1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
// SPDX-License-Identifier: GPL-2.0

//! Linked lists.
//!
//! TODO: This module is a work in progress.

use alloc::{boxed::Box, sync::Arc};
use core::ptr::NonNull;

pub use crate::raw_list::{Cursor, GetLinks, Links};
use crate::{raw_list, raw_list::RawList};

// TODO: Use the one from `kernel::file_operations::PointerWrapper` instead.
/// Wraps an object to be inserted in a linked list.
pub trait Wrapper<T: ?Sized> {
    /// Converts the wrapped object into a pointer that represents it.
    fn into_pointer(self) -> NonNull<T>;

    /// Converts the object back from the pointer representation.
    ///
    /// # Safety
    ///
    /// The passed pointer must come from a previous call to [`Wrapper::into_pointer()`].
    unsafe fn from_pointer(ptr: NonNull<T>) -> Self;

    /// Returns a reference to the wrapped object.
    fn as_ref(&self) -> &T;
}

impl<T: ?Sized> Wrapper<T> for Box<T> {
    fn into_pointer(self) -> NonNull<T> {
        NonNull::new(Box::into_raw(self)).unwrap()
    }

    unsafe fn from_pointer(ptr: NonNull<T>) -> Self {
        unsafe { Box::from_raw(ptr.as_ptr()) }
    }

    fn as_ref(&self) -> &T {
        AsRef::as_ref(self)
    }
}

impl<T: ?Sized> Wrapper<T> for Arc<T> {
    fn into_pointer(self) -> NonNull<T> {
        NonNull::new(Arc::into_raw(self) as _).unwrap()
    }

    unsafe fn from_pointer(ptr: NonNull<T>) -> Self {
        unsafe { Arc::from_raw(ptr.as_ptr()) }
    }

    fn as_ref(&self) -> &T {
        AsRef::as_ref(self)
    }
}

impl<T: ?Sized> Wrapper<T> for &T {
    fn into_pointer(self) -> NonNull<T> {
        NonNull::from(self)
    }

    unsafe fn from_pointer(ptr: NonNull<T>) -> Self {
        unsafe { &*ptr.as_ptr() }
    }

    fn as_ref(&self) -> &T {
        self
    }
}

/// A descriptor of wrapped list elements.
pub trait GetLinksWrapped: GetLinks {
    /// Specifies which wrapper (e.g., `Box` and `Arc`) wraps the list entries.
    type Wrapped: Wrapper<Self::EntryType>;
}

impl<T: ?Sized> GetLinksWrapped for Box<T>
where
    Box<T>: GetLinks,
{
    type Wrapped = Box<<Box<T> as GetLinks>::EntryType>;
}

impl<T: GetLinks + ?Sized> GetLinks for Box<T> {
    type EntryType = T::EntryType;
    fn get_links(data: &Self::EntryType) -> &Links<Self::EntryType> {
        <T as GetLinks>::get_links(data)
    }
}

impl<T: ?Sized> GetLinksWrapped for Arc<T>
where
    Arc<T>: GetLinks,
{
    type Wrapped = Arc<<Arc<T> as GetLinks>::EntryType>;
}

impl<T: GetLinks + ?Sized> GetLinks for Arc<T> {
    type EntryType = T::EntryType;
    fn get_links(data: &Self::EntryType) -> &Links<Self::EntryType> {
        <T as GetLinks>::get_links(data)
    }
}

/// A linked list.
///
/// Elements in the list are wrapped and ownership is transferred to the list while the element is
/// in the list.
pub struct List<G: GetLinksWrapped> {
    list: RawList<G>,
}

impl<G: GetLinksWrapped> List<G> {
    /// Constructs a new empty linked list.
    pub fn new() -> Self {
        Self {
            list: RawList::new(),
        }
    }

    /// Returns whether the list is empty.
    pub fn is_empty(&self) -> bool {
        self.list.is_empty()
    }

    /// Adds the given object to the end (back) of the list.
    ///
    /// It is dropped if it's already on this (or another) list; this can happen for
    /// reference-counted objects, so dropping means decrementing the reference count.
    pub fn push_back(&mut self, data: G::Wrapped) {
        let ptr = data.into_pointer();

        // SAFETY: We took ownership of the entry, so it is safe to insert it.
        if !unsafe { self.list.push_back(ptr.as_ref()) } {
            // If insertion failed, rebuild object so that it can be freed.
            // SAFETY: We just called `into_pointer` above.
            unsafe { G::Wrapped::from_pointer(ptr) };
        }
    }

    /// Inserts the given object after `existing`.
    ///
    /// It is dropped if it's already on this (or another) list; this can happen for
    /// reference-counted objects, so dropping means decrementing the reference count.
    ///
    /// # Safety
    ///
    /// Callers must ensure that `existing` points to a valid entry that is on the list.
    pub unsafe fn insert_after(&mut self, existing: NonNull<G::EntryType>, data: G::Wrapped) {
        let ptr = data.into_pointer();
        let entry = unsafe { &*existing.as_ptr() };
        if unsafe { !self.list.insert_after(entry, ptr.as_ref()) } {
            // If insertion failed, rebuild object so that it can be freed.
            unsafe { G::Wrapped::from_pointer(ptr) };
        }
    }

    /// Removes the given entry.
    ///
    /// # Safety
    ///
    /// Callers must ensure that `data` is either on this list or in no list. It being on another
    /// list leads to memory unsafety.
    pub unsafe fn remove(&mut self, data: &G::Wrapped) -> Option<G::Wrapped> {
        let entry_ref = Wrapper::as_ref(data);
        if unsafe { self.list.remove(entry_ref) } {
            Some(unsafe { G::Wrapped::from_pointer(NonNull::from(entry_ref)) })
        } else {
            None
        }
    }

    /// Removes the element currently at the front of the list and returns it.
    ///
    /// Returns `None` if the list is empty.
    pub fn pop_front(&mut self) -> Option<G::Wrapped> {
        let front = self.list.pop_front()?;
        // SAFETY: Elements on the list were inserted after a call to `into_pointer `.
        Some(unsafe { G::Wrapped::from_pointer(front) })
    }

    /// Returns a cursor starting on the first (front) element of the list.
    pub fn cursor_front(&self) -> Cursor<'_, G> {
        self.list.cursor_front()
    }

    /// Returns a mutable cursor starting on the first (front) element of the list.
    pub fn cursor_front_mut(&mut self) -> CursorMut<'_, G> {
        CursorMut::new(self.list.cursor_front_mut())
    }
}

impl<G: GetLinksWrapped> Default for List<G> {
    fn default() -> Self {
        Self::new()
    }
}

impl<G: GetLinksWrapped> Drop for List<G> {
    fn drop(&mut self) {
        while self.pop_front().is_some() {}
    }
}

/// A list cursor that allows traversing a linked list and inspecting & mutating elements.
pub struct CursorMut<'a, G: GetLinksWrapped> {
    cursor: raw_list::CursorMut<'a, G>,
}

impl<'a, G: GetLinksWrapped> CursorMut<'a, G> {
    fn new(cursor: raw_list::CursorMut<'a, G>) -> Self {
        Self { cursor }
    }

    /// Returns the element the cursor is currently positioned on.
    pub fn current(&mut self) -> Option<&mut G::EntryType> {
        self.cursor.current()
    }

    /// Removes the element the cursor is currently positioned on.
    ///
    /// After removal, it advances the cursor to the next element.
    pub fn remove_current(&mut self) -> Option<G::Wrapped> {
        let ptr = self.cursor.remove_current()?;

        // SAFETY: Elements on the list were inserted after a call to `into_pointer `.
        Some(unsafe { G::Wrapped::from_pointer(ptr) })
    }

    /// Returns the element immediately after the one the cursor is positioned on.
    pub fn peek_next(&mut self) -> Option<&mut G::EntryType> {
        self.cursor.peek_next()
    }

    /// Returns the element immediately before the one the cursor is positioned on.
    pub fn peek_prev(&mut self) -> Option<&mut G::EntryType> {
        self.cursor.peek_prev()
    }

    /// Moves the cursor to the next element.
    pub fn move_next(&mut self) {
        self.cursor.move_next();
    }
}