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From: cgxu <cgxu519@mykernel.net>
To: Amir Goldstein <amir73il@gmail.com>, Miklos Szeredi <miklos@szeredi.hu>
Cc: overlayfs <linux-unionfs@vger.kernel.org>
Subject: Re: [PATCH] ovl: fix incorrect extent info in metacopy case
Date: Thu, 25 Jun 2020 17:46:21 +0800
Message-ID: <9cecb52b-620b-69c1-059f-f782b946da1a@mykernel.net> (raw)
In-Reply-To: <CAOQ4uxh9gzdRJp4g1yjQy9nDMASdsdvkzBGhGL2_+3rOBJZFAw@mail.gmail.com>

On 6/25/20 4:35 PM, Amir Goldstein wrote:
> On Wed, Jun 24, 2020 at 3:53 PM Amir Goldstein <amir73il@gmail.com> wrote:
>> On Wed, Jun 24, 2020 at 1:23 PM Chengguang Xu <cgxu519@mykernel.net> wrote:
>>> In metacopy case, we should use ovl_inode_realdata() instead of
>>> ovl_inode_real() to get real inode which has data, so that
>>> we can get correct information of extentes in ->fiemap operation.
>>>
>>> Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
>> looks right
> Miklos,
>
> Not related to this patch, I noticed something that could be odd with
> ovl_fiemap().
>
> When passed the flag FIEMAP_FLAG_SYNC, ->fiemap() will trigger writeback
> of lower inode pages.
>
> This behavior is border line for overlayfs.
> I did not check if filemap_write_and_wait() ends up being a noop on read-only
> fs or if it can return an error.

vfs ioctl does the same behavior regardless of read-only fs and IIUC,
writeback functions will do DIRTY tag check before actually sync dirty data.

Thanks,
cgxu

> Following ovl_fsync() practice, we may want to silently drop the
> FIEMAP_FLAG_SYNC flag? but that could result in unexpected results.
>
> Am I overthinking this?
>
> Thanks,
> Amir.


      reply index

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-24 10:20 Chengguang Xu
2020-06-24 12:53 ` Amir Goldstein
2020-06-25  8:35   ` Amir Goldstein
2020-06-25  9:46     ` cgxu [this message]

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