3:11 p.m.
CI shows our async handle fails to build on FreeBSD and MacOS (where
epoll() is not available as a syscall, and therefore not available as
a Rust crate). We can instead accomplish the same level-probing
effects by doing a zero-timeout poll with mio (which defers under the
hood to epoll on Linux, and kqueue on BSD).
Fixes: 223a9965 ("rust: async: Create an async friendly handle type")
CC: Tage Johansson <tage.j.lists(a)posteo.net>
Signed-off-by: Eric Blake <eblake(a)redhat.com>
---
rust/Cargo.toml | 2 +-
rust/src/async_handle.rs | 46 +++++++++++++++++++++++++---------------
2 files changed, 30 insertions(+), 18 deletions(-)
diff --git a/rust/Cargo.toml b/rust/Cargo.toml
index 0879b34c..391c80e9 100644
--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@@ -49,7 +49,7 @@ thiserror = "1.0.40"
log = { version = "0.4.19", optional = true }
libc = "0.2.147"
tokio = { optional = true, version = "1.29.1", default-features = false,
features = ["rt", "sync", "net"] }
-epoll = "4.3.3"
+mio = "0.8.0"
[features]
default = ["log", "tokio"]
diff --git a/rust/src/async_handle.rs b/rust/src/async_handle.rs
index ab28b910..35b1c0d2 100644
--- a/rust/src/async_handle.rs
+++ b/rust/src/async_handle.rs
@@ -35,9 +35,11 @@ use crate::sys;
use crate::Handle;
use crate::{Error, FatalErrorKind, Result};
use crate::{AIO_DIRECTION_BOTH, AIO_DIRECTION_READ, AIO_DIRECTION_WRITE};
-use epoll::Events;
+use mio::unix::SourceFd;
+use mio::{Events, Interest as MioInterest, Poll, Token};
use std::sync::Arc;
use std::sync::Mutex;
+use std::time::Duration;
use tokio::io::{unix::AsyncFd, Interest, Ready as IoReady};
use tokio::sync::Notify;
use tokio::task;
@@ -176,12 +178,12 @@ async fn polling_task(handle_data: &HandleData) ->
Result<(), FatalErrorKind> {
} = handle_data;
let fd = handle.aio_get_fd().map_err(Error::to_fatal)?;
let tokio_fd = AsyncFd::new(fd)?;
- let epfd = epoll::create(false)?;
- epoll::ctl(
- epfd,
- epoll::ControlOptions::EPOLL_CTL_ADD,
- fd,
- epoll::Event::new(Events::EPOLLIN | Events::EPOLLOUT, 42),
+ let mut events = Events::with_capacity(1);
+ let mut poll = Poll::new()?;
+ poll.registry().register(
+ &mut SourceFd(&fd),
+ Token(0),
+ MioInterest::READABLE | MioInterest::WRITABLE,
)?;
// The following loop does approximately the following things:
@@ -248,19 +250,29 @@ async fn polling_task(handle_data: &HandleData) ->
Result<(), FatalErrorKind> {
}
drop(pending_cmds_lock);
- // Use epoll to check the current read/write availability on the fd.
+ // Use mio poll to check the current read/write availability on the fd.
// This is needed because Tokio supports only edge-triggered
// notifications but Libnbd requires level-triggered notifications.
- let mut revent = epoll::Event { data: 0, events: 0 };
// Setting timeout to 0 means that it will return immediately.
- epoll::wait(epfd, 0, std::slice::from_mut(&mut revent))?;
- let revents = Events::from_bits(revent.events).unwrap();
- if !revents.contains(Events::EPOLLIN) {
- ready_guard.clear_ready_matching(IoReady::READABLE);
- }
- if !revents.contains(Events::EPOLLOUT) {
- ready_guard.clear_ready_matching(IoReady::WRITABLE);
- }
+ // mio states that it is OS-dependent on whether a single event
+ // can be both readable and writable, but we survive just fine
+ // if we only see one direction even when both are available.
+ match poll.poll(&mut events, Some(Duration::ZERO)) {
+ Ok(_) => {
+ for event in &events {
+ if !event.is_readable() {
+ ready_guard.clear_ready_matching(IoReady::READABLE);
+ }
+ if !event.is_writable() {
+ ready_guard.clear_ready_matching(IoReady::WRITABLE);
+ }
+ }
+ }
+ Err(_) => {
+ ready_guard.clear_ready_matching(IoReady::READABLE);
+ ready_guard.clear_ready_matching(IoReady::WRITABLE);
+ }
+ };
ready_guard.retain_ready();
}
}
--
2.41.0