kernel/
init.rs

1// SPDX-License-Identifier: GPL-2.0
2
3//! Extensions to the [`pin-init`] crate.
4//!
5//! Most `struct`s from the [`sync`] module need to be pinned, because they contain self-referential
6//! `struct`s from C. [Pinning][pinning] is Rust's way of ensuring data does not move.
7//!
8//! The [`pin-init`] crate is the way such structs are initialized on the Rust side. Please refer
9//! to its documentation to better understand how to use it. Additionally, there are many examples
10//! throughout the kernel, such as the types from the [`sync`] module. And the ones presented
11//! below.
12//!
13//! [`sync`]: crate::sync
14//! [pinning]: https://doc.rust-lang.org/std/pin/index.html
15//! [`pin-init`]: https://rust.docs.kernel.org/pin_init/
16//!
17//! # [`Opaque<T>`]
18//!
19//! For the special case where initializing a field is a single FFI-function call that cannot fail,
20//! there exist the helper function [`Opaque::ffi_init`]. This function initialize a single
21//! [`Opaque<T>`] field by just delegating to the supplied closure. You can use these in
22//! combination with [`pin_init!`].
23//!
24//! [`Opaque<T>`]: crate::types::Opaque
25//! [`Opaque::ffi_init`]: crate::types::Opaque::ffi_init
26//! [`pin_init!`]: pin_init::pin_init
27//!
28//! # Examples
29//!
30//! ## General Examples
31//!
32//! ```rust,ignore
33//! # #![allow(clippy::disallowed_names)]
34//! use kernel::types::Opaque;
35//! use pin_init::pin_init_from_closure;
36//!
37//! // assume we have some `raw_foo` type in C:
38//! #[repr(C)]
39//! struct RawFoo([u8; 16]);
40//! extern {
41//!     fn init_foo(_: *mut RawFoo);
42//! }
43//!
44//! #[pin_data]
45//! struct Foo {
46//!     #[pin]
47//!     raw: Opaque<RawFoo>,
48//! }
49//!
50//! impl Foo {
51//!     fn setup(self: Pin<&mut Self>) {
52//!         pr_info!("Setting up foo\n");
53//!     }
54//! }
55//!
56//! let foo = pin_init!(Foo {
57//!     raw <- unsafe {
58//!         Opaque::ffi_init(|s| {
59//!             // note that this cannot fail.
60//!             init_foo(s);
61//!         })
62//!     },
63//! }).pin_chain(|foo| {
64//!     foo.setup();
65//!     Ok(())
66//! });
67//! ```
68//!
69//! ```rust,ignore
70//! # #![allow(unreachable_pub, clippy::disallowed_names)]
71//! use kernel::{prelude::*, types::Opaque};
72//! use core::{ptr::addr_of_mut, marker::PhantomPinned, pin::Pin};
73//! # mod bindings {
74//! #     #![allow(non_camel_case_types)]
75//! #     pub struct foo;
76//! #     pub unsafe fn init_foo(_ptr: *mut foo) {}
77//! #     pub unsafe fn destroy_foo(_ptr: *mut foo) {}
78//! #     pub unsafe fn enable_foo(_ptr: *mut foo, _flags: u32) -> i32 { 0 }
79//! # }
80//! # // `Error::from_errno` is `pub(crate)` in the `kernel` crate, thus provide a workaround.
81//! # trait FromErrno {
82//! #     fn from_errno(errno: core::ffi::c_int) -> Error {
83//! #         // Dummy error that can be constructed outside the `kernel` crate.
84//! #         Error::from(core::fmt::Error)
85//! #     }
86//! # }
87//! # impl FromErrno for Error {}
88//! /// # Invariants
89//! ///
90//! /// `foo` is always initialized
91//! #[pin_data(PinnedDrop)]
92//! pub struct RawFoo {
93//!     #[pin]
94//!     foo: Opaque<bindings::foo>,
95//!     #[pin]
96//!     _p: PhantomPinned,
97//! }
98//!
99//! impl RawFoo {
100//!     pub fn new(flags: u32) -> impl PinInit<Self, Error> {
101//!         // SAFETY:
102//!         // - when the closure returns `Ok(())`, then it has successfully initialized and
103//!         //   enabled `foo`,
104//!         // - when it returns `Err(e)`, then it has cleaned up before
105//!         unsafe {
106//!             pin_init::pin_init_from_closure(move |slot: *mut Self| {
107//!                 // `slot` contains uninit memory, avoid creating a reference.
108//!                 let foo = addr_of_mut!((*slot).foo);
109//!
110//!                 // Initialize the `foo`
111//!                 bindings::init_foo(Opaque::raw_get(foo));
112//!
113//!                 // Try to enable it.
114//!                 let err = bindings::enable_foo(Opaque::raw_get(foo), flags);
115//!                 if err != 0 {
116//!                     // Enabling has failed, first clean up the foo and then return the error.
117//!                     bindings::destroy_foo(Opaque::raw_get(foo));
118//!                     return Err(Error::from_errno(err));
119//!                 }
120//!
121//!                 // All fields of `RawFoo` have been initialized, since `_p` is a ZST.
122//!                 Ok(())
123//!             })
124//!         }
125//!     }
126//! }
127//!
128//! #[pinned_drop]
129//! impl PinnedDrop for RawFoo {
130//!     fn drop(self: Pin<&mut Self>) {
131//!         // SAFETY: Since `foo` is initialized, destroying is safe.
132//!         unsafe { bindings::destroy_foo(self.foo.get()) };
133//!     }
134//! }
135//! ```
136
137use crate::{
138    alloc::{AllocError, Flags},
139    error::{self, Error},
140};
141use pin_init::{init_from_closure, pin_init_from_closure, Init, PinInit};
142
143/// Smart pointer that can initialize memory in-place.
144pub trait InPlaceInit<T>: Sized {
145    /// Pinned version of `Self`.
146    ///
147    /// If a type already implicitly pins its pointee, `Pin<Self>` is unnecessary. In this case use
148    /// `Self`, otherwise just use `Pin<Self>`.
149    type PinnedSelf;
150
151    /// Use the given pin-initializer to pin-initialize a `T` inside of a new smart pointer of this
152    /// type.
153    ///
154    /// If `T: !Unpin` it will not be able to move afterwards.
155    fn try_pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> Result<Self::PinnedSelf, E>
156    where
157        E: From<AllocError>;
158
159    /// Use the given pin-initializer to pin-initialize a `T` inside of a new smart pointer of this
160    /// type.
161    ///
162    /// If `T: !Unpin` it will not be able to move afterwards.
163    fn pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> error::Result<Self::PinnedSelf>
164    where
165        Error: From<E>,
166    {
167        // SAFETY: We delegate to `init` and only change the error type.
168        let init = unsafe {
169            pin_init_from_closure(|slot| init.__pinned_init(slot).map_err(|e| Error::from(e)))
170        };
171        Self::try_pin_init(init, flags)
172    }
173
174    /// Use the given initializer to in-place initialize a `T`.
175    fn try_init<E>(init: impl Init<T, E>, flags: Flags) -> Result<Self, E>
176    where
177        E: From<AllocError>;
178
179    /// Use the given initializer to in-place initialize a `T`.
180    fn init<E>(init: impl Init<T, E>, flags: Flags) -> error::Result<Self>
181    where
182        Error: From<E>,
183    {
184        // SAFETY: We delegate to `init` and only change the error type.
185        let init = unsafe {
186            init_from_closure(|slot| init.__pinned_init(slot).map_err(|e| Error::from(e)))
187        };
188        Self::try_init(init, flags)
189    }
190}
191
192/// Construct an in-place fallible initializer for `struct`s.
193///
194/// This macro defaults the error to [`Error`]. If you need [`Infallible`], then use
195/// [`init!`].
196///
197/// The syntax is identical to [`try_pin_init!`]. If you want to specify a custom error,
198/// append `? $type` after the `struct` initializer.
199/// The safety caveats from [`try_pin_init!`] also apply:
200/// - `unsafe` code must guarantee either full initialization or return an error and allow
201///   deallocation of the memory.
202/// - the fields are initialized in the order given in the initializer.
203/// - no references to fields are allowed to be created inside of the initializer.
204///
205/// # Examples
206///
207/// ```rust
208/// use kernel::error::Error;
209/// use pin_init::zeroed;
210/// struct BigBuf {
211///     big: KBox<[u8; 1024 * 1024 * 1024]>,
212///     small: [u8; 1024 * 1024],
213/// }
214///
215/// impl BigBuf {
216///     fn new() -> impl Init<Self, Error> {
217///         try_init!(Self {
218///             big: KBox::init(zeroed(), GFP_KERNEL)?,
219///             small: [0; 1024 * 1024],
220///         }? Error)
221///     }
222/// }
223/// ```
224///
225/// [`Infallible`]: core::convert::Infallible
226/// [`init!`]: pin_init::init
227/// [`try_pin_init!`]: crate::try_pin_init!
228/// [`Error`]: crate::error::Error
229#[macro_export]
230macro_rules! try_init {
231    ($(&$this:ident in)? $t:ident $(::<$($generics:ty),* $(,)?>)? {
232        $($fields:tt)*
233    }) => {
234        ::pin_init::try_init!($(&$this in)? $t $(::<$($generics),* $(,)?>)? {
235            $($fields)*
236        }? $crate::error::Error)
237    };
238    ($(&$this:ident in)? $t:ident $(::<$($generics:ty),* $(,)?>)? {
239        $($fields:tt)*
240    }? $err:ty) => {
241        ::pin_init::try_init!($(&$this in)? $t $(::<$($generics),* $(,)?>)? {
242            $($fields)*
243        }? $err)
244    };
245}
246
247/// Construct an in-place, fallible pinned initializer for `struct`s.
248///
249/// If the initialization can complete without error (or [`Infallible`]), then use [`pin_init!`].
250///
251/// You can use the `?` operator or use `return Err(err)` inside the initializer to stop
252/// initialization and return the error.
253///
254/// IMPORTANT: if you have `unsafe` code inside of the initializer you have to ensure that when
255/// initialization fails, the memory can be safely deallocated without any further modifications.
256///
257/// This macro defaults the error to [`Error`].
258///
259/// The syntax is identical to [`pin_init!`] with the following exception: you can append `? $type`
260/// after the `struct` initializer to specify the error type you want to use.
261///
262/// # Examples
263///
264/// ```rust
265/// # #![feature(new_uninit)]
266/// use kernel::error::Error;
267/// use pin_init::zeroed;
268/// #[pin_data]
269/// struct BigBuf {
270///     big: KBox<[u8; 1024 * 1024 * 1024]>,
271///     small: [u8; 1024 * 1024],
272///     ptr: *mut u8,
273/// }
274///
275/// impl BigBuf {
276///     fn new() -> impl PinInit<Self, Error> {
277///         try_pin_init!(Self {
278///             big: KBox::init(zeroed(), GFP_KERNEL)?,
279///             small: [0; 1024 * 1024],
280///             ptr: core::ptr::null_mut(),
281///         }? Error)
282///     }
283/// }
284/// ```
285///
286/// [`Infallible`]: core::convert::Infallible
287/// [`pin_init!`]: pin_init::pin_init
288/// [`Error`]: crate::error::Error
289#[macro_export]
290macro_rules! try_pin_init {
291    ($(&$this:ident in)? $t:ident $(::<$($generics:ty),* $(,)?>)? {
292        $($fields:tt)*
293    }) => {
294        ::pin_init::try_pin_init!($(&$this in)? $t $(::<$($generics),* $(,)?>)? {
295            $($fields)*
296        }? $crate::error::Error)
297    };
298    ($(&$this:ident in)? $t:ident $(::<$($generics:ty),* $(,)?>)? {
299        $($fields:tt)*
300    }? $err:ty) => {
301        ::pin_init::try_pin_init!($(&$this in)? $t $(::<$($generics),* $(,)?>)? {
302            $($fields)*
303        }? $err)
304    };
305}
kernel/init.rs

kernel/
init.rs
