Re: [RFC PATCH 3/3] overlay: Add the ability to remount volatile directories when safe

[Vivek Goyal <vgoyal@redhat.com>]

On Tue, Nov 17, 2020 at 08:03:16PM +0200, Amir Goldstein wrote:
> > > C. "shutdown" the filesystem if writeback errors happened and return
> > >      EIO from any read, like some blockdev filesystems will do in face
> > >      of metadata write errors
> > >
> > > I happen to have a branch ready for that ;-)
> > > https://github.com/amir73il/linux/commits/ovl-shutdown
> >
> >
> > This branch seems to implement shutdown ioctl. So it will still need
> > glue code to detect writeback failure in upper/ and trigger shutdown
> > internally?
> >
> 
> Yes.
> ovl_get_acess() can check both the administrative ofs->goingdown
> command and the upper writeback error condition for volatile ovl
> or something like that.

This approach will not help mmaped() pages though, if I do.

- Store to addr
- msync
- Load from addr

There is a chance that I can still read back old data.

> 
> > And if that works, then Sargun's patches can fit in nicely on top which
> > detect writeback failures on remount and will shutdown fs.
> >
> 
> Not sure why remount needs to shutdown. It needs to fail mount,
> but yeh, all those things should fit nicely together.

Agreed. mount/remount can just fail in that case.

Thanks
Vivek