Messages in this thread | | | Date | Mon, 16 Nov 2015 21:43:04 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH V4] mm: fix kernel crash in khugepaged thread |
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On Tue, 17 Nov 2015 10:21:47 +0800 yalin wang <yalin.wang2010@gmail.com> 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
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