docs: rust: fix formatting for kernel::block::mq::Request

Fix several issues with rustdoc formatting for the
`kernel::block::mq::Request` module, in particular:

- An ordered list not rendering correctly.

- Code snippets formatted as regular text.

- References to types missing intra-doc links.

Additionally, to ensure that intra-doc links are rendered for private
types, add the `--document-private-items` flag to all rustdoc
invocations.

Finally, update the Rust coding guidelines to mention the syntax for
intra-doc links.

Closes: Rust-for-Linux#1108

Signed-off-by: Francesco Zardi <frazar0@hotmail.it>
Suggested-by: Miguel Ojeda <ojeda@kernel.org>

Documentation/rust/coding-guidelines.rst

@@ -162,7 +162,7 @@ in the kernel:
     a section called ``# Examples``.
 
   - Rust items (functions, types, constants...) must be linked appropriately
-    (``rustdoc`` will create a link automatically).
+    by wrapping them with square brackets (e.g. ``[`Foo::bar()`]``).
 
   - Any ``unsafe`` block must be preceded by a ``// SAFETY:`` comment
     describing why the code inside is sound.

Makefile

@@ -457,6 +457,7 @@ export rust_common_flags := --edition=2021 \
 			    -Wclippy::needless_continue \
 			    -Wclippy::no_mangle_with_rust_abi \
 			    -Wclippy::dbg_macro
+export rustdoc_common_flags := --document-private-items
 
 KBUILD_HOSTCFLAGS   := $(KBUILD_USERHOSTCFLAGS) $(HOST_LFS_CFLAGS) \
 		       $(HOSTCFLAGS) -I $(srctree)/scripts/include

rust/Makefile

@@ -61,7 +61,8 @@ alloc-cfgs = \
 quiet_cmd_rustdoc = RUSTDOC $(if $(rustdoc_host),H, ) $<
       cmd_rustdoc = \
 	OBJTREE=$(abspath $(objtree)) \
-	$(RUSTDOC) $(if $(rustdoc_host),$(rust_common_flags),$(rust_flags)) \
+	$(RUSTDOC) $(rustdoc_common_flags) \
+		$(if $(rustdoc_host),$(rust_common_flags),$(rust_flags)) \
 		$(rustc_target_flags) -L$(objtree)/$(obj) \
 		-Zunstable-options --generate-link-to-definition \
 		--output $(rustdoc_output) \
@@ -149,7 +150,7 @@ rusttestlib-uapi: $(src)/uapi/lib.rs FORCE
 quiet_cmd_rustdoc_test = RUSTDOC T $<
       cmd_rustdoc_test = \
 	OBJTREE=$(abspath $(objtree)) \
-	$(RUSTDOC) --test $(rust_common_flags) \
+	$(RUSTDOC) $(rustdoc_common_flags) --test $(rust_common_flags) \
 		@$(objtree)/include/generated/rustc_cfg \
 		$(rustc_target_flags) $(rustdoc_test_target_flags) \
 		$(rustdoc_test_quiet) \
@@ -161,7 +162,7 @@ quiet_cmd_rustdoc_test_kernel = RUSTDOC TK $<
 	rm -rf $(objtree)/$(obj)/test/doctests/kernel; \
 	mkdir -p $(objtree)/$(obj)/test/doctests/kernel; \
 	OBJTREE=$(abspath $(objtree)) \
-	$(RUSTDOC) --test $(rust_flags) \
+	$(RUSTDOC) $(rustdoc_common_flags) --test $(rust_flags) \
 		-L$(objtree)/$(obj) --extern alloc --extern kernel \
 		--extern build_error --extern macros \
 		--extern bindings --extern uapi \

rust/kernel/block/mq/request.rs

@@ -16,50 +16,56 @@ use core::{
     sync::atomic::{AtomicU64, Ordering},
 };
 
-/// A wrapper around a blk-mq `struct request`. This represents an IO request.
+#[allow(rustdoc::private_intra_doc_links)]
+/// 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
+/// 1. Request is owned by block layer (refcount 0)
+/// 2. 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
+/// 3. 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
+/// 4. 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
+/// We need to track 1 and 2 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
+/// We need to track 3 and 4 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`.
+/// [`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.
+/// * `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>`.
+///   and valid [`RequestDataWrapper<T>`].
 /// * `self` is reference counted by atomic modification of
-///   self.wrapper_ref().refcount().
+///   `self.wrapper_ref().refcount()`.
+///
+/// [`struct request`]: srctree/include/linux/blk-mq.h
 ///
 #[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.
+    /// 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`.
+    ///   returned [`ARef`].
+    /// * The type invariants for [`Request`] must hold for the pointee of `ptr`.
+    ///
+    /// [`struct request`]: srctree/include/linux/blk-mq.h
     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
@@ -84,12 +90,14 @@ impl<T: Operations> Request<T> {
     }
 
     /// 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`.
+    /// 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.
+    /// 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.
+    ///
+    /// [`struct request`]: srctree/include/linux/blk-mq.h
     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(
@@ -109,7 +117,7 @@ impl<T: Operations> Request<T> {
 
     /// Notify the block layer that the request has been completed without errors.
     ///
-    /// This function will return `Err` if `this` is not the only `ARef`
+    /// 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)?;
@@ -123,13 +131,13 @@ impl<T: Operations> Request<T> {
         Ok(())
     }
 
-    /// Return a pointer to the `RequestDataWrapper` stored in the private area
+    /// 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`.
+    ///   [`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
@@ -141,7 +149,7 @@ impl<T: Operations> Request<T> {
         unsafe { NonNull::new_unchecked(wrapper_ptr) }
     }
 
-    /// Return a reference to the `RequestDataWrapper` stored in the private
+    /// 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,
@@ -152,13 +160,15 @@ impl<T: Operations> Request<T> {
     }
 }
 
-/// A wrapper around data stored in the private area of the C `struct request`.
+/// A wrapper around data stored in the private area of the C [`struct request`].
+///
+/// [`struct request`]: srctree/include/linux/blk-mq.h
 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.
+    /// - 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,
 }
 
@@ -204,7 +214,7 @@ fn atomic_relaxed_op_return(target: &AtomicU64, op: impl Fn(u64) -> u64) -> u64
 }
 
 /// Store the result of `op(target.load)` in `target` if `target.load() !=
-/// pred`, returning true if the target was updated.
+/// 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| {