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rust: block: introduce kernel::block::mq module

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Add initial abstractions for working with blk-mq.

This patch is a maintained, refactored subset of code originally published
by Wedson Almeida Filho <wedsonaf@gmail.com> [1].

[1] f2cfd2fe0e/rust/kernel/blk/mq.rs

Cc: Wedson Almeida Filho <wedsonaf@gmail.com>
Signed-off-by: Andreas Hindborg <a.hindborg@samsung.com>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Link: https://lore.kernel.org/r/20240611114551.228679-2-nmi@metaspace.dk
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Andreas Hindborg 2024-06-11 13:45:49 +02:00 committed by Jens Axboe
parent c2670cf789
commit 3253aba340
11 changed files with 984 additions and 0 deletions
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3
rust/bindings/bindings_helper.h
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@ -7,6 +7,8 @@
*/
#include <kunit/test.h>
#include <linux/blk_types.h>
#include <linux/blk-mq.h>
#include <linux/errname.h>
#include <linux/ethtool.h>
#include <linux/jiffies.h>
@ -20,6 +22,7 @@
/* `bindgen` gets confused at certain things. */
const size_t RUST_CONST_HELPER_ARCH_SLAB_MINALIGN = ARCH_SLAB_MINALIGN;
const size_t RUST_CONST_HELPER_PAGE_SIZE = PAGE_SIZE;
const gfp_t RUST_CONST_HELPER_GFP_ATOMIC = GFP_ATOMIC;
const gfp_t RUST_CONST_HELPER_GFP_KERNEL = GFP_KERNEL;
const gfp_t RUST_CONST_HELPER_GFP_KERNEL_ACCOUNT = GFP_KERNEL_ACCOUNT;

16
rust/helpers.c
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@ -186,3 +186,19 @@ static_assert(
__alignof__(size_t) == __alignof__(uintptr_t),
"Rust code expects C `size_t` to match Rust `usize`"
);
// This will soon be moved to a separate file, so no need to merge with above.
#include <linux/blk-mq.h>
#include <linux/blkdev.h>
void *rust_helper_blk_mq_rq_to_pdu(struct request *rq)
{
return blk_mq_rq_to_pdu(rq);
}
EXPORT_SYMBOL_GPL(rust_helper_blk_mq_rq_to_pdu);
struct request *rust_helper_blk_mq_rq_from_pdu(void *pdu)
{
return blk_mq_rq_from_pdu(pdu);
}
EXPORT_SYMBOL_GPL(rust_helper_blk_mq_rq_from_pdu);

5
rust/kernel/block.rs Normal file
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@ -0,0 +1,5 @@
// SPDX-License-Identifier: GPL-2.0
//! Types for working with the block layer.
pub mod mq;

98
rust/kernel/block/mq.rs Normal file
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@ -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;

215
rust/kernel/block/mq/gen_disk.rs Normal file
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@ -0,0 +1,215 @@
// 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: `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(),
core::ptr::null_mut(), // TODO: We can pass queue limits right here
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`. We have exclusive access, so we cannot race.
unsafe {
bindings::blk_queue_logical_block_size((*gendisk).queue, self.logical_block_size)
};
// SAFETY: `gendisk` points to a valid and initialized instance of
// `struct gendisk`. We have exclusive access, so we cannot race.
unsafe {
bindings::blk_queue_physical_block_size((*gendisk).queue, self.physical_block_size)
};
// 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) };
if !self.rotational {
// SAFETY: `gendisk` points to a valid and initialized instance of
// `struct gendisk`. This operation uses a relaxed atomic bit flip
// operation, so there is no race on this field.
unsafe { bindings::blk_queue_flag_set(bindings::QUEUE_FLAG_NONROT, (*gendisk).queue) };
} else {
// SAFETY: `gendisk` points to a valid and initialized instance of
// `struct gendisk`. This operation uses a relaxed atomic bit flip
// operation, so there is no race on this field.
unsafe {
bindings::blk_queue_flag_clear(bindings::QUEUE_FLAG_NONROT, (*gendisk).queue)
};
}
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) };
}
}

245
rust/kernel/block/mq/operations.rs Normal file
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@ -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
}
}

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rust/kernel/block/mq/raw_writer.rs Normal file
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@ -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(())
}
}

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rust/kernel/block/mq/request.rs Normal file
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// 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");
}
}
}

86
rust/kernel/block/mq/tag_set.rs Normal file
View File

@ -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()) };
}
}

6
rust/kernel/error.rs
View File

@ -126,6 +126,12 @@ pub fn to_errno(self) -> core::ffi::c_int {
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 {

2
rust/kernel/lib.rs
View File

@ -27,6 +27,8 @@
extern crate self as kernel;
pub mod alloc;
#[cfg(CONFIG_BLOCK)]
pub mod block;
mod build_assert;
pub mod error;
pub mod init;