Re: [patch] perf_event_open.2 -- expand ERRORS section

[walter harms <wharms-fPG8STNUNVg@public.gmane.org>]

Am 15.04.2014 20:25, schrieb Vince Weaver:
> On Mon, 14 Apr 2014, Michael Kerrisk (man-pages) wrote:
> 
>>
>>        EACCES Returned when the requested event requires root  permis‐
>>               sions  (or  a  more  permissive perf_event paranoid set‐
>>               ting).  Some common cases where an unprivileged  process
>>               may  encounter  this  error:  are attaching to a process
>>               owned by a different user; monitoring all processes on a
>>               given CPU; and not setting exclude_kernel when the para‐
>>               noid setting requires it.
>>
>> But, now I have some more questions:
>>
>> * What are "root permissions" here? It's these days usual to express
>>   things precisely in terms of the required capability.
> 
> Yes, I guess that should really be CAP_SYS_ADMIN
> 
>> * I am puzzled by "monitoring all processes on a CPU"? So, monitoring 
>>   _some_ (i.e., < all) processes on a CPU won't trigger this error?
> 
> I was a bit confused here.
> 
> A regular user can monitor "the specified process on CPU X" or "the 
> specified process on any CPU".
> 
> A user running as root can also monitor "all procceses belonging to anyone 
> on CPU X"
> 

why not "can monitor any process" ?

re,
 wh

> Other combinations aren't possible.
> 
>>>>> +.B EPERM
>>>>> +Returned if sufficient permissions not available to create the event.
>>
>> Again, somewhere here, the text should mention the required capability.
> 
> Yes, it's CAP_SYS_ADMIN again.
> 
>>> This is a recent change.  
>>
>> So, the text should mention a kernel version number. Could you patch 
>> that please. I guess it should be something like:
>>
>>     and (since Linux 3.??) setting an ftrace function-trace tracepoint
> 
> Yes, I'll do that.
> 
> Vince
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