答复: [PATCH V2] ovl: fsync after metadata copy-up via mount option "fsync=strict"

["Lv Fei（吕飞）" <feilv@asrmicro.com>]

> 发件人: Amir Goldstein [mailto:amir73il@gmail.com] 
> 发送时间: 2024年8月23日 19:43
> 收件人: Lv Fei（吕飞） <feilv@asrmicro.com>
> 抄送: miklos@szeredi.hu; linux-unionfs@vger.kernel.org; linux-kernel@vger.kernel.org; Xu Lianghu（徐良虎） <lianghuxu@asrmicro.> com>
> 主题: Re: [PATCH V2] ovl: fsync after metadata copy-up via mount option "fsync=strict"
> 
> On Fri, Aug 23, 2024 at 11:51 AM Amir Goldstein <amir73il@gmail.com> wrote:
> >
> > On Mon, Jul 22, 2024 at 3:56 PM Amir Goldstein <amir73il@gmail.com> wrote:
> > >
> > > On Mon, Jul 22, 2024 at 1:14 PM Fei Lv <feilv@asrmicro.com> wrote:
> > > >
> > > > For upper filesystem which does not enforce ordering on storing of 
> > > > metadata changes(e.g. ubifs), when overlayfs file is modified for 
> > > > the first time, copy up will create a copy of the lower file and 
> > > > its parent directories in the upper layer. Permission lost of the 
> > > > new upper parent directory was observed during power-cut stress test.
> > > >
> > > > Fix by adding new mount opion "fsync=strict", make sure 

There is a typo here, "opion" should be "option", please help correct before merge.

> > > > data/metadata of copied up directory written to disk before 
> > > > renaming from tmp to final destination.
> > > >
> > > > Signed-off-by: Fei Lv <feilv@asrmicro.com>
> > >
> > > Reviewed-by: Amir Goldstein <amir73il@gmail.com>
> > >
> > > but I'd also like to wait for an ACK from Miklos on this feature.
> > >
> > > As for timing, we are in the middle of the merge window for 
> > > 6.11-rc1, so we have some time before this can be considered for 6.12.
> > > I will be on vacation for most of this development cycle, so either 
> > > Miklos will be able to queue it for 6.12 or I may be able to do near 
> > > the end of the 6.11 cycle.
> > >
> >
> > Miklos,
> >
> > Please let me know what you think of this approach to handle ubifs upper.
> > If you like it, I can queue this up for v6.12.
> >
> > Thanks,
> > Amir.
> >
> > >
> > > > ---
> > > > V1 -> V2:
> > > >  1. change open flags from "O_LARGEFILE | O_WRONLY" to "O_RDONLY".
> > > >  2. change mount option to "fsync=ordered/strict/volatile".
> > > >  3. ovl_should_sync_strict() implies ovl_should_sync().
> > > >  4. remove redundant ovl_should_sync_strict from ovl_copy_up_meta_inode_data.
> > > >  5. update commit log.
> > > >  6. update documentation overlayfs.rst.
> > > >
> 
> Hi Fei,
> 
> I started to test this patch and it occured to me that we have no test coverage for the "volatile" feature.
> 
> Filesystem durability tests are not easy to write and I know that you tested your own use case, so I will not ask you to write a regression test as a condition for merge, but if you are willing to help, it would be very nice to add this test coverage.

OK, I can have a try, need some time to study test suite. This is a new thing for me.

> 
> There is already one overlayfs test in fstests (overlay/078) which tests behavior of overlayfs copy up during power cut (a.k.a shutdown).

Do you mean overlay/078 in kernel/git/brauner/xfstests-dev.git ?

> 
> One thing that I do request is that you confirm that you tested that the legacy "volatile" mount option still works as before.

Yes, I tested basic function of "volatile" mount option with this patch.

> I saw that you took care of preserving the legacy mount option in display, which is good practice.
> 
> Thanks,
> Amir.

Thanks,
Fei