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Diffstat (limited to 'rust/kernel/kasync/net.rs')
| -rw-r--r-- | rust/kernel/kasync/net.rs | 322 |
1 files changed, 322 insertions, 0 deletions
diff --git a/rust/kernel/kasync/net.rs b/rust/kernel/kasync/net.rs new file mode 100644 index 000000000000..f7d15559e738 --- /dev/null +++ b/rust/kernel/kasync/net.rs @@ -0,0 +1,322 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! Async networking. + +use crate::{bindings, c_types, error::code::*, net, sync::NoWaitLock, types::Opaque, Result}; +use core::{ + future::Future, + marker::{PhantomData, PhantomPinned}, + ops::Deref, + pin::Pin, + task::{Context, Poll, Waker}, +}; + +/// A socket listening on a TCP port. +/// +/// The [`TcpListener::accept`] method is meant to be used in async contexts. +pub struct TcpListener { + listener: net::TcpListener, +} + +impl TcpListener { + /// Creates a new TCP listener. + /// + /// It is configured to listen on the given socket address for the given namespace. + pub fn try_new(ns: &net::Namespace, addr: &net::SocketAddr) -> Result<Self> { + Ok(Self { + listener: net::TcpListener::try_new(ns, addr)?, + }) + } + + /// Accepts a new connection. + /// + /// Returns a future that when ready indicates the result of the accept operation; on success, + /// it contains the newly-accepted tcp stream. + pub fn accept(&self) -> impl Future<Output = Result<TcpStream>> + '_ { + SocketFuture::from_listener( + self, + bindings::BINDINGS_EPOLLIN | bindings::BINDINGS_EPOLLERR, + || { + Ok(TcpStream { + stream: self.listener.accept(false)?, + }) + }, + ) + } +} + +impl Deref for TcpListener { + type Target = net::TcpListener; + + fn deref(&self) -> &Self::Target { + &self.listener + } +} + +/// A connected TCP socket. +/// +/// The potentially blocking methods (e.g., [`TcpStream::read`], [`TcpStream::write`]) are meant +/// to be used in async contexts. +/// +/// # Examples +/// +/// ``` +/// # use kernel::prelude::*; +/// # use kernel::kasync::net::TcpStream; +/// async fn echo_server(stream: TcpStream) -> Result { +/// let mut buf = [0u8; 1024]; +/// loop { +/// let n = stream.read(&mut buf).await?; +/// if n == 0 { +/// return Ok(()); +/// } +/// stream.write_all(&buf[..n]).await?; +/// } +/// } +/// ``` +pub struct TcpStream { + stream: net::TcpStream, +} + +impl TcpStream { + /// Reads data from a connected socket. + /// + /// Returns a future that when ready indicates the result of the read operation; on success, it + /// contains the number of bytes read, which will be zero if the connection is closed. + pub fn read<'a>(&'a self, buf: &'a mut [u8]) -> impl Future<Output = Result<usize>> + 'a { + SocketFuture::from_stream( + self, + bindings::BINDINGS_EPOLLIN | bindings::BINDINGS_EPOLLHUP | bindings::BINDINGS_EPOLLERR, + || self.stream.read(buf, false), + ) + } + + /// Writes data to the connected socket. + /// + /// Returns a future that when ready indicates the result of the write operation; on success, it + /// contains the number of bytes written. + pub fn write<'a>(&'a self, buf: &'a [u8]) -> impl Future<Output = Result<usize>> + 'a { + SocketFuture::from_stream( + self, + bindings::BINDINGS_EPOLLOUT | bindings::BINDINGS_EPOLLHUP | bindings::BINDINGS_EPOLLERR, + || self.stream.write(buf, false), + ) + } + + /// Writes all the data to the connected socket. + /// + /// Returns a future that when ready indicates the result of the write operation; on success, it + /// has written all the data. + pub async fn write_all<'a>(&'a self, buf: &'a [u8]) -> Result { + let mut rem = buf; + + while !rem.is_empty() { + let n = self.write(rem).await?; + rem = &rem[n..]; + } + + Ok(()) + } +} + +impl Deref for TcpStream { + type Target = net::TcpStream; + + fn deref(&self) -> &Self::Target { + &self.stream + } +} + +/// A future for a socket operation. +/// +/// # Invariants +/// +/// `sock` is always non-null and valid for the duration of the lifetime of the instance. +struct SocketFuture<'a, Out, F: FnMut() -> Result<Out> + Send + 'a> { + sock: *mut bindings::socket, + mask: u32, + is_queued: bool, + wq_entry: Opaque<bindings::wait_queue_entry>, + waker: NoWaitLock<Option<Waker>>, + _p: PhantomData<&'a ()>, + _pin: PhantomPinned, + operation: F, +} + +// SAFETY: A kernel socket can be used from any thread, `wq_entry` is only used on drop and when +// `is_queued` is initially `false`. +unsafe impl<Out, F: FnMut() -> Result<Out> + Send> Send for SocketFuture<'_, Out, F> {} + +impl<'a, Out, F: FnMut() -> Result<Out> + Send + 'a> SocketFuture<'a, Out, F> { + /// Creates a new socket future. + /// + /// # Safety + /// + /// Callers must ensure that `sock` is non-null, valid, and remains valid for the lifetime + /// (`'a`) of the returned instance. + unsafe fn new(sock: *mut bindings::socket, mask: u32, operation: F) -> Self { + Self { + sock, + mask, + is_queued: false, + wq_entry: Opaque::uninit(), + waker: NoWaitLock::new(None), + operation, + _p: PhantomData, + _pin: PhantomPinned, + } + } + + /// Creates a new socket future for a tcp listener. + fn from_listener(listener: &'a TcpListener, mask: u32, operation: F) -> Self { + // SAFETY: The socket is guaranteed to remain valid because it is bound to the reference to + // the listener (whose existence guarantees the socket remains valid). + unsafe { Self::new(listener.listener.sock, mask, operation) } + } + + /// Creates a new socket future for a tcp stream. + fn from_stream(stream: &'a TcpStream, mask: u32, operation: F) -> Self { + // SAFETY: The socket is guaranteed to remain valid because it is bound to the reference to + // the stream (whose existence guarantees the socket remains valid). + unsafe { Self::new(stream.stream.sock, mask, operation) } + } + + /// Callback called when the socket changes state. + /// + /// If the state matches the one we're waiting on, we wake up the task so that the future can be + /// polled again. + unsafe extern "C" fn wake_callback( + wq_entry: *mut bindings::wait_queue_entry, + _mode: c_types::c_uint, + _flags: c_types::c_int, + key: *mut c_types::c_void, + ) -> c_types::c_int { + let mask = key as u32; + + // SAFETY: The future is valid while this callback is called because we remove from the + // queue on drop. + // + // There is a potential soundness issue here because we're generating a shared reference to + // `Self` while `Self::poll` has a mutable (unique) reference. However, for `!Unpin` types + // (like `Self`), `&mut T` is treated as `*mut T` per + // https://github.com/rust-lang/rust/issues/63818 -- so we avoid the unsoundness. Once a + // more definitive solution is available, we can change this to use it. + let s = unsafe { &*crate::container_of!(wq_entry, Self, wq_entry) }; + if mask & s.mask == 0 { + // Nothing to do as this notification doesn't interest us. + return 0; + } + + // If we can't acquire the waker lock, the waker is in the process of being modified. Our + // attempt to acquire the lock will be reported to the lock owner, so it will trigger the + // wake up. + if let Some(guard) = s.waker.try_lock() { + if let Some(ref w) = *guard { + let cloned = w.clone(); + drop(guard); + cloned.wake(); + return 1; + } + } + 0 + } + + /// Poll the future once. + /// + /// It calls the operation and converts `EAGAIN` errors into a pending state. + fn poll_once(self: Pin<&mut Self>) -> Poll<Result<Out>> { + // SAFETY: We never move out of `this`. + let this = unsafe { self.get_unchecked_mut() }; + match (this.operation)() { + Ok(s) => Poll::Ready(Ok(s)), + Err(e) => { + if e == EAGAIN { + Poll::Pending + } else { + Poll::Ready(Err(e)) + } + } + } + } + + /// Updates the waker stored in the future. + /// + /// It automatically triggers a wake up on races with the reactor. + fn set_waker(&self, waker: &Waker) { + if let Some(mut guard) = self.waker.try_lock() { + let old = core::mem::replace(&mut *guard, Some(waker.clone())); + let contention = guard.unlock(); + drop(old); + if !contention { + return; + } + } + + // We either couldn't store the waker because the existing one is being awakened, or the + // reactor tried to acquire the lock while we held it (contention). In either case, we just + // wake it up to ensure we don't miss any notification. + waker.wake_by_ref(); + } +} + +impl<Out, F: FnMut() -> Result<Out> + Send> Future for SocketFuture<'_, Out, F> { + type Output = Result<Out>; + + fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> { + match self.as_mut().poll_once() { + Poll::Ready(r) => Poll::Ready(r), + Poll::Pending => { + // Store away the latest waker every time we may `Pending`. + self.set_waker(cx.waker()); + if self.is_queued { + // Nothing else to do was the waiter is already queued. + return Poll::Pending; + } + + // SAFETY: We never move out of `this`. + let this = unsafe { self.as_mut().get_unchecked_mut() }; + + this.is_queued = true; + + // SAFETY: `wq_entry` is valid for write. + unsafe { + bindings::init_waitqueue_func_entry( + this.wq_entry.get(), + Some(Self::wake_callback), + ) + }; + + // SAFETY: `wq_entry` was just initialised above and is valid for read/write. + // By the type invariants, the socket is always valid. + unsafe { + bindings::add_wait_queue( + core::ptr::addr_of_mut!((*this.sock).wq.wait), + this.wq_entry.get(), + ) + }; + + // If the future wasn't queued yet, we need to poll again in case it reached + // the desired state between the last poll and being queued (in which case we + // would have missed the notification). + self.poll_once() + } + } + } +} + +impl<Out, F: FnMut() -> Result<Out> + Send> Drop for SocketFuture<'_, Out, F> { + fn drop(&mut self) { + if !self.is_queued { + return; + } + + // SAFETY: `wq_entry` is initialised because `is_queued` is set to `true`, so it is valid + // for read/write. By the type invariants, the socket is always valid. + unsafe { + bindings::remove_wait_queue( + core::ptr::addr_of_mut!((*self.sock).wq.wait), + self.wq_entry.get(), + ) + }; + } +} |