Re: [PATCH bpf-next v2 00/28] Introduce eBPF support for HID devices

On Mon, Mar 7, 2022 at 7:12 PM Song Liu [off-list ref] wrote:

On Sat, Mar 5, 2022 at 2:23 AM Benjamin Tissoires
[off-list ref] wrote:

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The set looks good so far. I will review the rest later.

[...]

A quick note about how we organize these patches. Maybe we can
merge some of these patches like:

Just to be sure we are talking about the same thing: you mean squash
the patch together?

Right, squash some patches together.

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  bpf: introduce hid program type
  bpf/hid: add a new attach type to change the report descriptor
  bpf/hid: add new BPF type to trigger commands from userspace

I guess the three can merge into one.

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  HID: hook up with bpf
  HID: allow to change the report descriptor from an eBPF program
  HID: bpf: compute only the required buffer size for the device
  HID: bpf: only call hid_bpf_raw_event() if a ctx is available

I haven't read through all of them, but I guess they can probably merge
as well.

There are certainly patches that we could squash together (3 and 4
from this list into the previous ones), but I'd like to keep some sort
of granularity here to not have a patch bomb that gets harder to come
back later.

Totally agreed with the granularity of patches. I am not a big fan of patch
bombs either. :)

I guess the problem I have with the current version is that I don't have a
big picture of the design while reading through relatively big patches. A
overview with the following information in the cover letter would be really
help here:
  1. How different types of programs are triggered (IRQ, user input, etc.);
  2. What are the operations and/or outcomes of these programs;
  3. How would programs of different types (or attach types) interact
   with each other (via bpf maps? chaining?)
  4. What's the new uapi;
  5. New helpers and other logistics

Sometimes, I find the changes to uapi are the key for me to understand the
patches, and I would like to see one or two patches with all the UAPI
changes (i.e. bpf_hid_attach_type). However, that may or may not apply to
this set due to granularity concerns.

Does this make sense?

It definitely does. And as I read that, I realized that if I manage to
get such a clear depiction of what HID-BPF is, it would certainly be a
good idea to paste that in a file into the Documentation directory as
well :)

I think you have a slightly better picture now with the exchanges we
are having on the individual patches, but I'll try to come out with
that description in the cover letter for v3.

Cheers,
Benjamin