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// SPDX-FileCopyrightText: 2026 Dilluti0n <[email protected]>
// SPDX-License-Identifier: GPL-3.0-or-later
use std::os::fd::{RawFd, BorrowedFd, AsFd, OwnedFd, AsRawFd};
use std::io::Error;
use std::sync::atomic::{AtomicUsize, Ordering};
use libc::*;
use super::libc_s;
use libc_s::{setsockopt, SockOpt};
pub struct RxRing {
fd: OwnedFd,
ring: *mut u8,
/// Bytes of mmap'd [`ring`]
ring_size: usize,
req: tpacket_req,
/// Current frame index in the ring buffer (0..req.tp_frame_nr)
current: usize
}
#[derive(Clone, Copy, Debug, thiserror::Error)]
pub enum PktError {
#[error("malformed frame (mac/net/snaplen inconsistent)")]
Malformed,
}
pub struct Pkt<'a> {
rx: &'a mut RxRing,
/// L3 packet
net: Result<&'a [u8], PktError>,
}
/// Make [`sockfd`] as mmapable rxring with size of [`tp_block_size`] * [`tp_block_nr`]
/// and single frame [`tp_frame_size`] (each packet goes to frame).
fn setup_rxring(sockfd: RawFd,
tp_block_size: u32, tp_block_nr: u32, tp_frame_size: u32
) -> Result<tpacket_req, Error> {
if tp_frame_size == 0 { // to prevent div0
return Err(Error::from_raw_os_error(EINVAL));
}
let req = tpacket_req {
tp_block_size,
tp_block_nr,
tp_frame_size,
tp_frame_nr: tp_block_size / tp_frame_size * tp_block_nr,
};
setsockopt(sockfd, SockOpt::PACKET_RX_RING(&req))?;
Ok(req)
}
impl RxRing {
pub fn new(
filter: &[libc::sock_filter],
tp_block_size: u32, tp_block_nr: u32, tp_frame_size: u32
) -> Result<Self, Error> {
let fd = libc_s::socket(AF_PACKET, SOCK_RAW, (ETH_P_ALL as u16).to_be() as i32)?;
let raw = fd.as_raw_fd();
setsockopt(raw, SockOpt::SO_ATTACH_FILTER(&filter))?;
let req = setup_rxring(raw, tp_block_size, tp_block_nr, tp_frame_size)?;
let ring_size = req.tp_block_size as usize * req.tp_block_nr as usize;
// SAFETY: we munmap this when RxRing is dropped
let ring = unsafe {libc_s::mmap(
std::ptr::null_mut(),
ring_size,
PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_LOCKED,
raw,
0
)}?;
Ok(RxRing {
fd,
ring: ring as *mut u8,
ring_size,
req,
current: 0,
})
}
#[inline]
fn current_frame(&self) -> *mut u8 {
self.ring.wrapping_add(self.current * self.req.tp_frame_size as usize)
}
#[inline]
fn status(&self) -> &AtomicUsize {
// SAFETY:
// * Align: frame starts on TPACKET_ALIGNMENT(16) boundary in a page-aligned mmap
// * Valid r/w for 'a: ring outlives &self, currrent < frame_nr keeps the offset in-bounds
// * Memory model: on TPACKET_V1 tp_status is unsigned long == usize
unsafe { AtomicUsize::from_ptr(self.current_frame() as *mut usize) }
}
pub fn current_packet(&mut self) -> Option<Pkt<'_>> {
let status = self.status().load(Ordering::Acquire);
if status & TP_STATUS_USER as usize == 0 {
return None;
}
let hdr = self.current_frame() as *const tpacket_hdr;
// [ tpacket_hdr | payload ]
// |<--tp_mac--->|<---tp_snaplen------>|
// |<--tp_net------------>|
// | |<--mo-->|
// | |<-net_len-->|
// hdr net
let (tp_mac, tp_net, tp_snaplen) = unsafe {
((*hdr).tp_mac as usize, (*hdr).tp_net as usize, (*hdr).tp_snaplen as usize)
};
let net = tp_net.checked_sub(tp_mac)
.and_then(|mo| tp_snaplen.checked_sub(mo))
.map(|net_len| unsafe {
std::slice::from_raw_parts((hdr as *const u8).add(tp_net), net_len)
})
.ok_or(PktError::Malformed);
Some(Pkt { rx: self, net })
}
/// Return the current frame to kernel and move cursor. This must be called
/// only when the current state is TP_STATUS_USER. If not, ring protocol
/// may corrupted.
pub fn advance(&mut self) {
debug_assert!(
self.status().load(Ordering::Acquire) & TP_STATUS_USER as usize != 0,
"advance() on a frame not owned by user"
);
self.status().store(TP_STATUS_KERNEL as usize, Ordering::Release);
self.current = (self.current + 1) % self.req.tp_frame_nr as usize;
}
}
impl Pkt<'_> {
pub fn net(&self) -> Result<&[u8], PktError> {
self.net
}
}
impl Drop for Pkt<'_> {
fn drop(&mut self) {
self.rx.advance()
}
}
impl AsFd for RxRing {
fn as_fd(&self) -> BorrowedFd<'_> {
self.fd.as_fd()
}
}
impl AsRawFd for RxRing {
fn as_raw_fd(&self) -> RawFd {
self.fd.as_raw_fd()
}
}
impl Drop for RxRing {
fn drop(&mut self) {
// SAFETY: ring was mmap'd with ring_size bytes
match unsafe { libc_s::munmap(self.ring as *mut _, self.ring_size) } {
Err(e) => crate::warn!("rxring: cannot munmap: {}", e.kind()),
Ok(_) => {}
}
}
}
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