From: Nikanth Karthikesan <knikanth@suse.de>
Organization: suse.de
To: balbir@linux.vnet.ibm.com
Subject: Re: [RFC][PATCH] taskstats: Fix CGROUPSTATS_TYPE_CGROUP_STATS having same value as TASKSTATS_TYPE_PID
Date: Mon, 13 Jul 2009 21:16:43 +0530
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Cc: Paul Menage <menage@google.com>, lizf@cn.fujitsu.com,
       linux-kernel@vger.kernel.org
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On Monday 13 July 2009 19:11:58 Balbir Singh wrote:
> * Nikanth Karthikesan <knikanth@suse.de> [2009-07-13 18:31:12]:
> > Hi
> >
> > Currently we never get message from kernel to userspace of type
> > TASKSTATS_TYPE_PID. Otherwise this could have been spotted earlier.
> >
> > I was trying to add a new taskstat command that would return response of
> > type TASKSTATS_TYPE_PID.
> >
> > Having the same values would restrict one not to use the same netlink
> > socket for a command that would return response of type
> > TASKSTATS_TYPE_PID and the CGROUPSTATS_CMD_GET command.
> >
> > Should we fix it by using values after __TASKSTATS_TYPE_MAX.
> >
> > Changing this now might break pre-built binaries. Or is this intended,
> > and the application is not supposed to use CGROUPSTATS and TASKSTATS on
> > the same socket?
>
> Ideally they are supposed to be on different sockets, but nothing
> really is hard and fast in terms of rules.
>
> > Thanks
> > Nikanth
> >
> > Currently we never get message from kernel to userspace of type
> > TASKSTATS_TYPE_PID. Otherwise this could have been spotted earlier.
> > Having the values in the same range would restrict one not to use the
> > same netlink socket for a command that would return response of type
> > TASKSTATS_TYPE_PID and the CGROUPSTATS_CMD_GET command. Fix it by using
> > values after
> > __TASKSTATS_TYPE_MAX.
> >
> > Signed-off-by: Nikanth Karthikesan <knikanth@suse.de>
> >
> > ---
> >
> >
> > diff --git a/include/linux/cgroupstats.h b/include/linux/cgroupstats.h
> > index 3753c33..87b31f0 100644
> > --- a/include/linux/cgroupstats.h
> > +++ b/include/linux/cgroupstats.h
> > @@ -53,7 +53,7 @@ enum {
> >  #define CGROUPSTATS_CMD_MAX (__CGROUPSTATS_CMD_MAX - 1)
> >
> >  enum {
> > -	CGROUPSTATS_TYPE_UNSPEC = 0,	/* Reserved */
> > +	CGROUPSTATS_TYPE_UNSPEC = __TASKSTATS_TYPE_MAX,	/* Reserved */
> >  	CGROUPSTATS_TYPE_CGROUP_STATS,	/* contains name + stats */
> >  	__CGROUPSTATS_TYPE_MAX,
> >  };
>

Also this would unnecessarily increase the value of __CGROUPSTATS_TYPE_MAX. 
So, please dont take this patch. :) I would send a better fix, soon.

Thanks
Nikanth
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