Re: [PATCH v2 1/7] rust_binder: Add dynamic debug logging mask

["Gary Guo" <gary@garyguo.net>]

On Fri Jul 10, 2026 at 3:32 PM BST, Jahnavi MN via B4 Relay wrote:
> From: Jahnavi MN <jahnavimn@google.com>
>
> Implement a dynamic debug logging mask (`debug_mask`) for the
> `rust_binder` module to allow dynamic runtime configuration of log
> levels. This enables parity with the legacy C driver's debug mask.
>
> Since the Rust `module!` macro in the current kernel build does not yet
> support declaring module parameters directly in Rust, we define the
> `debug_mask` variable in a C companion file to expose it to the kernel
> runtime and import it using FFI with volatile reads.
>
> To verify the setup, instrument process lifecycle events (open, flush,
> and release) in `process.rs` under the new `BINDER_DEBUG_OPEN_CLOSE`
> logging mask. These entry-point events are chosen for initial validation
> because they represent the start of the Binder lifecycle and occur
> at low frequency, allowing simple runtime verification of the dynamic
> toggle without log noise.
>
> Signed-off-by: Jahnavi MN <jahnavimn@google.com>
> ---
>  drivers/android/binder/debug.rs            | 80 ++++++++++++++++++++++++++++++
>  drivers/android/binder/process.rs          |  7 ++-
>  drivers/android/binder/rust_binder_main.rs |  2 +
>  drivers/android/binder/rust_binderfs.c     |  3 ++
>  rust/kernel/task.rs                        |  7 +++
>  5 files changed, 98 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/android/binder/debug.rs b/drivers/android/binder/debug.rs
> new file mode 100644
> index 000000000000..da48bce3df54
> --- /dev/null
> +++ b/drivers/android/binder/debug.rs
> @@ -0,0 +1,80 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (C) 2026 Google LLC.
> +
> +//! Binder debugging helpers.
> +
> +#![allow(dead_code)]
> +
> +kernel::impl_flags!(
> +    /// Represents multiple debug mask flags.
> +    #[derive(Debug, Clone, Default, Copy, PartialEq, Eq)]
> +    pub struct DebugMasks(u32);
> +
> +    /// Represents a single debug mask category.
> +    #[derive(Debug, Clone, Copy, PartialEq, Eq)]
> +    pub enum DebugMask {
> +        UserError = 1 << 0,
> +        FailedTransaction = 1 << 1,
> +        DeadTransaction = 1 << 2,
> +        OpenClose = 1 << 3,
> +        DeadBinder = 1 << 4,
> +        DeathNotification = 1 << 5,
> +        ReadWrite = 1 << 6,
> +        UserRefs = 1 << 7,
> +        Threads = 1 << 8,
> +        Transaction = 1 << 9,
> +        TransactionComplete = 1 << 10,
> +        FreeBuffer = 1 << 11,
> +        InternalRefs = 1 << 12,
> +        PriorityCap = 1 << 13,
> +        Spinlocks = 1 << 14,
> +    }
> +);
> +
> +extern "C" {
> +    // Declared as static mut because the value is mutated dynamically by C sysfs.
> +    static mut rust_binder_debug_mask: u32;
> +}

This should be `Atomic<u32>` so the read_volatile below is avoided.

> +
> +/// Checks if the given debug logging category is enabled in the mask.
> +pub(crate) fn debug_mask_enabled(mask: DebugMask) -> bool {
> +    // SAFETY: `rust_binder_debug_mask` is defined in C and can be mutated at any time.
> +    // We read it via volatile to ensure we fetch the current value from memory.
> +    let current_mask = unsafe { core::ptr::read_volatile(&raw const rust_binder_debug_mask) };
> +    (current_mask & (mask as u32)) != 0
> +}
> +
> +/// Prints a debug log if the specified mask category is enabled.
> +#[macro_export]
> +macro_rules! binder_debug {
> +    // 1. Internal helper rule to do the raw print.

This 1, 2, 3 numbering is very strange.

> +    (raw, $($arg:tt)*) => {
> +        kernel::pr_info!($($arg)*);
> +    };

Why is this needed instead of just calling `pr_info!`?

Best,
Gary

> +
> +    // 2. Rule to explicitly specify a PID (used in kworkers).
> +    (pid=$pid:expr, $mask:ident, $($arg:tt)*) => {
> +        if $crate::debug::debug_mask_enabled($crate::debug::DebugMask::$mask) {
> +            $crate::binder_debug!(
> +                raw,
> +                "{}: {}\n",
> +                $pid,
> +                kernel::prelude::fmt!($($arg)*)
> +            );
> +        }
> +    };
> +
> +    // 3. Default rule (automatically prepends "PID:TID" of the current calling thread).
> +    ($mask:ident, $($arg:tt)*) => {
> +        if $crate::debug::debug_mask_enabled($crate::debug::DebugMask::$mask) {
> +            let thread = kernel::current!();
> +            $crate::binder_debug!(
> +                raw,
> +                "{}:{} {}\n",
> +                thread.tgid(),
> +                thread.pid(),
> +                kernel::prelude::fmt!($($arg)*)
> +            );
> +        }
> +    };
> +}