linux-kernel - RE: [RFC PATCH 0/3] ns, procfs: pid conversion between ns and showing pidns hierarchy

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Date:	Tue, 16 Sep 2014 09:06:58 +0000
From:	"Chen, Hanxiao" <chenhanxiao@...fujitsu.com>
To:	"Serge E. Hallyn" <serge@...lyn.com>
CC:	"containers@...ts.linux-foundation.org" 
	<containers@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Richard Weinberger <richard.weinberger@...il.com>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	"Oleg Nesterov" <oleg@...hat.com>,
	David Howells <dhowells@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: RE: [RFC PATCH 0/3] ns, procfs: pid conversion between ns and
 showing pidns hierarchy

Hi,

> -----Original Message-----
> From: Serge E. Hallyn [mailto:serge@...lyn.com]
> 
> Hi,
> 
> so the below is just 30 mins worth of playing around, will hang if you give
> it bad pids, and requires privilege, but shows how to get pid conversion
> in some cases.  Basically it gives you what I had previously suggested
> for the query_pid syscall before.
> 
Thanks for teaching me of how ucred could be used for this case.

> In general, usage is
> 
> translatepid reporter_pid dest_pid query_pid
> 
> where reporter_pid and dest_pid are pids in your pidns.  It will assume
> query_pid is a valid pid in reporter_pid's pidns, and return the pid of
> the same process in dest_pid's namespace.
> 
> In particular,
> 
> if a process in a container (say pid 1, pid 24444 in the host pidns)
> reports something about another process (say pid 262) in the container,
> and you have a shell (pid 1092) on the host, you can figure out the pid
> for 262 in your host pidns using
> 
> translatepid $$ 24444 262
> 
> or to figure out what pid 25152 on the host is knows as in the
> container,
> 
> translatepid 24444 $$ 25152
> 
It's very easy to use:)

> I wonder whether this is enough to give you all you need.  While it
> won't be super-fast, you could use and ppid info to figure out who
> is pid 1, etc.

Yes, functionally it's very good.
But for the cases of utilizes like sosreport, ps,
it's a bit of slow.

So the procfs still has its advantages.
And also, I think the pidns hierarchy is needed.
I'll send the v2 ns hierarchy patch soon.

Thanks,
- Chen