linux-kernel - Re: [PATCH v3] tools lib traceevent: add checks for returned EVENT

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Message-ID: <20150821133441.GE3154@kernel.org>
Date:	Fri, 21 Aug 2015 10:34:41 -0300
From:	Arnaldo Carvalho dn Melo <acme@...nel.org>
To:	Jiri Olsa <jolsa@...nel.org>
Cc:	Dean Nelson <dnelson@...hat.com>, a.p.zijlstra@...llo.org,
	mingo@...hat.com, rostedt@...dmis.org, namhyung@...nel.org,
	linux-kernel@...r.kernel.org, jolsa@...nel.org
Subject: Re: [PATCH v3] tools lib traceevent: add checks for returned
 EVENT_ERROR type

Em Thu, Aug 20, 2015 at 11:16:32AM -0400, Dean Nelson escreveu:
> Running the following perf-stat command on an arm64 system produces the
> following result...
 
>   [root@...ch64 ~]# perf stat -e kmem:mm_page_alloc -a sleep 1
>     Warning: [kmem:mm_page_alloc] function sizeof not defined
>     Warning: Error: expected type 4 but read 0
>   Segmentation fault
>   [root@...ch64 ~]#

Jiri, while testing this I noticed that when running as !root I get:

  $ perf stat -e kmem:mm_page_alloc -a sleep 1
  event syntax error: 'kmem:mm_page_alloc'
                       \___ unknown tracepoint
  Run 'perf list' for a list of valid events

 usage: perf stat [<options>] [<command>]

      -e, --event <event>   event selector. use 'perf list' to list available events
  [acme@zoo linux]$ 

Which could be a bit more friendly if it noticed that it may be a
tracepoint event and that if that is the case, the user needs to have
tracefs remounted with suitable permissions to be able to use
tracepoints, something like 'perf trace' does:

  [acme@zoo linux]$ trace ls
  Error:	No permissions to read
  /sys/kernel/debug/tracing/events/raw_syscalls/sys_(enter|exit)
  Hint:	Try 'sudo mount -o remount,mode=755 /sys/kernel/debug'

  [acme@zoo linux]$

Take that as a suggestion as you're more familiar with the event parsing
code :-)

- Arnaldo
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