linux-kernel - Re: [RFC][PATCH] taskstats: Fix CGROUPSTATS_TYPE_CGROUP_STATS having same value as TASKSTATS_TYPE

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Date:	Mon, 13 Jul 2009 21:24:39 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Nikanth Karthikesan <knikanth@...e.de>
Cc:	Paul Menage <menage@...gle.com>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] taskstats: Fix CGROUPSTATS_TYPE_CGROUP_STATS
	having same value as TASKSTATS_TYPE_PID

* Nikanth Karthikesan <knikanth@...e.de> [2009-07-13 21:16:43]:

> On Monday 13 July 2009 19:11:58 Balbir Singh wrote:
> > * Nikanth Karthikesan <knikanth@...e.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@...e.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.
>

Yes, agreed, but ideally __CGROUPSTATS_TYPE_MAX represents the max of
taskstats and cgroupstats so it should be OK in principle, but lets
try another approach to fix this.
 

-- 
	Balbir
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