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rust: init: update macro expansion example in docs

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Also improve the explaining comments.

Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Link: https://lore.kernel.org/r/20230424081112.99890-4-benno.lossin@proton.me
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Benno Lossin 2023-04-24 08:11:49 +00:00 committed by Miguel Ojeda
parent 52b7bb46ae
commit 309786c239
1 changed files with 48 additions and 37 deletions
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85
rust/kernel/init/macros.rs
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@ -16,8 +16,9 @@
//!
//! We will look at the following example:
//!
//! ```rust
//! ```rust,ignore
//! # use kernel::init::*;
//! # use core::pin::Pin;
//! #[pin_data]
//! #[repr(C)]
//! struct Bar<T> {
@ -71,11 +72,12 @@
//!
//! Here is the definition of `Bar` from our example:
//!
//! ```rust
//! ```rust,ignore
//! # use kernel::init::*;
//! #[pin_data]
//! #[repr(C)]
//! struct Bar<T> {
//! #[pin]
//! t: T,
//! pub x: usize,
//! }
@ -83,7 +85,7 @@
//!
//! This expands to the following code:
//!
//! ```rust
//! ```rust,ignore
//! // Firstly the normal definition of the struct, attributes are preserved:
//! #[repr(C)]
//! struct Bar<T> {
@ -116,20 +118,22 @@
//! unsafe fn t<E>(
//! self,
//! slot: *mut T,
//! init: impl ::kernel::init::Init<T, E>,
//! // Since `t` is `#[pin]`, this is `PinInit`.
//! init: impl ::kernel::init::PinInit<T, E>,
//! ) -> ::core::result::Result<(), E> {
//! unsafe { ::kernel::init::Init::__init(init, slot) }
//! unsafe { ::kernel::init::PinInit::__pinned_init(init, slot) }
//! }
//! pub unsafe fn x<E>(
//! self,
//! slot: *mut usize,
//! // Since `x` is not `#[pin]`, this is `Init`.
//! init: impl ::kernel::init::Init<usize, E>,
//! ) -> ::core::result::Result<(), E> {
//! unsafe { ::kernel::init::Init::__init(init, slot) }
//! }
//! }
//! // Implement the internal `HasPinData` trait that associates `Bar` with the pin-data struct
//! // that we constructed beforehand.
//! // that we constructed above.
//! unsafe impl<T> ::kernel::init::__internal::HasPinData for Bar<T> {
//! type PinData = __ThePinData<T>;
//! unsafe fn __pin_data() -> Self::PinData {
@ -160,6 +164,8 @@
//! struct __Unpin<'__pin, T> {
//! __phantom_pin: ::core::marker::PhantomData<fn(&'__pin ()) -> &'__pin ()>,
//! __phantom: ::core::marker::PhantomData<fn(Bar<T>) -> Bar<T>>,
//! // Our only `#[pin]` field is `t`.
//! t: T,
//! }
//! #[doc(hidden)]
//! impl<'__pin, T>
@ -193,7 +199,7 @@
//!
//! Here is the impl on `Bar` defining the new function:
//!
//! ```rust
//! ```rust,ignore
//! impl<T> Bar<T> {
//! fn new(t: T) -> impl PinInit<Self> {
//! pin_init!(Self { t, x: 0 })
@ -203,7 +209,7 @@
//!
//! This expands to the following code:
//!
//! ```rust
//! ```rust,ignore
//! impl<T> Bar<T> {
//! fn new(t: T) -> impl PinInit<Self> {
//! {
@ -232,25 +238,31 @@
//! // that will refer to this struct instead of the one defined above.
//! struct __InitOk;
//! // This is the expansion of `t,`, which is syntactic sugar for `t: t,`.
//! unsafe { ::core::ptr::write(&raw mut (*slot).t, t) };
//! unsafe { ::core::ptr::write(::core::addr_of_mut!((*slot).t), t) };
//! // Since initialization could fail later (not in this case, since the error
//! // type is `Infallible`) we will need to drop this field if it fails. This
//! // `DropGuard` will drop the field when it gets dropped and has not yet
//! // been forgotten. We make a reference to it, so users cannot `mem::forget`
//! // it from the initializer, since the name is the same as the field.
//! // type is `Infallible`) we will need to drop this field if there is an
//! // error later. This `DropGuard` will drop the field when it gets dropped
//! // and has not yet been forgotten. We make a reference to it, so users
//! // cannot `mem::forget` it from the initializer, since the name is the same
//! // as the field (including hygiene).
//! let t = &unsafe {
//! ::kernel::init::__internal::DropGuard::new(&raw mut (*slot).t)
//! ::kernel::init::__internal::DropGuard::new(
//! ::core::addr_of_mut!((*slot).t),
//! )
//! };
//! // Expansion of `x: 0,`:
//! // Since this can be an arbitrary expression we cannot place it inside of
//! // the `unsafe` block, so we bind it here.
//! let x = 0;
//! unsafe { ::core::ptr::write(&raw mut (*slot).x, x) };
//! unsafe { ::core::ptr::write(::core::addr_of_mut!((*slot).x), x) };
//! // We again create a `DropGuard`.
//! let x = &unsafe {
//! ::kernel::init::__internal::DropGuard::new(&raw mut (*slot).x)
//! ::kernel::init::__internal::DropGuard::new(
//! ::core::addr_of_mut!((*slot).x),
//! )
//! };
//!
//! // Here we use the type checker to ensuer that every field has been
//! // Here we use the type checker to ensure that every field has been
//! // initialized exactly once, since this is `if false` it will never get
//! // executed, but still type-checked.
//! // Additionally we abuse `slot` to automatically infer the correct type for
@ -272,7 +284,7 @@
//! };
//! }
//! // Since initialization has successfully completed, we can now forget the
//! // guards.
//! // guards. This is not `mem::forget`, since we only have `&DropGuard`.
//! unsafe { ::kernel::init::__internal::DropGuard::forget(t) };
//! unsafe { ::kernel::init::__internal::DropGuard::forget(x) };
//! }
@ -280,7 +292,7 @@
//! // `__InitOk` that we need to return.
//! Ok(__InitOk)
//! });
//! // Change the return type of the closure.
//! // Change the return type from `__InitOk` to `()`.
//! let init = move |slot| -> ::core::result::Result<(), ::core::convert::Infallible> {
//! init(slot).map(|__InitOk| ())
//! };
@ -299,7 +311,7 @@
//! Since we already took a look at `#[pin_data]` on `Bar`, this section will only explain the
//! differences/new things in the expansion of the `Foo` definition:
//!
//! ```rust
//! ```rust,ignore
//! #[pin_data(PinnedDrop)]
//! struct Foo {
//! a: usize,
@ -310,7 +322,7 @@
//!
//! This expands to the following code:
//!
//! ```rust
//! ```rust,ignore
//! struct Foo {
//! a: usize,
//! b: Bar<u32>,
@ -330,8 +342,6 @@
//! unsafe fn b<E>(
//! self,
//! slot: *mut Bar<u32>,
//! // Note that this is `PinInit` instead of `Init`, this is because `b` is
//! // structurally pinned, as marked by the `#[pin]` attribute.
//! init: impl ::kernel::init::PinInit<Bar<u32>, E>,
//! ) -> ::core::result::Result<(), E> {
//! unsafe { ::kernel::init::PinInit::__pinned_init(init, slot) }
@ -359,14 +369,13 @@
//! struct __Unpin<'__pin> {
//! __phantom_pin: ::core::marker::PhantomData<fn(&'__pin ()) -> &'__pin ()>,
//! __phantom: ::core::marker::PhantomData<fn(Foo) -> Foo>,
//! // Since this field is `#[pin]`, it is listed here.
//! b: Bar<u32>,
//! }
//! #[doc(hidden)]
//! impl<'__pin> ::core::marker::Unpin for Foo where __Unpin<'__pin>: ::core::marker::Unpin {}
//! // Since we specified `PinnedDrop` as the argument to `#[pin_data]`, we expect `Foo` to
//! // implement `PinnedDrop`. Thus we do not need to prevent `Drop` implementations like
//! // before, instead we implement it here and delegate to `PinnedDrop`.
//! // before, instead we implement `Drop` here and delegate to `PinnedDrop`.
//! impl ::core::ops::Drop for Foo {
//! fn drop(&mut self) {
//! // Since we are getting dropped, no one else has a reference to `self` and thus we
@ -388,7 +397,7 @@
//!
//! Here is the `PinnedDrop` impl for `Foo`:
//!
//! ```rust
//! ```rust,ignore
//! #[pinned_drop]
//! impl PinnedDrop for Foo {
//! fn drop(self: Pin<&mut Self>) {
@ -399,7 +408,7 @@
//!
//! This expands to the following code:
//!
//! ```rust
//! ```rust,ignore
//! // `unsafe`, full path and the token parameter are added, everything else stays the same.
//! unsafe impl ::kernel::init::PinnedDrop for Foo {
//! fn drop(self: Pin<&mut Self>, _: ::kernel::init::__internal::OnlyCallFromDrop) {
@ -410,10 +419,10 @@
//!
//! ## `pin_init!` on `Foo`
//!
//! Since we already took a look at `pin_init!` on `Bar`, this section will only explain the
//! differences/new things in the expansion of `pin_init!` on `Foo`:
//! Since we already took a look at `pin_init!` on `Bar`, this section will only show the expansion
//! of `pin_init!` on `Foo`:
//!
//! ```rust
//! ```rust,ignore
//! let a = 42;
//! let initializer = pin_init!(Foo {
//! a,
@ -423,7 +432,7 @@
//!
//! This expands to the following code:
//!
//! ```rust
//! ```rust,ignore
//! let a = 42;
//! let initializer = {
//! struct __InitOk;
@ -438,13 +447,15 @@
//! >(data, move |slot| {
//! {
//! struct __InitOk;
//! unsafe { ::core::ptr::write(&raw mut (*slot).a, a) };
//! let a = &unsafe { ::kernel::init::__internal::DropGuard::new(&raw mut (*slot).a) };
//! unsafe { ::core::ptr::write(::core::addr_of_mut!((*slot).a), a) };
//! let a = &unsafe {
//! ::kernel::init::__internal::DropGuard::new(::core::addr_of_mut!((*slot).a))
//! };
//! let b = Bar::new(36);
//! // Here we use `data` to access the correct field and require that `b` is of type
//! // `PinInit<Bar<u32>, Infallible>`.
//! unsafe { data.b(&raw mut (*slot).b, b)? };
//! let b = &unsafe { ::kernel::init::__internal::DropGuard::new(&raw mut (*slot).b) };
//! unsafe { data.b(::core::addr_of_mut!((*slot).b), b)? };
//! let b = &unsafe {
//! ::kernel::init::__internal::DropGuard::new(::core::addr_of_mut!((*slot).b))
//! };
//!
//! #[allow(unreachable_code, clippy::diverging_sub_expression)]
//! if false {