rust_binder: add transaction_log and failed_transaction_log

Implement the binder_logs/transaction_log and
binder_logs/failed_transaction_log binderfs files in Rust Binder,
matching the circular 32-entry transaction logs in C Binder.

Example output from /dev/binderfs/binder_logs/transaction_log:

  261251: call  from 6157:6171 to 391:0 context binder node 170 handle 34 size 256:0 ret 0/0 l=0
  261254: async from 606:783 to 669:0 context binder node 2048 handle 2 size 144:0 ret 0/0 l=0
  261255: reply from 391:552 to 6157:6171 context binder node 0 handle -1 size 2436:8 ret 0/0 l=0

Example output from /dev/binderfs/binder_logs/failed_transaction_log:

  194556: async from 6646:6853 to 7452:0 context binder node 177682 handle 450 size 160:0 ret 29189/0 l=process.rs:1081
  194846: reply from 6646:6775 to 7452:7544 context binder node 0 handle -1 size 8:0 ret 29201/0 l=process.rs:1081
  201573: call  from 7771:7793 to 6646:0 context binder node 198883 handle 28 size 0:0 ret 29189/0 l=process.rs:1081

Unlike C Binder, which writes to log entries without a lock using memory
barriers (smp_wmb/smp_rmb) and a debug_id_done field, each
TransactionLog uses an atomic index cursor with 32 cacheline-aligned
SpinLock<TransactionLogEntry> slots initialized in BinderModule::init
via SetOnce<_>. Using a SpinLock per slot avoids data races (such as
tearing when the ring buffer wraps around while an entry is being
printed) without requiring atomic accesses for every field, and has very
low risk of contention: concurrent transactions are spread across 32
separate cacheline-aligned locks, each lock is only held briefly for a
fixed-size copy, and two writers only contend on a slot if 32
transactions occur before a single copy completes.

Assisted-by: LLM
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20261001141114.2731136-1-aliceryhl@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

0 files changed, 0 insertions, 0 deletions