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Showing 2 changed files with 44 additions and 14 deletions.
30 changes: 19 additions & 11 deletions tracing-journald/src/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -86,6 +86,9 @@ pub struct Layer {
field_prefix: Option<String>,
}

#[cfg(unix)]
const JOURNALD_PATH: &str = "/run/systemd/journal/socket";

impl Layer {
/// Construct a journald layer
///
Expand All @@ -95,11 +98,14 @@ impl Layer {
#[cfg(unix)]
{
let socket = UnixDatagram::unbound()?;
socket.connect("/run/systemd/journal/socket")?;
Ok(Self {
let layer = Self {
socket,
field_prefix: Some("F".into()),
})
};
// Check that we can talk to journald, by sending empty payload which journald discards.
// However if the socket didn't exist or if none listened we'd get an error here.
layer.send_payload(&[])?;
Ok(layer)
}
#[cfg(not(unix))]
Err(io::Error::new(
Expand All @@ -125,13 +131,15 @@ impl Layer {

#[cfg(unix)]
fn send_payload(&self, payload: &[u8]) -> io::Result<usize> {
self.socket.send(payload).or_else(|error| {
if Some(libc::EMSGSIZE) == error.raw_os_error() {
self.send_large_payload(payload)
} else {
Err(error)
}
})
self.socket
.send_to(payload, JOURNALD_PATH)
.or_else(|error| {
if Some(libc::EMSGSIZE) == error.raw_os_error() {
self.send_large_payload(payload)
} else {
Err(error)
}
})
}

#[cfg(all(unix, not(target_os = "linux")))]
Expand All @@ -154,7 +162,7 @@ impl Layer {
// Fully seal the memfd to signal journald that its backing data won't resize anymore
// and so is safe to mmap.
memfd::seal_fully(mem.as_raw_fd())?;
socket::send_one_fd(&self.socket, mem.as_raw_fd())
socket::send_one_fd_to(&self.socket, mem.as_raw_fd(), JOURNALD_PATH)
}
}

Expand Down
28 changes: 25 additions & 3 deletions tracing-journald/src/socket.rs
Original file line number Diff line number Diff line change
Expand Up @@ -2,8 +2,10 @@
use std::io::{Error, Result};
use std::mem::{size_of, zeroed};
use std::os::unix::ffi::OsStrExt;
use std::os::unix::net::UnixDatagram;
use std::os::unix::prelude::{AsRawFd, RawFd};
use std::path::Path;
use std::ptr;

use libc::*;
Expand Down Expand Up @@ -31,18 +33,38 @@ fn cmsg_buffer_size_for_one_fd() {
assert_cmsg_bufsize()
}

pub fn send_one_fd(socket: &UnixDatagram, fd: RawFd) -> Result<usize> {
pub fn send_one_fd_to<P: AsRef<Path>>(socket: &UnixDatagram, fd: RawFd, path: P) -> Result<usize> {
assert_cmsg_bufsize();

let mut cmsg_buffer = AlignedBuffer {
buffer: ([0u8; CMSG_BUFSIZE]),
let mut addr: sockaddr_un = unsafe { zeroed() };
let path_bytes = path.as_ref().as_os_str().as_bytes();
// path_bytes may have at most sun_path + 1 bytes, to account for the trailing NUL byte.
if addr.sun_path.len() <= path_bytes.len() {
return Err(Error::from_raw_os_error(ENAMETOOLONG));
}

addr.sun_family = AF_UNIX as _;
unsafe {
std::ptr::copy_nonoverlapping(
path_bytes.as_ptr(),
addr.sun_path.as_mut_ptr() as *mut u8,
path_bytes.len(),
)
};

let mut msg: msghdr = unsafe { zeroed() };
// Set the target address.
msg.msg_name = &mut addr as *mut _ as *mut c_void;
msg.msg_namelen = size_of::<sockaddr_un>() as socklen_t;

// We send no data body with this message.
msg.msg_iov = ptr::null_mut();
msg.msg_iovlen = 0;

// Create and fill the control message buffer with our file descriptor
let mut cmsg_buffer = AlignedBuffer {
buffer: ([0u8; CMSG_BUFSIZE]),
};
msg.msg_control = unsafe { cmsg_buffer.buffer.as_mut_ptr() as _ };
msg.msg_controllen = unsafe { CMSG_SPACE(size_of::<RawFd>() as _) as _ };

Expand Down

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