On Tue, 1 Oct 2024 16:59:51 +0200
Danilo Krummrich <dakr@xxxxxxxxxx> wrote:
> `Vec` provides a contiguous growable array type with contents allocated
> with the kernel's allocators (e.g. `Kmalloc`, `Vmalloc` or `KVmalloc`).
>
> In contrast to Rust's stdlib `Vec` type, the kernel `Vec` type considers
> the kernel's GFP flags for all appropriate functions, always reports
> allocation failures through `Result<_, AllocError>` and remains
> independent from unstable features.
>
> Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
Thanks a lot for your work. I think this is much cleaner with the ZST
handling offloaded to `Allocator` and overload checking offloaded to
`ArrayLayout`.
Some nits below, although I think we should apply this and then address
the nits with follow up patches (some may also be good first issues).
Therefore:
Reviewed-by: Gary Guo <gary@xxxxxxxxxxx>
Best,
Gary
> ---
> rust/kernel/alloc.rs | 6 +
> rust/kernel/alloc/kvec.rs | 637 ++++++++++++++++++++++++++++++++++++++
> rust/kernel/prelude.rs | 2 +-
> 3 files changed, 644 insertions(+), 1 deletion(-)
> create mode 100644 rust/kernel/alloc/kvec.rs
>
> diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
> index bf143a71d53d..961070daf6db 100644
> --- a/rust/kernel/alloc.rs
> +++ b/rust/kernel/alloc.rs
> @@ -5,6 +5,7 @@
> #[cfg(not(any(test, testlib)))]
> pub mod allocator;
> pub mod kbox;
> +pub mod kvec;
> pub mod layout;
> pub mod vec_ext;
>
> @@ -19,6 +20,11 @@
> pub use self::kbox::KVBox;
> pub use self::kbox::VBox;
>
> +pub use self::kvec::KVVec;
> +pub use self::kvec::KVec;
> +pub use self::kvec::VVec;
> +pub use self::kvec::Vec;
> +
> /// Indicates an allocation error.
> #[derive(Copy, Clone, PartialEq, Eq, Debug)]
> pub struct AllocError;
> diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
> new file mode 100644
> index 000000000000..44aade0a653b
> --- /dev/null
> +++ b/rust/kernel/alloc/kvec.rs
> @@ -0,0 +1,637 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Implementation of [`Vec`].
> +
> +use super::{
> + allocator::{KVmalloc, Kmalloc, Vmalloc},
> + layout::ArrayLayout,
> + AllocError, Allocator, Box, Flags,
> +};
> +use core::{
> + fmt,
> + marker::PhantomData,
> + mem::{ManuallyDrop, MaybeUninit},
> + ops::Deref,
> + ops::DerefMut,
> + ops::Index,
> + ops::IndexMut,
> + ptr,
> + ptr::NonNull,
> + slice,
> + slice::SliceIndex,
> +};
> +
> +/// Create a [`KVec`] containing the arguments.
This should mention that it allocates using `GFP_KERNEL`.
> +///
> +/// # Examples
> +///
> +/// ```
> +/// let mut v = kernel::kvec![];
> +/// v.push(1, GFP_KERNEL)?;
> +/// assert_eq!(v, [1]);
> +///
> +/// let mut v = kernel::kvec![1; 3]?;
> +/// v.push(4, GFP_KERNEL)?;
> +/// assert_eq!(v, [1, 1, 1, 4]);
> +///
> +/// let mut v = kernel::kvec![1, 2, 3]?;
> +/// v.push(4, GFP_KERNEL)?;
> +/// assert_eq!(v, [1, 2, 3, 4]);
> +///
> +/// # Ok::<(), Error>(())
> +/// ```
> +#[macro_export]
> +macro_rules! kvec {
> + () => (
> + $crate::alloc::KVec::new()
> + );
> + ($elem:expr; $n:expr) => (
> + $crate::alloc::KVec::from_elem($elem, $n, GFP_KERNEL)
> + );
> + ($($x:expr),+ $(,)?) => (
> + match $crate::alloc::KBox::new_uninit(GFP_KERNEL) {
> + Ok(b) => Ok($crate::alloc::KVec::from($crate::alloc::KBox::write(b, [$($x),+]))),
> + Err(e) => Err(e),
> + }
> + );
> +}
> +
> +/// The kernel's [`Vec`] type.
> +///
> +/// A contiguous growable array type with contents allocated with the kernel's allocators (e.g.
> +/// [`Kmalloc`], [`Vmalloc`] or [`KVmalloc`]), written `Vec<T, A>`.
> +///
> +/// For non-zero-sized values, a [`Vec`] will use the given allocator `A` for its allocation. For
> +/// the most common allocators the type aliases [`KVec`], [`VVec`] and [`KVVec`] exist.
> +///
> +/// For zero-sized types the [`Vec`]'s pointer must be `dangling_mut::<T>`; no memory is allocated.
> +///
> +/// Generally, [`Vec`] consists of a pointer that represents the vector's backing buffer, the
> +/// capacity of the vector (the number of elements that currently fit into the vector), it's length
> +/// (the number of elements that are currently stored in the vector) and the `Allocator` type used
> +/// to allocate (and free) the backing buffer.
> +///
> +/// A [`Vec`] can be deconstructed into and (re-)constructed from it's previously named raw parts
> +/// and manually modified.
> +///
> +/// [`Vec`]'s backing buffer gets, if required, automatically increased (re-allocated) when elements
> +/// are added to the vector.
> +///
> +/// # Invariants
> +///
> +/// - `self.ptr` is always properly aligned and either points to memory allocated with `A` or, for
> +/// zero-sized types, is a dangling, well aligned pointer.
> +///
> +/// - `self.len` always represents the exact number of elements stored in the vector.
> +///
> +/// - `self.layout` represents the absolute number of elements that can be stored within the vector
> +/// without re-allocation. However, it is legal for the backing buffer to be larger than `layout`.
> +///
> +/// - The `Allocator` type `A` of the vector is the exact same `Allocator` type the backing buffer
> +/// was allocated with (and must be freed with).
> +pub struct Vec<T, A: Allocator> {
> + ptr: NonNull<T>,
> + /// Represents the actual buffer size as `cap` times `size_of::<T>` bytes.
> + ///
> + /// Note: This isn't quite the same as `Self::capacity`, which in contrast returns the number of
> + /// elements we can still store without reallocating.
> + layout: ArrayLayout<T>,
> + len: usize,
> + _p: PhantomData<A>,
> +}
> +
> +/// Type alias for [`Vec`] with a [`Kmalloc`] allocator.
> +///
> +/// # Examples
> +///
> +/// ```
> +/// let mut v = KVec::new();
> +/// v.push(1, GFP_KERNEL)?;
> +/// assert_eq!(&v, &[1]);
> +///
> +/// # Ok::<(), Error>(())
> +/// ```
> +pub type KVec<T> = Vec<T, Kmalloc>;
> +
> +/// Type alias for [`Vec`] with a [`Vmalloc`] allocator.
> +///
> +/// # Examples
> +///
> +/// ```
> +/// let mut v = VVec::new();
> +/// v.push(1, GFP_KERNEL)?;
> +/// assert_eq!(&v, &[1]);
> +///
> +/// # Ok::<(), Error>(())
> +/// ```
> +pub type VVec<T> = Vec<T, Vmalloc>;
> +
> +/// Type alias for [`Vec`] with a [`KVmalloc`] allocator.
> +///
> +/// # Examples
> +///
> +/// ```
> +/// let mut v = KVVec::new();
> +/// v.push(1, GFP_KERNEL)?;
> +/// assert_eq!(&v, &[1]);
> +///
> +/// # Ok::<(), Error>(())
> +/// ```
> +pub type KVVec<T> = Vec<T, KVmalloc>;
> +
> +// SAFETY: `Vec` is `Send` if `T` is `Send` because `Vec` owns its elements.
> +unsafe impl<T, A> Send for Vec<T, A>
> +where
> + T: Send,
> + A: Allocator,
> +{
> +}
> +
> +// SAFETY: `Vec` is `Sync` if `T` is `Sync` because `Vec` owns its elements.
> +unsafe impl<T, A> Sync for Vec<T, A>
> +where
> + T: Sync,
> + A: Allocator,
> +{
> +}
> +
> +impl<T, A> Vec<T, A>
> +where
> + A: Allocator,
> +{
> + #[inline]
> + const fn is_zst() -> bool {
> + core::mem::size_of::<T>() == 0
> + }
> +
> + /// Returns the number of elements that can be stored within the vector without allocating
> + /// additional memory.
> + pub fn capacity(&self) -> usize {
> + if const { Self::is_zst() } {
> + usize::MAX
> + } else {
> + self.layout.len()
> + }
> + }
> +
> + /// Returns the number of elements stored within the vector.
> + #[inline]
> + pub fn len(&self) -> usize {
> + self.len
> + }
> +
> + /// Forcefully sets `self.len` to `new_len`.
> + ///
> + /// # Safety
> + ///
> + /// - `new_len` must be less than or equal to [`Self::capacity`].
> + /// - If `new_len` is greater than `self.len`, all elements within the interval
> + /// [`self.len`,`new_len`) must be initialized.
> + #[inline]
> + pub unsafe fn set_len(&mut self, new_len: usize) {
> + debug_assert!(new_len <= self.capacity());
> + self.len = new_len;
> + }
> +
> + /// Returns a slice of the entire vector.
> + #[inline]
> + pub fn as_slice(&self) -> &[T] {
> + self
> + }
> +
> + /// Returns a mutable slice of the entire vector.
> + #[inline]
> + pub fn as_mut_slice(&mut self) -> &mut [T] {
> + self
> + }
> +
> + /// Returns a mutable raw pointer to the vector's backing buffer, or, if `T` is a ZST, a
> + /// dangling raw pointer.
> + #[inline]
> + pub fn as_mut_ptr(&mut self) -> *mut T {
> + self.ptr.as_ptr()
> + }
> +
> + /// Returns a raw pointer to the vector's backing buffer, or, if `T` is a ZST, a dangling raw
> + /// pointer.
> + #[inline]
> + pub fn as_ptr(&self) -> *const T {
> + self.ptr.as_ptr()
> + }
> +
> + /// Returns `true` if the vector contains no elements, `false` otherwise.
> + ///
> + /// # Examples
> + ///
> + /// ```
> + /// let mut v = KVec::new();
> + /// assert!(v.is_empty());
> + ///
> + /// v.push(1, GFP_KERNEL);
> + /// assert!(!v.is_empty());
> + /// ```
> + #[inline]
> + pub fn is_empty(&self) -> bool {
> + self.len() == 0
> + }
> +
> + /// Creates a new, empty Vec<T, A>.
> + ///
> + /// This method does not allocate by itself.
> + #[inline]
> + pub const fn new() -> Self {
Missing // INVARIANT here.
> + Self {
> + ptr: NonNull::dangling(),
> + layout: ArrayLayout::empty(),
> + len: 0,
> + _p: PhantomData::<A>,
> + }
> + }
> +
> + /// Returns a slice of `MaybeUninit<T>` for the remaining spare capacity of the vector.
> + pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
> + // SAFETY:
> + // - `self.len` is smaller than `self.capacity` and hence, the resulting pointer is
> + // guaranteed to be part of the same allocated object.
> + // - `self.len` can not overflow `isize`.
> + let ptr = unsafe { self.as_mut_ptr().add(self.len) } as *mut MaybeUninit<T>;
> +
> + // SAFETY: The memory between `self.len` and `self.capacity` is guaranteed to be allocated
> + // and valid, but uninitialized.
> + unsafe { slice::from_raw_parts_mut(ptr, self.capacity() - self.len) }
> + }
> +
> + /// Appends an element to the back of the [`Vec`] instance.
> + ///
> + /// # Examples
> + ///
> + /// ```
> + /// let mut v = KVec::new();
> + /// v.push(1, GFP_KERNEL)?;
> + /// assert_eq!(&v, &[1]);
> + ///
> + /// v.push(2, GFP_KERNEL)?;
> + /// assert_eq!(&v, &[1, 2]);
> + /// # Ok::<(), Error>(())
> + /// ```
> + pub fn push(&mut self, v: T, flags: Flags) -> Result<(), AllocError> {
> + self.reserve(1, flags)?;
> +
> + // SAFETY:
> + // - `self.len` is smaller than `self.capacity` and hence, the resulting pointer is
> + // guaranteed to be part of the same allocated object.
> + // - `self.len` can not overflow `isize`.
> + let ptr = unsafe { self.as_mut_ptr().add(self.len) };
> +
> + // SAFETY:
> + // - `ptr` is properly aligned and valid for writes.
> + unsafe { core::ptr::write(ptr, v) };
> +
> + // SAFETY: We just initialised the first spare entry, so it is safe to increase the length
> + // by 1. We also know that the new length is <= capacity because of the previous call to
> + // `reserve` above.
> + unsafe { self.set_len(self.len() + 1) };
> + Ok(())
> + }
> +
> + /// Creates a new [`Vec`] instance with at least the given capacity.
> + ///
> + /// # Examples
> + ///
> + /// ```
> + /// let v = KVec::<u32>::with_capacity(20, GFP_KERNEL)?;
> + ///
> + /// assert!(v.capacity() >= 20);
> + /// # Ok::<(), Error>(())
> + /// ```
> + pub fn with_capacity(capacity: usize, flags: Flags) -> Result<Self, AllocError> {
> + let mut v = Vec::new();
> +
> + v.reserve(capacity, flags)?;
> +
> + Ok(v)
> + }
> +
> + /// Creates a Vec<T, A> from a pointer, a length and a capacity using the allocator `A`.
> + ///
> + /// # Examples
> + ///
> + /// ```
> + /// let mut v = kernel::kvec![1, 2, 3]?;
> + /// v.reserve(1, GFP_KERNEL)?;
> + ///
> + /// let (mut ptr, mut len, cap) = v.into_raw_parts();
> + ///
> + /// // SAFETY: We've just reserved memory for another element.
> + /// unsafe { ptr.add(len).write(4) };
> + /// len += 1;
> + ///
> + /// // SAFETY: We only wrote an additional element at the end of the `KVec`'s buffer and
> + /// // correspondingly increased the length of the `KVec` by one. Otherwise, we construct it
> + /// // from the exact same raw parts.
> + /// let v = unsafe { KVec::from_raw_parts(ptr, len, cap) };
> + ///
> + /// assert_eq!(v, [1, 2, 3, 4]);
> + ///
> + /// # Ok::<(), Error>(())
> + /// ```
> + ///
> + /// # Safety
> + ///
> + /// If `T` is a ZST:
> + ///
> + /// - `ptr` must be a dangling, well aligned pointer.
> + ///
> + /// Otherwise:
> + ///
> + /// - `ptr` must have been allocated with the allocator `A`.
> + /// - `ptr` must satisfy or exceed the alignment requirements of `T`.
> + /// - `ptr` must point to memory with a size of at least `size_of::<T>() * capacity`.
> + /// bytes.
> + /// - The allocated size in bytes must not be larger than `isize::MAX`.
> + /// - `length` must be less than or equal to `capacity`.
> + /// - The first `length` elements must be initialized values of type `T`.
> + ///
> + /// It is also valid to create an empty `Vec` passing a dangling pointer for `ptr` and zero for
> + /// `cap` and `len`.
> + pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Self {
> + let layout = if Self::is_zst() {
> + ArrayLayout::empty()
> + } else {
> + // SAFETY: By the safety requirements of this function, `capacity * size_of::<T>()` is
> + // smaller than `isize::MAX`.
> + unsafe { ArrayLayout::new_unchecked(capacity) }
> + };
Missing // INVARIANT here.
> +
> + Self {
> + // SAFETY: By the safety requirements, `ptr` is either dangling or pointing to a valid
> + // memory allocation, allocated with `A`.
> + ptr: unsafe { NonNull::new_unchecked(ptr) },
> + layout,
> + len: length,
> + _p: PhantomData::<A>,
> + }
> + }
> +
> + /// Consumes the `Vec<T, A>` and returns its raw components `pointer`, `length` and `capacity`.
> + ///
> + /// This will not run the destructor of the contained elements and for non-ZSTs the allocation
> + /// will stay alive indefinitely. Use [`Vec::from_raw_parts`] to recover the [`Vec`], drop the
> + /// elements and free the allocation, if any.
> + pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
> + let mut me = ManuallyDrop::new(self);
> + let len = me.len();
> + let capacity = me.capacity();
> + let ptr = me.as_mut_ptr();
> + (ptr, len, capacity)
> + }
> +
> + /// Ensures that the capacity exceeds the length by at least `additional`
> + /// elements.
> + ///
> + /// # Examples
> + ///
> + /// ```
> + /// let mut v = KVec::new();
> + /// v.push(1, GFP_KERNEL)?;
> + ///
> + /// v.reserve(10, GFP_KERNEL)?;
> + /// let cap = v.capacity();
> + /// assert!(cap >= 10);
> + ///
> + /// v.reserve(10, GFP_KERNEL)?;
> + /// let new_cap = v.capacity();
> + /// assert_eq!(new_cap, cap);
> + ///
> + /// # Ok::<(), Error>(())
> + /// ```
> + pub fn reserve(&mut self, additional: usize, flags: Flags) -> Result<(), AllocError> {
> + let len = self.len();
> + let cap = self.capacity();
> +
> + if cap - len >= additional {
> + return Ok(());
> + }
> +
> + if Self::is_zst() {
> + // The capacity is already `usize::MAX` for ZSTs, we can't go higher.
> + return Err(AllocError);
> + }
> +
> + // We know that `cap <= isize::MAX` because of the type invariants of `Self`. So the
> + // multiplication by two won't overflow.
> + let new_cap = core::cmp::max(cap * 2, len.checked_add(additional).ok_or(AllocError)?);
> + let layout = ArrayLayout::new(new_cap).map_err(|_| AllocError)?;
> +
> + // SAFETY:
> + // - `ptr` is valid because it's either `None` or comes from a previous call to
> + // `A::realloc`.
> + // - `self.layout` matches the `ArrayLayout` of the preceeding allocation.
> + let ptr = unsafe {
> + A::realloc(
> + Some(self.ptr.cast()),
> + layout.into(),
> + self.layout.into(),
> + flags,
> + )?
> + };
Missing // INVARIANT here.
> +
> + self.ptr = ptr.cast();
> + self.layout = layout;
> +
> + Ok(())
> + }
> +}
