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Diffstat (limited to 'rust/kernel/block/mq/operations.rs')
| -rw-r--r-- | rust/kernel/block/mq/operations.rs | 245 |
1 files changed, 245 insertions, 0 deletions
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 + } +} |