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    SubjectRe: [PATCH -tip] tracing: use defined fields to print formats
    Steven Rostedt wrote:
    > On Thu, 16 Jul 2009, Lai Jiangshan wrote:
    >
    >> It seems that ftrace_format_##call() and ftrace_define_fields_##call()
    >> are duplicate more or less.
    >>
    >> trace_define_field() defines fields and links them into
    >> strcut ftrace_event_call. We reuse them to print formats
    >> and remove ftrace_format_##call(). It make all things simpler.
    >>
    >> TRACE_EVENT_FORMAT_NOFILTER is dropped. Because we should
    >> "trace_define_field()" fields for all struct ftrace_event_call,
    >> even it's no filter.
    >
    > OK, I added this and did a diff of the formats before this patch and
    > after the patch. Here they are (with a lot of duplicats cut out).
    >
    > [
    > '<' represents the old format
    > '>' represents the new format (with patch applied)
    > ]
    >
    > 4c4
    > < field:unsigned short common_type; offset:0; size:2;
    > ---
    >> field:int common_type; offset:0; size:2;
    >
    > We changed the common type from "unsigned short" to "int"?
    >
    > 45,46c45,46
    > < field:char rwbs[6]; offset:32; size:6;
    > < field:char comm[TASK_COMM_LEN]; offset:38; size:16;
    > ---
    >> field:char[6] rwbs; offset:32; size:6;
    >> field:char[TASK_COMM_LEN] comm; offset:38; size:16;
    >
    > I have several parsers that expect the '[6]' to come after the
    > declaration.
    >
    >
    > 390c390
    > < print fmt: "type:%u call_site:%lx ptr:%p"
    > ---
    >> print fmt: type:%u call_site:%lx ptr:%p
    >
    > The 'ftrace' events lost their quotes around the print format.
    >
    > 394c394
    > < field:unsigned short common_type; offset:0; size:2;
    > ---
    >> field:unsigned char common_type; offset:0; size:2;
    >
    > And the ftrace events also now use "unsigned char" for the common_type
    > instead of unsigned short?
    >
    >
    > 408c408
    > < print fmt: "type:%u call_site:%lx ptr:%p req:%lu alloc:%lu flags:%x node:%d"
    > ---
    >> print fmt: type:%u call_site:%lx ptr:%p req:%lu alloc:%lu flags:%x node:%d
    >
    > 423c423
    > < print fmt: "%llx->%llx type:%u state:%u"
    > ---
    >> print fmt: %llx->%llx type:%u state:%u
    >
    > 436c436
    > < print fmt: "from: %llx to: %llx"
    > ---
    >> print fmt: from: %llx to: %llx
    >
    >
    > Lots more quotes missing (I'll cut out the rest of the diff of quotes
    > missing).
    >
    > 447,448c447,448
    > < field special:char func[TRACE_FUNC_SIZE+1]; offset:16; size:31;
    > < field special:char file[TRACE_FUNC_SIZE+1]; offset:47; size:21;
    > ---
    >> field:char func[TRACE_FUNC_SIZE+1][TRACE_FUNC_SIZE+1] func; offset:16; size:31;
    >> field:char file[TRACE_FUNC_SIZE+1][TRACE_FUNC_SIZE+1] file; offset:47; size:21;
    >
    > This is interesting.
    >
    >
    >> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
    >
    > I really like the clean up this patch does, but it must not modify the
    > current format of the files unless there is a really good reason to do so.
    >
    > Thanks,
    >

    I'll fix it.

    There're 4 differences:

    1) the type of "common_type" is changed.
    It's brought by a bug `__common_field(int, type, 1);`
    It'll be fixed.

    2) Type Item[Len] ==> Type[Len] Item.
    (There are the same, )But it can't not be recovered as before.
    Because it's brought by `trace_define_field(event_call, #type "[" #len "]", #item,`
    I'll fix trace-cmd and make it supports these two style together.

    3) double quotation marks for the format is missing.
    It'll be fixed.

    4) a line in events/ftrace/print/format is missing.
    It'll be fixed.

    At the end(fixed patch), the only change is "Type Item[Len] ==> Type[Len] Item".

    The values of this patch are:
    1) A big function ftrace_format_##call() is defined for every event type.
    it waste a lot of memory. this patch saves these memory.

    2) reduce coupling: ftrace_format_##call() and
    ftrace_define_fields_##call() are almost the same.
    We need to maintain them together, it's not good design.

    The difference between ftrace_format_##call() and
    ftrace_define_fields_##call() implies a bug.

    Example: `__common_field(int, type, 1);` in
    ftrace_define_fields_##call() is a bug.

    Thank you.

    Lai.



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