linux-kernel - Re: [PATCH resend] vfs: Add ->statfs callback for pipefs

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Message-Id: <20110824012328.f7bfc68a.akpm@linux-foundation.org>
Date:	Wed, 24 Aug 2011 01:23:28 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Al Viro <viro@...IV.linux.org.uk>,
	James Bottomley <jbottomley@...allels.com>,
	Tejun Heo <tj@...nel.org>,
	Glauber Costa <glommer@...allels.com>,
	containers@...ts.osdl.org, linux-kernel@...r.kernel.org,
	Pavel Emelyanov <xemul@...allels.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Nathan Lynch <ntl@...ox.com>,
	Oren Laadan <orenl@...columbia.edu>,
	Daniel Lezcano <dlezcano@...ibm.com>,
	LINUXFS-ML <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH resend] vfs: Add ->statfs callback for pipefs

On Wed, 24 Aug 2011 12:09:24 +0400 Cyrill Gorcunov <gorcunov@...il.com> wrote:

> From: Pavel Emelyanov <xemul@...allels.com>
> 
> This is done to make it possible to distinguish pipes
> from fifos when opening one via /proc/<pid>/fd/ link.
> 
> Signed-off-by: Pavel Emelyanov <xemul@...allels.com>
> Reviewed-by: Tejun Heo <tj@...nel.org>
> Acked-by: Serge Hallyn <serge.hallyn@...onical.com>
> Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
> ---
>  fs/pipe.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> Any objections to this one? It was a part of a patchset
> but can be treated independently so I'm re-sending it alone.
> 
> Index: linux-2.6.git/fs/pipe.c
> ===================================================================
> --- linux-2.6.git.orig/fs/pipe.c
> +++ linux-2.6.git/fs/pipe.c
> @@ -1254,6 +1254,7 @@ out:
>  
>  static const struct super_operations pipefs_ops = {
>  	.destroy_inode = free_inode_nonrcu,
> +	.statfs = simple_statfs,
>  };
>  
>  /*

OK, I give up - how does it work?

<goes off and reads the kernel>

So it appears that the statfs call would previously return -ENOSYS, but
with this change the statfs will succeed and userspace can then inspect
f_type.  Yes?  I will fix your changelog by adding a description along these
lines.

And I'll ask you to fix it further by telling us why we want to do
this?  The kernel has had this issue for a long time - why does it now
matter?
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