Re: [PATCH v14 00/12] FUSE passthrough for file io

[Miklos Szeredi <miklos@szeredi.hu>]

On Wed, 29 Nov 2023 at 08:25, Amir Goldstein <amir73il@gmail.com> wrote:

> My proposed solution is to change the semantics with the init flag
> FUSE_PASSTHROUGH to disallow mmap on FOPEN_DIRECT_IO
> files.

Why?  FOPEN_DIRECT_IO and FUSE_PASSTHROUGH should mix much more
readily than FOPEN_DIRECT_IO with page cache.

> So with a filesystem that supports FUSE_PASSTHROUGH,
> FOPEN_DIRECT_IO files can only be used for direct read/write io and
> mmap maps either the fuse inode pages or the backing inode pages.
>
> This also means that FUSE_DIRECT_IO_RELAX conflicts with
> FUSE_PASSTHROUGH.
>
> Should we also deny mixing FUSE_HAS_INODE_DAX with
> FUSE_PASSTHROUGH? Anything else from virtiofs?

Virtiofs/DAX and passthrough are similar features in totally different
environments.   We just need to make sure the code paths don't
collide.

> While I have your attention, I am trying to consolidate the validation
> of FOPEN_ mode vs inode state into fuse_finish_open().
>
> What do you think about this partial patch that also moves
> fuse_finish_open() to after fuse_release_nowrite().
> Is it legit?

I suspect it won't work due to the i_size reset being in
fuse_finish_open().  But I feel there's not enough context to
understand why this is needed.

Thanks,
Miklos