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

From: Andrew Vagin
Date: Wed Jul 27 2016 - 00:45:46 EST

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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