linux-kernel - Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces

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Message-ID: <20160726191101.GB328@outlook.office365.com>
Date:	Tue, 26 Jul 2016 12:11:02 -0700
From:	Andrew Vagin <avagin@...tuozzo.com>
To:	"W. Trevor King" <wking@...mily.us>
CC:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Andrey Vagin <avagin@...nvz.org>,
	Linux API <linux-api@...r.kernel.org>,
	Linux Containers <containers@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"criu@...nvz.org" <criu@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	"James Bottomley" <James.Bottomley@...senpartnership.com>,
	Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 0/5 RFC] Add an interface to discover relationships
 between namespaces

On Tue, Jul 26, 2016 at 11:32:25AM -0700, W. Trevor King wrote:
> On Tue, Jul 26, 2016 at 11:25:24AM -0700, Andrew Vagin wrote:
> > Sure. If a process wants to compare two namespaces, it needs to get file
> > descriptors for them (open /proc/PID/ns/XXX, use new ioctl-s, find a
> > process which has them),
> > and then it calls kcmp(pid1, pid2, KCMP_NSFD, ns_fd1, ns_fd2)
> 
> If you use the new ioctl-s to get ns_fd2, do you walk your local /proc
> to find pid2?

If you use the new ioctl-s to get nf_fd2, you will have it in the
current process, so pid2 will be getpid().

pidX identifies a process where to find fdX.

man 2 kcmp:
 The kcmp() system call can be used to check whether the  two processes
 identified  by  pid1  and  pid2 share a kernel resource such as virtual
 memory, file descriptors, and so on.

> 
> Cheers,
> Trevor
> 
> -- 
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