netdev - Re: [PATCH net-next v3 7/8] rust: Add read_poll

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Message-ID: <CAH5fLgi0dN+hkTb0a29XWaGO1xsmyyJMAQyFJDH+geWZwsfAHw@mail.gmail.com>
Date: Wed, 16 Oct 2024 10:52:17 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: FUJITA Tomonori <fujita.tomonori@...il.com>
Cc: netdev@...r.kernel.org, rust-for-linux@...r.kernel.org, andrew@...n.ch, 
	hkallweit1@...il.com, tmgross@...ch.edu, ojeda@...nel.org, 
	alex.gaynor@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, 
	benno.lossin@...ton.me, a.hindborg@...sung.com, anna-maria@...utronix.de, 
	frederic@...nel.org, tglx@...utronix.de, arnd@...db.de, jstultz@...gle.com, 
	sboyd@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v3 7/8] rust: Add read_poll_timeout functions

On Wed, Oct 16, 2024 at 10:45 AM Alice Ryhl <aliceryhl@...gle.com> wrote:
>
> On Wed, Oct 16, 2024 at 5:54 AM FUJITA Tomonori
> <fujita.tomonori@...il.com> wrote:
> > +/// Polls periodically until a condition is met or a timeout is reached.
> > +///
> > +/// `op` is called repeatedly until `cond` returns `true` or the timeout is
> > +///  reached. The return value of `op` is passed to `cond`.
> > +///
> > +/// `sleep_delta` is the duration to sleep between calls to `op`.
> > +/// If `sleep_delta` is less than one microsecond, the function will busy-wait.
> > +///
> > +/// `timeout_delta` is the maximum time to wait for `cond` to return `true`.
> > +///
> > +/// This macro can only be used in a nonatomic context.
> > +#[macro_export]
> > +macro_rules! readx_poll_timeout {
> > +    ($op:expr, $cond:expr, $sleep_delta:expr, $timeout_delta:expr) => {{
> > +        #[cfg(CONFIG_DEBUG_ATOMIC_SLEEP)]
> > +        if !$sleep_delta.is_zero() {
> > +            // SAFETY: FFI call.
> > +            unsafe {
> > +                $crate::bindings::__might_sleep(
> > +                    ::core::file!().as_ptr() as *const i8,
> > +                    ::core::line!() as i32,
> > +                )
> > +            }
> > +        }
>
> I wonder if we can use #[track_caller] and
> core::panic::Location::caller [1] to do this without having to use a
> macro? I don't know whether it would work, but if it does, that would
> be super cool.
>
> #[track_caller]
> fn might_sleep() {
>     let location = core::panic::Location::caller();
>     // SAFETY: FFI call.
>     unsafe {
>         $crate::bindings::__might_sleep(
>             location.file().as_char_ptr(),
>             location.line() as i32,
>         )
>     }
> }

Actually, this raises a problem ... core::panic::Location doesn't give
us a nul-terminated string, so we probably can't pass it to
`__might_sleep`. The thing is, `::core::file!()` doesn't give us a
nul-terminated string either, so this code is probably incorrect
as-is.

Alice