linux-kernel - Re: [PATCH 5/5] kernfs: add exportfs operations

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Message-ID: <20170523185711.GB13222@htj.duckdns.org>
Date:   Tue, 23 May 2017 14:57:11 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Shaohua Li <shli@...com>, linux-kernel@...r.kernel.org,
        gregkh@...uxfoundation.org, viro@...iv.linux.org.uk,
        Kernel-team@...com
Subject: Re: [PATCH 5/5] kernfs: add exportfs operations

Hello, Christoph.

On Tue, May 23, 2017 at 12:40:19AM -0700, Christoph Hellwig wrote:
> On Mon, May 22, 2017 at 03:53:09PM -0700, Shaohua Li wrote:
> > Now we have the facilities to implement exportfs operations.
> 
> But do we have a use case?  I'd rather avoid this..

Yeah, this is one of the repeatedly requested features - a cgroup id
which can be looked up in a scalable way.  We probably should have
added this earlier too as we already have places where we're passing
in full cgroup path into the kernel (ipt_cgroup match).

IIUC, Shaohua is adding it so that block tracing can be made aware of
cgroups but something like this is necessary whenever we try to refer
to a cgroup in a race-free / scalable way.

If you have any other ideas, I'm all ears.

Thanks.

-- 
tejun