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

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Message-ID: <20170524173822.GB13151@infradead.org>
Date:   Wed, 24 May 2017 10:38:22 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Christoph Hellwig <hch@...radead.org>, 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

On Tue, May 23, 2017 at 02:57:11PM -0400, Tejun Heo wrote:
> 
> 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).

I still have no idea how this ties into export ops.  Currently I don't
see any tracing code using export operations, so maybe a big part of
the series is missing/

> 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.

You can already get i_ino using statx, and i_generation using
FS_IOC_GETVERSION, so I'm a little lost on why you need the full
exportfs infrastructure.