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

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Date:   Tue, 15 Nov 2016 17:35:39 +0530
From:   Hari Bathini <hbathini@...ux.vnet.ibm.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Peter Zijlstra <peterz@...radead.org>
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>,
        sargun@...gun.me, Aravinda Prasad <aravinda@...ux.vnet.ibm.com>,
        brendan.d.gregg@...il.com
Subject: Re: [PATCH 1/3] perf: add PERF_RECORD_NAMESPACES to include
 namespaces related info



On Tuesday 15 November 2016 02:27 AM, Eric W. Biederman wrote:
> Peter Zijlstra <peterz@...radead.org> 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.

struct namespace_info {
	u64	flags;
	u32	inode_num;
	/* any other essential namespace info */
};

struct {

	struct perf_event_header	header;

	u32				pid, tid;
	u64				time;
	struct namespace_info		ns_info[];
	struct sample_id		sample_id;
};

Something of this sort should do..?

Thanks
Hari