Re: [PATCH v3 07/10] io_uring/bpf: implement struct_ops registration

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

On Thu, Nov 13, 2025 at 11:59:44AM +0000, Pavel Begunkov wrote:
> Add ring_fd to the struct_ops and implement [un]registration.
> 
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>  include/linux/io_uring_types.h |  2 +
>  io_uring/bpf.c                 | 69 +++++++++++++++++++++++++++++++++-
>  2 files changed, 70 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
> index 43432a06d177..3a71ed2d05ea 100644
> --- a/include/linux/io_uring_types.h
> +++ b/include/linux/io_uring_types.h
> @@ -274,6 +274,8 @@ struct io_ring_ctx {
>  		unsigned int		compat: 1;
>  		unsigned int		iowq_limits_set : 1;
>  
> +		unsigned int		bpf_installed: 1;
> +
>  		struct task_struct	*submitter_task;
>  		struct io_rings		*rings;
>  		struct percpu_ref	refs;
> diff --git a/io_uring/bpf.c b/io_uring/bpf.c
> index 24dd2fe9134f..683e87f1a58b 100644
> --- a/io_uring/bpf.c
> +++ b/io_uring/bpf.c
> @@ -4,6 +4,7 @@
>  #include "bpf.h"
>  #include "register.h"
>  
> +static DEFINE_MUTEX(io_bpf_ctrl_mutex);
>  static const struct btf_type *loop_state_type;
>  
>  static int io_bpf_ops__loop(struct io_ring_ctx *ctx, struct iou_loop_state *ls)
> @@ -87,20 +88,86 @@ static int bpf_io_init_member(const struct btf_type *t,
>  			       const struct btf_member *member,
>  			       void *kdata, const void *udata)
>  {
> +	u32 moff = __btf_member_bit_offset(t, member) / 8;
> +	const struct io_uring_ops *uops = udata;
> +	struct io_uring_ops *ops = kdata;
> +
> +	switch (moff) {
> +	case offsetof(struct io_uring_ops, ring_fd):
> +		ops->ring_fd = uops->ring_fd;
> +		return 1;
> +	}
> +	return 0;
> +}
> +
> +static int io_install_bpf(struct io_ring_ctx *ctx, struct io_uring_ops *ops)
> +{
> +	if (ctx->bpf_ops)
> +		return -EBUSY;
> +	ops->priv = ctx;
> +	ctx->bpf_ops = ops;
> +	ctx->bpf_installed = 1;
>  	return 0;
>  }
>  
>  static int bpf_io_reg(void *kdata, struct bpf_link *link)
>  {
> -	return -EOPNOTSUPP;
> +	struct io_uring_ops *ops = kdata;
> +	struct io_ring_ctx *ctx;
> +	struct file *file;
> +	int ret = -EBUSY;
> +
> +	file = io_uring_register_get_file(ops->ring_fd, false);
> +	if (IS_ERR(file))
> +		return PTR_ERR(file);
> +	ctx = file->private_data;
> +
> +	scoped_guard(mutex, &io_bpf_ctrl_mutex) {
> +		guard(mutex)(&ctx->uring_lock);
> +		ret = io_install_bpf(ctx, ops);
> +	}

I feel per-io-uring struct_ops is less useful, because it means the io_uring
application has to be capable of loading/registering struct_ops prog, which
often needs privilege.

For example of IO link use case you mentioned, why does the application need
to get privilege for running IO link?


Thanks
Ming