linux-kernel - Question: How to switch a process namespace by nsfs "device" and inode number directly?

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Message-ID: <0eb9ec62-1c1b-5903-2db6-43ca571580b9@linux.alibaba.com>
Date:   Mon, 10 Sep 2018 16:50:42 +0800
From:   Chengdong Li <chengdong.li@...ux.alibaba.com>
To:     ebiederm@...ssion.com, peterz@...radead.org,
        kjlx@...pleofstupid.com
Cc:     hbathini@...ux.vnet.ibm.com, brendan.d.gregg@...il.com,
        ak@...ux.intel.com, linux-kernel@...r.kernel.org,
        chengdong.licd@...baba-inc.com
Subject: Question: How to switch a process namespace by nsfs "device" and
 inode number directly?

Hi folks,

I am getting stuck by the lack of approach to switch process namespace 
by nsfs "device" and inode number in user-space,  for example (mnt: 
0xf0000000)

 From my best understanding, the normal way to do that is by setns 
system call. But setns only accept fd that refer to a opened namespace, 
sometimes we couldn't get it.

For example:  After perf record, perf report couldn't work well once the 
process that runs inside a container has exited, as the /proc/pid/ns 
doesn't exist anymore after process exit.

Any comments are welcome!

Thanks,

Chengdong