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    Subject[RFC PATCH] ftrace trace event: introduce assignment macros
    This patch proposes encapsulation of the raw assignments within TP_fast_assign()
    by introducing tp_assign() and tp_memcpy() macros. This will allow us to:

    - generically filter from input fields,
    - redefine the field write primitives.

    The current macros map directly to the old code. I changed the documentation in
    tracepoint.txt to reflect these new primitives, but all TRACE_EVENT() users
    should gradually update their code to use these macro wrappers rather than raw
    "=" assignments or mempcy() calls.

    Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
    CC: Steven Rostedt <rostedt@goodmis.org>
    CC: Frederic Weisbecker <fweisbec@gmail.com>
    CC: Ingo Molnar <mingo@redhat.com>
    CC: Li Zefan <lizf@cn.fujitsu.com>
    CC: William Cohen <wcohen@redhat.com>
    CC: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
    CC: Theodore Ts'o <tytso@mit.edu>
    CC: Jason Baron <jbaron@redhat.com>
    CC: Mel Gorman <mel@csn.ul.ie>
    CC: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>
    CC: Marcelo Tosatti <mtosatti@redhat.com>
    CC: Avi Kivity <avi@redhat.com>
    CC: Gleb Natapov <gleb@redhat.com>
    CC: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
    CC: Neil Horman <nhorman@tuxdriver.com>
    CC: Arjan van de Ven <arjan@linux.intel.com>
    CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
    CC: Kei Tokunaga <tokunaga.keiich@jp.fujitsu.com>
    CC: Martin K. Petersen <martin.petersen@oracle.com>
    CC: Oleg Nesterov <oleg@redhat.com>
    CC: Masami Hiramatsu <mhiramat@redhat.com>
    CC: Josh Stone <jistone@redhat.com>
    CC: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
    CC: Thomas Gleixner <tglx@linutronix.de>
    CC: Zhaolei <zhaolei@cn.fujitsu.com>
    CC: Anton Blanchard <anton@samba.org>
    ---
    include/linux/tracepoint.h | 12 ++++++------
    include/trace/ftrace.h | 6 ++++++
    2 files changed, 12 insertions(+), 6 deletions(-)

    Index: linux-2.6-lttng.git/include/trace/ftrace.h
    ===================================================================
    --- linux-2.6-lttng.git.orig/include/trace/ftrace.h
    +++ linux-2.6-lttng.git/include/trace/ftrace.h
    @@ -1,4 +1,10 @@
    /*
    + * Macros mapping tp_assign() and tp_memcpy() to "=" and memcpy.
    + */
    +#define tp_assign(dest, src) __entry->dest = src
    +#define tp_memcpy(dest, src, len) memcpy(__entry->dest, src, len)
    +
    +/*
    * Stage 1 of the trace events.
    *
    * Override the macros in <trace/trace_events.h> to include the following:
    Index: linux-2.6-lttng.git/include/linux/tracepoint.h
    ===================================================================
    --- linux-2.6-lttng.git.orig/include/linux/tracepoint.h
    +++ linux-2.6-lttng.git/include/linux/tracepoint.h
    @@ -306,12 +306,12 @@ static inline void tracepoint_update_pro
    * *
    *
    * TP_fast_assign(
    - * memcpy(__entry->next_comm, next->comm, TASK_COMM_LEN);
    - * __entry->prev_pid = prev->pid;
    - * __entry->prev_prio = prev->prio;
    - * memcpy(__entry->prev_comm, prev->comm, TASK_COMM_LEN);
    - * __entry->next_pid = next->pid;
    - * __entry->next_prio = next->prio;
    + * tp_memcpy(next_comm, next->comm, TASK_COMM_LEN);
    + * tp_assign(prev_pid, prev->pid);
    + * tp_assign(prev_prio, prev->prio);
    + * tp_memcpy(prev_comm, prev->comm, TASK_COMM_LEN);
    + * tp_assign(next_pid, next->pid);
    + * tp_assign(next_prio, next->prio);
    * )
    *
    * *
    --
    Mathieu Desnoyers
    Operating System Efficiency R&D Consultant
    EfficiOS Inc.
    http://www.efficios.com


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