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Date: Thu, 10 May 2018 09:17:53 -0400
From: Vivek Goyal <vgoyal@redhat.com>
Subject: Re: [PATCH v15 10/30] ovl: Modify ovl_lookup() and friends to lookup
 metacopy dentry
Message-ID: <20180510131753.GB2728@redhat.com>
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In-Reply-To: <CAJfpegtizFNe3tm7reYMYGBsmD-dzZTHNsSGrb5BZ_gaeu2Sfw@mail.gmail.com>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: overlayfs <linux-unionfs@vger.kernel.org>, Amir Goldstein <amir73il@gmail.com>
List-ID: <linux-unionfs@vger.kernel.org>

On Thu, May 10, 2018 at 11:36:16AM +0200, Miklos Szeredi wrote:
> On Thu, May 10, 2018 at 11:19 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
> > On Mon, May 7, 2018 at 7:40 PM, Vivek Goyal <vgoyal@redhat.com> wrote:
> >>
> >> +               if (d.metacopy)
> >> +                       metacopy = true;
> >> +               /*
> >> +                * Do not store intermediate metacopy dentries in chain,
> >> +                * except top most lower metacopy dentry
> >
> > I don't get it.  We need the bottom most metacopy dentry, not the
> > topmost.  Am I missing something?
> 
> Okay, it's more complicated.
> 
> 1) there is an upper metacopy dentry:
> 
>  - store origin (pointed to by ORIGIN or topmost lower dentry) in stack[0]
>  - store data dentry (lowest in metacopy chain) in stack[1], unless
> it's the same as origin
> 
> 2) there is no upper dentry, but a lower metacopy dentry
> 
>  - store metacopy dentry in stack[0]
>  - store data dentry in stack[1]
> 
> Does that make more sense?

Right. That's what I am doing. lower layers can be a metacopy chain
itself (with data dentry at the end). So lowerstack[0] stores topmost
metacopy dentry and lowerstack[1] stores bottom most data dentry.

If upper metacopy dentry is present, then lowerstack[0] will be ORIGIN
too (in the case of non-copied layers). Now I will relax the check and
will have to keep some state to figure out of lowerstack[0] is verified
ORIGIN or not.

> 
> > We also need to check file type here, only regular file makes sense as
> > metacopy, so if it's something else, then get out with EIO.
> 
> I meant file type of *data* inode.  Type of metacopy inode is already
> checked by ovl_check_metacopy_xattr().

Ok.

Thanks
Vivek