linux-kernel - Re: [PATCH v6 1/3] perf: add PERF_RECORD_NAMESPACES to include namespaces related info

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Message-ID: <20170216103637.GL6536@twins.programming.kicks-ass.net>
Date:   Thu, 16 Feb 2017 11:36:37 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Hari Bathini <hbathini@...ux.vnet.ibm.com>
Cc:     ast@...com, lkml <linux-kernel@...r.kernel.org>, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, mingo@...hat.com,
        daniel@...earbox.net, rostedt@...dmis.org,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        ebiederm@...ssion.com, sargun@...gun.me,
        Aravinda Prasad <aravinda@...ux.vnet.ibm.com>,
        brendan.d.gregg@...il.com, jolsa@...hat.com
Subject: Re: [PATCH v6 1/3] perf: add PERF_RECORD_NAMESPACES to include
 namespaces related info

On Thu, Feb 16, 2017 at 11:28:24AM +0100, Peter Zijlstra wrote:
> On Wed, Feb 08, 2017 at 02:01:24PM +0530, Hari Bathini wrote:
> > @@ -862,6 +886,18 @@ enum perf_event_type {
> >  	 */
> >  	PERF_RECORD_SWITCH_CPU_WIDE		= 15,
> >  
> > +	/*
> > +	 * struct {
> > +	 *	struct perf_event_header	header;
> > +	 *	u32				pid;
> > +	 *	u32				tid;
> > +	 *	u32				nr_namespaces;
> > +	 *	struct namespace_link_info	link_info[NAMESPACES_MAX];
> > +	 *	struct sample_id		sample_id;
> > +	 * };
> > +	 */
> > +	PERF_RECORD_NAMESPACES			= 16,
> 
> This thing works by accident, there's a u32 hole in that structure.
> Also, the array isn't NAMESPACES_MAX long, its nr_namespaces, that's
> what its there for. The entries should be internally consistent.

Also, namespace_link_info isn't specified.

Easies would be to write something like:

	{ char name[8];
	  u64  inode;
	  u64  dev;    }[nr_namespace];