Re: LOOKUP_HANDLE and FUSE passthrough (was: Persistent FUSE file handles)

[Miklos Szeredi <miklos@szeredi.hu>]

On Wed, 19 Feb 2025 at 18:58, Amir Goldstein <amir73il@gmail.com> wrote:

> I circled back to this. I don't suppose you know of any patches
> in the works?

I'm not aware of any.


> I was thinking about LOOKUP_HANDLE in the context of our
> discussion at Plumbers on readdirplus passthrough.
>
> What we discussed is that kernel could instantiate some FUSE inodes
> (populated during readdirplus passthrough) and at some later time,
> kernel will notify server about those inodes via FUSE_INSTANTIATE
> or similar command, which will instantiate a fuse server inode with
> pre-defined nodeid.
>
> My thinking was to simplify a bit and require a 1-to-1 mapping
> of kernel-server inode numbers to enable the feature of
> FUSE_PASSTHOUGH_INODE (operations), meaning that
> every FUSE inode has at least a potential backing inode which
> reserves its inode number.
>
> But I think that 1-to-1 mapping of ino is not enough and to avoid
> races it is better to have 1-to-1 mapping of file handles so
> FUSE_INSTANTIATE would look a bit like LOOKUP_HANDLE
> but "found" server inode must match the kernel's file handle.
>
> Is any of this making any sense to you?

Not yet.  I remember you explaining why FUSE_INSTANTIATE is needed,
but I don't really remember.

Can you please remind me how exactly you envision readdir/lookup passthrough?

Thanks,
Miklos