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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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//! Abstractions for scatter-gather lists.//!//! C header: [`include/linux/scatterlist.h`](srctree/include/linux/scatterlist.h)//!//! Scatter-gather (SG) I/O is a memory access technique that allows devices to perform DMA//! operations on data buffers that are not physically contiguous in memory. It works by creating a//! "scatter-gather list", an array where each entry specifies the address and length of a//! physically contiguous memory segment.//!//! The device's DMA controller can then read this list and process the segments sequentially as//! part of one logical I/O request. This avoids the need for a single, large, physically contiguous//! memory buffer, which can be difficult or impossible to allocate.//!//! This module provides safe Rust abstractions over the kernel's `struct scatterlist` and//! `struct sg_table` types.//!//! The main entry point is the [`SGTable`] type, which represents a complete scatter-gather table.//! It can be either://!//! - An owned table ([`SGTable<Owned<P>>`]), created from a Rust memory buffer (e.g., [`VVec`]).//! This type manages the allocation of the `struct sg_table`, the DMA mapping of the buffer, and//! the automatic cleanup of all resources.//! - A borrowed reference (&[`SGTable`]), which provides safe, read-only access to a table that was//! allocated by other (e.g., C) code.//!//! Individual entries in the table are represented by [`SGEntry`], which can be accessed by//! iterating over an [`SGTable`].
use crate::{ alloc, alloc::allocator::VmallocPageIter, bindings, device::{Bound, Device}, devres::Devres, dma, error, io::ResourceSize, page, prelude::*, sync::aref::ARef, types::Opaque,};use core::{ops::Deref, ptr::NonNull};
/// A single entry in a scatter-gather list.////// An `SGEntry` represents a single, physically contiguous segment of memory that has been mapped/// for DMA.////// Instances of this struct are obtained by iterating over an [`SGTable`]. Drivers do not create/// or own [`SGEntry`] objects directly.#[repr(transparent)]pub struct SGEntry(Opaque<bindings::scatterlist>);
// SAFETY: `SGEntry` can be sent to any task.unsafe impl Send for SGEntry {}
// SAFETY: `SGEntry` has no interior mutability and can be accessed concurrently.unsafe impl Sync for SGEntry {}
impl SGEntry { /// Convert a raw `struct scatterlist *` to a `&'a SGEntry`. /// /// # Safety /// /// Callers must ensure that the `struct scatterlist` pointed to by `ptr` is valid for the /// lifetime `'a`. #[inline] unsafe fn from_raw<'a>(ptr: *mut bindings::scatterlist) -> &'a Self { // SAFETY: The safety requirements of this function guarantee that `ptr` is a valid pointer // to a `struct scatterlist` for the duration of `'a`. unsafe { &*ptr.cast() } }
/// Obtain the raw `struct scatterlist *`. #[inline] fn as_raw(&self) -> *mut bindings::scatterlist { self.0.get() }
/// Returns the DMA address of this SG entry. /// /// This is the address that the device should use to access the memory segment. #[inline] pub fn dma_address(&self) -> dma::DmaAddress { // SAFETY: `self.as_raw()` is a valid pointer to a `struct scatterlist`. unsafe { bindings::sg_dma_address(self.as_raw()) } }
/// Returns the length of this SG entry in bytes. #[inline] pub fn dma_len(&self) -> ResourceSize { #[allow(clippy::useless_conversion)] // SAFETY: `self.as_raw()` is a valid pointer to a `struct scatterlist`. unsafe { bindings::sg_dma_len(self.as_raw()) }.into() }}
/// The borrowed generic type of an [`SGTable`], representing a borrowed or externally managed/// table.#[repr(transparent)]pub struct Borrowed(Opaque<bindings::sg_table>);
// SAFETY: `Borrowed` can be sent to any task.unsafe impl Send for Borrowed {}
// SAFETY: `Borrowed` has no interior mutability and can be accessed concurrently.unsafe impl Sync for Borrowed {}
/// A scatter-gather table.////// This struct is a wrapper around the kernel's `struct sg_table`. It manages a list of DMA-mapped/// memory segments that can be passed to a device for I/O operations.////// The generic parameter `T` is used as a generic type to distinguish between owned and borrowed/// tables.////// - [`SGTable<Owned>`]: An owned table created and managed entirely by Rust code. It handles/// allocation, DMA mapping, and cleanup of all associated resources. See [`SGTable::new`]./// - [`SGTable<Borrowed>`} (or simply [`SGTable`]): Represents a table whose lifetime is managed/// externally. It can be used safely via a borrowed reference `&'a SGTable`, where `'a` is the/// external lifetime.////// All [`SGTable`] variants can be iterated over the individual [`SGEntry`]s.#[repr(transparent)]#[pin_data]pub struct SGTable<T: private::Sealed = Borrowed> { #[pin] inner: T,}
impl SGTable { /// Creates a borrowed `&'a SGTable` from a raw `struct sg_table` pointer. /// /// This allows safe access to an `sg_table` that is managed elsewhere (for example, in C code). /// /// # Safety /// /// Callers must ensure that: /// /// - the `struct sg_table` pointed to by `ptr` is valid for the entire lifetime of `'a`, /// - the data behind `ptr` is not modified concurrently for the duration of `'a`. #[inline] pub unsafe fn from_raw<'a>(ptr: *mut bindings::sg_table) -> &'a Self { // SAFETY: The safety requirements of this function guarantee that `ptr` is a valid pointer // to a `struct sg_table` for the duration of `'a`. unsafe { &*ptr.cast() } }
#[inline] fn as_raw(&self) -> *mut bindings::sg_table { self.inner.0.get() }
/// Returns an [`SGTableIter`] bound to the lifetime of `self`. pub fn iter(&self) -> SGTableIter<'_> { // SAFETY: `self.as_raw()` is a valid pointer to a `struct sg_table`. let nents = unsafe { (*self.as_raw()).nents };
let pos = if nents > 0 { // SAFETY: `self.as_raw()` is a valid pointer to a `struct sg_table`. let ptr = unsafe { (*self.as_raw()).sgl };
// SAFETY: `ptr` is guaranteed to be a valid pointer to a `struct scatterlist`. Some(unsafe { SGEntry::from_raw(ptr) }) } else { None };
SGTableIter { pos, nents } }}
/// Represents the DMA mapping state of a `struct sg_table`.////// This is used as an inner type of [`Owned`] to manage the DMA mapping lifecycle.////// # Invariants////// - `sgt` is a valid pointer to a `struct sg_table` for the entire lifetime of the/// [`DmaMappedSgt`]./// - `sgt` is always DMA mapped.struct DmaMappedSgt { sgt: NonNull<bindings::sg_table>, dev: ARef<Device>, dir: dma::DataDirection,}
// SAFETY: `DmaMappedSgt` can be sent to any task.unsafe impl Send for DmaMappedSgt {}
// SAFETY: `DmaMappedSgt` has no interior mutability and can be accessed concurrently.unsafe impl Sync for DmaMappedSgt {}
impl DmaMappedSgt { /// # Safety /// /// - `sgt` must be a valid pointer to a `struct sg_table` for the entire lifetime of the /// returned [`DmaMappedSgt`]. /// - The caller must guarantee that `sgt` remains DMA mapped for the entire lifetime of /// [`DmaMappedSgt`]. unsafe fn new( sgt: NonNull<bindings::sg_table>, dev: &Device<Bound>, dir: dma::DataDirection, ) -> Result<Self> { // SAFETY: // - `dev.as_raw()` is a valid pointer to a `struct device`, which is guaranteed to be // bound to a driver for the duration of this call. // - `sgt` is a valid pointer to a `struct sg_table`. error::to_result(unsafe { bindings::dma_map_sgtable(dev.as_raw(), sgt.as_ptr(), dir.into(), 0) })?;
// INVARIANT: By the safety requirements of this function it is guaranteed that `sgt` is // valid for the entire lifetime of this object instance. Ok(Self { sgt, dev: dev.into(), dir, }) }}
impl Drop for DmaMappedSgt { #[inline] fn drop(&mut self) { // SAFETY: // - `self.dev.as_raw()` is a pointer to a valid `struct device`. // - `self.dev` is the same device the mapping has been created for in `Self::new()`. // - `self.sgt.as_ptr()` is a valid pointer to a `struct sg_table` by the type invariants // of `Self`. // - `self.dir` is the same `dma::DataDirection` the mapping has been created with in // `Self::new()`. unsafe { bindings::dma_unmap_sgtable(self.dev.as_raw(), self.sgt.as_ptr(), self.dir.into(), 0) }; }}
/// A transparent wrapper around a `struct sg_table`.////// While we could also create the `struct sg_table` in the constructor of [`Owned`], we can't tear/// down the `struct sg_table` in [`Owned::drop`]; the drop order in [`Owned`] matters.#[repr(transparent)]struct RawSGTable(Opaque<bindings::sg_table>);
// SAFETY: `RawSGTable` can be sent to any task.unsafe impl Send for RawSGTable {}
// SAFETY: `RawSGTable` has no interior mutability and can be accessed concurrently.unsafe impl Sync for RawSGTable {}
impl RawSGTable { /// # Safety /// /// - `pages` must be a slice of valid `struct page *`. /// - The pages pointed to by `pages` must remain valid for the entire lifetime of the returned /// [`RawSGTable`]. unsafe fn new( pages: &mut [*mut bindings::page], size: usize, max_segment: u32, flags: alloc::Flags, ) -> Result<Self> { // `sg_alloc_table_from_pages_segment()` expects at least one page, otherwise it // produces a NPE. if pages.is_empty() { return Err(EINVAL); }
let sgt = Opaque::zeroed(); // SAFETY: // - `sgt.get()` is a valid pointer to uninitialized memory. // - As by the check above, `pages` is not empty. error::to_result(unsafe { bindings::sg_alloc_table_from_pages_segment( sgt.get(), pages.as_mut_ptr(), pages.len().try_into()?, 0, size, max_segment, flags.as_raw(), ) })?;
Ok(Self(sgt)) }
#[inline] fn as_raw(&self) -> *mut bindings::sg_table { self.0.get() }}
impl Drop for RawSGTable { #[inline] fn drop(&mut self) { // SAFETY: `sgt` is a valid and initialized `struct sg_table`. unsafe { bindings::sg_free_table(self.0.get()) }; }}
/// The [`Owned`] generic type of an [`SGTable`].////// A [`SGTable<Owned>`] signifies that the [`SGTable`] owns all associated resources:////// - The backing memory pages./// - The `struct sg_table` allocation (`sgt`)./// - The DMA mapping, managed through a [`Devres`]-managed `DmaMappedSgt`.////// Users interact with this type through the [`SGTable`] handle and do not need to manage/// [`Owned`] directly.#[pin_data]pub struct Owned<P> { // Note: The drop order is relevant; we first have to unmap the `struct sg_table`, then free the // `struct sg_table` and finally free the backing pages. #[pin] dma: Devres<DmaMappedSgt>, sgt: RawSGTable, _pages: P,}
// SAFETY: `Owned` can be sent to any task if `P` can be send to any task.unsafe impl<P: Send> Send for Owned<P> {}
// SAFETY: `Owned` has no interior mutability and can be accessed concurrently if `P` can be// accessed concurrently.unsafe impl<P: Sync> Sync for Owned<P> {}
impl<P> Owned<P>where for<'a> P: page::AsPageIter<Iter<'a> = VmallocPageIter<'a>> + 'static,{ fn new( dev: &Device<Bound>, mut pages: P, dir: dma::DataDirection, flags: alloc::Flags, ) -> Result<impl PinInit<Self, Error> + '_> { let page_iter = pages.page_iter(); let size = page_iter.size();
let mut page_vec: KVec<*mut bindings::page> = KVec::with_capacity(page_iter.page_count(), flags)?;
for page in page_iter { page_vec.push(page.as_ptr(), flags)?; }
// `dma_max_mapping_size` returns `size_t`, but `sg_alloc_table_from_pages_segment()` takes // an `unsigned int`. // // SAFETY: `dev.as_raw()` is a valid pointer to a `struct device`. let max_segment = match unsafe { bindings::dma_max_mapping_size(dev.as_raw()) } { 0 => u32::MAX, max_segment => u32::try_from(max_segment).unwrap_or(u32::MAX), };
Ok(try_pin_init!(&this in Self { // SAFETY: // - `page_vec` is a `KVec` of valid `struct page *` obtained from `pages`. // - The pages contained in `pages` remain valid for the entire lifetime of the // `RawSGTable`. sgt: unsafe { RawSGTable::new(&mut page_vec, size, max_segment, flags) }?, dma <- { // SAFETY: `this` is a valid pointer to uninitialized memory. let sgt = unsafe { &raw mut (*this.as_ptr()).sgt }.cast();
// SAFETY: `sgt` is guaranteed to be non-null. let sgt = unsafe { NonNull::new_unchecked(sgt) };
// SAFETY: // - It is guaranteed that the object returned by `DmaMappedSgt::new` won't out-live // `sgt`. // - `sgt` is never DMA unmapped manually. Devres::new(dev, unsafe { DmaMappedSgt::new(sgt, dev, dir) }) }, _pages: pages, })) }}
impl<P> SGTable<Owned<P>>where for<'a> P: page::AsPageIter<Iter<'a> = VmallocPageIter<'a>> + 'static,{ /// Allocates a new scatter-gather table from the given pages and maps it for DMA. /// /// This constructor creates a new [`SGTable<Owned>`] that takes ownership of `P`. /// It allocates a `struct sg_table`, populates it with entries corresponding to the physical /// pages of `P`, and maps the table for DMA with the specified [`Device`] and /// [`dma::DataDirection`]. /// /// The DMA mapping is managed through [`Devres`], ensuring that the DMA mapping is unmapped /// once the associated [`Device`] is unbound, or when the [`SGTable<Owned>`] is dropped. /// /// # Parameters /// /// * `dev`: The [`Device`] that will be performing the DMA. /// * `pages`: The entity providing the backing pages. It must implement [`page::AsPageIter`]. /// The ownership of this entity is moved into the new [`SGTable<Owned>`]. /// * `dir`: The [`dma::DataDirection`] of the DMA transfer. /// * `flags`: Allocation flags for internal allocations (e.g., [`GFP_KERNEL`]). /// /// # Examples /// /// ``` /// use kernel::{ /// device::{Bound, Device}, /// dma, page, /// prelude::*, /// scatterlist::{SGTable, Owned}, /// }; /// /// fn test(dev: &Device<Bound>) -> Result { /// let size = 4 * page::PAGE_SIZE; /// let pages = VVec::<u8>::with_capacity(size, GFP_KERNEL)?; /// /// let sgt = KBox::pin_init(SGTable::new( /// dev, /// pages, /// dma::DataDirection::ToDevice, /// GFP_KERNEL, /// ), GFP_KERNEL)?; /// /// Ok(()) /// } /// ``` pub fn new( dev: &Device<Bound>, pages: P, dir: dma::DataDirection, flags: alloc::Flags, ) -> impl PinInit<Self, Error> + '_ { try_pin_init!(Self { inner <- Owned::new(dev, pages, dir, flags)? }) }}
impl<P> Deref for SGTable<Owned<P>> { type Target = SGTable;
#[inline] fn deref(&self) -> &Self::Target { // SAFETY: // - `self.inner.sgt.as_raw()` is a valid pointer to a `struct sg_table` for the entire // lifetime of `self`. // - The backing `struct sg_table` is not modified for the entire lifetime of `self`. unsafe { SGTable::from_raw(self.inner.sgt.as_raw()) } }}
mod private { pub trait Sealed {}
impl Sealed for super::Borrowed {} impl<P> Sealed for super::Owned<P> {}}
/// An [`Iterator`] over the DMA mapped [`SGEntry`] items of an [`SGTable`].////// Note that the existence of an [`SGTableIter`] does not guarantee that the [`SGEntry`] items/// actually remain DMA mapped; they are prone to be unmapped on device unbind.pub struct SGTableIter<'a> { pos: Option<&'a SGEntry>, /// The number of DMA mapped entries in a `struct sg_table`. nents: c_uint,}
impl<'a> Iterator for SGTableIter<'a> { type Item = &'a SGEntry;
fn next(&mut self) -> Option<Self::Item> { let entry = self.pos?; self.nents = self.nents.saturating_sub(1);
// SAFETY: `entry.as_raw()` is a valid pointer to a `struct scatterlist`. let next = unsafe { bindings::sg_next(entry.as_raw()) };
self.pos = (!next.is_null() && self.nents > 0).then(|| { // SAFETY: If `next` is not NULL, `sg_next()` guarantees to return a valid pointer to // the next `struct scatterlist`. unsafe { SGEntry::from_raw(next) } });
Some(entry) }}