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

[Eric W. Biederman]

Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes:

> On Mon, Nov 14, 2016 at 04:02:30PM +0530, Hari Bathini wrote:
>
>> >>  	PERF_RECORD_SWITCH_CPU_WIDE		= 15,
>> >>+	/*
>> >>+	 * struct {
>> >>+	 *	struct perf_event_header	header;
>> >>+	 *
>> >>+	 *	u32				pid, tid;
>> >>+	 *	u64				time;
>> >>+	 *	u32				uts_ns_inum;
>> >>+	 *	u32				ipc_ns_inum;
>> >>+	 *	u32				mnt_ns_inum;
>> >>+	 *	u32				pid_ns_inum;
>> >>+	 *	u32				net_ns_inum;
>> >>+	 *	u32				cgroup_ns_inum;
>> >>+	 *	u32				user_ns_inum;
>> >>+	 * 	struct sample_id		sample_id;
>> >>+	 * };
>> >>+	 */
>> >>+	PERF_RECORD_NAMESPACES			= 16,
>> >So this format is not extensible, that is, if someone adds yet another
>> >namespace, we'll need to introduce PERF_RECORD_NAMESPACES2.
>> >
>> >Is there a 'natural' and exposed namespace index that we can use to
>> >change it like:
>> >
>> >	u32	nr_nss;
>> >	u32	namespace[nr_nss];
>> >
>> >?
>> 
>> Nothing of that sort exists, currently.
>> Maybe, time to introduce with this patch-set..?
>
> Would be good, but you'll have to sort that with the namespace folks.

The somewhat easy answer is to use the unshare flags.  AKA CLONE_NEWNS,
CLONE_NEWUSER, ...

In the worst case things may get extended to the point where perf would
have to use a different set of values than we use to unshare, clone, and
setns (as the clone flags are effectively all used up) but for the
existing namespaces that index should work just fine.

That won't allow for a natural array in the record but it will allow for
an array with that has a tag for which namespace it is in, or
alternative it will allow for one record per namespace.

Eric