Re: [PATCH V3 05/12] io_uring: bpf: extend io_uring with bpf struct_ops

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

On Wed, Mar 25, 2026 at 07:49:22PM -0600, Jens Axboe wrote:
> On 3/24/26 10:37 AM, Ming Lei wrote:
> > @@ -493,7 +494,16 @@ struct io_ring_ctx {
> >  	DECLARE_HASHTABLE(napi_ht, 4);
> >  #endif
> >  
> > -	struct io_uring_bpf_ops		*bpf_ops;
> > +	/*
> > +	 * bpf_ops and bpf_ext_ops are mutually exclusive: bpf_ops is used
> > +	 * for io_uring_bpf_ops struct_ops, while bpf_ext_ops provides
> > +	 * per-opcode BPF extension operations (IORING_SETUP_BPF_EXT).
> > +	 * The two cannot be active at the same time on the same ring.
> > +	 */
> > +	union {
> > +		struct io_uring_bpf_ops		*bpf_ops;
> > +		struct uring_bpf_ops_kern	*bpf_ext_ops;
> > +	};
> 
> What am I missing here, why is this the case? What makes the use of both
> at the same time impossible?

Please see the following code:

static inline bool io_has_loop_ops(struct io_ring_ctx *ctx)
{
        return data_race(ctx->loop_step);
}

io_uring_enter():
	...
	if (io_has_loop_ops(ctx)) {
		ret = io_run_loop(ctx);
		goto out;
	}
	...

So if ->loop_step is assigned from io_install_bpf() called from bpf_ops
registration, traditional userspace SQE submission and CQE reap are
bypassed completely, then IORING_OP_BPF and any other OP can't be handled
at all.

> 
> > diff --git a/io_uring/bpf-ops.c b/io_uring/bpf-ops.c
> > index e4b244337aa9..e91c6964405c 100644
> > --- a/io_uring/bpf-ops.c
> > +++ b/io_uring/bpf-ops.c
> > @@ -162,7 +162,6 @@ static int io_install_bpf(struct io_ring_ctx *ctx, struct io_uring_bpf_ops *ops)
> >  		return -EOPNOTSUPP;
> >  	if (!(ctx->flags & IORING_SETUP_DEFER_TASKRUN))
> >  		return -EOPNOTSUPP;
> > -
> >  	if (ctx->bpf_ops)
> >  		return -EBUSY;
> >  	if (WARN_ON_ONCE(!ops->loop_step))
> 
> Spurious whitespace change.

Will remove it in next version.

> 
> > diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
> > index 91cf67b5d85b..1af33a89ed2f 100644
> > --- a/io_uring/io_uring.h
> > +++ b/io_uring/io_uring.h
> > @@ -49,7 +49,8 @@ struct io_ctx_config {
> >  			IORING_FEAT_RECVSEND_BUNDLE |\
> >  			IORING_FEAT_MIN_TIMEOUT |\
> >  			IORING_FEAT_RW_ATTR |\
> > -			IORING_FEAT_NO_IOWAIT)
> > +			IORING_FEAT_NO_IOWAIT |\
> > +			IORING_FEAT_BPF)
> 
> Do we need this FEAT flag? If you think so, then it should at least be
> dependent on whether the kernel supports this feature, eg if
> CONFIG_IO_URING_BPF_EXT is set

Good catch!



Thanks,
Ming