Re: [PATCH v13 05/10] fuse: Handle asynchronous read and write in passthrough

[Amir Goldstein <amir73il@gmail.com>]

On Wed, May 24, 2023 at 1:03 PM Amir Goldstein <amir73il@gmail.com> wrote:
>
> On Mon, May 22, 2023 at 6:20 PM Miklos Szeredi <miklos@szeredi.hu> wrote:
> >
> > On Fri, 19 May 2023 at 14:57, Amir Goldstein <amir73il@gmail.com> wrote:
> > >
> > > Extend the passthrough feature by handling asynchronous IO both for read
> > > and write operations.
> > >
> > > When an AIO request is received, if the request targets a FUSE file with
> > > the passthrough functionality enabled, a new identical AIO request is
> > > created.  The new request targets the backing file and gets assigned
> > > a special FUSE passthrough AIO completion callback.
> > >
> > > When the backing file AIO request is completed, the FUSE
> > > passthrough AIO completion callback is executed and propagates the
> > > completion signal to the FUSE AIO request by triggering its completion
> > > callback as well.
> >
> > Overlayfs added refcounting to the async req (commit 9a2544037600
> > ("ovl: fix use after free in struct ovl_aio_req")).  Is that not
> > needed for fuse as well?
> >
> > Would it make sense to try and merge the two implementations?
> >
>
> Makes sense - I will look into it.


Hi Miklos,

Getting back to this.
Did you mean something like that? (only compile tested)

https://github.com/amir73il/linux/commits/backing_fs

If yes, then I wonder:
1. Is the difference between FUSE_IOCB_MASK and OVL_IOCB_MASK
    (i.e. the APPEND flag) intentional?
2. What would be the right way to do ovl_copyattr() on io completion?
    Pass another completion handler to read/write helpers?
    This seems a bit ugly. Do you have a nicer idea?

Thanks,
Amir.