Re: [PATCH 4/5] io_uring: bpf: add buffer support for IORING_OP_BPF

[Ming Lei <ming.lei@redhat.com>]

On Tue, Dec 30, 2025 at 08:42:11PM -0500, Caleb Sander Mateos wrote:
> On Tue, Nov 4, 2025 at 8:22 AM Ming Lei <ming.lei@redhat.com> wrote:
> >
> > Add support for passing 0-2 buffers to BPF operations through
> > IORING_OP_BPF. Buffer types are encoded in sqe->bpf_op_flags
> > using dedicated 3-bit fields for each buffer.
> 
> I agree the 2 buffer limit seems a bit restrictive, and it would make
> more sense to expose kfuncs to import plain and fixed buffers. Then
> the BPF program could decide what buffers to import based on the SQE,
> BPF maps, etc. This would be analogous to how uring_cmd
> implementations import buffers.

Yes, this way is too restrictive.

I think there are at least two approaches:

- define public buffer descriptor, which can describe plain, fixed, vector,
fixed vector buffer, ...

- user can pass this buffer descriptor array from sqe->addr & sqe->len (buf descriptor
  need to be defined in UAPI)

OR

- user can pass this buffer array from arena map (buf descriptor is just
API between bpf prog and userspace)

The former could be better, because `buf descriptor` is part of UAPI, and
user still can choose to use bpf map to pass buffer. But defining 'buf
descriptor' may take a while...

The latter way could be easier to start...

> 
> >
> > Buffer 1 can be:
> > - None (no buffer)
> > - Plain user buffer (addr=sqe->addr, len=sqe->len)
> > - Fixed/registered buffer (index=sqe->buf_index, offset=sqe->addr,
> 
> Should this say "addr=" instead of "offset="? It's passed as buf_addr
> to io_bpf_import_buffer(), so it's an absolute userspace address. The
> offset into the fixed buffer depends on the starting address of the
> fixed buffer.

For user fixed buffer, offset is the buff addr.

For kernel fixed buffer, it is offset.


Thanks, 
Ming