`ReallocFunc` is an abstraction for the kernel's realloc derivates, such
as `krealloc`, `vrealloc` and `kvrealloc`.
All of the named functions share the same function signature and
implement the same semantics. The `ReallocFunc` abstractions provides a
generalized wrapper around those, to trivialize the implementation of
`Kmalloc`, `Vmalloc` and `KVmalloc` in subsequent patches.
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
rust/kernel/alloc.rs | 8 ++++
rust/kernel/alloc/allocator.rs | 70 ++++++++++++++++++++++++++++++++++
2 files changed, 78 insertions(+)
diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
index 4deeea3488be..da49c5306431 100644
--- a/rust/kernel/alloc.rs
+++ b/rust/kernel/alloc.rs
@@ -187,3 +187,11 @@ unsafe fn free(ptr: NonNull<u8>, layout: Layout) {
let _ = unsafe { Self::realloc(Some(ptr), Layout::new::<()>(), layout, Flags(0)) };
}
}
+
+/// Returns a properly aligned dangling pointer from the given `layout`.
+pub(crate) fn dangling_from_layout(layout: Layout) -> NonNull<u8> {
+ let ptr = layout.align() as *mut u8;
+
+ // SAFETY: `layout.align()` (and hence `ptr`) is guaranteed to be non-zero.
+ unsafe { NonNull::new_unchecked(ptr) }
+}
diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
index e32182f91167..1f28b004b447 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -1,10 +1,20 @@
// SPDX-License-Identifier: GPL-2.0
//! Allocator support.
+//!
+//! Documentation for the kernel's memory allocators can found in the "Memory Allocation Guide"
+//! linked below. For instance, this includes the concept of "get free page" (GFP) flags and the
+//! typical application of the different kernel allocators.
+//!
+//! Reference: <https://docs.kernel.org/core-api/memory-allocation.html>
use super::{flags::*, Flags};
use core::alloc::{GlobalAlloc, Layout};
use core::ptr;
+use core::ptr::NonNull;
+
+use crate::alloc::AllocError;
+use crate::bindings;
struct Kmalloc;
@@ -36,6 +46,66 @@ pub(crate) unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: F
unsafe { bindings::krealloc(ptr as *const core::ffi::c_void, size, flags.0) as *mut u8 }
}
+/// # Invariants
+///
+/// One of the following `krealloc`, `vrealloc`, `kvrealloc`.
+struct ReallocFunc(
+ unsafe extern "C" fn(*const core::ffi::c_void, usize, u32) -> *mut core::ffi::c_void,
+);
+
+#[expect(dead_code)]
+impl ReallocFunc {
+ /// # Safety
+ ///
+ /// This method has the same safety requirements as [`Allocator::realloc`].
+ ///
+ /// # Guarantees
+ ///
+ /// This method has the same guarantees as `Allocator::realloc`. Additionally
+ /// - it accepts any pointer to a valid memory allocation allocated by this function.
+ /// - memory allocated by this function remains valid until it is passed to this function.
+ unsafe fn call(
+ &self,
+ ptr: Option<NonNull<u8>>,
+ layout: Layout,
+ old_layout: Layout,
+ flags: Flags,
+ ) -> Result<NonNull<[u8]>, AllocError> {
+ let size = aligned_size(layout);
+ let ptr = match ptr {
+ Some(ptr) => {
+ if old_layout.size() == 0 {
+ ptr::null()
+ } else {
+ ptr.as_ptr()
+ }
+ }
+ None => ptr::null(),
+ };
+
+ // SAFETY:
+ // - `self.0` is one of `krealloc`, `vrealloc`, `kvrealloc` and thus only requires that
+ // `ptr` is NULL or valid.
+ // - `ptr` is either NULL or valid by the safety requirements of this function.
+ //
+ // GUARANTEE:
+ // - `self.0` is one of `krealloc`, `vrealloc`, `kvrealloc`.
+ // - Those functions provide the guarantees of this function.
+ let raw_ptr = unsafe {
+ // If `size == 0` and `ptr != NULL` the memory behind the pointer is freed.
+ self.0(ptr.cast(), size, flags.0).cast()
+ };
+
+ let ptr = if size == 0 {
+ crate::alloc::dangling_from_layout(layout)
+ } else {
+ NonNull::new(raw_ptr).ok_or(AllocError)?
+ };
+
+ Ok(NonNull::slice_from_raw_parts(ptr, size))
+ }
+}
+
unsafe impl GlobalAlloc for Kmalloc {
unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
// SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
--
2.46.1