tracing: Have large events show up as '[LINE TOO BIG]' instead of nothing
authorSteven Rostedt (Google) <rostedt@goodmis.org>
Sat, 9 Dec 2023 22:10:58 +0000 (17:10 -0500)
committerSteven Rostedt (Google) <rostedt@goodmis.org>
Wed, 13 Dec 2023 00:00:36 +0000 (19:00 -0500)
commitb55b0a0d7c4aa2dac3579aa7e6802d1f57445096
treedee065a1d9ee706eeea6e9243a6ffb30569154ee
parentb3ae7b67b87fed771fa5bf95389df06b0433603e
tracing: Have large events show up as '[LINE TOO BIG]' instead of nothing

If a large event was added to the ring buffer that is larger than what the
trace_seq can handle, it just drops the output:

 ~# cat /sys/kernel/tracing/trace
 # tracer: nop
 #
 # entries-in-buffer/entries-written: 2/2   #P:8
 #
 #                                _-----=> irqs-off/BH-disabled
 #                               / _----=> need-resched
 #                              | / _---=> hardirq/softirq
 #                              || / _--=> preempt-depth
 #                              ||| / _-=> migrate-disable
 #                              |||| /     delay
 #           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
 #              | |         |   |||||     |         |
            <...>-859     [001] .....   141.118951: tracing_mark_write           <...>-859     [001] .....   141.148201: tracing_mark_write: 78901234

Instead, catch this case and add some context:

 ~# cat /sys/kernel/tracing/trace
 # tracer: nop
 #
 # entries-in-buffer/entries-written: 2/2   #P:8
 #
 #                                _-----=> irqs-off/BH-disabled
 #                               / _----=> need-resched
 #                              | / _---=> hardirq/softirq
 #                              || / _--=> preempt-depth
 #                              ||| / _-=> migrate-disable
 #                              |||| /     delay
 #           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
 #              | |         |   |||||     |         |
            <...>-852     [001] .....   121.550551: tracing_mark_write[LINE TOO BIG]
            <...>-852     [001] .....   121.550581: tracing_mark_write: 78901234

This now emulates the same output as trace_pipe.

Link: https://lore.kernel.org/linux-trace-kernel/20231209171058.78c1a026@gandalf.local.home
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
kernel/trace/trace.c