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

[Pavel Begunkov <asml.silence@gmail.com>]

On 11/24/25 03:44, Ming Lei wrote:
> On Thu, Nov 13, 2025 at 11:59:44AM +0000, Pavel Begunkov wrote:
>> Add ring_fd to the struct_ops and implement [un]registration.
...
>> +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.

I gave it a thought before, there would need to be a way to pass a
program from one (e.g. privileged) task to another, e.g. by putting
it into a list on attachment from where it can be imported. That
can be extended, and I needed to start somewhere.

Furthermore, it might even be nice to have a library of common
programs, but it's early for that.

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

Links are there to compare with existing features. It's more interesting
to allow arbitrary relations / result propagation between requests. Maybe
some common patterns can be generalised, but otherwise nothing can be
done with this without custom tailored bpf programs.

-- 
Pavel Begunkov