On Thu Jul 3, 2025 at 3:55 PM CEST, Tamir Duberstein wrote: > On Thu, Jul 3, 2025 at 5:32 AM Benno Lossin <lossin@xxxxxxxxxx> wrote: >> On Tue Jul 1, 2025 at 6:49 PM CEST, Tamir Duberstein wrote: >> > 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. >> > >> > Replace all direct calls to `format_args!` with `fmt!`. >> > >> > Replace all implementations of `core::fmt::Display` with implementations >> > of `kernel::fmt::Display`. >> > >> > Suggested-by: Alice Ryhl <aliceryhl@xxxxxxxxxx> >> > Link: https://rust-for-linux.zulipchat.com/#narrow/channel/288089-General/topic/Custom.20formatting/with/516476467 >> > Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> >> > Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx> >> > Signed-off-by: Tamir Duberstein <tamird@xxxxxxxxx> >> > --- >> > drivers/block/rnull.rs | 2 +- >> > drivers/gpu/nova-core/gpu.rs | 4 +- >> > rust/kernel/block/mq.rs | 2 +- >> > rust/kernel/device.rs | 2 +- >> > rust/kernel/fmt.rs | 89 +++++++++++++++++++++++++++++++++++++++ >> > 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 | 22 ++++------ >> > rust/macros/fmt.rs | 99 ++++++++++++++++++++++++++++++++++++++++++++ >> > rust/macros/lib.rs | 19 +++++++++ >> > rust/macros/quote.rs | 7 ++++ >> > scripts/rustdoc_test_gen.rs | 2 +- >> > 15 files changed, 236 insertions(+), 28 deletions(-) >> >> This would be a lot easier to review if he proc-macro and the call >> replacement were different patches. >> >> Also the `kernel/fmt.rs` file should be a different commit. > > Can you help me understand why? The changes you ask to be separated > would all be in different files, so why would separate commits make it > easier to review? It takes less time to go through the entire patch and give a RB. I can take smaller time chunks and don't have to get back into the entire context of the patch when I don't have 30-60min available. In this patch the biggest problem is the rename & addition of new things, maybe just adding 200 lines in those files could be okay to go together, see below for more. > I prefer to keep things in one commit because the changes are highly > interdependent. The proc macro doesn't make sense without > kernel/fmt.rs and kernel/fmt.rs is useless without the proc macro. I think that `Adapter`, the custom `Display` and their impl blocks don't need to be in the same commit as the proc-macro. They are related, but maybe someone is not well-versed in proc-macros and thus doesn't want to review that part. >> > diff --git a/rust/kernel/fmt.rs b/rust/kernel/fmt.rs >> > new file mode 100644 >> > index 000000000000..348d16987de6 >> > --- /dev/null >> > +++ b/rust/kernel/fmt.rs >> > @@ -0,0 +1,89 @@ >> > +// SPDX-License-Identifier: GPL-2.0 >> > + >> > +//! Formatting utilities. >> > + >> > +use core::fmt; >> >> I think we should pub export all types that we are still using from >> `core::fmt`. For example `Result`, `Formatter`, `Debug` etc. >> >> That way I can still use the same pattern of importing `fmt` and then >> writing >> >> impl fmt::Display for MyType { >> fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {} >> } > > Great idea, done for the next spin. It would be nice to be able to > lint against references to `core::fmt` outside of kernel/fmt.rs. I think there was something in clippy that can do that globally and we could allow that in this file? >> > + >> > +/// 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); >> > + >> > +/// A copy of [`fmt::Display`] that allows us to implement it for foreign types. >> > +/// >> > +/// Types should implement this trait rather than [`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 [`fmt::Display`] directly. >> > +/// >> > +/// [`fmt!`]: crate::prelude::fmt! >> > +pub trait Display { >> > + /// Same as [`fmt::Display::fmt`]. >> > + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result; >> > +} >> > + >> > +impl<T: ?Sized + Display> Display for &T { >> > + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { >> > + Display::fmt(*self, f) >> > + } >> > +} >> > + >> > +impl<T: ?Sized + Display> fmt::Display for Adapter<&T> { >> > + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { >> > + let Self(t) = self; >> > + Display::fmt(t, f) >> >> Why not `Display::fmt(&self.0, f)`? > > I like destructuring because it shows me that there's only one field. > With `self.0` I don't see that. And what is the benefit here? >> > + >> > + let mut args = TokenStream::from_iter(first_opt); >> > + { >> > + let mut flush = |args: &mut TokenStream, current: &mut TokenStream| { >> >> You don't need to pass `args` as a closure argument, since you always >> call it with `&mut args`. > > This doesn't work because of the borrow checker. If I wrote what you > suggest, then `args` is mutably borrowed by the closure, which > prohibits the mutable borrow needed for the .extend() call here: Ahh right... Well then it's fine. --- Cheers, Benno
