108 lines
3.3 KiB
Rust
108 lines
3.3 KiB
Rust
// Copyright 2019 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#[derive(Copy, Clone, PartialEq, Eq)]
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#[cfg_attr(feature = "std", derive(Debug))]
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pub struct Index {
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pub page: usize,
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pub byte: usize,
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}
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#[derive(Debug)]
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pub enum StorageError {
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BadFlash,
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NotAligned,
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OutOfBounds,
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KernelError { code: isize },
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}
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pub type StorageResult<T> = Result<T, StorageError>;
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/// Abstraction for embedded flash storage.
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pub trait Storage {
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/// Returns the size of a word in bytes.
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fn word_size(&self) -> usize;
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/// Returns the size of a page in bytes.
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fn page_size(&self) -> usize;
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/// Returns the number of pages in the storage.
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fn num_pages(&self) -> usize;
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/// Returns how many times a word can be written between page erasures.
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fn max_word_writes(&self) -> usize;
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/// Returns how many times a page can be erased in the lifetime of the flash.
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fn max_page_erases(&self) -> usize;
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/// Reads a slice from the storage.
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///
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/// The slice does not need to be word-aligned.
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///
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/// # Errors
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///
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/// The `index` must designate `length` bytes in the storage.
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fn read_slice(&self, index: Index, length: usize) -> StorageResult<&[u8]>;
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/// Writes a word-aligned slice to the storage.
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///
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/// The written words should not have been written too many times since last page erasure.
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///
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/// # Errors
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///
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/// The following preconditions must hold:
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/// - `index` must be word-aligned.
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/// - `value.len()` must be a multiple of the word size.
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/// - `index` must designate `value.len()` bytes in the storage.
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/// - `value` must be in memory until [read-only allow][tock_1274] is resolved.
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///
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/// [tock_1274]: https://github.com/tock/tock/issues/1274.
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fn write_slice(&mut self, index: Index, value: &[u8]) -> StorageResult<()>;
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/// Erases a page of the storage.
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///
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/// # Errors
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///
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/// The `page` must be in the storage.
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fn erase_page(&mut self, page: usize) -> StorageResult<()>;
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}
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impl Index {
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/// Returns whether a slice fits in a storage page.
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fn is_valid(self, length: usize, storage: &impl Storage) -> bool {
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self.page < storage.num_pages()
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&& storage
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.page_size()
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.checked_sub(length)
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.map(|limit| self.byte <= limit)
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.unwrap_or(false)
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}
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/// Returns the range of a valid slice.
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///
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/// The range starts at `self` with `length` bytes.
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pub fn range(
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self,
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length: usize,
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storage: &impl Storage,
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) -> StorageResult<core::ops::Range<usize>> {
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if self.is_valid(length, storage) {
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let start = self.page * storage.page_size() + self.byte;
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Ok(start..start + length)
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} else {
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Err(StorageError::OutOfBounds)
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}
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}
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}
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