storage_device/
lib.rs

1// Copyright 2021 The Fuchsia Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5//! `storage_device` provides a higher-level portable API ([`Device`]) for interacting with block
6//! devices.  This library also provides the [`Buffer`] type which is a contiguous, splittable
7//! transfer buffer allocated out of a shared pool which can be used for I/O.
8//!
9//! The two main implementations are
10//!   - [`block_device::BlockDevice`], which is backed by a [`block_client::Device`] and used on
11//!     Fuchsia devices, and
12//!   - [`file_backed_device::FileBackedDevice`], which is backed by a regular file and is portable.
13
14use crate::buffer::{BufferFuture, BufferRef, MutableBufferRef};
15use anyhow::{Error, bail};
16use async_trait::async_trait;
17// pub so `Device` trait implementations don't need to depend on the `block_protocol` crate
18pub use block_protocol::{ReadOptions, WriteOptions};
19use futures::channel::oneshot::{Sender, channel};
20use std::future::Future;
21use std::mem::ManuallyDrop;
22use std::ops::{Deref, Range};
23use std::sync::{Arc, OnceLock};
24
25pub mod buffer;
26pub mod buffer_allocator;
27
28#[cfg(target_os = "fuchsia")]
29pub mod block_device;
30
31#[cfg(target_family = "unix")]
32pub mod file_backed_device;
33
34pub mod fake_device;
35
36#[async_trait]
37/// Device is an abstract representation of an underlying block device.
38pub trait Device: Send + Sync {
39    /// Allocates a transfer buffer of at least |size| bytes for doing I/O with the device.
40    /// The actual size of the buffer will be rounded up to a block-aligned size.
41    /// Blocks until enough capacity is available in the buffer.
42    fn allocate_buffer(&self, size: usize) -> BufferFuture<'_>;
43
44    /// Returns the block size of the device. Buffers are aligned to block-aligned chunks.
45    fn block_size(&self) -> u32;
46
47    /// Returns the number of blocks of the device.
48    fn block_count(&self) -> u64;
49
50    /// Returns the size in bytes of the device.
51    fn size(&self) -> u64 {
52        self.block_size() as u64 * self.block_count()
53    }
54
55    /// Fills |buffer| with blocks read from |offset|.
56    async fn read(&self, offset: u64, buffer: MutableBufferRef<'_>) -> Result<(), Error> {
57        self.read_with_opts(offset, buffer, ReadOptions::default()).await
58    }
59
60    /// Fills |buffer| with blocks read from |offset|.
61    async fn read_with_opts(
62        &self,
63        offset: u64,
64        buffer: MutableBufferRef<'_>,
65        read_opts: ReadOptions,
66    ) -> Result<(), Error>;
67
68    /// Writes the contents of |buffer| to the device at |offset|.
69    async fn write(&self, offset: u64, buffer: BufferRef<'_>) -> Result<(), Error> {
70        self.write_with_opts(offset, buffer, WriteOptions::default()).await
71    }
72
73    /// Writes the contents of |buffer| to the device at |offset|.
74    async fn write_with_opts(
75        &self,
76        offset: u64,
77        buffer: BufferRef<'_>,
78        write_opts: WriteOptions,
79    ) -> Result<(), Error>;
80
81    /// Trims the given device |range|.
82    async fn trim(&self, range: Range<u64>) -> Result<(), Error>;
83
84    /// Closes the block device. It is an error to continue using the device after this, but close
85    /// itself is idempotent.
86    async fn close(&self) -> Result<(), Error>;
87
88    /// Flush the device.
89    async fn flush(&self) -> Result<(), Error>;
90
91    /// Attach a barrier to the next write made to the device.
92    fn barrier(&self);
93
94    /// Reopens the device, making it usable again. (Only implemented for testing devices.)
95    fn reopen(&self, _read_only: bool) {
96        unreachable!();
97    }
98    /// Returns whether the device is read-only.
99    fn is_read_only(&self) -> bool;
100
101    /// Returns whether the device supports trim.
102    fn supports_trim(&self) -> bool;
103
104    /// Returns a snapshot of the device.
105    fn snapshot(&self) -> Result<DeviceHolder, Error> {
106        bail!("Not supported");
107    }
108
109    /// Discards random blocks since the last flush.
110    fn discard_random_since_last_flush(&self) -> Result<(), Error> {
111        bail!("Not supported");
112    }
113
114    /// Poisons a device to panic on drop. Used to find hanging references.
115    fn poison(&self) -> Result<(), Error> {
116        bail!("Not supported");
117    }
118}
119
120// Arc<dyn Device> can easily be cloned and supports concurrent access, but sometimes exclusive
121// access is required, in which case APIs should accept DeviceHolder.  It doesn't guarantee there
122// aren't some users that hold an Arc<dyn Device> somewhere, but it does mean that something that
123// accepts a DeviceHolder won't be sharing the device with something else that accepts a
124// DeviceHolder.  For example, FxFilesystem accepts a DeviceHolder which means that you cannot
125// create two FxFilesystem instances that are both sharing the same device.
126pub struct DeviceHolder {
127    device: ManuallyDrop<Arc<dyn Device>>,
128    on_drop: OnceLock<Sender<DeviceHolder>>,
129}
130
131impl DeviceHolder {
132    pub fn new(device: impl Device + 'static) -> Self {
133        DeviceHolder { device: ManuallyDrop::new(Arc::new(device)), on_drop: OnceLock::new() }
134    }
135
136    // Ensures there are no dangling references to the device. Useful for tests to ensure orderly
137    // shutdown.
138    pub fn ensure_unique(&self) {
139        assert_eq!(Arc::strong_count(&self.device), 1);
140    }
141
142    pub fn take_when_dropped(&self) -> impl Future<Output = DeviceHolder> {
143        let (sender, receiver) = channel::<DeviceHolder>();
144        self.on_drop
145            .set(sender)
146            .unwrap_or_else(|_| panic!("take_when_dropped should only be called once"));
147        async { receiver.await.unwrap() }
148    }
149}
150
151impl Drop for DeviceHolder {
152    fn drop(&mut self) {
153        if let Some(sender) = self.on_drop.take() {
154            // SAFETY: `device` is not used again.
155            let device = ManuallyDrop::new(unsafe { ManuallyDrop::take(&mut self.device) });
156            // We don't care if this fails to send.
157            let _ = sender.send(DeviceHolder { device, on_drop: OnceLock::new() });
158        } else {
159            // SAFETY: `device` is not used again.
160            unsafe { ManuallyDrop::drop(&mut self.device) }
161        }
162    }
163}
164
165impl Deref for DeviceHolder {
166    type Target = Arc<dyn Device>;
167
168    fn deref(&self) -> &Self::Target {
169        &self.device
170    }
171}
172
173#[cfg(test)]
174mod tests {
175    use super::DeviceHolder;
176    use crate::fake_device::FakeDevice;
177
178    #[fuchsia::test]
179    async fn test_take_when_dropped() {
180        let holder = DeviceHolder::new(FakeDevice::new(1, 512));
181        let fut = holder.take_when_dropped();
182        std::mem::drop(holder);
183        fut.await.ensure_unique();
184    }
185}
storage_device/lib.rs

storage_device/
lib.rs
