linux-kernel - Re: d_path() and overlay fs

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Message-ID: <20150320165352.GF20913@tucsk>
Date:	Fri, 20 Mar 2015 17:53:52 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Josh Boyer <jwboyer@...oraproject.org>,
	Karel Zak <kzak@...hat.com>, dhowells@...hat.com,
	linux-kernel@...r.kernel.org, linux-unionfs@...r.kernel.org
Subject: Re: d_path() and overlay fs

On Fri, Mar 20, 2015 at 04:25:58PM +0000, Al Viro wrote:
> On Fri, Mar 20, 2015 at 05:01:23PM +0100, Miklos Szeredi wrote:
> 
> > But it does take care of the majority of f_path users that actually want the
> > covering path.
> 
> Bloody bad idea, IMO.  I have no objections against adding _helpers_ from
> that patch (seq_file_path(), etc.), but I really don't like adding that
> second struct path there.  And it still doesn't fix the issue with
> LSM, etc., so we'll _still_ need to fix it sane way.

Obviously getting rid of the extra path would be good.  But we still have lots
of f_path.dentry in filesystems and we need to start with that.

struct dentry *file_dentry(struct file *) ?  Implemented how?  Rename f_inode to
f_dentry and reimplement file_inode() based on that.

BTW, since nobody is accessing ->f_covering_path directly except the single
f_covering_path() helper, it would be extremely easy to get rid of it later.
That's why I posted this patch, I think it's simple enough to get it into v4.0
which would fix the majority of cases that people complain about.

The thing could even be made dependent on CONFIG_OVERLAY_FS if the addition
actually increases the footprint of struct file (I haven't checked).

Thanks,
Miklos
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