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

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

On Fri Jul 3, 2026 at 4:29 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            | 49 ++++++++++++++++++++++++++++++
>  drivers/android/binder/process.rs          | 15 +++++++--
>  drivers/android/binder/rust_binder_main.rs |  2 ++
>  drivers/android/binder/rust_binderfs.c     |  3 ++
>  drivers/android/binder/thread.rs           |  1 +
>  drivers/android/binder/transaction.rs      |  5 +--
>  6 files changed, 71 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/android/binder/debug.rs b/drivers/android/binder/debug.rs
> new file mode 100644
> index 000000000000..5e4daa823377
> --- /dev/null
> +++ b/drivers/android/binder/debug.rs
> @@ -0,0 +1,49 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +// Copyright (C) 2026 Google LLC.
> +
> +//! Binder debugging helpers.
> +
> +#![allow(dead_code)]
> +
> +pub(crate) const BINDER_DEBUG_USER_ERROR: u32 = 1 << 0;
> +pub(crate) const BINDER_DEBUG_FAILED_TRANSACTION: u32 = 1 << 1;
> +pub(crate) const BINDER_DEBUG_DEAD_TRANSACTION: u32 = 1 << 2;
> +pub(crate) const BINDER_DEBUG_OPEN_CLOSE: u32 = 1 << 3;
> +pub(crate) const BINDER_DEBUG_DEAD_BINDER: u32 = 1 << 4;
> +pub(crate) const BINDER_DEBUG_DEATH_NOTIFICATION: u32 = 1 << 5;
> +pub(crate) const BINDER_DEBUG_READ_WRITE: u32 = 1 << 6;
> +pub(crate) const BINDER_DEBUG_USER_REFS: u32 = 1 << 7;
> +pub(crate) const BINDER_DEBUG_THREADS: u32 = 1 << 8;
> +pub(crate) const BINDER_DEBUG_TRANSACTION: u32 = 1 << 9;
> +pub(crate) const BINDER_DEBUG_TRANSACTION_COMPLETE: u32 = 1 << 10;
> +pub(crate) const BINDER_DEBUG_FREE_BUFFER: u32 = 1 << 11;
> +pub(crate) const BINDER_DEBUG_INTERNAL_REFS: u32 = 1 << 12;
> +pub(crate) const BINDER_DEBUG_PRIORITY_CAP: u32 = 1 << 13;
> +pub(crate) const BINDER_DEBUG_SPINLOCKS: u32 = 1 << 14;

This should be defined as bitflags:
https://rust.docs.kernel.org/next/kernel/macro.impl_flags.html

> +
> +extern "C" {
> +    static rust_binder_debug_mask: u32;

It's UB for this to be mutated. This should either be `static mut` or
`Atomic<u32>`.

> +}
> +
> +/// Checks if the given debug logging category is enabled in the mask.
> +pub(crate) fn debug_mask_enabled(mask: u32) -> bool {
> +    let ptr = &raw const rust_binder_debug_mask;
> +    // SAFETY: `rust_binder_debug_mask` is defined in the companion C code linked in the module.
> +    let current_mask = unsafe { core::ptr::read_volatile(ptr) };
> +    (current_mask & mask) != 0
> +}
> +
> +/// Prints a debug log if the specified mask category is enabled.
> +#[macro_export]
> +macro_rules! binder_debug {
> +    ($mask:expr, $fmt:literal $(, $($arg:tt)*)?) => {
> +        if $crate::debug::debug_mask_enabled($mask) {

The mask should probably just be an identifier and then the macro builds the
full mask, so crate::debug::... is not needed.

Best,
Gary

> +            kernel::pr_info!(
> +                "{}: {}\n",
> +                kernel::current!().pid(),
> +                format_args!($fmt $(, $($arg)*)?)
> +            );
> +        }
> +    };
> +}