1 // SPDX-License-Identifier: GPL-2.0 2 3 //! Extensions to the [`alloc`] crate. 4 5 #[cfg(not(any(test, testlib)))] 6 pub mod allocator; 7 pub mod kbox; 8 pub mod kvec; 9 pub mod layout; 10 pub mod vec_ext; 11 12 #[cfg(any(test, testlib))] 13 pub mod allocator_test; 14 15 #[cfg(any(test, testlib))] 16 pub use self::allocator_test as allocator; 17 18 pub use self::kbox::Box; 19 pub use self::kbox::KBox; 20 pub use self::kbox::KVBox; 21 pub use self::kbox::VBox; 22 23 pub use self::kvec::KVVec; 24 pub use self::kvec::KVec; 25 pub use self::kvec::VVec; 26 pub use self::kvec::Vec; 27 28 /// Indicates an allocation error. 29 #[derive(Copy, Clone, PartialEq, Eq, Debug)] 30 pub struct AllocError; 31 use core::{alloc::Layout, ptr::NonNull}; 32 33 /// Flags to be used when allocating memory. 34 /// 35 /// They can be combined with the operators `|`, `&`, and `!`. 36 /// 37 /// Values can be used from the [`flags`] module. 38 #[derive(Clone, Copy)] 39 pub struct Flags(u32); 40 41 impl Flags { 42 /// Get the raw representation of this flag. 43 pub(crate) fn as_raw(self) -> u32 { 44 self.0 45 } 46 } 47 48 impl core::ops::BitOr for Flags { 49 type Output = Self; 50 fn bitor(self, rhs: Self) -> Self::Output { 51 Self(self.0 | rhs.0) 52 } 53 } 54 55 impl core::ops::BitAnd for Flags { 56 type Output = Self; 57 fn bitand(self, rhs: Self) -> Self::Output { 58 Self(self.0 & rhs.0) 59 } 60 } 61 62 impl core::ops::Not for Flags { 63 type Output = Self; 64 fn not(self) -> Self::Output { 65 Self(!self.0) 66 } 67 } 68 69 /// Allocation flags. 70 /// 71 /// These are meant to be used in functions that can allocate memory. 72 pub mod flags { 73 use super::Flags; 74 75 /// Zeroes out the allocated memory. 76 /// 77 /// This is normally or'd with other flags. 78 pub const __GFP_ZERO: Flags = Flags(bindings::__GFP_ZERO); 79 80 /// Allow the allocation to be in high memory. 81 /// 82 /// Allocations in high memory may not be mapped into the kernel's address space, so this can't 83 /// be used with `kmalloc` and other similar methods. 84 /// 85 /// This is normally or'd with other flags. 86 pub const __GFP_HIGHMEM: Flags = Flags(bindings::__GFP_HIGHMEM); 87 88 /// Users can not sleep and need the allocation to succeed. 89 /// 90 /// A lower watermark is applied to allow access to "atomic reserves". The current 91 /// implementation doesn't support NMI and few other strict non-preemptive contexts (e.g. 92 /// raw_spin_lock). The same applies to [`GFP_NOWAIT`]. 93 pub const GFP_ATOMIC: Flags = Flags(bindings::GFP_ATOMIC); 94 95 /// Typical for kernel-internal allocations. The caller requires ZONE_NORMAL or a lower zone 96 /// for direct access but can direct reclaim. 97 pub const GFP_KERNEL: Flags = Flags(bindings::GFP_KERNEL); 98 99 /// The same as [`GFP_KERNEL`], except the allocation is accounted to kmemcg. 100 pub const GFP_KERNEL_ACCOUNT: Flags = Flags(bindings::GFP_KERNEL_ACCOUNT); 101 102 /// For kernel allocations that should not stall for direct reclaim, start physical IO or 103 /// use any filesystem callback. It is very likely to fail to allocate memory, even for very 104 /// small allocations. 105 pub const GFP_NOWAIT: Flags = Flags(bindings::GFP_NOWAIT); 106 107 /// Suppresses allocation failure reports. 108 /// 109 /// This is normally or'd with other flags. 110 pub const __GFP_NOWARN: Flags = Flags(bindings::__GFP_NOWARN); 111 } 112 113 /// The kernel's [`Allocator`] trait. 114 /// 115 /// An implementation of [`Allocator`] can allocate, re-allocate and free memory buffers described 116 /// via [`Layout`]. 117 /// 118 /// [`Allocator`] is designed to be implemented as a ZST; [`Allocator`] functions do not operate on 119 /// an object instance. 120 /// 121 /// In order to be able to support `#[derive(SmartPointer)]` later on, we need to avoid a design 122 /// that requires an `Allocator` to be instantiated, hence its functions must not contain any kind 123 /// of `self` parameter. 124 /// 125 /// # Safety 126 /// 127 /// - A memory allocation returned from an allocator must remain valid until it is explicitly freed. 128 /// 129 /// - Any pointer to a valid memory allocation must be valid to be passed to any other [`Allocator`] 130 /// function of the same type. 131 /// 132 /// - Implementers must ensure that all trait functions abide by the guarantees documented in the 133 /// `# Guarantees` sections. 134 pub unsafe trait Allocator { 135 /// Allocate memory based on `layout` and `flags`. 136 /// 137 /// On success, returns a buffer represented as `NonNull<[u8]>` that satisfies the layout 138 /// constraints (i.e. minimum size and alignment as specified by `layout`). 139 /// 140 /// This function is equivalent to `realloc` when called with `None`. 141 /// 142 /// # Guarantees 143 /// 144 /// When the return value is `Ok(ptr)`, then `ptr` is 145 /// - valid for reads and writes for `layout.size()` bytes, until it is passed to 146 /// [`Allocator::free`] or [`Allocator::realloc`], 147 /// - aligned to `layout.align()`, 148 /// 149 /// Additionally, `Flags` are honored as documented in 150 /// <https://docs.kernel.org/core-api/mm-api.html#mm-api-gfp-flags>. 151 fn alloc(layout: Layout, flags: Flags) -> Result<NonNull<[u8]>, AllocError> { 152 // SAFETY: Passing `None` to `realloc` is valid by its safety requirements and asks for a 153 // new memory allocation. 154 unsafe { Self::realloc(None, layout, Layout::new::<()>(), flags) } 155 } 156 157 /// Re-allocate an existing memory allocation to satisfy the requested `layout`. 158 /// 159 /// If the requested size is zero, `realloc` behaves equivalent to `free`. 160 /// 161 /// If the requested size is larger than the size of the existing allocation, a successful call 162 /// to `realloc` guarantees that the new or grown buffer has at least `Layout::size` bytes, but 163 /// may also be larger. 164 /// 165 /// If the requested size is smaller than the size of the existing allocation, `realloc` may or 166 /// may not shrink the buffer; this is implementation specific to the allocator. 167 /// 168 /// On allocation failure, the existing buffer, if any, remains valid. 169 /// 170 /// The buffer is represented as `NonNull<[u8]>`. 171 /// 172 /// # Safety 173 /// 174 /// - If `ptr == Some(p)`, then `p` must point to an existing and valid memory allocation 175 /// created by this [`Allocator`]; if `old_layout` is zero-sized `p` does not need to be a 176 /// pointer returned by this [`Allocator`]. 177 /// - `ptr` is allowed to be `None`; in this case a new memory allocation is created and 178 /// `old_layout` is ignored. 179 /// - `old_layout` must match the `Layout` the allocation has been created with. 180 /// 181 /// # Guarantees 182 /// 183 /// This function has the same guarantees as [`Allocator::alloc`]. When `ptr == Some(p)`, then 184 /// it additionally guarantees that: 185 /// - the contents of the memory pointed to by `p` are preserved up to the lesser of the new 186 /// and old size, i.e. `ret_ptr[0..min(layout.size(), old_layout.size())] == 187 /// p[0..min(layout.size(), old_layout.size())]`. 188 /// - when the return value is `Err(AllocError)`, then `ptr` is still valid. 189 unsafe fn realloc( 190 ptr: Option<NonNull<u8>>, 191 layout: Layout, 192 old_layout: Layout, 193 flags: Flags, 194 ) -> Result<NonNull<[u8]>, AllocError>; 195 196 /// Free an existing memory allocation. 197 /// 198 /// # Safety 199 /// 200 /// - `ptr` must point to an existing and valid memory allocation created by this [`Allocator`]; 201 /// if `old_layout` is zero-sized `p` does not need to be a pointer returned by this 202 /// [`Allocator`]. 203 /// - `layout` must match the `Layout` the allocation has been created with. 204 /// - The memory allocation at `ptr` must never again be read from or written to. 205 unsafe fn free(ptr: NonNull<u8>, layout: Layout) { 206 // SAFETY: The caller guarantees that `ptr` points at a valid allocation created by this 207 // allocator. We are passing a `Layout` with the smallest possible alignment, so it is 208 // smaller than or equal to the alignment previously used with this allocation. 209 let _ = unsafe { Self::realloc(Some(ptr), Layout::new::<()>(), layout, Flags(0)) }; 210 } 211 } 212 213 #[allow(dead_code)] 214 /// Returns a properly aligned dangling pointer from the given `layout`. 215 pub(crate) fn dangling_from_layout(layout: Layout) -> NonNull<u8> { 216 let ptr = layout.align() as *mut u8; 217 218 // SAFETY: `layout.align()` (and hence `ptr`) is guaranteed to be non-zero. 219 unsafe { NonNull::new_unchecked(ptr) } 220 } 221