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-rw-r--r--rust/macros/lib.rs62
1 files changed, 52 insertions, 10 deletions
diff --git a/rust/macros/lib.rs b/rust/macros/lib.rs
index c42105c2ff96..f489f3157383 100644
--- a/rust/macros/lib.rs
+++ b/rust/macros/lib.rs
@@ -20,7 +20,7 @@ use proc_macro::TokenStream;
/// The `type` argument should be a type which implements the [`Module`]
/// trait. Also accepts various forms of kernel metadata.
///
-/// C header: [`include/linux/moduleparam.h`](../../../include/linux/moduleparam.h)
+/// C header: [`include/linux/moduleparam.h`](srctree/include/linux/moduleparam.h)
///
/// [`Module`]: ../kernel/trait.Module.html
///
@@ -87,27 +87,49 @@ pub fn module(ts: TokenStream) -> TokenStream {
/// implementation could just return `Error::EINVAL`); Linux typically use C
/// `NULL` pointers to represent these functions.
///
-/// This attribute is intended to close the gap. Traits can be declared and
-/// implemented with the `#[vtable]` attribute, and a `HAS_*` associated constant
-/// will be generated for each method in the trait, indicating if the implementor
-/// has overridden a method.
+/// This attribute closes that gap. A trait can be annotated with the
+/// `#[vtable]` attribute. Implementers of the trait will then also have to
+/// annotate the trait with `#[vtable]`. This attribute generates a `HAS_*`
+/// associated constant bool for each method in the trait that is set to true if
+/// the implementer has overridden the associated method.
+///
+/// For a trait method to be optional, it must have a default implementation.
+/// This is also the case for traits annotated with `#[vtable]`, but in this
+/// case the default implementation will never be executed. The reason for this
+/// is that the functions will be called through function pointers installed in
+/// C side vtables. When an optional method is not implemented on a `#[vtable]`
+/// trait, a NULL entry is installed in the vtable. Thus the default
+/// implementation is never called. Since these traits are not designed to be
+/// used on the Rust side, it should not be possible to call the default
+/// implementation. This is done to ensure that we call the vtable methods
+/// through the C vtable, and not through the Rust vtable. Therefore, the
+/// default implementation should call `kernel::build_error`, which prevents
+/// calls to this function at compile time:
+///
+/// ```compile_fail
+/// # use kernel::error::VTABLE_DEFAULT_ERROR;
+/// kernel::build_error(VTABLE_DEFAULT_ERROR)
+/// ```
+///
+/// Note that you might need to import [`kernel::error::VTABLE_DEFAULT_ERROR`].
///
-/// This attribute is not needed if all methods are required.
+/// This macro should not be used when all functions are required.
///
/// # Examples
///
/// ```ignore
+/// use kernel::error::VTABLE_DEFAULT_ERROR;
/// use kernel::prelude::*;
///
/// // Declares a `#[vtable]` trait
/// #[vtable]
/// pub trait Operations: Send + Sync + Sized {
/// fn foo(&self) -> Result<()> {
-/// Err(EINVAL)
+/// kernel::build_error(VTABLE_DEFAULT_ERROR)
/// }
///
/// fn bar(&self) -> Result<()> {
-/// Err(EINVAL)
+/// kernel::build_error(VTABLE_DEFAULT_ERROR)
/// }
/// }
///
@@ -125,6 +147,8 @@ pub fn module(ts: TokenStream) -> TokenStream {
/// assert_eq!(<Foo as Operations>::HAS_FOO, true);
/// assert_eq!(<Foo as Operations>::HAS_BAR, false);
/// ```
+///
+/// [`kernel::error::VTABLE_DEFAULT_ERROR`]: ../kernel/error/constant.VTABLE_DEFAULT_ERROR.html
#[proc_macro_attribute]
pub fn vtable(attr: TokenStream, ts: TokenStream) -> TokenStream {
vtable::vtable(attr, ts)
@@ -254,8 +278,8 @@ pub fn pinned_drop(args: TokenStream, input: TokenStream) -> TokenStream {
/// Within the `paste!` macro, identifiers inside `[<` and `>]` are concatenated together to form a
/// single identifier.
///
-/// This is similar to the [`paste`] crate, but with pasting feature limited to identifiers
-/// (literals, lifetimes and documentation strings are not supported). There is a difference in
+/// This is similar to the [`paste`] crate, but with pasting feature limited to identifiers and
+/// literals (lifetimes and documentation strings are not supported). There is a difference in
/// supported modifiers as well.
///
/// # Example
@@ -337,6 +361,24 @@ pub fn pinned_drop(args: TokenStream, input: TokenStream) -> TokenStream {
/// assert_eq!(br_ok(), binder_driver_return_protocol_BR_OK);
/// ```
///
+/// # Literals
+///
+/// Literals can also be concatenated with other identifiers:
+///
+/// ```ignore
+/// macro_rules! create_numbered_fn {
+/// ($name:literal, $val:literal) => {
+/// kernel::macros::paste! {
+/// fn [<some_ $name _fn $val>]() -> u32 { $val }
+/// }
+/// };
+/// }
+///
+/// create_numbered_fn!("foo", 100);
+///
+/// assert_eq!(some_foo_fn100(), 100)
+/// ```
+///
/// [`paste`]: https://docs.rs/paste/
#[proc_macro]
pub fn paste(input: TokenStream) -> TokenStream {