Attribute Macro kernel::prelude::vtable

#[vtable]

Declares or implements a vtable trait.

Linux’s use of pure vtables is very close to Rust traits, but they differ in how unimplemented functions are represented. In Rust, traits can provide default implementation for all non-required methods (and the default 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 is not needed if all methods are required.

Examples

use kernel::prelude::*;

// Declares a `#[vtable]` trait
#[vtable]
pub trait Operations: Send + Sync + Sized {
    fn foo(&self) -> Result<()> {
        Err(EINVAL)
    }

    fn bar(&self) -> Result<()> {
        Err(EINVAL)
    }
}

struct Foo;

// Implements the `#[vtable]` trait
#[vtable]
impl Operations for Foo {
    fn foo(&self) -> Result<()> {
        // ...
    }
}

assert_eq!(<Foo as Operations>::HAS_FOO, true);
assert_eq!(<Foo as Operations>::HAS_BAR, false);