Re: [PATCH v2 13/14] fuse: add zero-copy over io-uring

[Jeff Layton <jlayton@kernel.org>]

On Thu, 2026-04-02 at 09:28 -0700, Joanne Koong wrote:
> Implement zero-copy data transfer for fuse over io-uring, eliminating
> memory copies between userspace, the kernel, and the fuse server for
> page-backed read/write operations.
> 
> When the FUSE_URING_ZERO_COPY flag is set alongside FUSE_URING_BUFRING,
> the kernel registers the client's underlying pages as a sparse buffer at
> the entry's fixed id via io_buffer_register_bvec(). The fuse server can
> then perform io_uring read/write operations directly on these pages.
> Non-page-backed args (eg out headers) go through the payload buffer as
> normal.
> 
> This requires CAP_SYS_ADMIN and buffer rings with pinned headers and
> buffers. Gating on pinned headers and buffers keeps the configuration
> space small and avoids partially-optimized modes that are unlikely to be
> useful in practice. Pages are unregistered when the request completes.
> 

Can you elaborate a bit more on why CAP_SYS_ADMIN is needed here? It's
not immediately obvious to me.

-- 
Jeff Layton <jlayton@kernel.org>