linux-kernel - Re: Testing lxc 0.6.5 in Fedora 13

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Message-ID: <20100326124522.GD17113@megiteam.pl>
Date:	Fri, 26 Mar 2010 13:45:22 +0100
From:	Grzegorz Nosek <root@...aldomain.pl>
To:	Matt Helsley <matthltc@...ibm.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Roland McGrath <roland@...hat.com>,
	Sukadev Bhattiprolu <sukadev@...ibm.com>,
	containers@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: Testing lxc 0.6.5 in Fedora 13

On Fri, Mar 26, 2010 at 04:53:57AM -0700, Matt Helsley wrote:
> Yup. strace would need to be modified to use that. I tried that and it still
> won't work -- I seem to recall it didn't work because strace uses pid values
> obtained from the wait syscall too. To make it work we'd need to be able to
> translate those pids in userspace. That's do-able from userspace if you trace
> all forks descending from the pidns init task. But it's not do-able for
> simple attaches. That's why I was thinking Eric's setns() might be able to
> help if strace used it to enter the tracee's pid namespace whenever we need to.
> 
> gdb often doesn't use the same methods but has similar problems with pid
> namespaces.

Hmm, is there a good reason why strace does not use the data explicitly
provided by the kernel but instead second-guesses it from syscall return
values? I don't know anything about ptrace, really, but I'd expect the
kernel to provide the tracer with out-of-band information otherwise
taken from clone/waitpid/other syscalls?

Best regards,
 Grzegorz Nosek
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