| Message ID | 20240812182355.11641-23-dakr@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Generic `Allocator` support for Rust | expand |
On Mon Aug 12, 2024 at 9:23 PM EEST, Danilo Krummrich wrote: > So far the kernel's `Box` and `Vec` types can't be used by userspace > test cases, since all users of those types (e.g. `CString`) use kernel > allocators for instantiation. > > In order to allow userspace test cases to make use of such types as > well, implement the `Cmalloc` allocator within the allocator_test module > and type alias all kernel allocators to `Cmalloc`. The `Cmalloc` > allocator uses libc's realloc() function as allocator backend. > > Signed-off-by: Danilo Krummrich <dakr@kernel.org> > --- > I know, having an `old_size` parameter would indeed help implementing `Cmalloc`. > > However, I really don't want test infrastructure to influence the design of > kernel internal APIs. > > It's on the test infrastructure to find a way to deal with it, even if it's more > complicated. > --- > rust/kernel/alloc/allocator_test.rs | 175 ++++++++++++++++++++++++++-- > 1 file changed, 168 insertions(+), 7 deletions(-) > > diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs > index 1b2642c547ec..7a20e64431ea 100644 > --- a/rust/kernel/alloc/allocator_test.rs > +++ b/rust/kernel/alloc/allocator_test.rs > @@ -2,20 +2,181 @@ > > #![allow(missing_docs)] > > -use super::{AllocError, Allocator, Flags}; > +use super::{flags::*, AllocError, Allocator, Flags}; > use core::alloc::Layout; > +use core::cmp; > +use core::mem; > +use core::ptr; > use core::ptr::NonNull; > > -pub struct Kmalloc; > +pub struct Cmalloc; > +pub type Kmalloc = Cmalloc; > pub type Vmalloc = Kmalloc; > pub type KVmalloc = Kmalloc; > > -unsafe impl Allocator for Kmalloc { > +extern "C" { > + #[link_name = "aligned_alloc"] > + fn libc_aligned_alloc(align: usize, size: usize) -> *mut core::ffi::c_void; > + > + #[link_name = "free"] > + fn libc_free(ptr: *mut core::ffi::c_void); > +} > + > +struct CmallocData { > + // The actual size as requested through `Cmalloc::alloc` or `Cmalloc::realloc`. > + size: usize, > + // The offset from the pointer returned to the caller of `Cmalloc::alloc` or `Cmalloc::realloc` > + // to the actual base address of the allocation. > + offset: usize, > +} > + > +impl Cmalloc { > + /// Adjust the size and alignment such that we can additionally store `CmallocData` right > + /// before the actual data described by `layout`. > + /// > + /// Example: > + /// > + /// For `CmallocData` assume an alignment of 8 and a size of 16. > + /// For `layout` assume and alignment of 16 and a size of 64. > + /// > + /// 0 16 32 96 > + /// |----------------|----------------|------------------------------------------------| > + /// empty CmallocData data > + /// > + /// For this example the returned `Layout` has an alignment of 32 and a size of 96. > + fn layout_adjust(layout: Layout) -> Result<Layout, AllocError> { > + let layout = layout.pad_to_align(); > + > + // Ensure that `CmallocData` fits into half the alignment. Additionally, this guarantees > + // that advancing a pointer aligned to `align` by `align / 2` we still satisfy or exceed > + // the alignment requested through `layout`. > + let align = cmp::max( > + layout.align(), > + mem::size_of::<CmallocData>().next_power_of_two(), > + ) * 2; > + > + // Add the additional space required for `CmallocData`. > + let size = layout.size() + mem::size_of::<CmallocData>(); > + > + Ok(Layout::from_size_align(size, align) > + .map_err(|_| AllocError)? > + .pad_to_align()) > + } > + > + fn alloc_store_data(layout: Layout) -> Result<NonNull<u8>, AllocError> { > + let requested_size = layout.size(); > + > + let layout = Self::layout_adjust(layout)?; > + let min_align = layout.align() / 2; > + > + // SAFETY: Returns either NULL or a pointer to a memory allocation that satisfies or > + // exceeds the given size and alignment requirements. > + let raw_ptr = unsafe { libc_aligned_alloc(layout.align(), layout.size()) } as *mut u8; > + > + let priv_ptr = NonNull::new(raw_ptr).ok_or(AllocError)?; > + > + // SAFETY: Advance the pointer by `min_align`. The adjustments from `Self::layout_adjust` > + // ensure that after this operation the original size and alignment requirements are still > + // satisfied or exceeded. > + let ptr = unsafe { priv_ptr.as_ptr().add(min_align) }; > + > + // SAFETY: `min_align` is greater than or equal to the size of `CmallocData`, hence we > + // don't exceed the allocation boundaries. > + let data_ptr: *mut CmallocData = unsafe { ptr.sub(mem::size_of::<CmallocData>()) }.cast(); > + > + let data = CmallocData { > + size: requested_size, > + offset: min_align, > + }; > + > + // SAFETY: `data_ptr` is properly aligned and within the allocation boundaries reserved for > + // `CmallocData`. > + unsafe { data_ptr.write(data) }; > + > + NonNull::new(ptr).ok_or(AllocError) > + } > + > + /// # Safety > + /// > + /// `ptr` must have been previously allocated with `Self::alloc_store_data`. > + unsafe fn data<'a>(ptr: NonNull<u8>) -> &'a CmallocData { > + // SAFETY: `Self::alloc_store_data` stores the `CmallocData` right before the address > + // returned to callers of `Self::alloc_store_data`. > + let data_ptr: *mut CmallocData = > + unsafe { ptr.as_ptr().sub(mem::size_of::<CmallocData>()) }.cast(); > + > + // SAFETY: The `CmallocData` has been previously stored at this offset with > + // `Self::alloc_store_data`. > + unsafe { &*data_ptr } > + } > + > + /// # Safety > + /// > + /// This function must not be called more than once for the same allocation. > + /// > + /// `ptr` must have been previously allocated with `Self::alloc_store_data`. > + unsafe fn free_read_data(ptr: NonNull<u8>) { > + // SAFETY: `ptr` has been created by `Self::alloc_store_data`. > + let data = unsafe { Self::data(ptr) }; > + > + // SAFETY: `ptr` has been created by `Self::alloc_store_data`. > + let priv_ptr = unsafe { ptr.as_ptr().sub(data.offset) }; > + > + // SAFETY: `priv_ptr` has previously been allocatored with this `Allocator`. > + unsafe { libc_free(priv_ptr.cast()) }; > + } > +} > + > +unsafe impl Allocator for Cmalloc { > + fn alloc(layout: Layout, flags: Flags) -> Result<NonNull<[u8]>, AllocError> { > + if layout.size() == 0 { > + return Ok(NonNull::slice_from_raw_parts(NonNull::dangling(), 0)); > + } > + > + let ptr = Self::alloc_store_data(layout)?; > + > + if flags.contains(__GFP_ZERO) { > + // SAFETY: `Self::alloc_store_data` guarantees that `ptr` points to memory of at least > + // `layout.size()` bytes. > + unsafe { ptr.as_ptr().write_bytes(0, layout.size()) }; > + } > + > + Ok(NonNull::slice_from_raw_parts(ptr, layout.size())) > + } > + > unsafe fn realloc( > - _ptr: Option<NonNull<u8>>, > - _layout: Layout, > - _flags: Flags, > + ptr: Option<NonNull<u8>>, > + layout: Layout, > + flags: Flags, > ) -> Result<NonNull<[u8]>, AllocError> { > - panic!(); > + let src: NonNull<u8> = if let Some(src) = ptr { > + src.cast() > + } else { > + return Self::alloc(layout, flags); > + }; > + > + if layout.size() == 0 { > + // SAFETY: `src` has been created by `Self::alloc_store_data`. > + unsafe { Self::free_read_data(src) }; > + > + return Ok(NonNull::slice_from_raw_parts(NonNull::dangling(), 0)); > + } > + > + let dst = Self::alloc(layout, flags)?; > + > + // SAFETY: `src` has been created by `Self::alloc_store_data`. > + let data = unsafe { Self::data(src) }; > + > + // SAFETY: `src` has previously been allocated with this `Allocator`; `dst` has just been > + // newly allocated. Copy up to the smaller of both sizes. > + unsafe { > + ptr::copy_nonoverlapping( > + src.as_ptr(), > + dst.as_ptr().cast(), > + cmp::min(layout.size(), data.size), > + ) > + }; > + At this point should we free the src? Or is the original pointer expected to remain valid? > + Ok(dst) > } > } > -- > 2.45.2
On Tue, Aug 13, 2024 at 07:07:46AM +0000, Heghedus Razvan wrote: > On Mon Aug 12, 2024 at 9:23 PM EEST, Danilo Krummrich wrote: > > So far the kernel's `Box` and `Vec` types can't be used by userspace > > test cases, since all users of those types (e.g. `CString`) use kernel > > allocators for instantiation. > > > > In order to allow userspace test cases to make use of such types as > > well, implement the `Cmalloc` allocator within the allocator_test module > > and type alias all kernel allocators to `Cmalloc`. The `Cmalloc` > > allocator uses libc's realloc() function as allocator backend. > > > > Signed-off-by: Danilo Krummrich <dakr@kernel.org> > > --- > > I know, having an `old_size` parameter would indeed help implementing `Cmalloc`. > > > > However, I really don't want test infrastructure to influence the design of > > kernel internal APIs. > > > > It's on the test infrastructure to find a way to deal with it, even if it's more > > complicated. > > --- > > rust/kernel/alloc/allocator_test.rs | 175 ++++++++++++++++++++++++++-- > > 1 file changed, 168 insertions(+), 7 deletions(-) > > > > diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs > > index 1b2642c547ec..7a20e64431ea 100644 > > --- a/rust/kernel/alloc/allocator_test.rs > > +++ b/rust/kernel/alloc/allocator_test.rs > > @@ -2,20 +2,181 @@ > > > > #![allow(missing_docs)] > > > > -use super::{AllocError, Allocator, Flags}; > > +use super::{flags::*, AllocError, Allocator, Flags}; > > use core::alloc::Layout; > > +use core::cmp; > > +use core::mem; > > +use core::ptr; > > use core::ptr::NonNull; > > > > -pub struct Kmalloc; > > +pub struct Cmalloc; > > +pub type Kmalloc = Cmalloc; > > pub type Vmalloc = Kmalloc; > > pub type KVmalloc = Kmalloc; > > > > -unsafe impl Allocator for Kmalloc { > > +extern "C" { > > + #[link_name = "aligned_alloc"] > > + fn libc_aligned_alloc(align: usize, size: usize) -> *mut core::ffi::c_void; > > + > > + #[link_name = "free"] > > + fn libc_free(ptr: *mut core::ffi::c_void); > > +} > > + > > +struct CmallocData { > > + // The actual size as requested through `Cmalloc::alloc` or `Cmalloc::realloc`. > > + size: usize, > > + // The offset from the pointer returned to the caller of `Cmalloc::alloc` or `Cmalloc::realloc` > > + // to the actual base address of the allocation. > > + offset: usize, > > +} > > + > > +impl Cmalloc { > > + /// Adjust the size and alignment such that we can additionally store `CmallocData` right > > + /// before the actual data described by `layout`. > > + /// > > + /// Example: > > + /// > > + /// For `CmallocData` assume an alignment of 8 and a size of 16. > > + /// For `layout` assume and alignment of 16 and a size of 64. > > + /// > > + /// 0 16 32 96 > > + /// |----------------|----------------|------------------------------------------------| > > + /// empty CmallocData data > > + /// > > + /// For this example the returned `Layout` has an alignment of 32 and a size of 96. > > + fn layout_adjust(layout: Layout) -> Result<Layout, AllocError> { > > + let layout = layout.pad_to_align(); > > + > > + // Ensure that `CmallocData` fits into half the alignment. Additionally, this guarantees > > + // that advancing a pointer aligned to `align` by `align / 2` we still satisfy or exceed > > + // the alignment requested through `layout`. > > + let align = cmp::max( > > + layout.align(), > > + mem::size_of::<CmallocData>().next_power_of_two(), > > + ) * 2; > > + > > + // Add the additional space required for `CmallocData`. > > + let size = layout.size() + mem::size_of::<CmallocData>(); > > + > > + Ok(Layout::from_size_align(size, align) > > + .map_err(|_| AllocError)? > > + .pad_to_align()) > > + } > > + > > + fn alloc_store_data(layout: Layout) -> Result<NonNull<u8>, AllocError> { > > + let requested_size = layout.size(); > > + > > + let layout = Self::layout_adjust(layout)?; > > + let min_align = layout.align() / 2; > > + > > + // SAFETY: Returns either NULL or a pointer to a memory allocation that satisfies or > > + // exceeds the given size and alignment requirements. > > + let raw_ptr = unsafe { libc_aligned_alloc(layout.align(), layout.size()) } as *mut u8; > > + > > + let priv_ptr = NonNull::new(raw_ptr).ok_or(AllocError)?; > > + > > + // SAFETY: Advance the pointer by `min_align`. The adjustments from `Self::layout_adjust` > > + // ensure that after this operation the original size and alignment requirements are still > > + // satisfied or exceeded. > > + let ptr = unsafe { priv_ptr.as_ptr().add(min_align) }; > > + > > + // SAFETY: `min_align` is greater than or equal to the size of `CmallocData`, hence we > > + // don't exceed the allocation boundaries. > > + let data_ptr: *mut CmallocData = unsafe { ptr.sub(mem::size_of::<CmallocData>()) }.cast(); > > + > > + let data = CmallocData { > > + size: requested_size, > > + offset: min_align, > > + }; > > + > > + // SAFETY: `data_ptr` is properly aligned and within the allocation boundaries reserved for > > + // `CmallocData`. > > + unsafe { data_ptr.write(data) }; > > + > > + NonNull::new(ptr).ok_or(AllocError) > > + } > > + > > + /// # Safety > > + /// > > + /// `ptr` must have been previously allocated with `Self::alloc_store_data`. > > + unsafe fn data<'a>(ptr: NonNull<u8>) -> &'a CmallocData { > > + // SAFETY: `Self::alloc_store_data` stores the `CmallocData` right before the address > > + // returned to callers of `Self::alloc_store_data`. > > + let data_ptr: *mut CmallocData = > > + unsafe { ptr.as_ptr().sub(mem::size_of::<CmallocData>()) }.cast(); > > + > > + // SAFETY: The `CmallocData` has been previously stored at this offset with > > + // `Self::alloc_store_data`. > > + unsafe { &*data_ptr } > > + } > > + > > + /// # Safety > > + /// > > + /// This function must not be called more than once for the same allocation. > > + /// > > + /// `ptr` must have been previously allocated with `Self::alloc_store_data`. > > + unsafe fn free_read_data(ptr: NonNull<u8>) { > > + // SAFETY: `ptr` has been created by `Self::alloc_store_data`. > > + let data = unsafe { Self::data(ptr) }; > > + > > + // SAFETY: `ptr` has been created by `Self::alloc_store_data`. > > + let priv_ptr = unsafe { ptr.as_ptr().sub(data.offset) }; > > + > > + // SAFETY: `priv_ptr` has previously been allocatored with this `Allocator`. > > + unsafe { libc_free(priv_ptr.cast()) }; > > + } > > +} > > + > > +unsafe impl Allocator for Cmalloc { > > + fn alloc(layout: Layout, flags: Flags) -> Result<NonNull<[u8]>, AllocError> { > > + if layout.size() == 0 { > > + return Ok(NonNull::slice_from_raw_parts(NonNull::dangling(), 0)); > > + } > > + > > + let ptr = Self::alloc_store_data(layout)?; > > + > > + if flags.contains(__GFP_ZERO) { > > + // SAFETY: `Self::alloc_store_data` guarantees that `ptr` points to memory of at least > > + // `layout.size()` bytes. > > + unsafe { ptr.as_ptr().write_bytes(0, layout.size()) }; > > + } > > + > > + Ok(NonNull::slice_from_raw_parts(ptr, layout.size())) > > + } > > + > > unsafe fn realloc( > > - _ptr: Option<NonNull<u8>>, > > - _layout: Layout, > > - _flags: Flags, > > + ptr: Option<NonNull<u8>>, > > + layout: Layout, > > + flags: Flags, > > ) -> Result<NonNull<[u8]>, AllocError> { > > - panic!(); > > + let src: NonNull<u8> = if let Some(src) = ptr { > > + src.cast() > > + } else { > > + return Self::alloc(layout, flags); > > + }; > > + > > + if layout.size() == 0 { > > + // SAFETY: `src` has been created by `Self::alloc_store_data`. > > + unsafe { Self::free_read_data(src) }; > > + > > + return Ok(NonNull::slice_from_raw_parts(NonNull::dangling(), 0)); > > + } > > + > > + let dst = Self::alloc(layout, flags)?; > > + > > + // SAFETY: `src` has been created by `Self::alloc_store_data`. > > + let data = unsafe { Self::data(src) }; > > + > > + // SAFETY: `src` has previously been allocated with this `Allocator`; `dst` has just been > > + // newly allocated. Copy up to the smaller of both sizes. > > + unsafe { > > + ptr::copy_nonoverlapping( > > + src.as_ptr(), > > + dst.as_ptr().cast(), > > + cmp::min(layout.size(), data.size), > > + ) > > + }; > > + > At this point should we free the src? Or is the original pointer expected to remain valid? Yes, we're indeed missing `Self::free_read_data(src)` here. > > > + Ok(dst) > > } > > } > > -- > > 2.45.2 > >
diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs index 1b2642c547ec..7a20e64431ea 100644 --- a/rust/kernel/alloc/allocator_test.rs +++ b/rust/kernel/alloc/allocator_test.rs @@ -2,20 +2,181 @@ #![allow(missing_docs)] -use super::{AllocError, Allocator, Flags}; +use super::{flags::*, AllocError, Allocator, Flags}; use core::alloc::Layout; +use core::cmp; +use core::mem; +use core::ptr; use core::ptr::NonNull; -pub struct Kmalloc; +pub struct Cmalloc; +pub type Kmalloc = Cmalloc; pub type Vmalloc = Kmalloc; pub type KVmalloc = Kmalloc; -unsafe impl Allocator for Kmalloc { +extern "C" { + #[link_name = "aligned_alloc"] + fn libc_aligned_alloc(align: usize, size: usize) -> *mut core::ffi::c_void; + + #[link_name = "free"] + fn libc_free(ptr: *mut core::ffi::c_void); +} + +struct CmallocData { + // The actual size as requested through `Cmalloc::alloc` or `Cmalloc::realloc`. + size: usize, + // The offset from the pointer returned to the caller of `Cmalloc::alloc` or `Cmalloc::realloc` + // to the actual base address of the allocation. + offset: usize, +} + +impl Cmalloc { + /// Adjust the size and alignment such that we can additionally store `CmallocData` right + /// before the actual data described by `layout`. + /// + /// Example: + /// + /// For `CmallocData` assume an alignment of 8 and a size of 16. + /// For `layout` assume and alignment of 16 and a size of 64. + /// + /// 0 16 32 96 + /// |----------------|----------------|------------------------------------------------| + /// empty CmallocData data + /// + /// For this example the returned `Layout` has an alignment of 32 and a size of 96. + fn layout_adjust(layout: Layout) -> Result<Layout, AllocError> { + let layout = layout.pad_to_align(); + + // Ensure that `CmallocData` fits into half the alignment. Additionally, this guarantees + // that advancing a pointer aligned to `align` by `align / 2` we still satisfy or exceed + // the alignment requested through `layout`. + let align = cmp::max( + layout.align(), + mem::size_of::<CmallocData>().next_power_of_two(), + ) * 2; + + // Add the additional space required for `CmallocData`. + let size = layout.size() + mem::size_of::<CmallocData>(); + + Ok(Layout::from_size_align(size, align) + .map_err(|_| AllocError)? + .pad_to_align()) + } + + fn alloc_store_data(layout: Layout) -> Result<NonNull<u8>, AllocError> { + let requested_size = layout.size(); + + let layout = Self::layout_adjust(layout)?; + let min_align = layout.align() / 2; + + // SAFETY: Returns either NULL or a pointer to a memory allocation that satisfies or + // exceeds the given size and alignment requirements. + let raw_ptr = unsafe { libc_aligned_alloc(layout.align(), layout.size()) } as *mut u8; + + let priv_ptr = NonNull::new(raw_ptr).ok_or(AllocError)?; + + // SAFETY: Advance the pointer by `min_align`. The adjustments from `Self::layout_adjust` + // ensure that after this operation the original size and alignment requirements are still + // satisfied or exceeded. + let ptr = unsafe { priv_ptr.as_ptr().add(min_align) }; + + // SAFETY: `min_align` is greater than or equal to the size of `CmallocData`, hence we + // don't exceed the allocation boundaries. + let data_ptr: *mut CmallocData = unsafe { ptr.sub(mem::size_of::<CmallocData>()) }.cast(); + + let data = CmallocData { + size: requested_size, + offset: min_align, + }; + + // SAFETY: `data_ptr` is properly aligned and within the allocation boundaries reserved for + // `CmallocData`. + unsafe { data_ptr.write(data) }; + + NonNull::new(ptr).ok_or(AllocError) + } + + /// # Safety + /// + /// `ptr` must have been previously allocated with `Self::alloc_store_data`. + unsafe fn data<'a>(ptr: NonNull<u8>) -> &'a CmallocData { + // SAFETY: `Self::alloc_store_data` stores the `CmallocData` right before the address + // returned to callers of `Self::alloc_store_data`. + let data_ptr: *mut CmallocData = + unsafe { ptr.as_ptr().sub(mem::size_of::<CmallocData>()) }.cast(); + + // SAFETY: The `CmallocData` has been previously stored at this offset with + // `Self::alloc_store_data`. + unsafe { &*data_ptr } + } + + /// # Safety + /// + /// This function must not be called more than once for the same allocation. + /// + /// `ptr` must have been previously allocated with `Self::alloc_store_data`. + unsafe fn free_read_data(ptr: NonNull<u8>) { + // SAFETY: `ptr` has been created by `Self::alloc_store_data`. + let data = unsafe { Self::data(ptr) }; + + // SAFETY: `ptr` has been created by `Self::alloc_store_data`. + let priv_ptr = unsafe { ptr.as_ptr().sub(data.offset) }; + + // SAFETY: `priv_ptr` has previously been allocatored with this `Allocator`. + unsafe { libc_free(priv_ptr.cast()) }; + } +} + +unsafe impl Allocator for Cmalloc { + fn alloc(layout: Layout, flags: Flags) -> Result<NonNull<[u8]>, AllocError> { + if layout.size() == 0 { + return Ok(NonNull::slice_from_raw_parts(NonNull::dangling(), 0)); + } + + let ptr = Self::alloc_store_data(layout)?; + + if flags.contains(__GFP_ZERO) { + // SAFETY: `Self::alloc_store_data` guarantees that `ptr` points to memory of at least + // `layout.size()` bytes. + unsafe { ptr.as_ptr().write_bytes(0, layout.size()) }; + } + + Ok(NonNull::slice_from_raw_parts(ptr, layout.size())) + } + unsafe fn realloc( - _ptr: Option<NonNull<u8>>, - _layout: Layout, - _flags: Flags, + ptr: Option<NonNull<u8>>, + layout: Layout, + flags: Flags, ) -> Result<NonNull<[u8]>, AllocError> { - panic!(); + let src: NonNull<u8> = if let Some(src) = ptr { + src.cast() + } else { + return Self::alloc(layout, flags); + }; + + if layout.size() == 0 { + // SAFETY: `src` has been created by `Self::alloc_store_data`. + unsafe { Self::free_read_data(src) }; + + return Ok(NonNull::slice_from_raw_parts(NonNull::dangling(), 0)); + } + + let dst = Self::alloc(layout, flags)?; + + // SAFETY: `src` has been created by `Self::alloc_store_data`. + let data = unsafe { Self::data(src) }; + + // SAFETY: `src` has previously been allocated with this `Allocator`; `dst` has just been + // newly allocated. Copy up to the smaller of both sizes. + unsafe { + ptr::copy_nonoverlapping( + src.as_ptr(), + dst.as_ptr().cast(), + cmp::min(layout.size(), data.size), + ) + }; + + Ok(dst) } }
So far the kernel's `Box` and `Vec` types can't be used by userspace test cases, since all users of those types (e.g. `CString`) use kernel allocators for instantiation. In order to allow userspace test cases to make use of such types as well, implement the `Cmalloc` allocator within the allocator_test module and type alias all kernel allocators to `Cmalloc`. The `Cmalloc` allocator uses libc's realloc() function as allocator backend. Signed-off-by: Danilo Krummrich <dakr@kernel.org> --- I know, having an `old_size` parameter would indeed help implementing `Cmalloc`. However, I really don't want test infrastructure to influence the design of kernel internal APIs. It's on the test infrastructure to find a way to deal with it, even if it's more complicated. --- rust/kernel/alloc/allocator_test.rs | 175 ++++++++++++++++++++++++++-- 1 file changed, 168 insertions(+), 7 deletions(-)