diff options
Diffstat (limited to 'rust/kernel')
| -rw-r--r-- | rust/kernel/block.rs | 5 | ||||
| -rw-r--r-- | rust/kernel/block/mq.rs | 98 | ||||
| -rw-r--r-- | rust/kernel/block/mq/gen_disk.rs | 198 | ||||
| -rw-r--r-- | rust/kernel/block/mq/operations.rs | 245 | ||||
| -rw-r--r-- | rust/kernel/block/mq/raw_writer.rs | 55 | ||||
| -rw-r--r-- | rust/kernel/block/mq/request.rs | 253 | ||||
| -rw-r--r-- | rust/kernel/block/mq/tag_set.rs | 86 | ||||
| -rw-r--r-- | rust/kernel/error.rs | 6 | ||||
| -rw-r--r-- | rust/kernel/lib.rs | 2 |
9 files changed, 948 insertions, 0 deletions
diff --git a/rust/kernel/block.rs b/rust/kernel/block.rs new file mode 100644 index 000000000000..150f710efe5b --- /dev/null +++ b/rust/kernel/block.rs @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! Types for working with the block layer. + +pub mod mq; diff --git a/rust/kernel/block/mq.rs b/rust/kernel/block/mq.rs new file mode 100644 index 000000000000..fb0f393c1cea --- /dev/null +++ b/rust/kernel/block/mq.rs @@ -0,0 +1,98 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! This module provides types for implementing block drivers that interface the +//! blk-mq subsystem. +//! +//! To implement a block device driver, a Rust module must do the following: +//! +//! - Implement [`Operations`] for a type `T`. +//! - Create a [`TagSet<T>`]. +//! - Create a [`GenDisk<T>`], via the [`GenDiskBuilder`]. +//! - Add the disk to the system by calling [`GenDiskBuilder::build`] passing in +//! the `TagSet` reference. +//! +//! The types available in this module that have direct C counterparts are: +//! +//! - The [`TagSet`] type that abstracts the C type `struct tag_set`. +//! - The [`GenDisk`] type that abstracts the C type `struct gendisk`. +//! - The [`Request`] type that abstracts the C type `struct request`. +//! +//! The kernel will interface with the block device driver by calling the method +//! implementations of the `Operations` trait. +//! +//! IO requests are passed to the driver as [`kernel::types::ARef<Request>`] +//! instances. The `Request` type is a wrapper around the C `struct request`. +//! The driver must mark end of processing by calling one of the +//! `Request::end`, methods. Failure to do so can lead to deadlock or timeout +//! errors. Please note that the C function `blk_mq_start_request` is implicitly +//! called when the request is queued with the driver. +//! +//! The `TagSet` is responsible for creating and maintaining a mapping between +//! `Request`s and integer ids as well as carrying a pointer to the vtable +//! generated by `Operations`. This mapping is useful for associating +//! completions from hardware with the correct `Request` instance. The `TagSet` +//! determines the maximum queue depth by setting the number of `Request` +//! instances available to the driver, and it determines the number of queues to +//! instantiate for the driver. If possible, a driver should allocate one queue +//! per core, to keep queue data local to a core. +//! +//! One `TagSet` instance can be shared between multiple `GenDisk` instances. +//! This can be useful when implementing drivers where one piece of hardware +//! with one set of IO resources are represented to the user as multiple disks. +//! +//! One significant difference between block device drivers implemented with +//! these Rust abstractions and drivers implemented in C, is that the Rust +//! drivers have to own a reference count on the `Request` type when the IO is +//! in flight. This is to ensure that the C `struct request` instances backing +//! the Rust `Request` instances are live while the Rust driver holds a +//! reference to the `Request`. In addition, the conversion of an integer tag to +//! a `Request` via the `TagSet` would not be sound without this bookkeeping. +//! +//! [`GenDisk`]: gen_disk::GenDisk +//! [`GenDisk<T>`]: gen_disk::GenDisk +//! [`GenDiskBuilder`]: gen_disk::GenDiskBuilder +//! [`GenDiskBuilder::build`]: gen_disk::GenDiskBuilder::build +//! +//! # Example +//! +//! ```rust +//! use kernel::{ +//! alloc::flags, +//! block::mq::*, +//! new_mutex, +//! prelude::*, +//! sync::{Arc, Mutex}, +//! types::{ARef, ForeignOwnable}, +//! }; +//! +//! struct MyBlkDevice; +//! +//! #[vtable] +//! impl Operations for MyBlkDevice { +//! +//! fn queue_rq(rq: ARef<Request<Self>>, _is_last: bool) -> Result { +//! Request::end_ok(rq); +//! Ok(()) +//! } +//! +//! fn commit_rqs() {} +//! } +//! +//! let tagset: Arc<TagSet<MyBlkDevice>> = +//! Arc::pin_init(TagSet::new(1, 256, 1), flags::GFP_KERNEL)?; +//! let mut disk = gen_disk::GenDiskBuilder::new() +//! .capacity_sectors(4096) +//! .build(format_args!("myblk"), tagset)?; +//! +//! # Ok::<(), kernel::error::Error>(()) +//! ``` + +pub mod gen_disk; +mod operations; +mod raw_writer; +mod request; +mod tag_set; + +pub use operations::Operations; +pub use request::Request; +pub use tag_set::TagSet; diff --git a/rust/kernel/block/mq/gen_disk.rs b/rust/kernel/block/mq/gen_disk.rs new file mode 100644 index 000000000000..f548a6199847 --- /dev/null +++ b/rust/kernel/block/mq/gen_disk.rs @@ -0,0 +1,198 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! Generic disk abstraction. +//! +//! C header: [`include/linux/blkdev.h`](srctree/include/linux/blkdev.h) +//! C header: [`include/linux/blk_mq.h`](srctree/include/linux/blk_mq.h) + +use crate::block::mq::{raw_writer::RawWriter, Operations, TagSet}; +use crate::error; +use crate::{bindings, error::from_err_ptr, error::Result, sync::Arc}; +use core::fmt::{self, Write}; + +/// A builder for [`GenDisk`]. +/// +/// Use this struct to configure and add new [`GenDisk`] to the VFS. +pub struct GenDiskBuilder { + rotational: bool, + logical_block_size: u32, + physical_block_size: u32, + capacity_sectors: u64, +} + +impl Default for GenDiskBuilder { + fn default() -> Self { + Self { + rotational: false, + logical_block_size: bindings::PAGE_SIZE as u32, + physical_block_size: bindings::PAGE_SIZE as u32, + capacity_sectors: 0, + } + } +} + +impl GenDiskBuilder { + /// Create a new instance. + pub fn new() -> Self { + Self::default() + } + + /// Set the rotational media attribute for the device to be built. + pub fn rotational(mut self, rotational: bool) -> Self { + self.rotational = rotational; + self + } + + /// Validate block size by verifying that it is between 512 and `PAGE_SIZE`, + /// and that it is a power of two. + fn validate_block_size(size: u32) -> Result<()> { + if !(512..=bindings::PAGE_SIZE as u32).contains(&size) || !size.is_power_of_two() { + Err(error::code::EINVAL) + } else { + Ok(()) + } + } + + /// Set the logical block size of the device to be built. + /// + /// This method will check that block size is a power of two and between 512 + /// and 4096. If not, an error is returned and the block size is not set. + /// + /// This is the smallest unit the storage device can address. It is + /// typically 4096 bytes. + pub fn logical_block_size(mut self, block_size: u32) -> Result<Self> { + Self::validate_block_size(block_size)?; + self.logical_block_size = block_size; + Ok(self) + } + + /// Set the physical block size of the device to be built. + /// + /// This method will check that block size is a power of two and between 512 + /// and 4096. If not, an error is returned and the block size is not set. + /// + /// This is the smallest unit a physical storage device can write + /// atomically. It is usually the same as the logical block size but may be + /// bigger. One example is SATA drives with 4096 byte physical block size + /// that expose a 512 byte logical block size to the operating system. + pub fn physical_block_size(mut self, block_size: u32) -> Result<Self> { + Self::validate_block_size(block_size)?; + self.physical_block_size = block_size; + Ok(self) + } + + /// Set the capacity of the device to be built, in sectors (512 bytes). + pub fn capacity_sectors(mut self, capacity: u64) -> Self { + self.capacity_sectors = capacity; + self + } + + /// Build a new `GenDisk` and add it to the VFS. + pub fn build<T: Operations>( + self, + name: fmt::Arguments<'_>, + tagset: Arc<TagSet<T>>, + ) -> Result<GenDisk<T>> { + let lock_class_key = crate::sync::LockClassKey::new(); + + // SAFETY: `bindings::queue_limits` contain only fields that are valid when zeroed. + let mut lim: bindings::queue_limits = unsafe { core::mem::zeroed() }; + + lim.logical_block_size = self.logical_block_size; + lim.physical_block_size = self.physical_block_size; + if self.rotational { + lim.features = bindings::BLK_FEAT_ROTATIONAL; + } + + // SAFETY: `tagset.raw_tag_set()` points to a valid and initialized tag set + let gendisk = from_err_ptr(unsafe { + bindings::__blk_mq_alloc_disk( + tagset.raw_tag_set(), + &mut lim, + core::ptr::null_mut(), + lock_class_key.as_ptr(), + ) + })?; + + const TABLE: bindings::block_device_operations = bindings::block_device_operations { + submit_bio: None, + open: None, + release: None, + ioctl: None, + compat_ioctl: None, + check_events: None, + unlock_native_capacity: None, + getgeo: None, + set_read_only: None, + swap_slot_free_notify: None, + report_zones: None, + devnode: None, + alternative_gpt_sector: None, + get_unique_id: None, + // TODO: Set to THIS_MODULE. Waiting for const_refs_to_static feature to + // be merged (unstable in rustc 1.78 which is staged for linux 6.10) + // https://github.com/rust-lang/rust/issues/119618 + owner: core::ptr::null_mut(), + pr_ops: core::ptr::null_mut(), + free_disk: None, + poll_bio: None, + }; + + // SAFETY: `gendisk` is a valid pointer as we initialized it above + unsafe { (*gendisk).fops = &TABLE }; + + let mut raw_writer = RawWriter::from_array( + // SAFETY: `gendisk` points to a valid and initialized instance. We + // have exclusive access, since the disk is not added to the VFS + // yet. + unsafe { &mut (*gendisk).disk_name }, + )?; + raw_writer.write_fmt(name)?; + raw_writer.write_char('\0')?; + + // SAFETY: `gendisk` points to a valid and initialized instance of + // `struct gendisk`. `set_capacity` takes a lock to synchronize this + // operation, so we will not race. + unsafe { bindings::set_capacity(gendisk, self.capacity_sectors) }; + + crate::error::to_result( + // SAFETY: `gendisk` points to a valid and initialized instance of + // `struct gendisk`. + unsafe { + bindings::device_add_disk(core::ptr::null_mut(), gendisk, core::ptr::null_mut()) + }, + )?; + + // INVARIANT: `gendisk` was initialized above. + // INVARIANT: `gendisk` was added to the VFS via `device_add_disk` above. + Ok(GenDisk { + _tagset: tagset, + gendisk, + }) + } +} + +/// A generic block device. +/// +/// # Invariants +/// +/// - `gendisk` must always point to an initialized and valid `struct gendisk`. +/// - `gendisk` was added to the VFS through a call to +/// `bindings::device_add_disk`. +pub struct GenDisk<T: Operations> { + _tagset: Arc<TagSet<T>>, + gendisk: *mut bindings::gendisk, +} + +// SAFETY: `GenDisk` is an owned pointer to a `struct gendisk` and an `Arc` to a +// `TagSet` It is safe to send this to other threads as long as T is Send. +unsafe impl<T: Operations + Send> Send for GenDisk<T> {} + +impl<T: Operations> Drop for GenDisk<T> { + fn drop(&mut self) { + // SAFETY: By type invariant, `self.gendisk` points to a valid and + // initialized instance of `struct gendisk`, and it was previously added + // to the VFS. + unsafe { bindings::del_gendisk(self.gendisk) }; + } +} diff --git a/rust/kernel/block/mq/operations.rs b/rust/kernel/block/mq/operations.rs new file mode 100644 index 000000000000..9ba7fdfeb4b2 --- /dev/null +++ b/rust/kernel/block/mq/operations.rs @@ -0,0 +1,245 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! This module provides an interface for blk-mq drivers to implement. +//! +//! C header: [`include/linux/blk-mq.h`](srctree/include/linux/blk-mq.h) + +use crate::{ + bindings, + block::mq::request::RequestDataWrapper, + block::mq::Request, + error::{from_result, Result}, + types::ARef, +}; +use core::{marker::PhantomData, sync::atomic::AtomicU64, sync::atomic::Ordering}; + +/// Implement this trait to interface blk-mq as block devices. +/// +/// To implement a block device driver, implement this trait as described in the +/// [module level documentation]. The kernel will use the implementation of the +/// functions defined in this trait to interface a block device driver. Note: +/// There is no need for an exit_request() implementation, because the `drop` +/// implementation of the [`Request`] type will be invoked by automatically by +/// the C/Rust glue logic. +/// +/// [module level documentation]: kernel::block::mq +#[macros::vtable] +pub trait Operations: Sized { + /// Called by the kernel to queue a request with the driver. If `is_last` is + /// `false`, the driver is allowed to defer committing the request. + fn queue_rq(rq: ARef<Request<Self>>, is_last: bool) -> Result; + + /// Called by the kernel to indicate that queued requests should be submitted. + fn commit_rqs(); + + /// Called by the kernel to poll the device for completed requests. Only + /// used for poll queues. + fn poll() -> bool { + crate::build_error(crate::error::VTABLE_DEFAULT_ERROR) + } +} + +/// A vtable for blk-mq to interact with a block device driver. +/// +/// A `bindings::blk_mq_ops` vtable is constructed from pointers to the `extern +/// "C"` functions of this struct, exposed through the `OperationsVTable::VTABLE`. +/// +/// For general documentation of these methods, see the kernel source +/// documentation related to `struct blk_mq_operations` in +/// [`include/linux/blk-mq.h`]. +/// +/// [`include/linux/blk-mq.h`]: srctree/include/linux/blk-mq.h +pub(crate) struct OperationsVTable<T: Operations>(PhantomData<T>); + +impl<T: Operations> OperationsVTable<T> { + /// This function is called by the C kernel. A pointer to this function is + /// installed in the `blk_mq_ops` vtable for the driver. + /// + /// # Safety + /// + /// - The caller of this function must ensure that the pointee of `bd` is + /// valid for reads for the duration of this function. + /// - This function must be called for an initialized and live `hctx`. That + /// is, `Self::init_hctx_callback` was called and + /// `Self::exit_hctx_callback()` was not yet called. + /// - `(*bd).rq` must point to an initialized and live `bindings:request`. + /// That is, `Self::init_request_callback` was called but + /// `Self::exit_request_callback` was not yet called for the request. + /// - `(*bd).rq` must be owned by the driver. That is, the block layer must + /// promise to not access the request until the driver calls + /// `bindings::blk_mq_end_request` for the request. + unsafe extern "C" fn queue_rq_callback( + _hctx: *mut bindings::blk_mq_hw_ctx, + bd: *const bindings::blk_mq_queue_data, + ) -> bindings::blk_status_t { + // SAFETY: `bd.rq` is valid as required by the safety requirement for + // this function. + let request = unsafe { &*(*bd).rq.cast::<Request<T>>() }; + + // One refcount for the ARef, one for being in flight + request.wrapper_ref().refcount().store(2, Ordering::Relaxed); + + // SAFETY: + // - We own a refcount that we took above. We pass that to `ARef`. + // - By the safety requirements of this function, `request` is a valid + // `struct request` and the private data is properly initialized. + // - `rq` will be alive until `blk_mq_end_request` is called and is + // reference counted by `ARef` until then. + let rq = unsafe { Request::aref_from_raw((*bd).rq) }; + + // SAFETY: We have exclusive access and we just set the refcount above. + unsafe { Request::start_unchecked(&rq) }; + + let ret = T::queue_rq( + rq, + // SAFETY: `bd` is valid as required by the safety requirement for + // this function. + unsafe { (*bd).last }, + ); + + if let Err(e) = ret { + e.to_blk_status() + } else { + bindings::BLK_STS_OK as _ + } + } + + /// This function is called by the C kernel. A pointer to this function is + /// installed in the `blk_mq_ops` vtable for the driver. + /// + /// # Safety + /// + /// This function may only be called by blk-mq C infrastructure. + unsafe extern "C" fn commit_rqs_callback(_hctx: *mut bindings::blk_mq_hw_ctx) { + T::commit_rqs() + } + + /// This function is called by the C kernel. It is not currently + /// implemented, and there is no way to exercise this code path. + /// + /// # Safety + /// + /// This function may only be called by blk-mq C infrastructure. + unsafe extern "C" fn complete_callback(_rq: *mut bindings::request) {} + + /// This function is called by the C kernel. A pointer to this function is + /// installed in the `blk_mq_ops` vtable for the driver. + /// + /// # Safety + /// + /// This function may only be called by blk-mq C infrastructure. + unsafe extern "C" fn poll_callback( + _hctx: *mut bindings::blk_mq_hw_ctx, + _iob: *mut bindings::io_comp_batch, + ) -> core::ffi::c_int { + T::poll().into() + } + + /// This function is called by the C kernel. A pointer to this function is + /// installed in the `blk_mq_ops` vtable for the driver. + /// + /// # Safety + /// + /// This function may only be called by blk-mq C infrastructure. This + /// function may only be called once before `exit_hctx_callback` is called + /// for the same context. + unsafe extern "C" fn init_hctx_callback( + _hctx: *mut bindings::blk_mq_hw_ctx, + _tagset_data: *mut core::ffi::c_void, + _hctx_idx: core::ffi::c_uint, + ) -> core::ffi::c_int { + from_result(|| Ok(0)) + } + + /// This function is called by the C kernel. A pointer to this function is + /// installed in the `blk_mq_ops` vtable for the driver. + /// + /// # Safety + /// + /// This function may only be called by blk-mq C infrastructure. + unsafe extern "C" fn exit_hctx_callback( + _hctx: *mut bindings::blk_mq_hw_ctx, + _hctx_idx: core::ffi::c_uint, + ) { + } + + /// This function is called by the C kernel. A pointer to this function is + /// installed in the `blk_mq_ops` vtable for the driver. + /// + /// # Safety + /// + /// - This function may only be called by blk-mq C infrastructure. + /// - `_set` must point to an initialized `TagSet<T>`. + /// - `rq` must point to an initialized `bindings::request`. + /// - The allocation pointed to by `rq` must be at the size of `Request` + /// plus the size of `RequestDataWrapper`. + unsafe extern "C" fn init_request_callback( + _set: *mut bindings::blk_mq_tag_set, + rq: *mut bindings::request, + _hctx_idx: core::ffi::c_uint, + _numa_node: core::ffi::c_uint, + ) -> core::ffi::c_int { + from_result(|| { + // SAFETY: By the safety requirements of this function, `rq` points + // to a valid allocation. + let pdu = unsafe { Request::wrapper_ptr(rq.cast::<Request<T>>()) }; + + // SAFETY: The refcount field is allocated but not initialized, so + // it is valid for writes. + unsafe { RequestDataWrapper::refcount_ptr(pdu.as_ptr()).write(AtomicU64::new(0)) }; + + Ok(0) + }) + } + + /// This function is called by the C kernel. A pointer to this function is + /// installed in the `blk_mq_ops` vtable for the driver. + /// + /// # Safety + /// + /// - This function may only be called by blk-mq C infrastructure. + /// - `_set` must point to an initialized `TagSet<T>`. + /// - `rq` must point to an initialized and valid `Request`. + unsafe extern "C" fn exit_request_callback( + _set: *mut bindings::blk_mq_tag_set, + rq: *mut bindings::request, + _hctx_idx: core::ffi::c_uint, + ) { + // SAFETY: The tagset invariants guarantee that all requests are allocated with extra memory + // for the request data. + let pdu = unsafe { bindings::blk_mq_rq_to_pdu(rq) }.cast::<RequestDataWrapper>(); + + // SAFETY: `pdu` is valid for read and write and is properly initialised. + unsafe { core::ptr::drop_in_place(pdu) }; + } + + const VTABLE: bindings::blk_mq_ops = bindings::blk_mq_ops { + queue_rq: Some(Self::queue_rq_callback), + queue_rqs: None, + commit_rqs: Some(Self::commit_rqs_callback), + get_budget: None, + put_budget: None, + set_rq_budget_token: None, + get_rq_budget_token: None, + timeout: None, + poll: if T::HAS_POLL { + Some(Self::poll_callback) + } else { + None + }, + complete: Some(Self::complete_callback), + init_hctx: Some(Self::init_hctx_callback), + exit_hctx: Some(Self::exit_hctx_callback), + init_request: Some(Self::init_request_callback), + exit_request: Some(Self::exit_request_callback), + cleanup_rq: None, + busy: None, + map_queues: None, + #[cfg(CONFIG_BLK_DEBUG_FS)] + show_rq: None, + }; + + pub(crate) const fn build() -> &'static bindings::blk_mq_ops { + &Self::VTABLE + } +} diff --git a/rust/kernel/block/mq/raw_writer.rs b/rust/kernel/block/mq/raw_writer.rs new file mode 100644 index 000000000000..9222465d670b --- /dev/null +++ b/rust/kernel/block/mq/raw_writer.rs @@ -0,0 +1,55 @@ +// SPDX-License-Identifier: GPL-2.0 + +use core::fmt::{self, Write}; + +use crate::error::Result; +use crate::prelude::EINVAL; + +/// A mutable reference to a byte buffer where a string can be written into. +/// +/// # Invariants +/// +/// `buffer` is always null terminated. +pub(crate) struct RawWriter<'a> { + buffer: &'a mut [u8], + pos: usize, +} + +impl<'a> RawWriter<'a> { + /// Create a new `RawWriter` instance. + fn new(buffer: &'a mut [u8]) -> Result<RawWriter<'a>> { + *(buffer.last_mut().ok_or(EINVAL)?) = 0; + + // INVARIANT: We null terminated the buffer above. + Ok(Self { buffer, pos: 0 }) + } + + pub(crate) fn from_array<const N: usize>( + a: &'a mut [core::ffi::c_char; N], + ) -> Result<RawWriter<'a>> { + Self::new( + // SAFETY: the buffer of `a` is valid for read and write as `u8` for + // at least `N` bytes. + unsafe { core::slice::from_raw_parts_mut(a.as_mut_ptr().cast::<u8>(), N) }, + ) + } +} + +impl Write for RawWriter<'_> { + fn write_str(&mut self, s: &str) -> fmt::Result { + let bytes = s.as_bytes(); + let len = bytes.len(); + + // We do not want to overwrite our null terminator + if self.pos + len > self.buffer.len() - 1 { + return Err(fmt::Error); + } + + // INVARIANT: We are not overwriting the last byte + self.buffer[self.pos..self.pos + len].copy_from_slice(bytes); + + self.pos += len; + + Ok(()) + } +} diff --git a/rust/kernel/block/mq/request.rs b/rust/kernel/block/mq/request.rs new file mode 100644 index 000000000000..a0e22827f3f4 --- /dev/null +++ b/rust/kernel/block/mq/request.rs @@ -0,0 +1,253 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! This module provides a wrapper for the C `struct request` type. +//! +//! C header: [`include/linux/blk-mq.h`](srctree/include/linux/blk-mq.h) + +use crate::{ + bindings, + block::mq::Operations, + error::Result, + types::{ARef, AlwaysRefCounted, Opaque}, +}; +use core::{ + marker::PhantomData, + ptr::{addr_of_mut, NonNull}, + sync::atomic::{AtomicU64, Ordering}, +}; + +/// A wrapper around a blk-mq `struct request`. This represents an IO request. +/// +/// # Implementation details +/// +/// There are four states for a request that the Rust bindings care about: +/// +/// A) Request is owned by block layer (refcount 0) +/// B) Request is owned by driver but with zero `ARef`s in existence +/// (refcount 1) +/// C) Request is owned by driver with exactly one `ARef` in existence +/// (refcount 2) +/// D) Request is owned by driver with more than one `ARef` in existence +/// (refcount > 2) +/// +/// +/// We need to track A and B to ensure we fail tag to request conversions for +/// requests that are not owned by the driver. +/// +/// We need to track C and D to ensure that it is safe to end the request and hand +/// back ownership to the block layer. +/// +/// The states are tracked through the private `refcount` field of +/// `RequestDataWrapper`. This structure lives in the private data area of the C +/// `struct request`. +/// +/// # Invariants +/// +/// * `self.0` is a valid `struct request` created by the C portion of the kernel. +/// * The private data area associated with this request must be an initialized +/// and valid `RequestDataWrapper<T>`. +/// * `self` is reference counted by atomic modification of +/// self.wrapper_ref().refcount(). +/// +#[repr(transparent)] +pub struct Request<T: Operations>(Opaque<bindings::request>, PhantomData<T>); + +impl<T: Operations> Request<T> { + /// Create an `ARef<Request>` from a `struct request` pointer. + /// + /// # Safety + /// + /// * The caller must own a refcount on `ptr` that is transferred to the + /// returned `ARef`. + /// * The type invariants for `Request` must hold for the pointee of `ptr`. + pub(crate) unsafe fn aref_from_raw(ptr: *mut bindings::request) -> ARef<Self> { + // INVARIANT: By the safety requirements of this function, invariants are upheld. + // SAFETY: By the safety requirement of this function, we own a + // reference count that we can pass to `ARef`. + unsafe { ARef::from_raw(NonNull::new_unchecked(ptr as *const Self as *mut Self)) } + } + + /// Notify the block layer that a request is going to be processed now. + /// + /// The block layer uses this hook to do proper initializations such as + /// starting the timeout timer. It is a requirement that block device + /// drivers call this function when starting to process a request. + /// + /// # Safety + /// + /// The caller must have exclusive ownership of `self`, that is + /// `self.wrapper_ref().refcount() == 2`. + pub(crate) unsafe fn start_unchecked(this: &ARef<Self>) { + // SAFETY: By type invariant, `self.0` is a valid `struct request` and + // we have exclusive access. + unsafe { bindings::blk_mq_start_request(this.0.get()) }; + } + + /// Try to take exclusive ownership of `this` by dropping the refcount to 0. + /// This fails if `this` is not the only `ARef` pointing to the underlying + /// `Request`. + /// + /// If the operation is successful, `Ok` is returned with a pointer to the + /// C `struct request`. If the operation fails, `this` is returned in the + /// `Err` variant. + fn try_set_end(this: ARef<Self>) -> Result<*mut bindings::request, ARef<Self>> { + // We can race with `TagSet::tag_to_rq` + if let Err(_old) = this.wrapper_ref().refcount().compare_exchange( + 2, + 0, + Ordering::Relaxed, + Ordering::Relaxed, + ) { + return Err(this); + } + + let request_ptr = this.0.get(); + core::mem::forget(this); + + Ok(request_ptr) + } + + /// Notify the block layer that the request has been completed without errors. + /// + /// This function will return `Err` if `this` is not the only `ARef` + /// referencing the request. + pub fn end_ok(this: ARef<Self>) -> Result<(), ARef<Self>> { + let request_ptr = Self::try_set_end(this)?; + + // SAFETY: By type invariant, `this.0` was a valid `struct request`. The + // success of the call to `try_set_end` guarantees that there are no + // `ARef`s pointing to this request. Therefore it is safe to hand it + // back to the block layer. + unsafe { bindings::blk_mq_end_request(request_ptr, bindings::BLK_STS_OK as _) }; + + Ok(()) + } + + /// Return a pointer to the `RequestDataWrapper` stored in the private area + /// of the request structure. + /// + /// # Safety + /// + /// - `this` must point to a valid allocation of size at least size of + /// `Self` plus size of `RequestDataWrapper`. + pub(crate) unsafe fn wrapper_ptr(this: *mut Self) -> NonNull<RequestDataWrapper> { + let request_ptr = this.cast::<bindings::request>(); + // SAFETY: By safety requirements for this function, `this` is a + // valid allocation. + let wrapper_ptr = + unsafe { bindings::blk_mq_rq_to_pdu(request_ptr).cast::<RequestDataWrapper>() }; + // SAFETY: By C API contract, wrapper_ptr points to a valid allocation + // and is not null. + unsafe { NonNull::new_unchecked(wrapper_ptr) } + } + + /// Return a reference to the `RequestDataWrapper` stored in the private + /// area of the request structure. + pub(crate) fn wrapper_ref(&self) -> &RequestDataWrapper { + // SAFETY: By type invariant, `self.0` is a valid allocation. Further, + // the private data associated with this request is initialized and + // valid. The existence of `&self` guarantees that the private data is + // valid as a shared reference. + unsafe { Self::wrapper_ptr(self as *const Self as *mut Self).as_ref() } + } +} + +/// A wrapper around data stored in the private area of the C `struct request`. +pub(crate) struct RequestDataWrapper { + /// The Rust request refcount has the following states: + /// + /// - 0: The request is owned by C block layer. + /// - 1: The request is owned by Rust abstractions but there are no ARef references to it. + /// - 2+: There are `ARef` references to the request. + refcount: AtomicU64, +} + +impl RequestDataWrapper { + /// Return a reference to the refcount of the request that is embedding + /// `self`. + pub(crate) fn refcount(&self) -> &AtomicU64 { + &self.refcount + } + + /// Return a pointer to the refcount of the request that is embedding the + /// pointee of `this`. + /// + /// # Safety + /// + /// - `this` must point to a live allocation of at least the size of `Self`. + pub(crate) unsafe fn refcount_ptr(this: *mut Self) -> *mut AtomicU64 { + // SAFETY: Because of the safety requirements of this function, the + // field projection is safe. + unsafe { addr_of_mut!((*this).refcount) } + } +} + +// SAFETY: Exclusive access is thread-safe for `Request`. `Request` has no `&mut +// self` methods and `&self` methods that mutate `self` are internally +// synchronized. +unsafe impl<T: Operations> Send for Request<T> {} + +// SAFETY: Shared access is thread-safe for `Request`. `&self` methods that +// mutate `self` are internally synchronized` +unsafe impl<T: Operations> Sync for Request<T> {} + +/// Store the result of `op(target.load())` in target, returning new value of +/// target. +fn atomic_relaxed_op_return(target: &AtomicU64, op: impl Fn(u64) -> u64) -> u64 { + let old = target.fetch_update(Ordering::Relaxed, Ordering::Relaxed, |x| Some(op(x))); + + // SAFETY: Because the operation passed to `fetch_update` above always + // return `Some`, `old` will always be `Ok`. + let old = unsafe { old.unwrap_unchecked() }; + + op(old) +} + +/// Store the result of `op(target.load)` in `target` if `target.load() != +/// pred`, returning true if the target was updated. +fn atomic_relaxed_op_unless(target: &AtomicU64, op: impl Fn(u64) -> u64, pred: u64) -> bool { + target + .fetch_update(Ordering::Relaxed, Ordering::Relaxed, |x| { + if x == pred { + None + } else { + Some(op(x)) + } + }) + .is_ok() +} + +// SAFETY: All instances of `Request<T>` are reference counted. This +// implementation of `AlwaysRefCounted` ensure that increments to the ref count +// keeps the object alive in memory at least until a matching reference count +// decrement is executed. +unsafe impl<T: Operations> AlwaysRefCounted for Request<T> { + fn inc_ref(&self) { + let refcount = &self.wrapper_ref().refcount(); + + #[cfg_attr(not(CONFIG_DEBUG_MISC), allow(unused_variables))] + let updated = atomic_relaxed_op_unless(refcount, |x| x + 1, 0); + + #[cfg(CONFIG_DEBUG_MISC)] + if !updated { + panic!("Request refcount zero on clone") + } + } + + unsafe fn dec_ref(obj: core::ptr::NonNull<Self>) { + // SAFETY: The type invariants of `ARef` guarantee that `obj` is valid + // for read. + let wrapper_ptr = unsafe { Self::wrapper_ptr(obj.as_ptr()).as_ptr() }; + // SAFETY: The type invariant of `Request` guarantees that the private + // data area is initialized and valid. + let refcount = unsafe { &*RequestDataWrapper::refcount_ptr(wrapper_ptr) }; + + #[cfg_attr(not(CONFIG_DEBUG_MISC), allow(unused_variables))] + let new_refcount = atomic_relaxed_op_return(refcount, |x| x - 1); + + #[cfg(CONFIG_DEBUG_MISC)] + if new_refcount == 0 { + panic!("Request reached refcount zero in Rust abstractions"); + } + } +} diff --git a/rust/kernel/block/mq/tag_set.rs b/rust/kernel/block/mq/tag_set.rs new file mode 100644 index 000000000000..f9a1ca655a35 --- /dev/null +++ b/rust/kernel/block/mq/tag_set.rs @@ -0,0 +1,86 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! This module provides the `TagSet` struct to wrap the C `struct blk_mq_tag_set`. +//! +//! C header: [`include/linux/blk-mq.h`](srctree/include/linux/blk-mq.h) + +use core::pin::Pin; + +use crate::{ + bindings, + block::mq::{operations::OperationsVTable, request::RequestDataWrapper, Operations}, + error, + prelude::PinInit, + try_pin_init, + types::Opaque, +}; +use core::{convert::TryInto, marker::PhantomData}; +use macros::{pin_data, pinned_drop}; + +/// A wrapper for the C `struct blk_mq_tag_set`. +/// +/// `struct blk_mq_tag_set` contains a `struct list_head` and so must be pinned. +/// +/// # Invariants +/// +/// - `inner` is initialized and valid. +#[pin_data(PinnedDrop)] +#[repr(transparent)] +pub struct TagSet<T: Operations> { + #[pin] + inner: Opaque<bindings::blk_mq_tag_set>, + _p: PhantomData<T>, +} + +impl<T: Operations> TagSet<T> { + /// Try to create a new tag set + pub fn new( + nr_hw_queues: u32, + num_tags: u32, + num_maps: u32, + ) -> impl PinInit<Self, error::Error> { + // SAFETY: `blk_mq_tag_set` only contains integers and pointers, which + // all are allowed to be 0. + let tag_set: bindings::blk_mq_tag_set = unsafe { core::mem::zeroed() }; + let tag_set = core::mem::size_of::<RequestDataWrapper>() + .try_into() + .map(|cmd_size| { + bindings::blk_mq_tag_set { + ops: OperationsVTable::<T>::build(), + nr_hw_queues, + timeout: 0, // 0 means default which is 30Hz in C + numa_node: bindings::NUMA_NO_NODE, + queue_depth: num_tags, + cmd_size, + flags: bindings::BLK_MQ_F_SHOULD_MERGE, + driver_data: core::ptr::null_mut::<core::ffi::c_void>(), + nr_maps: num_maps, + ..tag_set + } + }); + + try_pin_init!(TagSet { + inner <- PinInit::<_, error::Error>::pin_chain(Opaque::new(tag_set?), |tag_set| { + // SAFETY: we do not move out of `tag_set`. + let tag_set = unsafe { Pin::get_unchecked_mut(tag_set) }; + // SAFETY: `tag_set` is a reference to an initialized `blk_mq_tag_set`. + error::to_result( unsafe { bindings::blk_mq_alloc_tag_set(tag_set.get())}) + }), + _p: PhantomData, + }) + } + + /// Return the pointer to the wrapped `struct blk_mq_tag_set` + pub(crate) fn raw_tag_set(&self) -> *mut bindings::blk_mq_tag_set { + self.inner.get() + } +} + +#[pinned_drop] +impl<T: Operations> PinnedDrop for TagSet<T> { + fn drop(self: Pin<&mut Self>) { + // SAFETY: By type invariant `inner` is valid and has been properly + // initialized during construction. + unsafe { bindings::blk_mq_free_tag_set(self.inner.get()) }; + } +} diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs index 55280ae9fe40..145f5c397009 100644 --- a/rust/kernel/error.rs +++ b/rust/kernel/error.rs @@ -126,6 +126,12 @@ impl Error { self.0 } + #[cfg(CONFIG_BLOCK)] + pub(crate) fn to_blk_status(self) -> bindings::blk_status_t { + // SAFETY: `self.0` is a valid error due to its invariant. + unsafe { bindings::errno_to_blk_status(self.0) } + } + /// Returns the error encoded as a pointer. #[allow(dead_code)] pub(crate) fn to_ptr<T>(self) -> *mut T { diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index fbd91a48ff8b..2cf7c6b6f66b 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -27,6 +27,8 @@ compile_error!("Missing kernel configuration for conditional compilation"); extern crate self as kernel; pub mod alloc; +#[cfg(CONFIG_BLOCK)] +pub mod block; mod build_assert; pub mod error; pub mod init; |