linux-kernel - Re: [POC/RFC PATCH] overlayfs: constant inode numbers

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Message-ID: <CAOQ4uxjT8Vprx9zNXkJ7pv+OvgB7yU8LW=Ge=WiQBd5jmNMGDg@mail.gmail.com>
Date:   Mon, 5 Dec 2016 16:05:24 +0200
From:   Amir Goldstein <amir73il@...il.com>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     "linux-unionfs@...r.kernel.org" <linux-unionfs@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [POC/RFC PATCH] overlayfs: constant inode numbers

On Tue, Nov 29, 2016 at 11:49 PM, Miklos Szeredi <miklos@...redi.hu> wrote:
> On Tue, Nov 29, 2016 at 1:03 PM, Amir Goldstein <amir73il@...il.com> wrote:
>> On Tue, Nov 29, 2016 at 1:34 PM, Amir Goldstein <amir73il@...il.com> wrote:

...
>>> Not sure that I understand what you are suggesting, but I would be happy
>>> to make the needed adjustments to redirect_fh per your request if you clarify
>>> what you mean. From what I understand:
>>>
>>> 1. If redirect_dir=fh (and supported by layers), store lower handle
>>>     on dir copy up in new xattr OVL_XATTR_FH
>>> 2. In ovl_rename(), set OVL_XATTR_REDIRECT regardless of OVL_XATTR_FH
>>> 3. In ovl_lookup_single(), carry both d.redirct and d.redirect_fh to next layer
>>> 4. In ovl_lookup_layer(), lookup by handle first then by path
>>>

Miklos,

FYI, this part of the work is done and pushed to #redirect_fh branch
on my github.
It is tested on same and not same fs and it is used as the base of
current #ovl_snapshot
branch and tested along with it.

>>> not sure what you meant by "... and provide a good way to get the stable ino."
>>> Either I managed to confuse you, or I am missing something?
>
> I meant that we can unify OVL_XATTR_INO  with "redirect/fh"
> functionality and get something good out of it.
>
>> Perhaps you meant for non-dir:
>>
>> 5. If redirect_dir=fh, *propagate* lowest-handle on non-dir copy up
>> 6. In ovl_lookup() of non-dir, decode lowest-handle to set oe->ino
>
> Yes.
>
> OVL_XATTR_FH would be safe to ignore, so this is back and forward
> compatible..  And the cost is probably not prohitive, since copy ups
> should be relatively rare.
>

I am still trying to figure out the best way of "getting something good"
out of this merger, because changing ovl_getattr() to use redirect_fh
instead of stored ino is not such a big win.

More thought are welcome.

Amir.