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// SPDX-License-Identifier: GPL-2.0
use core::ptr::NonNull;
use kernel::{
linked_list::{CursorMut, GetLinks, Links, List},
prelude::*,
};
pub(crate) struct RangeAllocator<T> {
list: List<Box<Descriptor<T>>>,
}
#[derive(Debug, PartialEq, Eq)]
enum DescriptorState {
Free,
Reserved,
Allocated,
}
impl<T> RangeAllocator<T> {
pub(crate) fn new(size: usize) -> Result<Self> {
let desc = Box::try_new(Descriptor::new(0, size))?;
let mut list = List::new();
list.push_back(desc);
Ok(Self { list })
}
fn find_best_match(&self, size: usize) -> Option<NonNull<Descriptor<T>>> {
// TODO: Use a binary tree instead of list for this lookup.
let mut best = None;
let mut best_size = usize::MAX;
let mut cursor = self.list.cursor_front();
while let Some(desc) = cursor.current() {
if desc.state == DescriptorState::Free {
if size == desc.size {
return Some(NonNull::from(desc));
}
if size < desc.size && desc.size < best_size {
best = Some(NonNull::from(desc));
best_size = desc.size;
}
}
cursor.move_next();
}
best
}
pub(crate) fn reserve_new(&mut self, size: usize) -> Result<usize> {
let desc_ptr = match self.find_best_match(size) {
None => return Err(ENOMEM),
Some(found) => found,
};
// SAFETY: We hold the only mutable reference to list, so it cannot have changed.
let desc = unsafe { &mut *desc_ptr.as_ptr() };
if desc.size == size {
desc.state = DescriptorState::Reserved;
return Ok(desc.offset);
}
// We need to break up the descriptor.
let new = Box::try_new(Descriptor::new(desc.offset + size, desc.size - size))?;
unsafe { self.list.insert_after(desc_ptr, new) };
desc.state = DescriptorState::Reserved;
desc.size = size;
Ok(desc.offset)
}
fn free_with_cursor(cursor: &mut CursorMut<'_, Box<Descriptor<T>>>) -> Result {
let mut size = match cursor.current() {
None => return Err(EINVAL),
Some(ref mut entry) => {
match entry.state {
DescriptorState::Free => return Err(EINVAL),
DescriptorState::Allocated => return Err(EPERM),
DescriptorState::Reserved => {}
}
entry.state = DescriptorState::Free;
entry.size
}
};
// Try to merge with the next entry.
if let Some(next) = cursor.peek_next() {
if next.state == DescriptorState::Free {
next.offset -= size;
next.size += size;
size = next.size;
cursor.remove_current();
}
}
// Try to merge with the previous entry.
if let Some(prev) = cursor.peek_prev() {
if prev.state == DescriptorState::Free {
prev.size += size;
cursor.remove_current();
}
}
Ok(())
}
fn find_at_offset(&mut self, offset: usize) -> Option<CursorMut<'_, Box<Descriptor<T>>>> {
let mut cursor = self.list.cursor_front_mut();
while let Some(desc) = cursor.current() {
if desc.offset == offset {
return Some(cursor);
}
if desc.offset > offset {
return None;
}
cursor.move_next();
}
None
}
pub(crate) fn reservation_abort(&mut self, offset: usize) -> Result {
// TODO: The force case is currently O(n), but could be made O(1) with unsafe.
let mut cursor = self.find_at_offset(offset).ok_or(EINVAL)?;
Self::free_with_cursor(&mut cursor)
}
pub(crate) fn reservation_commit(&mut self, offset: usize, data: Option<T>) -> Result {
// TODO: This is currently O(n), make it O(1).
let mut cursor = self.find_at_offset(offset).ok_or(ENOENT)?;
let desc = cursor.current().unwrap();
desc.state = DescriptorState::Allocated;
desc.data = data;
Ok(())
}
/// Takes an entry at the given offset from [`DescriptorState::Allocated`] to
/// [`DescriptorState::Reserved`].
///
/// Returns the size of the existing entry and the data associated with it.
pub(crate) fn reserve_existing(&mut self, offset: usize) -> Result<(usize, Option<T>)> {
// TODO: This is currently O(n), make it O(log n).
let mut cursor = self.find_at_offset(offset).ok_or(ENOENT)?;
let desc = cursor.current().unwrap();
if desc.state != DescriptorState::Allocated {
return Err(ENOENT);
}
desc.state = DescriptorState::Reserved;
Ok((desc.size, desc.data.take()))
}
pub(crate) fn for_each<F: Fn(usize, usize, Option<T>)>(&mut self, callback: F) {
let mut cursor = self.list.cursor_front_mut();
while let Some(desc) = cursor.current() {
if desc.state == DescriptorState::Allocated {
callback(desc.offset, desc.size, desc.data.take());
}
cursor.move_next();
}
}
}
struct Descriptor<T> {
state: DescriptorState,
size: usize,
offset: usize,
links: Links<Descriptor<T>>,
data: Option<T>,
}
impl<T> Descriptor<T> {
fn new(offset: usize, size: usize) -> Self {
Self {
size,
offset,
state: DescriptorState::Free,
links: Links::new(),
data: None,
}
}
}
impl<T> GetLinks for Descriptor<T> {
type EntryType = Self;
fn get_links(desc: &Self) -> &Links<Self> {
&desc.links
}
}
|
