Re: [PATCH 5/7] rust: init: add `..Zeroable::zeroed()` syntax for zeroing all missing fields
From: Björn Roy Baron
Date: Sat Jun 24 2023 - 11:12:10 EST
On Saturday, June 24th, 2023 at 11:25, Benno Lossin <benno.lossin@xxxxxxxxx> wrote:
> Add the struct update syntax to the init macros, but only for
> `..Zeroable::zeroed()`. Adding this at the end of the struct initializer
> allows one to omit fields from the initializer, these fields will be
> initialized with 0x00 set to every byte. Only types that implement the
> `Zeroable` trait can utilize this.
>
> Suggested-by: Asahi Lina <lina@xxxxxxxxxxxxx>
> Signed-off-by: Benno Lossin <benno.lossin@xxxxxxxxx>
> ---
> rust/kernel/init.rs | 16 +++++-
> rust/kernel/init/macros.rs | 114 ++++++++++++++++++++++++++++++++++++-
> 2 files changed, 128 insertions(+), 2 deletions(-)
>
> diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
> index ecf6a4bd0ce4..44bc3e77419a 100644
> --- a/rust/kernel/init.rs
> +++ b/rust/kernel/init.rs
> @@ -508,14 +508,18 @@ macro_rules! stack_try_pin_init {
> /// - Fields that you want to initialize in-place have to use `<-` instead of `:`.
> /// - In front of the initializer you can write `&this in` to have access to a [`NonNull<Self>`]
> /// pointer named `this` inside of the initializer.
> +/// - Using struct update syntax one can place `..Zeroable::zeroed()` at the very end of the
> +/// struct, this initializes every field with 0 and then runs all initializers specified in the
> +/// body. This can only be done if [`Zeroable`] is implemented for the struct.
> ///
> /// For instance:
> ///
> /// ```rust
> /// # use kernel::pin_init;
> -/// # use macros::pin_data;
> +/// # use macros::{pin_data, Zeroable};
> /// # use core::{ptr::addr_of_mut, marker::PhantomPinned};
> /// #[pin_data]
> +/// #[derive(Zeroable)]
> /// struct Buf {
> /// // `ptr` points into `buf`.
> /// ptr: *mut u8,
> @@ -528,6 +532,10 @@ macro_rules! stack_try_pin_init {
> /// ptr: unsafe { addr_of_mut!((*this.as_ptr()).buf).cast() },
> /// pin: PhantomPinned,
> /// });
> +/// pin_init!(Buf {
> +/// buf: [1; 64],
> +/// ..Zeroable::zeroed(),
> +/// });
> /// ```
> ///
> /// [`try_pin_init!`]: kernel::try_pin_init
> @@ -547,6 +555,7 @@ macro_rules! pin_init {
> @data(PinData, use_data),
> @has_data(HasPinData, __pin_data),
> @construct_closure(pin_init_from_closure),
> + @munch_fields($($fields)*),
> )
> };
> }
> @@ -603,6 +612,7 @@ macro_rules! try_pin_init {
> @data(PinData, use_data),
> @has_data(HasPinData, __pin_data),
> @construct_closure(pin_init_from_closure),
> + @munch_fields($($fields)*),
> )
> };
> ($(&$this:ident in)? $t:ident $(::<$($generics:ty),* $(,)?>)? {
> @@ -616,6 +626,7 @@ macro_rules! try_pin_init {
> @data(PinData, use_data),
> @has_data(HasPinData, __pin_data),
> @construct_closure(pin_init_from_closure),
> + @munch_fields($($fields)*),
> )
> };
> }
> @@ -650,6 +661,7 @@ macro_rules! init {
> @data(InitData, /*no use_data*/),
> @has_data(HasInitData, __init_data),
> @construct_closure(init_from_closure),
> + @munch_fields($($fields)*),
> )
> }
> }
> @@ -700,6 +712,7 @@ macro_rules! try_init {
> @data(InitData, /*no use_data*/),
> @has_data(HasInitData, __init_data),
> @construct_closure(init_from_closure),
> + @munch_fields($($fields)*),
> )
> };
> ($(&$this:ident in)? $t:ident $(::<$($generics:ty),* $(,)?>)? {
> @@ -713,6 +726,7 @@ macro_rules! try_init {
> @data(InitData, /*no use_data*/),
> @has_data(HasInitData, __init_data),
> @construct_closure(init_from_closure),
> + @munch_fields($($fields)*),
> )
> };
> }
> diff --git a/rust/kernel/init/macros.rs b/rust/kernel/init/macros.rs
> index 1e0c4aca055a..5dcb2e513f26 100644
> --- a/rust/kernel/init/macros.rs
> +++ b/rust/kernel/init/macros.rs
> @@ -989,6 +989,7 @@ impl<$($impl_generics)*> $pin_data<$($ty_generics)*>
> ///
> /// This macro has multiple internal call configurations, these are always the very first ident:
> /// - nothing: this is the base case and called by the `{try_}{pin_}init!` macros.
> +/// - `with_update_parsed`: when the `..Zeroable::zeroed()` syntax has been handled.
> /// - `init_slot`: recursively creates the code that initializes all fields in `slot`.
> /// - `make_initializer`: recursively create the struct initializer that guarantees that every
> /// field has been initialized exactly once.
> @@ -1007,6 +1008,82 @@ macro_rules! __init_internal {
> @has_data($has_data:ident, $get_data:ident),
> // `pin_init_from_closure` or `init_from_closure`.
> @construct_closure($construct_closure:ident),
> + @munch_fields(),
> + ) => {
> + $crate::__init_internal!(with_update_parsed:
> + @this($($this)?),
> + @typ($t $(::<$($generics),*>)? ),
> + @fields($($fields)*),
> + @error($err),
> + @data($data, $($use_data)?),
> + @has_data($has_data, $get_data),
> + @construct_closure($construct_closure),
> + @zeroed(), // nothing means default behavior.
> + )
> + };
> + (
> + @this($($this:ident)?),
> + @typ($t:ident $(::<$($generics:ty),*>)?),
> + @fields($($fields:tt)*),
> + @error($err:ty),
> + // Either `PinData` or `InitData`, `$use_data` should only be present in the `PinData`
> + // case.
> + @data($data:ident, $($use_data:ident)?),
> + // `HasPinData` or `HasInitData`.
> + @has_data($has_data:ident, $get_data:ident),
> + // `pin_init_from_closure` or `init_from_closure`.
> + @construct_closure($construct_closure:ident),
> + @munch_fields(..Zeroable::zeroed()),
> + ) => {
> + $crate::__init_internal!(with_update_parsed:
> + @this($($this)?),
> + @typ($t $(::<$($generics),*>)? ),
> + @fields($($fields)*),
> + @error($err),
> + @data($data, $($use_data)?),
> + @has_data($has_data, $get_data),
> + @construct_closure($construct_closure),
> + @zeroed(()), // `()` means zero all fields not mentioned.
> + )
> + };
> + (
> + @this($($this:ident)?),
> + @typ($t:ident $(::<$($generics:ty),*>)?),
> + @fields($($fields:tt)*),
> + @error($err:ty),
> + // Either `PinData` or `InitData`, `$use_data` should only be present in the `PinData`
> + // case.
> + @data($data:ident, $($use_data:ident)?),
> + // `HasPinData` or `HasInitData`.
> + @has_data($has_data:ident, $get_data:ident),
> + // `pin_init_from_closure` or `init_from_closure`.
> + @construct_closure($construct_closure:ident),
> + @munch_fields($ignore:tt $($rest:tt)*),
> + ) => {
> + $crate::__init_internal!(
> + @this($($this)?),
> + @typ($t $(::<$($generics),*>)? ),
> + @fields($($fields)*),
> + @error($err),
> + @data($data, $($use_data)?),
> + @has_data($has_data, $get_data),
> + @construct_closure($construct_closure),
> + @munch_fields($($rest)*),
> + )
> + };
> + (with_update_parsed:
> + @this($($this:ident)?),
> + @typ($t:ident $(::<$($generics:ty),*>)?),
> + @fields($($fields:tt)*),
> + @error($err:ty),
> + // Either `PinData` or `InitData`, `$use_data` should only be present in the `PinData`
> + // case.
> + @data($data:ident, $($use_data:ident)?),
> + // `HasPinData` or `HasInitData`.
> + @has_data($has_data:ident, $get_data:ident),
> + // `pin_init_from_closure` or `init_from_closure`.
> + @construct_closure($construct_closure:ident),
> + @zeroed($($init_zeroed:expr)?),
> ) => {{
> // We do not want to allow arbitrary returns, so we declare this type as the `Ok` return
> // type and shadow it later when we insert the arbitrary user code. That way there will be
> @@ -1024,6 +1101,17 @@ macro_rules! __init_internal {
> {
> // Shadow the structure so it cannot be used to return early.
> struct __InitOk;
> + // If `$init_zeroed` is present we should zero the slot now and not emit an
> + // error when fields are missing (since they will be zeroed). We also have to
> + // check that the type actually implements `Zeroable`.
> + $(
> + fn is_zeroable<T: Zeroable>(ptr: *mut T) {}
Maybe call this assert_zeroable?
> + // Ensure that the struct is indeed `Zeroable`.
> + is_zeroable(slot);
> + // SAFETY: The type implements `Zeroable` by the check above.
> + unsafe { ::core::ptr::write_bytes(slot, 0, 1) };
> + $init_zeroed // this will be `()` if set.
How does this work? Shouldn't there be a ; after $init_zeroed to consume the () value?
> + )?
> // Create the `this` so it can be referenced by the user inside of the
> // expressions creating the individual fields.
> $(let $this = unsafe { ::core::ptr::NonNull::new_unchecked(slot) };)?
> @@ -1064,7 +1152,7 @@ macro_rules! __init_internal {
> @data($data:ident),
> @slot($slot:ident),
> @guards($($guards:ident,)*),
> - @munch_fields($(,)?),
> + @munch_fields($(..Zeroable::zeroed())? $(,)?),
> ) => {
> // Endpoint of munching, no fields are left. If execution reaches this point, all fields
> // have been initialized. Therefore we can now dismiss the guards by forgetting them.
> @@ -1157,6 +1245,30 @@ macro_rules! __init_internal {
> @munch_fields($($rest)*),
> );
> };
> + (make_initializer:
> + @slot($slot:ident),
> + @type_name($t:ident),
> + @munch_fields(..Zeroable::zeroed() $(,)?),
> + @acc($($acc:tt)*),
> + ) => {
> + // Endpoint, nothing more to munch, create the initializer. Since the users specified
> + // `..Zeroable::zeroed()`, the slot will already have been zeroed and all field that have
> + // not been overwritten are thus zero and initialized. We still check that all fields are
> + // actually accessible by using the struct update syntax ourselves.
> + // Since we are in the `if false` branch, this will never get executed. We abuse `slot` to
> + // get the correct type inference here:
> + unsafe {
> + let mut zeroed = ::core::mem::zeroed();
> + // We have to use type inference her to make zeroed have the correct type. This does
*here
> + // not get executed, so it has no effect.
> + ::core::ptr::write($slot, zeroed);
> + zeroed = ::core::mem::zeroed();
> + ::core::ptr::write($slot, $t {
> + $($acc)*
> + ..zeroed
> + });
> + }
> + };
> (make_initializer:
> @slot($slot:ident),
> @type_name($t:ident),
> --
> 2.41.0
Cheers,
Björn