[marbu]

> What is the overhead on a FUSE filesystem compared to being implemented in the kernel?

The overhead is quite high, because of the additional context switching and copying of data between user and kernel space.

> Could something like eBPF be used to make a faster FUSE-like filesystem driver?

eBPF can't really change any of the problems I noted above. To improve performance one would need to change how the interface between kernel and user space part of FUSE filesystem works to make it more efficient.

That said FUSE support for io_uring, which got merged recently in Linux 6.14, has a potential there, see:

https://www.phoronix.com/news/Linux-6.14-FUSE