1 // SPDX-License-Identifier: GPL-2.0 2 3 // Copyright (C) 2024 Google LLC. 4 5 //! Helpers for implementing list traits safely. 6 7 /// Declares that this type has a [`ListLinks<ID>`] field. 8 /// 9 /// This trait is only used to help implement [`ListItem`] safely. If [`ListItem`] is implemented 10 /// manually, then this trait is not needed. Use the [`impl_has_list_links!`] macro to implement 11 /// this trait. 12 /// 13 /// # Safety 14 /// 15 /// The methods on this trait must have exactly the behavior that the definitions given below have. 16 /// 17 /// [`ListLinks<ID>`]: crate::list::ListLinks 18 /// [`ListItem`]: crate::list::ListItem 19 pub unsafe trait HasListLinks<const ID: u64 = 0> { 20 /// Returns a pointer to the [`ListLinks<ID>`] field. 21 /// 22 /// # Safety 23 /// 24 /// The provided pointer must point at a valid struct of type `Self`. 25 /// 26 /// [`ListLinks<ID>`]: crate::list::ListLinks raw_get_list_links(ptr: *mut Self) -> *mut crate::list::ListLinks<ID>27 unsafe fn raw_get_list_links(ptr: *mut Self) -> *mut crate::list::ListLinks<ID>; 28 } 29 30 /// Implements the [`HasListLinks`] trait for the given type. 31 #[macro_export] 32 macro_rules! impl_has_list_links { 33 ($(impl$({$($generics:tt)*})? 34 HasListLinks$(<$id:tt>)? 35 for $self:ty 36 { self$(.$field:ident)* } 37 )*) => {$( 38 // SAFETY: The implementation of `raw_get_list_links` only compiles if the field has the 39 // right type. 40 unsafe impl$(<$($generics)*>)? $crate::list::HasListLinks$(<$id>)? for $self { 41 #[inline] 42 unsafe fn raw_get_list_links(ptr: *mut Self) -> *mut $crate::list::ListLinks$(<$id>)? { 43 // Statically ensure that `$(.field)*` doesn't follow any pointers. 44 // 45 // Cannot be `const` because `$self` may contain generics and E0401 says constants 46 // "can't use {`Self`,generic parameters} from outer item". 47 if false { let _: usize = ::core::mem::offset_of!(Self, $($field).*); } 48 49 // SAFETY: The caller promises that the pointer is not dangling. We know that this 50 // expression doesn't follow any pointers, as the `offset_of!` invocation above 51 // would otherwise not compile. 52 unsafe { ::core::ptr::addr_of_mut!((*ptr)$(.$field)*) } 53 } 54 } 55 )*}; 56 } 57 pub use impl_has_list_links; 58 59 /// Declares that the [`ListLinks<ID>`] field in this struct is inside a 60 /// [`ListLinksSelfPtr<T, ID>`]. 61 /// 62 /// # Safety 63 /// 64 /// The [`ListLinks<ID>`] field of this struct at [`HasListLinks<ID>::raw_get_list_links`] must be 65 /// inside a [`ListLinksSelfPtr<T, ID>`]. 66 /// 67 /// [`ListLinks<ID>`]: crate::list::ListLinks 68 /// [`ListLinksSelfPtr<T, ID>`]: crate::list::ListLinksSelfPtr 69 pub unsafe trait HasSelfPtr<T: ?Sized, const ID: u64 = 0> 70 where 71 Self: HasListLinks<ID>, 72 { 73 } 74 75 /// Implements the [`HasListLinks`] and [`HasSelfPtr`] traits for the given type. 76 #[macro_export] 77 macro_rules! impl_has_list_links_self_ptr { 78 ($(impl$({$($generics:tt)*})? 79 HasSelfPtr<$item_type:ty $(, $id:tt)?> 80 for $self:ty 81 { self$(.$field:ident)* } 82 )*) => {$( 83 // SAFETY: The implementation of `raw_get_list_links` only compiles if the field has the 84 // right type. 85 unsafe impl$(<$($generics)*>)? $crate::list::HasSelfPtr<$item_type $(, $id)?> for $self {} 86 87 unsafe impl$(<$($generics)*>)? $crate::list::HasListLinks$(<$id>)? for $self { 88 #[inline] 89 unsafe fn raw_get_list_links(ptr: *mut Self) -> *mut $crate::list::ListLinks$(<$id>)? { 90 // SAFETY: The caller promises that the pointer is not dangling. 91 let ptr: *mut $crate::list::ListLinksSelfPtr<$item_type $(, $id)?> = 92 unsafe { ::core::ptr::addr_of_mut!((*ptr)$(.$field)*) }; 93 ptr.cast() 94 } 95 } 96 )*}; 97 } 98 pub use impl_has_list_links_self_ptr; 99 100 /// Implements the [`ListItem`] trait for the given type. 101 /// 102 /// Requires that the type implements [`HasListLinks`]. Use the [`impl_has_list_links!`] macro to 103 /// implement that trait. 104 /// 105 /// [`ListItem`]: crate::list::ListItem 106 /// 107 /// # Examples 108 /// 109 /// ``` 110 /// #[pin_data] 111 /// struct SimpleListItem { 112 /// value: u32, 113 /// #[pin] 114 /// links: kernel::list::ListLinks, 115 /// } 116 /// 117 /// kernel::list::impl_list_arc_safe! { 118 /// impl ListArcSafe<0> for SimpleListItem { untracked; } 119 /// } 120 /// 121 /// kernel::list::impl_list_item! { 122 /// impl ListItem<0> for SimpleListItem { using ListLinks { self.links }; } 123 /// } 124 /// 125 /// struct ListLinksHolder { 126 /// inner: kernel::list::ListLinks, 127 /// } 128 /// 129 /// #[pin_data] 130 /// struct ComplexListItem<T, U> { 131 /// value: Result<T, U>, 132 /// #[pin] 133 /// links: ListLinksHolder, 134 /// } 135 /// 136 /// kernel::list::impl_list_arc_safe! { 137 /// impl{T, U} ListArcSafe<0> for ComplexListItem<T, U> { untracked; } 138 /// } 139 /// 140 /// kernel::list::impl_list_item! { 141 /// impl{T, U} ListItem<0> for ComplexListItem<T, U> { using ListLinks { self.links.inner }; } 142 /// } 143 /// ``` 144 /// 145 /// ``` 146 /// #[pin_data] 147 /// struct SimpleListItem { 148 /// value: u32, 149 /// #[pin] 150 /// links: kernel::list::ListLinksSelfPtr<SimpleListItem>, 151 /// } 152 /// 153 /// kernel::list::impl_list_arc_safe! { 154 /// impl ListArcSafe<0> for SimpleListItem { untracked; } 155 /// } 156 /// 157 /// kernel::list::impl_list_item! { 158 /// impl ListItem<0> for SimpleListItem { using ListLinksSelfPtr { self.links }; } 159 /// } 160 /// 161 /// struct ListLinksSelfPtrHolder<T, U> { 162 /// inner: kernel::list::ListLinksSelfPtr<ComplexListItem<T, U>>, 163 /// } 164 /// 165 /// #[pin_data] 166 /// struct ComplexListItem<T, U> { 167 /// value: Result<T, U>, 168 /// #[pin] 169 /// links: ListLinksSelfPtrHolder<T, U>, 170 /// } 171 /// 172 /// kernel::list::impl_list_arc_safe! { 173 /// impl{T, U} ListArcSafe<0> for ComplexListItem<T, U> { untracked; } 174 /// } 175 /// 176 /// kernel::list::impl_list_item! { 177 /// impl{T, U} ListItem<0> for ComplexListItem<T, U> { 178 /// using ListLinksSelfPtr { self.links.inner }; 179 /// } 180 /// } 181 /// ``` 182 #[macro_export] 183 macro_rules! impl_list_item { 184 ( 185 $(impl$({$($generics:tt)*})? ListItem<$num:tt> for $self:ty { 186 using ListLinks { self$(.$field:ident)* }; 187 })* 188 ) => {$( 189 $crate::list::impl_has_list_links! { 190 impl$({$($generics)*})? HasListLinks<$num> for $self { self$(.$field)* } 191 } 192 193 // SAFETY: See GUARANTEES comment on each method. 194 unsafe impl$(<$($generics)*>)? $crate::list::ListItem<$num> for $self { 195 // GUARANTEES: 196 // * This returns the same pointer as `prepare_to_insert` because `prepare_to_insert` 197 // is implemented in terms of `view_links`. 198 // * By the type invariants of `ListLinks`, the `ListLinks` has two null pointers when 199 // this value is not in a list. 200 unsafe fn view_links(me: *const Self) -> *mut $crate::list::ListLinks<$num> { 201 // SAFETY: The caller guarantees that `me` points at a valid value of type `Self`. 202 unsafe { 203 <Self as $crate::list::HasListLinks<$num>>::raw_get_list_links(me.cast_mut()) 204 } 205 } 206 207 // GUARANTEES: 208 // * `me` originates from the most recent call to `prepare_to_insert`, which calls 209 // `raw_get_list_link`, which is implemented using `addr_of_mut!((*self)$(.$field)*)`. 210 // This method uses `container_of` to perform the inverse operation, so it returns the 211 // pointer originally passed to `prepare_to_insert`. 212 // * The pointer remains valid until the next call to `post_remove` because the caller 213 // of the most recent call to `prepare_to_insert` promised to retain ownership of the 214 // `ListArc` containing `Self` until the next call to `post_remove`. The value cannot 215 // be destroyed while a `ListArc` reference exists. 216 unsafe fn view_value(me: *mut $crate::list::ListLinks<$num>) -> *const Self { 217 // SAFETY: `me` originates from the most recent call to `prepare_to_insert`, so it 218 // points at the field `$field` in a value of type `Self`. Thus, reversing that 219 // operation is still in-bounds of the allocation. 220 $crate::container_of!(me, Self, $($field).*) 221 } 222 223 // GUARANTEES: 224 // This implementation of `ListItem` will not give out exclusive access to the same 225 // `ListLinks` several times because calls to `prepare_to_insert` and `post_remove` 226 // must alternate and exclusive access is given up when `post_remove` is called. 227 // 228 // Other invocations of `impl_list_item!` also cannot give out exclusive access to the 229 // same `ListLinks` because you can only implement `ListItem` once for each value of 230 // `ID`, and the `ListLinks` fields only work with the specified `ID`. 231 unsafe fn prepare_to_insert(me: *const Self) -> *mut $crate::list::ListLinks<$num> { 232 // SAFETY: The caller promises that `me` points at a valid value. 233 unsafe { <Self as $crate::list::ListItem<$num>>::view_links(me) } 234 } 235 236 // GUARANTEES: 237 // * `me` originates from the most recent call to `prepare_to_insert`, which calls 238 // `raw_get_list_link`, which is implemented using `addr_of_mut!((*self)$(.$field)*)`. 239 // This method uses `container_of` to perform the inverse operation, so it returns the 240 // pointer originally passed to `prepare_to_insert`. 241 unsafe fn post_remove(me: *mut $crate::list::ListLinks<$num>) -> *const Self { 242 // SAFETY: `me` originates from the most recent call to `prepare_to_insert`, so it 243 // points at the field `$field` in a value of type `Self`. Thus, reversing that 244 // operation is still in-bounds of the allocation. 245 $crate::container_of!(me, Self, $($field).*) 246 } 247 } 248 )*}; 249 250 ( 251 $(impl$({$($generics:tt)*})? ListItem<$num:tt> for $self:ty { 252 using ListLinksSelfPtr { self$(.$field:ident)* }; 253 })* 254 ) => {$( 255 $crate::list::impl_has_list_links_self_ptr! { 256 impl$({$($generics)*})? HasSelfPtr<$self> for $self { self$(.$field)* } 257 } 258 259 // SAFETY: See GUARANTEES comment on each method. 260 unsafe impl$(<$($generics)*>)? $crate::list::ListItem<$num> for $self { 261 // GUARANTEES: 262 // This implementation of `ListItem` will not give out exclusive access to the same 263 // `ListLinks` several times because calls to `prepare_to_insert` and `post_remove` 264 // must alternate and exclusive access is given up when `post_remove` is called. 265 // 266 // Other invocations of `impl_list_item!` also cannot give out exclusive access to the 267 // same `ListLinks` because you can only implement `ListItem` once for each value of 268 // `ID`, and the `ListLinks` fields only work with the specified `ID`. 269 unsafe fn prepare_to_insert(me: *const Self) -> *mut $crate::list::ListLinks<$num> { 270 // SAFETY: The caller promises that `me` points at a valid value of type `Self`. 271 let links_field = unsafe { <Self as $crate::list::ListItem<$num>>::view_links(me) }; 272 273 let container = $crate::container_of!( 274 links_field, $crate::list::ListLinksSelfPtr<Self, $num>, inner 275 ); 276 277 // SAFETY: By the same reasoning above, `links_field` is a valid pointer. 278 let self_ptr = unsafe { 279 $crate::list::ListLinksSelfPtr::raw_get_self_ptr(container) 280 }; 281 282 let cell_inner = $crate::types::Opaque::cast_into(self_ptr); 283 284 // SAFETY: This value is not accessed in any other places than `prepare_to_insert`, 285 // `post_remove`, or `view_value`. By the safety requirements of those methods, 286 // none of these three methods may be called in parallel with this call to 287 // `prepare_to_insert`, so this write will not race with any other access to the 288 // value. 289 unsafe { ::core::ptr::write(cell_inner, me) }; 290 291 links_field 292 } 293 294 // GUARANTEES: 295 // * This returns the same pointer as `prepare_to_insert` because `prepare_to_insert` 296 // returns the return value of `view_links`. 297 // * By the type invariants of `ListLinks`, the `ListLinks` has two null pointers when 298 // this value is not in a list. 299 unsafe fn view_links(me: *const Self) -> *mut $crate::list::ListLinks<$num> { 300 // SAFETY: The caller promises that `me` points at a valid value of type `Self`. 301 unsafe { 302 <Self as $crate::list::HasListLinks<$num>>::raw_get_list_links(me.cast_mut()) 303 } 304 } 305 306 // This function is also used as the implementation of `post_remove`, so the caller 307 // may choose to satisfy the safety requirements of `post_remove` instead of the safety 308 // requirements for `view_value`. 309 // 310 // GUARANTEES: (always) 311 // * This returns the same pointer as the one passed to the most recent call to 312 // `prepare_to_insert` since that call wrote that pointer to this location. The value 313 // is only modified in `prepare_to_insert`, so it has not been modified since the 314 // most recent call. 315 // 316 // GUARANTEES: (only when using the `view_value` safety requirements) 317 // * The pointer remains valid until the next call to `post_remove` because the caller 318 // of the most recent call to `prepare_to_insert` promised to retain ownership of the 319 // `ListArc` containing `Self` until the next call to `post_remove`. The value cannot 320 // be destroyed while a `ListArc` reference exists. 321 unsafe fn view_value(links_field: *mut $crate::list::ListLinks<$num>) -> *const Self { 322 let container = $crate::container_of!( 323 links_field, $crate::list::ListLinksSelfPtr<Self, $num>, inner 324 ); 325 326 // SAFETY: By the same reasoning above, `links_field` is a valid pointer. 327 let self_ptr = unsafe { 328 $crate::list::ListLinksSelfPtr::raw_get_self_ptr(container) 329 }; 330 331 let cell_inner = $crate::types::Opaque::cast_into(self_ptr); 332 333 // SAFETY: This is not a data race, because the only function that writes to this 334 // value is `prepare_to_insert`, but by the safety requirements the 335 // `prepare_to_insert` method may not be called in parallel with `view_value` or 336 // `post_remove`. 337 unsafe { ::core::ptr::read(cell_inner) } 338 } 339 340 // GUARANTEES: 341 // The first guarantee of `view_value` is exactly what `post_remove` guarantees. 342 unsafe fn post_remove(me: *mut $crate::list::ListLinks<$num>) -> *const Self { 343 // SAFETY: This specific implementation of `view_value` allows the caller to 344 // promise the safety requirements of `post_remove` instead of the safety 345 // requirements for `view_value`. 346 unsafe { <Self as $crate::list::ListItem<$num>>::view_value(me) } 347 } 348 } 349 )*}; 350 } 351 pub use impl_list_item; 352