Re: [PATCH io_uring-7.1 v6 0/5] BPF controlled io_uring

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

On 2/11/26 19:04, Pavel Begunkov wrote:
> This series introduces a way to override the standard io_uring_enter
> syscall execution with an extendible event loop, which can be controlled
> by BPF via new io_uring struct_ops or from within the kernel.

Let me know if there are any concerns or comments. There are some
parts that I'll need to add like timeouts for waiting, but those
will be natural extensions, and this feels like a good base to
move forward in general.

> There are multiple use cases I want to cover with this:
> 
> - Syscall avoidance. Instead of returning to the userspace for
>    CQE processing, a part of the logic can be moved into BPF to
>    avoid excessive number of syscalls.
> 
> - Access to in-kernel io_uring resources. For example, there are
>    registered buffers that can't be directly accessed by the userspace,
>    however we can give BPF the ability to peek at them. It can be used
>    to take a look at in-buffer app level headers to decide what to do
>    with data next and issuing IO using it.
> 
> - Smarter request ordering and linking. Request links are pretty
>    limited and inflexible as they can't pass information from one
>    request to another. With BPF we can peek at CQEs and memory and
>    compile a subsequent request.
> 
> - Feature semi-deprecation. It can be used to simplify handling
>    of deprecated features by moving it into the callback out core
>    io_uring. For example, it should be trivial to simulate
>    IOSQE_IO_DRAIN. Another target could be request linking logic.
> 
> - It can serve as a base for custom algorithms and fine tuning.
>    Often, it'd be impractical to introduce a generic feature because
>    it's either niche or requires a lot of configuration. For example,
>    there is support min-wait, however BPF can help to further fine tune
>    it by doing it in multiple steps with different number of CQEs /
>    timeouts. Another feature people were asking about is allowing
>    to over queue SQEs but make the kernel to maintain a given QD.
> 
> - Smarter polling. Napi polling is performed only once per syscall
>    and then it switches to waiting. We can do smarter and intermix
>    polling with waiting using the hook.
-- 
Pavel Begunkov