[PATCH 0/7] rust_binder : Implement dynamic debug logging mask

[Jahnavi MN via B4 Relay <devnull+jahnavimn.google.com@kernel.org>]

Why we implemented this feature : 

While working with and testing the Rust implementation of the Binder 
driver (rust_binder), we realized that diagnosing transaction failures 
and protocol errors was extremely difficult. When a user-space application 
sends malformed data or makes a lifecycle mistake, the driver rejects it 
with a generic error code (like `-EINVAL`). Without internal logs, the 
driver acts as a "black box," forcing developers to guess which check 
failed.

In the legacy C Binder driver, this issue is solved using a dynamic 
`debug_mask` module parameter that toggles verbose logs for specific 
subsystems. This series brings the same critical capability to the Rust 
Binder driver to provide developers with clear, real-time feedback.

How this helps and simplifies debugging : 
Instead of rebuilds, reboots, or guessing:
- Developers can enable logs instantly on a running device by writing to 
  `/sys/module/rust_binder/parameters/debug_mask`.
- It prints the exact reason for failures (such as alignment errors, 
  mismatched call stacks, or invalid handle references) directly into 
  `dmesg`, reducing debugging time from hours to seconds.
- It protects system logs by keeping logging off by default and only 
  enabling it when developers are actively troubleshooting.

Code development approach : 
We built this system in a structured, progressive approach:
1. Infrastructure Bridging (C/Rust FFI) :
   Because the Rust `module!` macro cannot yet declare parameters, we 
   declared `debug_mask` in a C companion file and linked to it in Rust via 
   FFI. We used volatile memory reads to ensure changes to the mask are 
   detected instantly at runtime.
   
2. Verification Setup :
   We created a `binder_debug!` macro and instrumented process `open`, 
   `flush`, and `release` calls under the `BINDER_DEBUG_OPEN_CLOSE` mask. 
   These low-frequency events allowed us to verify the setup without log 
   flooding.
   
3. Targeted Instrumentation :
   We then systematically added detailed logs across 3 major categories:
   - User Error : Captures API misuse like misaligned FD arrays, 
     negative reference count transitions, and invalid death/freeze 
     notifications.
   - Failed Transaction : Dumps a complete diagnostics log on 
     transaction errors (IDs, PIDs, sizes, OOM states, and line numbers).
   - Dead Transaction : Logs in-flight cancellations, aborted 
     replies, and notification cleanups when processes exit prematurely.

Signed-off-by: Jahnavi MN <jahnavimn@google.com>
---
Jahnavi MN (7):
      rust_binder: Add dynamic debug logging mask
      rust_binder: Implement the BINDER_DEBUG_USER_ERROR logging mask for freezer-related operation
      rust_binder: Implement the BINDER_DEBUG_USER_ERROR logging mask for reference counting and death notification operations
      rust_binder: Implement the BINDER_DEBUG_USER_ERROR logging mask for transaction parsing and protocol validation failures
      rust_binder: Implement the BINDER_DEBUG_FAILED_TRANSACTION logging mask for transaction parsing and routing failures
      rust_binder: Implement BINDER_DEBUG_FAILED_TRANSACTION logging for death notification allocation failures
      rust_binder: Implement the BINDER_DEBUG_DEAD_TRANSACTION logging mask to trace in-flight cancellations during teardown

 drivers/android/binder/debug.rs            |  49 ++++++++++
 drivers/android/binder/freeze.rs           |  57 ++++++++---
 drivers/android/binder/node.rs             |  24 ++++-
 drivers/android/binder/process.rs          |  71 +++++++++++---
 drivers/android/binder/rust_binder_main.rs |  11 ++-
 drivers/android/binder/rust_binderfs.c     |   3 +
 drivers/android/binder/thread.rs           | 147 +++++++++++++++++++++++++----
 drivers/android/binder/transaction.rs      |  16 +++-
 8 files changed, 328 insertions(+), 50 deletions(-)
---
base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
change-id: 20260702-rust_binder_debug_mask-636737015624

Best regards,
-- 
Jahnavi MN <jahnavimn@google.com>