> On Nov 17, 2015, at 10:43, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> On Tue, 17 Nov 2015 10:21:47 +0800
> yalin wang <yalin.wang2010@xxxxxxxxx> wrote:
>
>
>> i have not tried ,
>> just a question,
>> if you print a %s , but don’t call trace_define_field() do define this string in
>> __entry , how does user space perf tool to get this string info and print it ?
>> i am curious ..
>> i can try this when i have time. and report to you .
>
> Because the print_fmt has nothing to do with the fields. You can have
> as your print_fmt as:
>
> TP_printk("Message = %s", "hello dolly!")
>
> And both userspace and the kernel with process that correctly (if I got
> string processing working in userspace, which I believe I do). The
> string is processed, it's not dependent on TP_STRUCT__entry() unless it
> references a field there. Which can also be used too:
>
> TP_printk("Message = %s", __entry->musical ? "Hello dolly!" :
> "Death Trap!")
>
> userspace will see in the entry:
>
> print_fmt: "Message = %s", REC->musical ? "Hello dolly!" : "Death Trap!"
>
> as long as the field "musical" exists, all is well.
>
> -- Steve
Aha, i see.
Thanks very much for your explanation.
Better print fat is :
TP_printk("mm=%p, scan_pfn=%s, writable=%d, referenced=%d, none_or_zero=%d, status=%s, unmapped=%d",
__entry->mm,
__entry->pfn == (-1UL) ? "(null)" : itoa(buff, __entry->pin, 10), …..)
is this possible ?
Thanks
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