Re: [PATCH] ovl: Allow changing default fsync_mode

[Amir Goldstein]

On Tue, Jun 23, 2026 at 3:47 PM Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx> wrote:
>
> Hi Christoph,
>
> On 2026/6/23 21:42, Christoph Hellwig wrote:
> > I have no idea where this coming from as I can't find an earlier
> > version in the fsdevel archives.  But changing user visible mount
> > options through konfig options is simply bonkers.
> >
> > I'd also like to not that the submitter does have a history of crazy
> > patches including those to support proprietary modules and then
> > attacking people criticizing those patches, so I can only suggest to
> > every maintainer to ignore them for their own sanity.
>
> Sorry about that I didn't Cc the proper list at first,
> but it could be checked by using lore:
> https://lore.kernel.org/linux-unionfs/20260623084337.54344-1-laoar.shao@xxxxxxxxx/T/#u
>
> This topic is very specific to overlayfs details, I'm
> not sure how I could say the background in brief.
>
> But almost every single container user uses overlayfs
> now, so in order to be responsible for end users,
> container runtimes and applications, I used some
> aggressive way this time.

Gao,

Thank you for holding the fort!
and for foreseeing this containerd regression.

I also agree with all your other arguments that "volatile" should never be the
system/module default - it is too risky - one needs to know what they are doing
when using  "volatile".

I will respect your NACK.

Yafang,

I agree with you that your patch appears to follow precedents
in overlayfs, but I also think that "volatile" is not a good candidate for
this practice, mostly because it makes mount cycle fail.

Since it is so much easier for your employer to live patch the kernel
than to upgrade/patch docker, how about applying this live patch to
your kernels?

diff --git a/fs/overlayfs/params.c b/fs/overlayfs/params.c
index c93fcaa45d4a3..2105a51d12439 100644
--- a/fs/overlayfs/params.c
+++ b/fs/overlayfs/params.c
@@ -155,7 +155,7 @@ static const char *ovl_fsync_mode(struct ovl_config *config)

 static int ovl_fsync_mode_def(void)
 {
-       return OVL_FSYNC_AUTO;
+       return OVL_FSYNC_VOLATILE;
 }

Thanks,
Amir.