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Date: Wed, 7 Sep 2016 01:02:13 +0300
From: Alexey Dobriyan <adobriyan@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
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Cc: ksummit-discuss@lists.linuxfoundation.org
Subject: Re: [Ksummit-discuss] [topic proposal] tracepoints and ABI
 stability warranties
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On Wed, Sep 07, 2016 at 12:36:44AM +0300, Alexey Dobriyan wrote:
> P.S.: techically every kernel release almost certainly breaks crash(1)
> program, program many people on this list should be familiar with.
> It is unclear why rules should be different for tracepoints.

Concrete example:

	TRACE_EVENT(sched_switch,
        TP_STRUCT__entry(
                __array(        char,   prev_comm,      TASK_COMM_LEN   )
                __field(        pid_t,  prev_pid                        )
                __field(        int,    prev_prio                       )
                __field(        long,   prev_state
		^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

struct task_struct::state is long but it looks like a historical
artifact, it can be just int. In this case it is easy to extend value and
preserve compatibility.