[Virtio-fs] [fuse-devel] 'FORGET' ordering semantics (vs unlink & NFS)

[Amir Goldstein]

> > Miklos,
> >
> > I would like to point out that this discussion is relevant to any low level
> > fuse filesystem, but especially those that are proxying a real filesystem.
> >
> > I have raised this question before in the FUSE_PASSTHROUGH threads.
> > There is a lot of code duplication among various low-level fuse projects and
> > as we get to NFS export support and complex issues like this one, is it
> > getting unlikely that all projects will handle this correctly.
> >
> > Do you think there is room for some more generic code in libfuse and if
> > so how? Following an example implementation (assuming it gets fixed)
> > and hand picking fixes to projects cannot scale for long.
> >
> > The challenge is that most of the generic code would be in lookup and
> > maintaining the internal inode cache, but each filesystem may need
> > different representations of the Inode object.
> >
> > I was thinking of something along the lines of an OO library that
> > implements the generic lookup/inode cache for a base FuseInode class
> > that implementers can inherit from.
> >
> > This doesn't need to be in the libfuse project at all.
> > Seeing the virtiofsd already has a Rust implementation that is BSD
> > licensed, maybe that can be used as a starting point?
> >
> > David,
> >
> > How hard do you think it would be to re-factor virtiofsd-rs to
> > an implementation that inherits from a base passthroughfsd-rs?
> >
> > BTW, is virtiofsd-rs the offical virtiofsd or an experimental one?
> > Which tree does Miklos' patch apply to?
> >
> > Anyone has other thoughts about how to reduce fragmentation in
> > implementations?
>
> There's an fuse-backend-rs[1] project hosted on cloud-hypervisor, it is
> a library to communicate with the Linux FUSE clients, which includes:
>
> - ABI layer, which defines all data structures shared between linux Fuse
>   framework and Fuse daemons.
> - API layer, defines the interfaces for Fuse daemons to implement a
>   userspace file system.
> - Transport layer, which supports both the Linux Fuse device and
>   virtio-fs protocol.
> - VFS/pseudo_fs, an abstraction layer to support multiple file systems
>   by a single virtio-fs device.
> - A sample passthrough file system implementation, which passes through
>   files from daemons to clients.
>
> I'm wondering if fuse-backend-rs is a proper project to work on, and
> maybe virtiofsd-rs could be switched to use it as well in the future.
>
> Thanks,
> Eryu
>
> [1] https://github.com/cloud-hypervisor/fuse-backend-rs


Hi Eryu!

This looks very interesting.
Can you guys say a few words about the maturity of this project.
Does it have any CI? any beta/production workloads that use it?
I would be happy to contribute the open_by_handle_at() changes
if I know they will get properly tested.

As demonstrated in this demo fs [1], with xfs/ext4 as underlying filesystem,
full NFS support can be implemented by implementing lookup in filesystem
by inode only, before fuse adds support to LOOKUP_HANDLE in the protocol.

Thanks,
Amir.

[1] https://github.com/amir73il/libfuse/commits/cachegwfs