Re: [PATCH v4 1/3] perf: add PERF_RECORD_NAMESPACES to include namespaces related info

[Hari Bathini]

Hi Peter,


On Saturday 17 December 2016 01:35 AM, Peter Zijlstra wrote:
> On Fri, Dec 16, 2016 at 11:51:20PM +0530, Hari Bathini wrote:
> > Hi Peter,
> >
> >
> > On Friday 16 December 2016 01:27 PM, Peter Zijlstra wrote:
> > > On Fri, Dec 16, 2016 at 11:57:47AM +0530, Hari Bathini wrote:
> > > > On Friday 16 December 2016 12:16 AM, Peter Zijlstra wrote:
> > > > > On Fri, Dec 16, 2016 at 12:07:06AM +0530, Hari Bathini wrote:
> > > > > > +struct perf_ns_link_info {
> > > > > > +	__u64	dev;
> > > > > > +	__u64	ino;
> > > > > > +};
> > > > > > +
> > > > > > +enum {
> > > > > > +	NET_NS_INDEX		= 0,
> > > > > > +	UTS_NS_INDEX		= 1,
> > > > > > +	IPC_NS_INDEX		= 2,
> > > > > > +	PID_NS_INDEX		= 3,
> > > > > > +	USER_NS_INDEX		= 4,
> > > > > > +	MNT_NS_INDEX		= 5,
> > > > > > +	CGROUP_NS_INDEX		= 6,
> > > > > > +
> > > > > > +	NAMESPACES_MAX,		/* maximum available namespaces */
> > > > > > +};
> > > > > > +
> > > > > >   enum perf_event_type {
> > > > > >   	/*
> > > > > > @@ -862,6 +880,17 @@ enum perf_event_type {
> > > > > >   	 */
> > > > > >   	PERF_RECORD_SWITCH_CPU_WIDE		= 15,
> > > > > > +	/*
> > > > > > +	 * struct {
> > > > > > +	 *	struct perf_event_header	header;
> > > > > > +	 *	u32				pid;
> > > > > > +	 *	u32				tid;
> > > > > > +	 *	struct namespace_link_info	link_info[NAMESPACES_MAX];
> > > > > > +	 *	struct sample_id		sample_id;
> > > > > > +	 * };
> > > > > > +	 */
> > > > > > +	PERF_RECORD_NAMESPACES			= 16,
> > > > > > +
> > > > > >   	PERF_RECORD_MAX,			/* non-ABI */
> > > > > >   };
> > > > > What happens if a future kernel adds another namespace?
> > > > No impact unless NAMESPACES_MAX in include/uapi/linux/perf_event.h is
> > > > updated to accommodate that..
> > > > And if it is updated, the corresponding change is expected in perf-tool as
> > > > well..
> > > And what happens if you try and process old data files with the new
> > > tools or the other way around?
> > It works fine either way. I tested that..
> I don't see how the tool can parse old records (with NAMESPACES_MAX ==
> 7) if you set its NAMESPACES_MAX to say 10.
>
> Then it will expect the link_info array to be 10 entries and either read
> past the end of the record (if !sample_all) or try and interpret
> sample_id as link_info records.

Right. There will be inconsistency with data the perf tool tries to read 
beyond
what the kernel supports. IIUC, you mean, include nr_namespaces field in the
record and warn the user if it doesn't match with the one perf-tool supports
before proceeding..?

Thanks
Hari

PS: I am on vacation. Will post next version early January.