Message-ID: <1416962697.2509.60.camel@pluto.fritz.box>
Subject: Re: [RFC PATCH 3/4] kmod - add call_usermodehelper_ns() helper
From: Ian Kent <ikent@redhat.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@redhat.com>,
        Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        Stanislav Kinsbursky <skinsbursky@parallels.com>,
        Trond Myklebust <trond.myklebust@primarydata.com>,
        David Howells <dhowells@redhat.com>,
        Benjamin Coddington <bcodding@redhat.com>,
        Al Viro <viro@ZenIV.linux.org.uk>
Date: Wed, 26 Nov 2014 08:44:57 +0800
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On Wed, 2014-11-26 at 07:50 +0800, Ian Kent wrote:
> > 
> > If we are going to set this stuff up in the kernel we need a reference
> > process that we can create children of because what is possible with
> > respect to containers keeps changing, and it is extremely error prone to
> > figure out what all othe crazy little bits are, and to update everything
> > every time someone tweaks the kernel's capabilities.  We have kthreadd
> > because it was too error prone to scrub a userspace thread of all of the
> > userspace bits and make it the equivalent of what kthreadd is today.
> > 
> > Of course it is also rather nice to have something to hang everything
> > else on.
> > 
> > In summary we need a reference struct task that is all setup properly
> > so that we can create an appropriate kernel thread.
> 
> I'm having trouble understanding what your getting at here but I'm not
> that sharp so bear with me.
> 
> When call_usermodehelper() is called it's called from a process that is
> within the context within which the execution is required.

Umm .. OK, that's probably not quite right either ....

For nfsd I think it's OK but for nfs clients the context is probably
that of the caller ....

Whereas the helper to get a key info maybe does need to be called in the
context of the caller .....

> 
> So what information do we not have available for setup?
> 
> Are you saying that the problem is that when the user mode helper run
> thread is invoked we don't have the information available that was
> present when call_usermodehelper() was called and that's where the
> challenge lies?
> 
> Ian
> 


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