On Sat May 24, 2025 at 10:33 PM CEST, Tamir Duberstein wrote:
> Introduce a `fmt!` macro which wraps all arguments in
> `kernel::fmt::Adapter` This enables formatting of foreign types (like
> `core::ffi::CStr`) that do not implement `fmt::Display` due to concerns
> around lossy conversions which do not apply in the kernel.
>
> Replace all direct calls to `format_args!` with `fmt!`.
>
> In preparation for replacing our `CStr` with `core::ffi::CStr`, move its
> `fmt::Display` implementation to `kernel::fmt::Adapter<&CStr>`.
>
> Suggested-by: Alice Ryhl <alicer...@google.com>
> Link:
> https://rust-for-linux.zulipchat.com/#narrow/channel/288089-General/topic/Custom.20formatting/with/516476467
> Signed-off-by: Tamir Duberstein <tam...@gmail.com>
> ---
> drivers/block/rnull.rs | 2 +-
> rust/kernel/block/mq.rs | 2 +-
> rust/kernel/device.rs | 2 +-
> rust/kernel/fmt.rs | 77 +++++++++++++++++++++++++++++
> rust/kernel/kunit.rs | 6 +--
> rust/kernel/lib.rs | 1 +
> rust/kernel/prelude.rs | 3 +-
> rust/kernel/print.rs | 4 +-
> rust/kernel/seq_file.rs | 2 +-
> rust/kernel/str.rs | 23 ++++-----
> rust/macros/fmt.rs | 118
> ++++++++++++++++++++++++++++++++++++++++++++
> rust/macros/lib.rs | 19 +++++++
> scripts/rustdoc_test_gen.rs | 2 +-
> 13 files changed, 235 insertions(+), 26 deletions(-)
Can you split this into creating the proc-macro, forwarding the display
impls and replacing all the uses with the proc macro?
> diff --git a/drivers/block/rnull.rs b/drivers/block/rnull.rs
> index d07e76ae2c13..6366da12c5a5 100644
> --- a/drivers/block/rnull.rs
> +++ b/drivers/block/rnull.rs
> @@ -51,7 +51,7 @@ fn init(_module: &'static ThisModule) -> impl PinInit<Self,
> Error> {
> .logical_block_size(4096)?
> .physical_block_size(4096)?
> .rotational(false)
> - .build(format_args!("rnullb{}", 0), tagset)
> + .build(fmt!("rnullb{}", 0), tagset)
> })();
>
> try_pin_init!(Self {
> diff --git a/rust/kernel/block/mq.rs b/rust/kernel/block/mq.rs
> index fb0f393c1cea..842be88aa1cf 100644
> --- a/rust/kernel/block/mq.rs
> +++ b/rust/kernel/block/mq.rs
> @@ -82,7 +82,7 @@
> //! Arc::pin_init(TagSet::new(1, 256, 1), flags::GFP_KERNEL)?;
> //! let mut disk = gen_disk::GenDiskBuilder::new()
> //! .capacity_sectors(4096)
> -//! .build(format_args!("myblk"), tagset)?;
> +//! .build(fmt!("myblk"), tagset)?;
> //!
> //! # Ok::<(), kernel::error::Error>(())
> //! ```
> diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
> index 5c372cf27ed0..99d99a76934c 100644
> --- a/rust/kernel/device.rs
> +++ b/rust/kernel/device.rs
> @@ -240,7 +240,7 @@ impl DeviceContext for Normal {}
> macro_rules! dev_printk {
> ($method:ident, $dev:expr, $($f:tt)*) => {
> {
> - ($dev).$method(core::format_args!($($f)*));
> + ($dev).$method($crate::prelude::fmt!($($f)*));
> }
> }
> }
> diff --git a/rust/kernel/fmt.rs b/rust/kernel/fmt.rs
> new file mode 100644
> index 000000000000..12b08debc3b3
> --- /dev/null
> +++ b/rust/kernel/fmt.rs
> @@ -0,0 +1,77 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Formatting utilities.
> +
> +use core::fmt;
> +
> +/// Internal adapter used to route allow implementations of formatting
> traits for foreign types.
> +///
> +/// It is inserted automatically by the [`fmt!`] macro and is not meant to
> be used directly.
> +///
> +/// [`fmt!`]: crate::prelude::fmt!
> +#[doc(hidden)]
> +pub struct Adapter<T>(pub T);
> +
> +macro_rules! impl_fmt_adapter_forward {
> + ($($trait:ident),* $(,)?) => {
> + $(
> + impl<T: fmt::$trait> fmt::$trait for Adapter<T> {
> + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
> + let Self(t) = self;
> + fmt::$trait::fmt(t, f)
> + }
> + }
> + )*
> + };
> +}
> +
> +impl_fmt_adapter_forward!(Debug, LowerHex, UpperHex, Octal, Binary, Pointer,
> LowerExp, UpperExp);
> +
> +macro_rules! impl_display_forward {
> + ($(
> + $( { $($generics:tt)* } )? $ty:ty $( { where $($where:tt)* } )?
You don't need `{}` around the `where` clause, as a `where` keyword can
follow a `ty` fragment.
> + ),* $(,)?) => {
> + $(
> + impl$($($generics)*)? fmt::Display for Adapter<&$ty>
> + $(where $($where)*)? {
> + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
> + let Self(t) = self;
> + fmt::Display::fmt(t, f)
> + }
> + }
> + )*
> + };
> +}
> +
> +impl<T: ?Sized> fmt::Display for Adapter<&&T>
> +where
> + for<'a> Adapter<&'a T>: fmt::Display,
> +{
> + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
> + let Self(t) = self;
> + Adapter::<&T>(**t).fmt(f)
> + }
> +}
> +
> +impl_display_forward!(
> + bool,
> + char,
> + core::panic::PanicInfo<'_>,
> + crate::str::BStr,
> + fmt::Arguments<'_>,
> + i128,
> + i16,
> + i32,
> + i64,
> + i8,
> + isize,
> + str,
> + u128,
> + u16,
> + u32,
> + u64,
> + u8,
> + usize,
> + {<T: ?Sized>} crate::sync::Arc<T> {where crate::sync::Arc<T>:
> fmt::Display},
> + {<T: ?Sized>} crate::sync::UniqueArc<T> {where
> crate::sync::UniqueArc<T>: fmt::Display},
> +);
If we use `{}` instead of `()`, then we can format the contents
differently:
impl_display_forward! {
i8, i16, i32, i64, i128, isize,
u8, u16, u32, u64, u128, usize,
bool, char, str,
crate::str::BStr,
fmt::Arguments<'_>,
core::panic::PanicInfo<'_>,
{<T: ?Sized>} crate::sync::Arc<T> {where Self: fmt::Display},
{<T: ?Sized>} crate::sync::UniqueArc<T> {where Self: fmt::Display},
}
> diff --git a/rust/macros/fmt.rs b/rust/macros/fmt.rs
> new file mode 100644
> index 000000000000..6b6bd9295d18
> --- /dev/null
> +++ b/rust/macros/fmt.rs
> @@ -0,0 +1,118 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +use proc_macro::{Delimiter, Group, Ident, Punct, Spacing, Span, TokenStream,
> TokenTree};
> +use std::collections::BTreeSet;
> +
> +/// Please see [`crate::fmt`] for documentation.
> +pub(crate) fn fmt(input: TokenStream) -> TokenStream {
> + let mut input = input.into_iter();
> +
> + let first_opt = input.next();
> + let first_owned_str;
> + let mut names = BTreeSet::new();
> + let first_lit = {
> + let Some((mut first_str, first_lit)) = (match first_opt.as_ref() {
> + Some(TokenTree::Literal(first_lit)) => {
> + first_owned_str = first_lit.to_string();
> + Some(first_owned_str.as_str()).and_then(|first| {
> + let first = first.strip_prefix('"')?;
> + let first = first.strip_suffix('"')?;
> + Some((first, first_lit))
> + })
> + }
> + _ => None,
> + }) else {
> + return first_opt.into_iter().chain(input).collect();
> + };
This usage of let-else + match is pretty confusing and could just be a
single match statement.
> + while let Some((_, rest)) = first_str.split_once('{') {
> + first_str = rest;
> + if let Some(rest) = first_str.strip_prefix('{') {
> + first_str = rest;
> + continue;
> + }
> + while let Some((name, rest)) = first_str.split_once('}') {
> + first_str = rest;
> + if let Some(rest) = first_str.strip_prefix('}') {
This doesn't make sense, we've matched a `{`, some text and a `}`. You
can't escape a `}` that is associated to a `{`.
> + first_str = rest;
> + continue;
> + }
> + let name = name.split_once(':').map_or(name, |(name, _)|
> name);
> + if !name.is_empty() && !name.chars().all(|c|
> c.is_ascii_digit()) {
> + names.insert(name);
> + }
> + break;
> + }
> + }
> + first_lit
`first_lit` is not modified, so could we just the code above it into a
block instead of keeping it in the expr for `first_lit`?
> + };
> +
> + let first_span = first_lit.span();
> + let adapt = |expr| {
> + let mut borrow =
> + TokenStream::from_iter([TokenTree::Punct(Punct::new('&',
> Spacing::Alone))]);
> + borrow.extend(expr);
> + make_ident(first_span, ["kernel", "fmt", "Adapter"])
> + .chain([TokenTree::Group(Group::new(Delimiter::Parenthesis,
> borrow))])
This should be fine with using `quote!`:
quote!(::kernel::fmt::Adapter(&#expr))
> + };
> +
> + let flush = |args: &mut TokenStream, current: &mut TokenStream| {
> + let current = std::mem::take(current);
> + if !current.is_empty() {
> + args.extend(adapt(current));
> + }
> + };
> +
> + let mut args = TokenStream::from_iter(first_opt);
> + {
> + let mut current = TokenStream::new();
> + for tt in input {
> + match &tt {
> + TokenTree::Punct(p) => match p.as_char() {
> + ',' => {
> + flush(&mut args, &mut current);
> + &mut args
> + }
> + '=' => {
> + names.remove(current.to_string().as_str());
> + args.extend(std::mem::take(&mut current));
> + &mut args
> + }
> + _ => &mut current,
> + },
> + _ => &mut current,
> + }
> + .extend([tt]);
> + }
This doesn't handle the following code correctly ):
let mut a = 0;
pr_info!("{a:?}", a = a = a);
Looks like we'll have to remember what "kind" of an equals we parsed...
> + flush(&mut args, &mut current);
> + }
> +
> + for name in names {
> + args.extend(
> + [
> + TokenTree::Punct(Punct::new(',', Spacing::Alone)),
> + TokenTree::Ident(Ident::new(name, first_span)),
> + TokenTree::Punct(Punct::new('=', Spacing::Alone)),
> + ]
> + .into_iter()
> + .chain(adapt(TokenTree::Ident(Ident::new(name,
> first_span)).into())),
> + );
This can probably be:
let name = Ident::new(name, first_span);
let value = adapt(name.clone());
args.extend(quote!(, #name = #value));
> + }
> +
> + TokenStream::from_iter(make_ident(first_span, ["core",
> "format_args"]).chain([
> + TokenTree::Punct(Punct::new('!', Spacing::Alone)),
> + TokenTree::Group(Group::new(Delimiter::Parenthesis, args)),
> + ]))
This can be:
quote!(::core::format_args!(#args))
(not sure if you need `#(#args)*`)
> +}
> +
> +fn make_ident<'a, T: IntoIterator<Item = &'a str>>(
> + span: Span,
> + names: T,
> +) -> impl Iterator<Item = TokenTree> + use<'a, T> {
> + names.into_iter().flat_map(move |name| {
> + [
> + TokenTree::Punct(Punct::new(':', Spacing::Joint)),
> + TokenTree::Punct(Punct::new(':', Spacing::Alone)),
> + TokenTree::Ident(Ident::new(name, span)),
> + ]
> + })
> +}
> diff --git a/rust/macros/lib.rs b/rust/macros/lib.rs
> index d31e50c446b0..fa956eaa3ba7 100644
> --- a/rust/macros/lib.rs
> +++ b/rust/macros/lib.rs
> @@ -10,6 +10,7 @@
> mod quote;
> mod concat_idents;
> mod export;
> +mod fmt;
> mod helpers;
> mod kunit;
> mod module;
> @@ -196,6 +197,24 @@ pub fn export(attr: TokenStream, ts: TokenStream) ->
> TokenStream {
> export::export(attr, ts)
> }
>
> +/// Like [`core::format_args!`], but automatically wraps arguments in
> [`kernel::fmt::Adapter`].
> +///
> +/// This macro allows generating `core::fmt::Arguments` while ensuring that
> each argument is wrapped
> +/// with `::kernel::fmt::Adapter`, which customizes formatting behavior for
> kernel logging.
> +///
> +/// Named arguments used in the format string (e.g. `{foo}`) are detected
> and resolved from local
> +/// bindings. All positional and named arguments are automatically wrapped.
> +///
> +/// This macro is an implementation detail of other kernel logging macros
> like [`pr_info!`] and
> +/// should not typically be used directly.
> +///
> +/// [`kernel::fmt::Adapter`]: ../kernel/fmt/struct.Adapter.html
> +/// [`pr_info!`]: ../kernel/macro.pr_info.html
> +#[proc_macro]
> +pub fn fmt(input: TokenStream) -> TokenStream {
I'm wondering if we should name this `format_args` instead in order to
better communicate that it's a replacement for `core::format_args!`.
---
Cheers,
Benno
> + fmt::fmt(input)
> +}
> +
> /// Concatenate two identifiers.
> ///
> /// This is useful in macros that need to declare or reference items with
> names
> diff --git a/scripts/rustdoc_test_gen.rs b/scripts/rustdoc_test_gen.rs
> index ec8d70ac888b..22ed9ee14053 100644
> --- a/scripts/rustdoc_test_gen.rs
> +++ b/scripts/rustdoc_test_gen.rs
> @@ -197,7 +197,7 @@ macro_rules! assert_eq {{
> // This follows the syntax for declaring test metadata in the proposed
> KTAP v2 spec, which may
> // be used for the proposed KUnit test attributes API. Thus hopefully
> this will make migration
> // easier later on.
> - kernel::kunit::info(format_args!(" # {kunit_name}.location:
> {real_path}:{line}\n"));
> + kernel::kunit::info(fmt!(" # {kunit_name}.location:
> {real_path}:{line}\n"));
>
> /// The anchor where the test code body starts.
> #[allow(unused)]
