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Date: Mon, 16 Nov 2015 21:43:04 -0500 From: Steven Rostedt <rostedt@...dmis.org> To: yalin wang <yalin.wang2010@...il.com> Cc: Vlastimil Babka <vbabka@...e.cz>, Ingo Molnar <mingo@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>, Ebru Akagunduz <ebru.akagunduz@...il.com>, Rik van Riel <riel@...hat.com>, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, jmarchan@...hat.com, mgorman@...hsingularity.net, willy@...ux.intel.com, linux-kernel <linux-kernel@...r.kernel.org>, linux-mm@...ck.org Subject: Re: [PATCH V4] mm: fix kernel crash in khugepaged thread On Tue, 17 Nov 2015 10:21:47 +0800 yalin wang <yalin.wang2010@...il.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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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