linux-kernel - Re: [PATCH] core_pattern: set core helpers root and namespace to crashing process

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Date:	Fri, 14 Dec 2012 09:04:18 +0000
From:	"Daniel P. Berrange" <berrange@...hat.com>
To:	Neil Horman <nhorman@...driver.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	containers@...ts.linux-foundation.org
Subject: Re: [PATCH] core_pattern: set core helpers root and namespace to
 crashing process

On Thu, Dec 13, 2012 at 09:49:39PM -0500, Neil Horman wrote:
> On Thu, Dec 13, 2012 at 02:25:34PM -0800, Andrew Morton wrote:
> > On Thu, 13 Dec 2012 13:12:20 -0500
> > Neil Horman <nhorman@...driver.com> wrote:
> > 
> > > On Thu, Dec 13, 2012 at 06:20:48AM -0600, Serge Hallyn wrote:
> > > > Quoting Neil Horman (nhorman@...driver.com):
> > > > > Theres one problem I currently see with it, and that is that I'm not sure we can
> > > > > change the current behavior of how the root fs is set for the pipe reader, lest
> > > > > we break some user space expectations. As such, I've added a sysctl in this
> > > > > patch to allow administrators to globally select if a core reader specified via
> > > > > /proc/sys/kernel/core_pattern should use the global rootfs, or the (possibly)
> > > > > chrooted fs of the crashing process.
> > > > 
> > > > Practical question:  How is the admin to make an educated decision on
> > > > how to set the sysctl?
> > 
> > By reading the documentation which Neil didn't include?
> > 
> Yeah, that was stupid of me, I'll respin this with docs.
> 
> > > My thought was that the admin typically wouldn't touch this at all.  I really
> > > added it as a backwards compatibility option only.  Setting the user space
> > > helper task to the root of the crashing parent has the possibility of breaking
> > > existing installs because the core_pattern helper might be expecting global file
> > > system access.  Moving forward, my expectation would be that core_pattern
> > > helpers would be written with the default setting in mind, and we could
> > > eventually deprecate the control entirely.
> > > 
> > > If you have a better mechanism in mind however (or if you think that removing
> > > the control is a resaonable approach), I'm certainly open to that.
> > 
> > Yeah, this is a tiresome patch but I can't think of a better way.
> > 
> > Except, perhaps, adding a new token to the core_pattern which says
> > "switch namespaces"?
> >
> I like that idea, perhaps '||' instead of '|' as the leading token can indicate
> "use the namespace root" vs. "use the global root".  Thoughts?

That seems like a nicer idea to me, than the extra sysctl knob.

Daniel
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