linux-kernel - Re: [RFC PATCH 0/5] Second attempt at contained helper execution

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Message-ID: <20150121143819.GA28392@fieldses.org>
Date:	Wed, 21 Jan 2015 09:38:19 -0500
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Ian Kent <ikent@...hat.com>
Cc:	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	David Howells <dhowells@...hat.com>,
	Oleg Nesterov <onestero@...hat.com>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	Benjamin Coddington <bcodding@...hat.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	Jeff Layton <jeff.layton@...marydata.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [RFC PATCH 0/5] Second attempt at contained helper execution

On Wed, Jan 21, 2015 at 03:05:25PM +0800, Ian Kent wrote:
> On Fri, 2015-01-16 at 10:25 -0500, J. Bruce Fields wrote:
> > On Fri, Jan 16, 2015 at 09:01:13AM +0800, Ian Kent wrote:
> > > On Thu, 2015-01-15 at 11:27 -0500, J. Bruce Fields wrote:
> > > > On Thu, Jan 15, 2015 at 08:26:12AM +0800, Ian Kent wrote:
> > > > > On Wed, 2015-01-14 at 17:10 -0500, J. Bruce Fields wrote:
> > > > > > > On Wed, Jan 14, 2015 at 05:32:22PM +0800, Ian Kent wrote:
> > > > > > > > There are other difficulties to tackle as well, such as how to decide
> > > > > > > > if contained helper execution is needed. For example, if a mount has
> > > > > > > > been propagated to a container or bound into the container tree (such
> > > > > > > > as with the --volume option of "docker run") the root init namespace
> > > > > > > > may need to be used and not the container namespace.
> > > > > > 
> > > > > > I think you have to go through each of the existing upcall examples and
> > > > > > decide what's needed for each.
> > > > > > 
> > > > > > At least for the nfsv4 idmapper I would've thought the namespace the
> > > > > > mount was done in would be the right choice, hence my previous question.
> > > > > 
> > > > > Probably but you don't necessarily know what namespace the mount was
> > > > > done in. It may have been propagated from another namespace or (although
> > > > > I don't think it works yet) bound from another container using the
> > > > > volumes-from docker option.
> > > > 
> > > > Name-id mappings should be associated with the superblock, I guess--so
> > > > don't you store a pointer to the right thing there?
> > > 
> > > Quite possibly but my original point was, without an acceptable
> > > mechanism to execute the helper we can't know what might need to be done
> > > to use it.
> > 
> > At least for me it would be easier to review if it came with at least
> > one example user.
> 
> Haven't seen any negative responses but perhaps people are still away
> over Xmas.
> 
> In the mean time it's probably a good idea to add some use cases to the
> series in case the approach is OK.
> 
> I'll have a look at the nfsd code and see if I can spot the places.

On the nfsd side it's just the one call_usermodehelper in
fs/nfsd/nfs4recover.c.  The tricky part is figuring out where the
namespace information should come from.

--b.
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