Commit 8a799831 authored by Danilo Krummrich's avatar Danilo Krummrich Committed by Miguel Ojeda
Browse files

rust: alloc: implement `ReallocFunc` 



`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.

Reviewed-by: default avatarBenno Lossin <benno.lossin@proton.me>
Reviewed-by: default avatarGary Guo <gary@garyguo.net>
Signed-off-by: default avatarDanilo Krummrich <dakr@kernel.org>
Link: https://lore.kernel.org/r/20241004154149.93856-5-dakr@kernel.org


[ Added temporary `allow(dead_code)` for `dangling_from_layout` to clean
  warning in `rusttest` target as discussed in the list (but it is
  needed earlier, i.e. in this patch already). Added colon. - Miguel ]
Signed-off-by: default avatarMiguel Ojeda <ojeda@kernel.org>
parent 941e6553

rust/kernel/alloc.rs

+9 −0
Original line number Diff line number Diff line
@@ -187,3 +187,12 @@ unsafe fn free(ptr: NonNull<u8>, layout: Layout) { 
        let _ = unsafe { Self::realloc(Some(ptr), Layout::new::<()>(), layout, Flags(0)) };

    }

}



#[allow(dead_code)]

/// 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) }

}

rust/kernel/alloc/allocator.rs

+70 −0
Original line number Diff line number Diff line 
// 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))

    }

}



// SAFETY: TODO.

unsafe impl GlobalAlloc for Kmalloc {

    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {