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Wed, 15 Oct 2025 12:25:22 -0700 (PDT) Received: from 136.1.168.192.in-addr.arpa ([2600:4808:6353:5c00:8573:f4c5:e7a9:9cd9]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-87c012b165asm24076996d6.59.2025.10.15.12.25.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Oct 2025 12:25:21 -0700 (PDT) From: Tamir Duberstein Date: Wed, 15 Oct 2025 15:24:40 -0400 Subject: [PATCH v17 10/11] rust: support formatting of foreign types Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20251015-cstr-core-v17-10-dc5e7aec870d@gmail.com> References: <20251015-cstr-core-v17-0-dc5e7aec870d@gmail.com> In-Reply-To: <20251015-cstr-core-v17-0-dc5e7aec870d@gmail.com> To: Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich , Greg Kroah-Hartman , "Rafael J. Wysocki" , Luis Chamberlain , Russ Weight , Peter Zijlstra , Ingo Molnar , Will Deacon , Waiman Long , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , Christian Brauner , Alexander Viro , Jan Kara , =?utf-8?q?Arve_Hj=C3=B8nnev=C3=A5g?= , Todd Kjos , Martijn Coenen , Joel Fernandes , Carlos Llamas , Suren Baghdasaryan , Jens Axboe , Lorenzo Stoakes , Vlastimil Babka , "Liam R. Howlett" , Uladzislau Rezki , Bjorn Helgaas , =?utf-8?q?Krzysztof_Wilczy=C5=84ski?= Cc: rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-pci@vger.kernel.org, Tamir Duberstein X-Mailer: b4 0.15-dev X-Developer-Signature: v=1; a=openssh-sha256; t=1760556296; l=11126; i=tamird@gmail.com; h=from:subject:message-id; bh=56qk4oXZToDCRjUenEK2FztuuA7wWME8i0VRUMgg2i0=; b=U1NIU0lHAAAAAQAAADMAAAALc3NoLWVkMjU1MTkAAAAgtYz36g7iDMSkY5K7Ab51ksGX7hJgs MRt+XVZTrIzMVIAAAAGcGF0YXR0AAAAAAAAAAZzaGE1MTIAAABTAAAAC3NzaC1lZDI1NTE5AAAA QFrNY4+4m4vAKukuSLoJFRCfJDb+Tq/Q2hqOOgtZg/QKSE2wld7ttq7E3MYm2zyTtcUPVBf4tcF KzbGgVn8QZwU= X-Developer-Key: i=tamird@gmail.com; a=openssh; fpr=SHA256:264rPmnnrb+ERkS7DDS3tuwqcJss/zevJRzoylqMsbc Introduce a `fmt!` macro which wraps all arguments in `kernel::fmt::Adapter` and a `kernel::fmt::Display` trait. This enables formatting of foreign types (like `core::ffi::CStr`) that do not implement `core::fmt::Display` due to concerns around lossy conversions which do not apply in the kernel. Suggested-by: Alice Ryhl Link: https://rust-for-linux.zulipchat.com/#narrow/channel/288089-General/topic/Custom.20formatting/with/516476467 Acked-by: Greg Kroah-Hartman Reviewed-by: Alice Ryhl Acked-by: Danilo Krummrich Reviewed-by: Benno Lossin Signed-off-by: Tamir Duberstein --- rust/kernel/fmt.rs | 87 +++++++++++++++++++++++++++++++++++++++++++++- rust/kernel/prelude.rs | 3 +- rust/macros/fmt.rs | 94 ++++++++++++++++++++++++++++++++++++++++++++++++++ rust/macros/lib.rs | 19 ++++++++++ rust/macros/quote.rs | 7 ++++ 5 files changed, 207 insertions(+), 3 deletions(-) diff --git a/rust/kernel/fmt.rs b/rust/kernel/fmt.rs index 0306e8388968..84d634201d90 100644 --- a/rust/kernel/fmt.rs +++ b/rust/kernel/fmt.rs @@ -4,4 +4,89 @@ //! //! This module is intended to be used in place of `core::fmt` in kernel code. -pub use core::fmt::{Arguments, Debug, Display, Error, Formatter, Result, Write}; +pub use core::fmt::{Arguments, Debug, Error, Formatter, Result, Write}; + +/// 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(pub T); + +macro_rules! impl_fmt_adapter_forward { + ($($trait:ident),* $(,)?) => { + $( + impl $trait for Adapter { + fn fmt(&self, f: &mut Formatter<'_>) -> Result { + let Self(t) = self; + $trait::fmt(t, f) + } + } + )* + }; +} + +use core::fmt::{Binary, LowerExp, LowerHex, Octal, Pointer, UpperExp, UpperHex}; +impl_fmt_adapter_forward!(Debug, LowerHex, UpperHex, Octal, Binary, Pointer, LowerExp, UpperExp); + +/// A copy of [`core::fmt::Display`] that allows us to implement it for foreign types. +/// +/// Types should implement this trait rather than [`core::fmt::Display`]. Together with the +/// [`Adapter`] type and [`fmt!`] macro, it allows for formatting foreign types (e.g. types from +/// core) which do not implement [`core::fmt::Display`] directly. +/// +/// [`fmt!`]: crate::prelude::fmt! +pub trait Display { + /// Same as [`core::fmt::Display::fmt`]. + fn fmt(&self, f: &mut Formatter<'_>) -> Result; +} + +impl Display for &T { + fn fmt(&self, f: &mut Formatter<'_>) -> Result { + Display::fmt(*self, f) + } +} + +impl core::fmt::Display for Adapter<&T> { + fn fmt(&self, f: &mut Formatter<'_>) -> Result { + let Self(t) = self; + Display::fmt(t, f) + } +} + +macro_rules! impl_display_forward { + ($( + $( { $($generics:tt)* } )? $ty:ty $( { where $($where:tt)* } )? + ),* $(,)?) => { + $( + impl$($($generics)*)? Display for $ty $(where $($where)*)? { + fn fmt(&self, f: &mut Formatter<'_>) -> Result { + core::fmt::Display::fmt(self, f) + } + } + )* + }; +} + +impl_display_forward!( + bool, + char, + core::panic::PanicInfo<'_>, + Arguments<'_>, + i128, + i16, + i32, + i64, + i8, + isize, + str, + u128, + u16, + u32, + u64, + u8, + usize, + {} crate::sync::Arc {where crate::sync::Arc: core::fmt::Display}, + {} crate::sync::UniqueArc {where crate::sync::UniqueArc: core::fmt::Display}, +); diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs index 198d09a31449..26424ad7e989 100644 --- a/rust/kernel/prelude.rs +++ b/rust/kernel/prelude.rs @@ -25,7 +25,7 @@ pub use crate::alloc::{flags::*, Box, KBox, KVBox, KVVec, KVec, VBox, VVec, Vec}; #[doc(no_inline)] -pub use macros::{export, kunit_tests, module, vtable}; +pub use macros::{export, fmt, kunit_tests, module, vtable}; pub use pin_init::{init, pin_data, pin_init, pinned_drop, InPlaceWrite, Init, PinInit, Zeroable}; @@ -36,7 +36,6 @@ pub use super::dbg; pub use super::{dev_alert, dev_crit, dev_dbg, dev_emerg, dev_err, dev_info, dev_notice, dev_warn}; pub use super::{pr_alert, pr_crit, pr_debug, pr_emerg, pr_err, pr_info, pr_notice, pr_warn}; -pub use core::format_args as fmt; pub use super::{try_init, try_pin_init}; diff --git a/rust/macros/fmt.rs b/rust/macros/fmt.rs new file mode 100644 index 000000000000..2f4b9f6e2211 --- /dev/null +++ b/rust/macros/fmt.rs @@ -0,0 +1,94 @@ +// SPDX-License-Identifier: GPL-2.0 + +use proc_macro::{Ident, 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_span = { + let Some((mut first_str, first_span)) = (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.span())) + }) + } + _ => None, + }) else { + return first_opt.into_iter().chain(input).collect(); + }; + + // Parse `identifier`s from the format string. + // + // See https://doc.rust-lang.org/std/fmt/index.html#syntax. + while let Some((_, rest)) = first_str.split_once('{') { + first_str = rest; + if let Some(rest) = first_str.strip_prefix('{') { + first_str = rest; + continue; + } + if let Some((name, rest)) = first_str.split_once('}') { + first_str = rest; + 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); + } + } + } + first_span + }; + + let adapter = quote_spanned!(first_span => ::kernel::fmt::Adapter); + + let mut args = TokenStream::from_iter(first_opt); + { + let mut flush = |args: &mut TokenStream, current: &mut TokenStream| { + let current = std::mem::take(current); + if !current.is_empty() { + let (lhs, rhs) = (|| { + let mut current = current.into_iter(); + let mut acc = TokenStream::new(); + while let Some(tt) = current.next() { + // Split on `=` only once to handle cases like `a = b = c`. + if matches!(&tt, TokenTree::Punct(p) if p.as_char() == '=') { + names.remove(acc.to_string().as_str()); + // Include the `=` itself to keep the handling below uniform. + acc.extend([tt]); + return (Some(acc), current.collect::()); + } + acc.extend([tt]); + } + (None, acc) + })(); + args.extend(quote_spanned!(first_span => #lhs #adapter(&#rhs))); + } + }; + + let mut current = TokenStream::new(); + for tt in input { + match &tt { + TokenTree::Punct(p) if p.as_char() == ',' => { + flush(&mut args, &mut current); + &mut args + } + _ => &mut current, + } + .extend([tt]); + } + flush(&mut args, &mut current); + } + + for name in names { + let name = Ident::new(name, first_span); + args.extend(quote_spanned!(first_span => , #name = #adapter(&#name))); + } + + quote_spanned!(first_span => ::core::format_args!(#args)) +} diff --git a/rust/macros/lib.rs b/rust/macros/lib.rs index fa847cf3a9b5..793f712dbf7c 100644 --- a/rust/macros/lib.rs +++ b/rust/macros/lib.rs @@ -15,6 +15,7 @@ mod quote; mod concat_idents; mod export; +mod fmt; mod helpers; mod kunit; mod module; @@ -201,6 +202,24 @@ 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 `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 { + fmt::fmt(input) +} + /// Concatenate two identifiers. /// /// This is useful in macros that need to declare or reference items with names diff --git a/rust/macros/quote.rs b/rust/macros/quote.rs index acc140c18653..ddfc21577539 100644 --- a/rust/macros/quote.rs +++ b/rust/macros/quote.rs @@ -48,6 +48,7 @@ macro_rules! quote_spanned { ($span:expr => $($tt:tt)*) => {{ let mut tokens = ::proc_macro::TokenStream::new(); { + #[allow(unused_variables)] let span = $span; quote_spanned!(@proc tokens span $($tt)*); } @@ -146,6 +147,12 @@ macro_rules! quote_spanned { )]); quote_spanned!(@proc $v $span $($tt)*); }; + (@proc $v:ident $span:ident & $($tt:tt)*) => { + $v.extend([::proc_macro::TokenTree::Punct( + ::proc_macro::Punct::new('&', ::proc_macro::Spacing::Alone), + )]); + quote_spanned!(@proc $v $span $($tt)*); + }; (@proc $v:ident $span:ident _ $($tt:tt)*) => { $v.extend([::proc_macro::TokenTree::Ident( ::proc_macro::Ident::new("_", $span), -- 2.51.0