[PATCH v2 1/3] rust: kernel: add ScatterList abstraction

["Qingsong Chen" <changxian.cqs@antgroup.com>]

Add a wrapper for `struct scatterlist`.

Signed-off-by: Qingsong Chen <changxian.cqs@antgroup.com>
---
 rust/bindings/bindings_helper.h |   1 +
 rust/helpers.c                  |  14 ++
 rust/kernel/lib.rs              |   1 +
 rust/kernel/scatterlist.rs      | 280 ++++++++++++++++++++++++++++++++
 4 files changed, 296 insertions(+)
 create mode 100644 rust/kernel/scatterlist.rs

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 50e7a76d5455..9cfa1ef92a04 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -10,6 +10,7 @@
 #include <linux/refcount.h>
 #include <linux/wait.h>
 #include <linux/sched.h>
+#include <linux/scatterlist.h>
 
 /* `bindgen` gets confused at certain things. */
 const gfp_t BINDINGS_GFP_KERNEL = GFP_KERNEL;
diff --git a/rust/helpers.c b/rust/helpers.c
index 81e80261d597..1714ed05f561 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -26,6 +26,7 @@
 #include <linux/spinlock.h>
 #include <linux/sched/signal.h>
 #include <linux/wait.h>
+#include <linux/scatterlist.h>
 
 __noreturn void rust_helper_BUG(void)
 {
@@ -128,6 +129,19 @@ void rust_helper_put_task_struct(struct task_struct *t)
 }
 EXPORT_SYMBOL_GPL(rust_helper_put_task_struct);
 
+void rust_helper_sg_set_buf(struct scatterlist *sg, const void *buf,
+			    unsigned int buflen)
+{
+	sg_set_buf(sg, buf, buflen);
+}
+EXPORT_SYMBOL_GPL(rust_helper_sg_set_buf);
+
+void *rust_helper_sg_virt(struct scatterlist *sg)
+{
+	return sg_virt(sg);
+}
+EXPORT_SYMBOL_GPL(rust_helper_sg_virt);
+
 /*
  * We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type
  * as the Rust `usize` type, so we can use it in contexts where Rust
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 676995d4e460..d8dbcde4ad5c 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -40,6 +40,7 @@ pub mod init;
 pub mod ioctl;
 pub mod prelude;
 pub mod print;
+pub mod scatterlist;
 mod static_assert;
 #[doc(hidden)]
 pub mod std_vendor;
diff --git a/rust/kernel/scatterlist.rs b/rust/kernel/scatterlist.rs
new file mode 100644
index 000000000000..8d6a34afb191
--- /dev/null
+++ b/rust/kernel/scatterlist.rs
@@ -0,0 +1,280 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Scatterlist.
+//!
+//! C header: [`include/linux/scatterlist.h`](../../../../include/linux/scatterlist.h)
+
+use crate::prelude::*;
+use crate::types::Opaque;
+use core::marker::PhantomData;
+use core::ptr::NonNull;
+
+/// Wrap the kernel's `struct scatterlist`.
+///
+/// According to the design of kernel's `struct sg_table`, the `page_link`
+/// field of one `scatterlist` may contain a pointer to another. That is,
+/// there could exist external pointers to it, making it necessary to pin
+/// this struct.
+///
+/// # Invirants
+///
+/// All instances should be valid, either created by the `new` constructor
+/// (see [`pin_init`]), or transmuted from raw pointers (which could be used
+/// to reference a valid entry of `sg_table`).
+///
+/// # Examples
+///
+/// The following is some use cases of [`ScatterList`].
+///
+/// ```rust
+/// use core::pin::pin;
+/// # use kernel::error::Result;
+/// # use kernel::scatterlist::ScatterList;
+///
+/// // Prepare memory buffers.
+/// let buf0: Pin<&mut [u8]> = pin!([0u8; 512]);
+/// let buf1: Pin<&mut [u8]> = pin!([1u8; 512]);
+///
+/// // Allocates an instance on stack.
+/// kernel::stack_pin_init!(let foo = ScatterList::new(&buf0));
+/// let mut foo: Pin<&mut ScatterList<'_>> = foo;
+/// assert_eq!(foo.length(), 512);
+///
+/// // Alloccate an instance by Box::pin_init.
+/// let bar: Pin<Box<ScatterList<'_>>> = Box::pin_init(ScatterList::new(&buf1))?;
+/// assert_eq!(bar.length(), 512);
+///
+/// // Assert other attributes of a instance.
+/// assert_eq!(foo.is_dma_bus_address(), false);
+/// assert_eq!(foo.is_chain(), false);
+/// assert_eq!(foo.is_last(), true);
+/// assert_eq!(foo.count(), 1);
+///
+/// // Get a immutable reference to memory buffer.
+/// assert_eq!(foo.get_buf(), [0u8; 512]);
+///
+/// // Reset the memory buffer.
+/// foo.set_buf(&buf1);
+/// assert_eq!(foo.get_buf(), [1u8; 512]);
+///
+/// // Get a mutable reference to memory buffer.
+/// foo.get_mut_buf().fill(2);
+/// assert_eq!(foo.get_buf(), [2u8; 512]);
+/// ```
+#[pin_data]
+pub struct ScatterList<'a> {
+    #[pin]
+    opaque: Opaque<bindings::scatterlist>,
+    _p: PhantomData<&'a mut bindings::scatterlist>,
+}
+
+impl<'a> ScatterList<'a> {
+    /// Construct a new initializer.
+    pub fn new(buf: &'a Pin<&mut [u8]>) -> impl PinInit<ScatterList<'a>> {
+        // SAFETY: `slot` is valid while the closure is called, the memory
+        // buffer is pinned and valid.
+        unsafe {
+            init::pin_init_from_closure(move |slot: *mut Self| {
+                (*slot).set_buf(buf);
+                (*slot).mark_end();
+                Ok(())
+            })
+        }
+    }
+
+    /// Obtain a pinned reference to an immutable scatterlist from a raw pointer.
+    pub fn as_ref(ptr: *mut bindings::scatterlist) -> Option<Pin<&'a Self>> {
+        // SAFETY: `sgl` is non-null and valid.
+        NonNull::new(ptr).map(|sgl| Pin::new(unsafe { &*(sgl.as_ptr() as *const ScatterList<'_>) }))
+    }
+
+    /// Obtain a pinned reference to a mutable scatterlist from a raw pointer.
+    pub fn as_mut(ptr: *mut bindings::scatterlist) -> Option<Pin<&'a mut Self>> {
+        // SAFETY: `sgl` is non-null and valid.
+        NonNull::new(ptr)
+            .map(|sgl| Pin::new(unsafe { &mut *(sgl.as_ptr() as *mut ScatterList<'_>) }))
+    }
+}
+
+impl ScatterList<'_> {
+    /// Return the offset of memory buffer into the page.
+    pub fn offset(&self) -> usize {
+        // SAFETY: By the type invariant, we know that `self.opaque` is valid.
+        unsafe { (*self.opaque.get()).offset as _ }
+    }
+
+    /// Return the length of memory buffer.
+    pub fn length(&self) -> usize {
+        // SAFETY: By the type invariant, we know that `self.opaque` is valid.
+        unsafe { (*self.opaque.get()).length as _ }
+    }
+
+    /// Return the mapped DMA address.
+    ///
+    /// # Safety
+    ///
+    /// It is only valid after this scatterlist has been mapped to some bus
+    /// address and then called `set_dma` method to setup it.
+    pub fn dma_address(&self) -> usize {
+        // SAFETY: By the type invariant, we know that `self.opaque` is valid.
+        unsafe { (*self.opaque.get()).dma_address as _ }
+    }
+
+    /// Return the mapped DMA length.
+    ///
+    /// # Safety
+    ///
+    /// It is only valid after this scatterlist has been mapped to some bus
+    /// address and then called `set_dma` method to setup it.
+    pub fn dma_length(&self) -> usize {
+        // SAFETY: By the type invariant, we know that `self.opaque` is valid.
+        #[cfg(CONFIG_NEED_SG_DMA_LENGTH)]
+        unsafe {
+            (*self.opaque.get()).dma_length as _
+        }
+        #[cfg(not(CONFIG_NEED_SG_DMA_LENGTH))]
+        unsafe {
+            (*self.opaque.get()).length as _
+        }
+    }
+
+    /// Setup the DMA address and length.
+    pub fn set_dma(&mut self, addr: usize, len: usize) {
+        // SAFETY: By the type invariant, we know that `self.opaque` is valid.
+        #[cfg(CONFIG_NEED_SG_DMA_LENGTH)]
+        unsafe {
+            (*self.opaque.get()).dma_address = addr as _;
+            (*self.opaque.get()).dma_length = len as _;
+        }
+        #[cfg(not(CONFIG_NEED_SG_DMA_LENGTH))]
+        unsafe {
+            (*self.opaque.get()).dma_address = addr as _;
+            (*self.opaque.get()).length = len as _;
+        }
+        self.dma_mark_bus_address();
+    }
+
+    /// Return `true` if it is mapped with a DMA address.
+    pub fn is_dma_bus_address(&self) -> bool {
+        // SAFETY: By the type invariant, we know that `self.opaque` is valid.
+        #[cfg(CONFIG_PCI_P2PDMA)]
+        unsafe {
+            ((*self.opaque.get()).dma_flags & bindings::SG_DMA_BUS_ADDRESS) != 0
+        }
+        #[cfg(not(CONFIG_PCI_P2PDMA))]
+        false
+    }
+
+    /// Mark it as mapped to a DMA address.
+    pub fn dma_mark_bus_address(&mut self) {
+        // SAFETY: By the type invariant, we know that `self.opaque` is valid.
+        #[cfg(CONFIG_PCI_P2PDMA)]
+        unsafe {
+            (*self.opaque.get()).dma_flags |= bindings::SG_DMA_BUS_ADDRESS;
+        }
+    }
+
+    /// Mark it as `not` mapped to a DMA address.
+    pub fn dma_unmark_bus_address(&mut self) {
+        // SAFETY: By the type invariant, we know that `self.opaque` is valid.
+        #[cfg(CONFIG_PCI_P2PDMA)]
+        unsafe {
+            (*self.opaque.get()).dma_flags &= !bindings::SG_DMA_BUS_ADDRESS;
+        }
+    }
+
+    /// Return `true` if it is a chainable entry.
+    pub fn is_chain(&self) -> bool {
+        // SAFETY: By the type invariant, we know that `self.opaque` is valid.
+        unsafe {
+            ((*self.opaque.get()).page_link
+                & (bindings::SG_PAGE_LINK_MASK as u64)
+                & (bindings::SG_CHAIN as u64))
+                != 0
+        }
+    }
+
+    /// Transfer this scatterlist as a chainable entry, linked to `sgl`.
+    pub fn chain_sgl(&mut self, sgl: Pin<&mut ScatterList<'_>>) {
+        let addr = sgl.opaque.get() as u64;
+        // SAFETY: By the type invariant, we know that `self.opaque` is valid.
+        unsafe {
+            (*self.opaque.get()).offset = 0;
+            (*self.opaque.get()).length = 0;
+            (*self.opaque.get()).page_link = addr | (bindings::SG_CHAIN as u64);
+        }
+        self.unmark_end();
+    }
+
+    /// Return `true` if it is the last normal entry in scatterlist.
+    pub fn is_last(&self) -> bool {
+        // SAFETY: By the type invariant, we know that `self.opaque` is valid.
+        unsafe {
+            ((*self.opaque.get()).page_link
+                & (bindings::SG_PAGE_LINK_MASK as u64)
+                & (bindings::SG_END as u64))
+                != 0
+        }
+    }
+
+    /// Mark it as the last normal entry in scatterlist.
+    pub fn mark_end(&mut self) {
+        // SAFETY: By the type invariant, we know that `self.opaque` is valid.
+        unsafe {
+            (*self.opaque.get()).page_link |= bindings::SG_END as u64;
+            (*self.opaque.get()).page_link &= !(bindings::SG_CHAIN as u64);
+        }
+    }
+
+    /// Mark it as `not` the last normal entry in scatterlist.
+    pub fn unmark_end(&mut self) {
+        // SAFETY: By the type invariant, we know that `self.opaque` is valid.
+        unsafe {
+            (*self.opaque.get()).page_link &= !(bindings::SG_END as u64);
+        }
+    }
+
+    /// Get an immutable reference to memory buffer.
+    pub fn get_buf(&self) -> &[u8] {
+        // SAFETY: By the type invariant, we know that `self.opaque` is valid.
+        let addr = unsafe { bindings::sg_virt(self.opaque.get()) };
+        let len = self.length();
+        // SAFETY: `addr` is returned by `sg_virt`, so it is valid. And the memory
+        // buffer is set by `new` constructor or `set_buf` method, so it's pinned
+        // and valid.
+        unsafe { core::slice::from_raw_parts(addr as _, len) }
+    }
+
+    /// Get a mutable reference to memory buffer.
+    pub fn get_mut_buf(&mut self) -> &mut [u8] {
+        // SAFETY: By the type invariant, we know that `self.opaque` is valid.
+        let addr = unsafe { bindings::sg_virt(self.opaque.get()) };
+        let len = self.length();
+        // SAFETY: `addr` is returned by `sg_virt`, so it is valid. And the memory
+        // buffer is set by `new` constructor or `set_buf` method, so it's pinned
+        // and valid.
+        unsafe { core::slice::from_raw_parts_mut(addr as _, len) }
+    }
+
+    /// Set the memory buffer.
+    pub fn set_buf(&mut self, buf: &Pin<&mut [u8]>) {
+        // SAFETY: By the type invariant, we know that `self.opaque` is valid.
+        // And `buf` is pinned and valid.
+        unsafe {
+            bindings::sg_set_buf(
+                self.opaque.get(),
+                buf.as_ptr() as *const core::ffi::c_void,
+                buf.len() as core::ffi::c_uint,
+            );
+        }
+    }
+
+    /// Return the total count of normal entries in scatterlist.
+    ///
+    /// Allows to know how many entries are in scatterlist, taking into account
+    /// chaining as well.
+    pub fn count(&self) -> usize {
+        // SAFETY: By the type invariant, we know that `self.opaque` is valid.
+        unsafe { bindings::sg_nents(self.opaque.get()) as _ }
+    }
+}
-- 
2.40.1