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

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Message-ID: <CAJfpegtLj44fTAAUvQqBafD51WMHMMq6xxjF819fFftzM8Peog@mail.gmail.com>
Date:	Fri, 20 Mar 2015 19:16:17 +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>,
	David Howells <dhowells@...hat.com>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-unionfs@...r.kernel.org" <linux-unionfs@...r.kernel.org>
Subject: Re: d_path() and overlay fs

On Fri, Mar 20, 2015 at 5:53 PM, Miklos Szeredi <miklos@...redi.hu> wrote:
> 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.

So we'd need the following helpers:

file_path() - d_path() but gets file
seq_file_path() - seq_path() but gets file
f_covering_path() - other uses of ->f_path that don't want the backing
filesystem's dentry
file_dentry() - uses of f_path.dentry that want the backing filesystem's dentry
file_mount() - uses of f_path.mnt

Hopefully that would cover all f_path uses.

I'd really not want to keep f_path with that name, because it would
just breed new f_path.dentry uses in filesystems.  Better no direct
f_path references at all.

Thanks,
Miklos
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