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rust: init: add PinnedDrop trait and macros
The `PinnedDrop` trait that facilitates destruction of pinned types. It has to be implemented via the `#[pinned_drop]` macro, since the `drop` function should not be called by normal code, only by other destructors. It also only works on structs that are annotated with `#[pin_data(PinnedDrop)]`. Co-developed-by: Gary Guo <gary@garyguo.net> Signed-off-by: Gary Guo <gary@garyguo.net> Signed-off-by: Benno Lossin <benno.lossin@proton.me> Reviewed-by: Alice Ryhl <aliceryhl@google.com> Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com> Link: https://lore.kernel.org/r/20230408122429.1103522-10-y86-dev@protonmail.com Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Benno Lossin
Miguel Ojeda
parent
92c4a1e7e8
commit
d0fdc39612
5 changed files with 488 additions and 0 deletions
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@ -104,6 +104,78 @@
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//! }
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//! ```
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//!
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//! ## Manual creation of an initializer
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//!
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//! Often when working with primitives the previous approaches are not sufficient. That is where
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//! [`pin_init_from_closure()`] comes in. This `unsafe` function allows you to create a
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//! [`impl PinInit<T, E>`] directly from a closure. Of course you have to ensure that the closure
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//! actually does the initialization in the correct way. Here are the things to look out for
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//! (we are calling the parameter to the closure `slot`):
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//! - when the closure returns `Ok(())`, then it has completed the initialization successfully, so
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//! `slot` now contains a valid bit pattern for the type `T`,
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//! - when the closure returns `Err(e)`, then the caller may deallocate the memory at `slot`, so
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//! you need to take care to clean up anything if your initialization fails mid-way,
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//! - you may assume that `slot` will stay pinned even after the closure returns until `drop` of
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//! `slot` gets called.
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//!
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//! ```rust
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//! use kernel::{prelude::*, init};
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//! use core::{ptr::addr_of_mut, marker::PhantomPinned, pin::Pin};
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//! # mod bindings {
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//! # pub struct foo;
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//! # pub unsafe fn init_foo(_ptr: *mut foo) {}
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//! # pub unsafe fn destroy_foo(_ptr: *mut foo) {}
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//! # pub unsafe fn enable_foo(_ptr: *mut foo, _flags: u32) -> i32 { 0 }
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//! # }
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//! /// # Invariants
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//! ///
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//! /// `foo` is always initialized
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//! #[pin_data(PinnedDrop)]
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//! pub struct RawFoo {
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//! #[pin]
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//! foo: Opaque<bindings::foo>,
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//! #[pin]
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//! _p: PhantomPinned,
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//! }
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//!
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//! impl RawFoo {
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//! pub fn new(flags: u32) -> impl PinInit<Self, Error> {
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//! // SAFETY:
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//! // - when the closure returns `Ok(())`, then it has successfully initialized and
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//! // enabled `foo`,
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//! // - when it returns `Err(e)`, then it has cleaned up before
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//! unsafe {
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//! init::pin_init_from_closure(move |slot: *mut Self| {
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//! // `slot` contains uninit memory, avoid creating a reference.
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//! let foo = addr_of_mut!((*slot).foo);
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//!
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//! // Initialize the `foo`
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//! bindings::init_foo(Opaque::raw_get(foo));
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//!
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//! // Try to enable it.
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//! let err = bindings::enable_foo(Opaque::raw_get(foo), flags);
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//! if err != 0 {
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//! // Enabling has failed, first clean up the foo and then return the error.
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//! bindings::destroy_foo(Opaque::raw_get(foo));
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//! return Err(Error::from_kernel_errno(err));
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//! }
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//!
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//! // All fields of `RawFoo` have been initialized, since `_p` is a ZST.
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//! Ok(())
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//! })
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//! }
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//! }
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//! }
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//!
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//! #[pinned_drop]
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//! impl PinnedDrop for RawFoo {
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//! fn drop(self: Pin<&mut Self>) {
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//! // SAFETY: Since `foo` is initialized, destroying is safe.
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//! unsafe { bindings::destroy_foo(self.foo.get()) };
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//! }
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//! }
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//! ```
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//!
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//! [`sync`]: kernel::sync
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//! [pinning]: https://doc.rust-lang.org/std/pin/index.html
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//! [structurally pinned fields]:
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@ -1084,3 +1156,42 @@ fn try_init<E>(init: impl Init<T, E>) -> Result<Self, E>
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Ok(unsafe { this.assume_init() })
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}
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}
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/// Trait facilitating pinned destruction.
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///
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/// Use [`pinned_drop`] to implement this trait safely:
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///
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/// ```rust
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/// # use kernel::sync::Mutex;
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/// use kernel::macros::pinned_drop;
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/// use core::pin::Pin;
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/// #[pin_data(PinnedDrop)]
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/// struct Foo {
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/// #[pin]
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/// mtx: Mutex<usize>,
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/// }
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///
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/// #[pinned_drop]
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/// impl PinnedDrop for Foo {
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/// fn drop(self: Pin<&mut Self>) {
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/// pr_info!("Foo is being dropped!");
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/// }
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/// }
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/// ```
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///
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/// # Safety
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///
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/// This trait must be implemented via the [`pinned_drop`] proc-macro attribute on the impl.
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///
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/// [`pinned_drop`]: kernel::macros::pinned_drop
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pub unsafe trait PinnedDrop: __internal::HasPinData {
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/// Executes the pinned destructor of this type.
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///
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/// While this function is marked safe, it is actually unsafe to call it manually. For this
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/// reason it takes an additional parameter. This type can only be constructed by `unsafe` code
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/// and thus prevents this function from being called where it should not.
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///
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/// This extra parameter will be generated by the `#[pinned_drop]` proc-macro attribute
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/// automatically.
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fn drop(self: Pin<&mut Self>, only_call_from_drop: __internal::OnlyCallFromDrop);
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}
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@ -161,3 +161,18 @@ fn drop(&mut self) {
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}
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}
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}
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/// Token used by `PinnedDrop` to prevent calling the function without creating this unsafely
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/// created struct. This is needed, because the `drop` function is safe, but should not be called
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/// manually.
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pub struct OnlyCallFromDrop(());
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impl OnlyCallFromDrop {
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/// # Safety
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///
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/// This function should only be called from the [`Drop::drop`] function and only be used to
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/// delegate the destruction to the pinned destructor [`PinnedDrop::drop`] of the same type.
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pub unsafe fn new() -> Self {
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Self(())
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}
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}
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@ -31,6 +31,26 @@
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//! pin_init!(Self { t, x: 0 })
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//! }
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//! }
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//!
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//! #[pin_data(PinnedDrop)]
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//! struct Foo {
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//! a: usize,
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//! #[pin]
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//! b: Bar<u32>,
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//! }
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//!
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//! #[pinned_drop]
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//! impl PinnedDrop for Foo {
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//! fn drop(self: Pin<&mut Self>) {
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//! println!("{self:p} is getting dropped.");
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//! }
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//! }
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//!
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//! let a = 42;
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//! let initializer = pin_init!(Foo {
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//! a,
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//! b <- Bar::new(36),
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//! });
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//! ```
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//!
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//! This example includes the most common and important features of the pin-init API.
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@ -155,6 +175,14 @@
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//! #[allow(drop_bounds)]
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//! impl<T: ::core::ops::Drop> MustNotImplDrop for T {}
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//! impl<T> MustNotImplDrop for Bar<T> {}
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//! // Here comes a convenience check, if one implemented `PinnedDrop`, but forgot to add it to
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//! // `#[pin_data]`, then this will error with the same mechanic as above, this is not needed
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//! // for safety, but a good sanity check, since no normal code calls `PinnedDrop::drop`.
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//! #[allow(non_camel_case_types)]
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//! trait UselessPinnedDropImpl_you_need_to_specify_PinnedDrop {}
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//! impl<T: ::kernel::init::PinnedDrop>
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//! UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for T {}
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//! impl<T> UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for Bar<T> {}
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//! };
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//! ```
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//!
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@ -265,6 +293,210 @@
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//! }
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//! }
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//! ```
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//!
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//! ## `#[pin_data]` on `Foo`
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//!
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//! Since we already took a look at `#[pin_data]` on `Bar`, this section will only explain the
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//! differences/new things in the expansion of the `Foo` definition:
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//!
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//! ```rust
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//! #[pin_data(PinnedDrop)]
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//! struct Foo {
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//! a: usize,
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//! #[pin]
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//! b: Bar<u32>,
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//! }
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//! ```
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//!
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//! This expands to the following code:
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//!
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//! ```rust
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//! struct Foo {
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//! a: usize,
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//! b: Bar<u32>,
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//! }
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//! const _: () = {
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//! struct __ThePinData {
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//! __phantom: ::core::marker::PhantomData<fn(Foo) -> Foo>,
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//! }
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//! impl ::core::clone::Clone for __ThePinData {
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//! fn clone(&self) -> Self {
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//! *self
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//! }
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//! }
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//! impl ::core::marker::Copy for __ThePinData {}
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//! #[allow(dead_code)]
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//! impl __ThePinData {
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//! unsafe fn b<E>(
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//! self,
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//! slot: *mut Bar<u32>,
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//! // Note that this is `PinInit` instead of `Init`, this is because `b` is
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//! // structurally pinned, as marked by the `#[pin]` attribute.
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//! init: impl ::kernel::init::PinInit<Bar<u32>, E>,
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//! ) -> ::core::result::Result<(), E> {
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//! unsafe { ::kernel::init::PinInit::__pinned_init(init, slot) }
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//! }
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//! unsafe fn a<E>(
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//! self,
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//! slot: *mut usize,
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//! init: impl ::kernel::init::Init<usize, E>,
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//! ) -> ::core::result::Result<(), E> {
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//! unsafe { ::kernel::init::Init::__init(init, slot) }
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//! }
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//! }
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//! unsafe impl ::kernel::init::__internal::HasPinData for Foo {
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//! type PinData = __ThePinData;
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//! unsafe fn __pin_data() -> Self::PinData {
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//! __ThePinData {
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//! __phantom: ::core::marker::PhantomData,
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//! }
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//! }
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//! }
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//! unsafe impl ::kernel::init::__internal::PinData for __ThePinData {
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//! type Datee = Foo;
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//! }
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//! #[allow(dead_code)]
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//! struct __Unpin<'__pin> {
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//! __phantom_pin: ::core::marker::PhantomData<fn(&'__pin ()) -> &'__pin ()>,
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//! __phantom: ::core::marker::PhantomData<fn(Foo) -> Foo>,
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//! // Since this field is `#[pin]`, it is listed here.
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//! b: Bar<u32>,
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//! }
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//! #[doc(hidden)]
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//! impl<'__pin> ::core::marker::Unpin for Foo where __Unpin<'__pin>: ::core::marker::Unpin {}
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//! // Since we specified `PinnedDrop` as the argument to `#[pin_data]`, we expect `Foo` to
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//! // implement `PinnedDrop`. Thus we do not need to prevent `Drop` implementations like
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//! // before, instead we implement it here and delegate to `PinnedDrop`.
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//! impl ::core::ops::Drop for Foo {
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//! fn drop(&mut self) {
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//! // Since we are getting dropped, no one else has a reference to `self` and thus we
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//! // can assume that we never move.
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//! let pinned = unsafe { ::core::pin::Pin::new_unchecked(self) };
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//! // Create the unsafe token that proves that we are inside of a destructor, this
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//! // type is only allowed to be created in a destructor.
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//! let token = unsafe { ::kernel::init::__internal::OnlyCallFromDrop::new() };
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//! ::kernel::init::PinnedDrop::drop(pinned, token);
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//! }
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//! }
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//! };
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//! ```
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//!
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//! ## `#[pinned_drop]` on `impl PinnedDrop for Foo`
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//!
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//! This macro is used to implement the `PinnedDrop` trait, since that trait is `unsafe` and has an
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//! extra parameter that should not be used at all. The macro hides that parameter.
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//!
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//! Here is the `PinnedDrop` impl for `Foo`:
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//!
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//! ```rust
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//! #[pinned_drop]
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//! impl PinnedDrop for Foo {
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//! fn drop(self: Pin<&mut Self>) {
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//! println!("{self:p} is getting dropped.");
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//! }
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//! }
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//! ```
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//!
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//! This expands to the following code:
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//!
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//! ```rust
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//! // `unsafe`, full path and the token parameter are added, everything else stays the same.
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//! unsafe impl ::kernel::init::PinnedDrop for Foo {
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//! fn drop(self: Pin<&mut Self>, _: ::kernel::init::__internal::OnlyCallFromDrop) {
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//! println!("{self:p} is getting dropped.");
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//! }
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//! }
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//! ```
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//!
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//! ## `pin_init!` on `Foo`
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//!
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//! Since we already took a look at `pin_init!` on `Bar`, this section will only explain the
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//! differences/new things in the expansion of `pin_init!` on `Foo`:
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//!
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//! ```rust
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//! let a = 42;
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//! let initializer = pin_init!(Foo {
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//! a,
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//! b <- Bar::new(36),
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//! });
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//! ```
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//!
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//! This expands to the following code:
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//!
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//! ```rust
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//! let a = 42;
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//! let initializer = {
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//! struct __InitOk;
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//! let data = unsafe {
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//! use ::kernel::init::__internal::HasPinData;
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//! Foo::__pin_data()
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//! };
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//! let init = ::kernel::init::__internal::PinData::make_closure::<
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//! _,
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//! __InitOk,
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//! ::core::convert::Infallible,
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//! >(data, move |slot| {
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//! {
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//! struct __InitOk;
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//! unsafe { ::core::ptr::write(&raw mut (*slot).a, a) };
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//! let a = &unsafe { ::kernel::init::__internal::DropGuard::new(&raw mut (*slot).a) };
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//! let b = Bar::new(36);
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//! // Here we use `data` to access the correct field and require that `b` is of type
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//! // `PinInit<Bar<u32>, Infallible>`.
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//! unsafe { data.b(&raw mut (*slot).b, b)? };
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//! let b = &unsafe { ::kernel::init::__internal::DropGuard::new(&raw mut (*slot).b) };
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//!
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//! #[allow(unreachable_code, clippy::diverging_sub_expression)]
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//! if false {
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//! unsafe {
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//! ::core::ptr::write(
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//! slot,
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//! Foo {
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//! a: ::core::panic!(),
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//! b: ::core::panic!(),
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//! },
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//! );
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//! };
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//! }
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//! unsafe { ::kernel::init::__internal::DropGuard::forget(a) };
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//! unsafe { ::kernel::init::__internal::DropGuard::forget(b) };
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//! }
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//! Ok(__InitOk)
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//! });
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//! let init = move |slot| -> ::core::result::Result<(), ::core::convert::Infallible> {
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//! init(slot).map(|__InitOk| ())
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//! };
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//! let init = unsafe {
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//! ::kernel::init::pin_init_from_closure::<_, ::core::convert::Infallible>(init)
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//! };
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//! init
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//! };
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//! ```
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/// Creates a `unsafe impl<...> PinnedDrop for $type` block.
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///
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/// See [`PinnedDrop`] for more information.
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#[doc(hidden)]
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#[macro_export]
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macro_rules! __pinned_drop {
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(
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@impl_sig($($impl_sig:tt)*),
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@impl_body(
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$(#[$($attr:tt)*])*
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fn drop($($sig:tt)*) {
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$($inner:tt)*
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}
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),
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) => {
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unsafe $($impl_sig)* {
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// Inherit all attributes and the type/ident tokens for the signature.
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$(#[$($attr)*])*
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fn drop($($sig)*, _: $crate::init::__internal::OnlyCallFromDrop) {
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$($inner)*
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}
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}
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}
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}
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/// This macro first parses the struct definition such that it separates pinned and not pinned
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/// fields. Afterwards it declares the struct and implement the `PinData` trait safely.
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@ -653,6 +885,38 @@ trait MustNotImplDrop {}
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impl<T: ::core::ops::Drop> MustNotImplDrop for T {}
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impl<$($impl_generics)*> MustNotImplDrop for $name<$($ty_generics)*>
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where $($whr)* {}
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// We also take care to prevent users from writing a useless `PinnedDrop` implementation.
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// They might implement `PinnedDrop` correctly for the struct, but forget to give
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// `PinnedDrop` as the parameter to `#[pin_data]`.
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#[allow(non_camel_case_types)]
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trait UselessPinnedDropImpl_you_need_to_specify_PinnedDrop {}
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impl<T: $crate::init::PinnedDrop>
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UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for T {}
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impl<$($impl_generics)*>
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UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for $name<$($ty_generics)*>
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where $($whr)* {}
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};
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// When `PinnedDrop` was specified we just implement `Drop` and delegate.
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(drop_prevention:
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@name($name:ident),
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@impl_generics($($impl_generics:tt)*),
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@ty_generics($($ty_generics:tt)*),
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@where($($whr:tt)*),
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@pinned_drop(PinnedDrop),
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) => {
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impl<$($impl_generics)*> ::core::ops::Drop for $name<$($ty_generics)*>
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where $($whr)*
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{
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fn drop(&mut self) {
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// SAFETY: Since this is a destructor, `self` will not move after this function
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// terminates, since it is inaccessible.
|
||||
let pinned = unsafe { ::core::pin::Pin::new_unchecked(self) };
|
||||
// SAFETY: Since this is a drop function, we can create this token to call the
|
||||
// pinned destructor of this type.
|
||||
let token = unsafe { $crate::init::__internal::OnlyCallFromDrop::new() };
|
||||
$crate::init::PinnedDrop::drop(pinned, token);
|
||||
}
|
||||
}
|
||||
};
|
||||
// If some other parameter was specified, we emit a readable error.
|
||||
(drop_prevention:
|
||||
|
|
|
|||
|
|
@ -8,6 +8,7 @@
|
|||
mod helpers;
|
||||
mod module;
|
||||
mod pin_data;
|
||||
mod pinned_drop;
|
||||
mod vtable;
|
||||
|
||||
use proc_macro::TokenStream;
|
||||
|
|
@ -180,6 +181,10 @@ pub fn concat_idents(ts: TokenStream) -> TokenStream {
|
|||
/// This macro enables the use of the [`pin_init!`] macro. When pin-initializing a `struct`,
|
||||
/// then `#[pin]` directs the type of initializer that is required.
|
||||
///
|
||||
/// If your `struct` implements `Drop`, then you need to add `PinnedDrop` as arguments to this
|
||||
/// macro, and change your `Drop` implementation to `PinnedDrop` annotated with
|
||||
/// `#[`[`macro@pinned_drop`]`]`, since dropping pinned values requires extra care.
|
||||
///
|
||||
/// # Examples
|
||||
///
|
||||
/// ```rust,ignore
|
||||
|
|
@ -191,9 +196,53 @@ pub fn concat_idents(ts: TokenStream) -> TokenStream {
|
|||
/// }
|
||||
/// ```
|
||||
///
|
||||
/// ```rust,ignore
|
||||
/// #[pin_data(PinnedDrop)]
|
||||
/// struct DriverData {
|
||||
/// #[pin]
|
||||
/// queue: Mutex<Vec<Command>>,
|
||||
/// buf: Box<[u8; 1024 * 1024]>,
|
||||
/// raw_info: *mut Info,
|
||||
/// }
|
||||
///
|
||||
/// #[pinned_drop]
|
||||
/// impl PinnedDrop for DriverData {
|
||||
/// fn drop(self: Pin<&mut Self>) {
|
||||
/// unsafe { bindings::destroy_info(self.raw_info) };
|
||||
/// }
|
||||
/// }
|
||||
/// ```
|
||||
///
|
||||
/// [`pin_init!`]: ../kernel/macro.pin_init.html
|
||||
// ^ cannot use direct link, since `kernel` is not a dependency of `macros`.
|
||||
#[proc_macro_attribute]
|
||||
pub fn pin_data(inner: TokenStream, item: TokenStream) -> TokenStream {
|
||||
pin_data::pin_data(inner, item)
|
||||
}
|
||||
|
||||
/// Used to implement `PinnedDrop` safely.
|
||||
///
|
||||
/// Only works on structs that are annotated via `#[`[`macro@pin_data`]`]`.
|
||||
///
|
||||
/// # Examples
|
||||
///
|
||||
/// ```rust,ignore
|
||||
/// #[pin_data(PinnedDrop)]
|
||||
/// struct DriverData {
|
||||
/// #[pin]
|
||||
/// queue: Mutex<Vec<Command>>,
|
||||
/// buf: Box<[u8; 1024 * 1024]>,
|
||||
/// raw_info: *mut Info,
|
||||
/// }
|
||||
///
|
||||
/// #[pinned_drop]
|
||||
/// impl PinnedDrop for DriverData {
|
||||
/// fn drop(self: Pin<&mut Self>) {
|
||||
/// unsafe { bindings::destroy_info(self.raw_info) };
|
||||
/// }
|
||||
/// }
|
||||
/// ```
|
||||
#[proc_macro_attribute]
|
||||
pub fn pinned_drop(args: TokenStream, input: TokenStream) -> TokenStream {
|
||||
pinned_drop::pinned_drop(args, input)
|
||||
}
|
||||
|
|
|
|||
49
rust/macros/pinned_drop.rs
Normal file
49
rust/macros/pinned_drop.rs
Normal file
|
|
@ -0,0 +1,49 @@
|
|||
// SPDX-License-Identifier: Apache-2.0 OR MIT
|
||||
|
||||
use proc_macro::{TokenStream, TokenTree};
|
||||
|
||||
pub(crate) fn pinned_drop(_args: TokenStream, input: TokenStream) -> TokenStream {
|
||||
let mut toks = input.into_iter().collect::<Vec<_>>();
|
||||
assert!(!toks.is_empty());
|
||||
// Ensure that we have an `impl` item.
|
||||
assert!(matches!(&toks[0], TokenTree::Ident(i) if i.to_string() == "impl"));
|
||||
// Ensure that we are implementing `PinnedDrop`.
|
||||
let mut nesting: usize = 0;
|
||||
let mut pinned_drop_idx = None;
|
||||
for (i, tt) in toks.iter().enumerate() {
|
||||
match tt {
|
||||
TokenTree::Punct(p) if p.as_char() == '<' => {
|
||||
nesting += 1;
|
||||
}
|
||||
TokenTree::Punct(p) if p.as_char() == '>' => {
|
||||
nesting = nesting.checked_sub(1).unwrap();
|
||||
continue;
|
||||
}
|
||||
_ => {}
|
||||
}
|
||||
if i >= 1 && nesting == 0 {
|
||||
// Found the end of the generics, this should be `PinnedDrop`.
|
||||
assert!(
|
||||
matches!(tt, TokenTree::Ident(i) if i.to_string() == "PinnedDrop"),
|
||||
"expected 'PinnedDrop', found: '{:?}'",
|
||||
tt
|
||||
);
|
||||
pinned_drop_idx = Some(i);
|
||||
break;
|
||||
}
|
||||
}
|
||||
let idx = pinned_drop_idx
|
||||
.unwrap_or_else(|| panic!("Expected an `impl` block implementing `PinnedDrop`."));
|
||||
// Fully qualify the `PinnedDrop`, as to avoid any tampering.
|
||||
toks.splice(idx..idx, quote!(::kernel::init::));
|
||||
// Take the `{}` body and call the declarative macro.
|
||||
if let Some(TokenTree::Group(last)) = toks.pop() {
|
||||
let last = last.stream();
|
||||
quote!(::kernel::__pinned_drop! {
|
||||
@impl_sig(#(#toks)*),
|
||||
@impl_body(#last),
|
||||
})
|
||||
} else {
|
||||
TokenStream::from_iter(toks)
|
||||
}
|
||||
}
|
||||
Loading…
Reference in a new issue