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

[Peter Zijlstra]

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.