Re: [PATCH v3 1/2] media: rc: introduce BPF_PROG_RAWIR_EVENT

[Sean Young <sean@mess.org>]

Hi Quentin,

On Thu, May 17, 2018 at 01:10:56PM +0100, Quentin Monnet wrote:
> 2018-05-16 22:04 UTC+0100 ~ Sean Young <sean@mess.org>
> > Add support for BPF_PROG_RAWIR_EVENT. This type of BPF program can call
> > rc_keydown() to reported decoded IR scancodes, or rc_repeat() to report
> > that the last key should be repeated.
> > 
> > The bpf program can be attached to using the bpf(BPF_PROG_ATTACH) syscall;
> > the target_fd must be the /dev/lircN device.
> > 
> > Signed-off-by: Sean Young <sean@mess.org>
> > ---
> >  drivers/media/rc/Kconfig           |  13 ++
> >  drivers/media/rc/Makefile          |   1 +
> >  drivers/media/rc/bpf-rawir-event.c | 363 +++++++++++++++++++++++++++++
> >  drivers/media/rc/lirc_dev.c        |  24 ++
> >  drivers/media/rc/rc-core-priv.h    |  24 ++
> >  drivers/media/rc/rc-ir-raw.c       |  14 +-
> >  include/linux/bpf_rcdev.h          |  30 +++
> >  include/linux/bpf_types.h          |   3 +
> >  include/uapi/linux/bpf.h           |  55 ++++-
> >  kernel/bpf/syscall.c               |   7 +
> >  10 files changed, 531 insertions(+), 3 deletions(-)
> >  create mode 100644 drivers/media/rc/bpf-rawir-event.c
> >  create mode 100644 include/linux/bpf_rcdev.h
> > 
> 
> [...]
> 
> Hi Sean,
> 
> Please find below some nitpicks on the documentation for the two helpers.

I agree with all your points. I will reword and fix this for v4.

Thanks,

Sean
> 
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index d94d333a8225..243e141e8a5b 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> 
> [...]
> 
> > @@ -1902,6 +1904,35 @@ union bpf_attr {
> >   *		egress otherwise). This is the only flag supported for now.
> >   *	Return
> >   *		**SK_PASS** on success, or **SK_DROP** on error.
> > + *
> > + * int bpf_rc_keydown(void *ctx, u32 protocol, u32 scancode, u32 toggle)
> > + *	Description
> > + *		Report decoded scancode with toggle value. For use in
> > + *		BPF_PROG_TYPE_RAWIR_EVENT, to report a successfully
> 
> Could you please use bold RST markup for constants and function names?
> Typically for BPF_PROG_TYPE_RAWIR_EVENT here and the enum below.
> 
> > + *		decoded scancode. This is will generate a keydown event,
> 
> s/This is will/This will/?
> 
> > + *		and a keyup event once the scancode is no longer repeated.
> > + *
> > + *		*ctx* pointer to bpf_rawir_event, *protocol* is decoded
> > + *		protocol (see RC_PROTO_* enum).
> 
> This documentation is intended to be compiled as a man page. Could you
> please use a complete sentence here?
> Also, this could do with additional markup as well: **struct
> bpf_rawir_event**.
> 
> > + *
> > + *		Some protocols include a toggle bit, in case the button
> > + *		was released and pressed again between consecutive scancodes,
> > + *		copy this bit into *toggle* if it exists, else set to 0.
> > + *
> > + *     Return
> 
> The "Return" lines here and in the second helper use space indent
> instead as tabs (as all other lines do). Would you mind fixing it for
> consistency?
> 
> > + *		Always return 0 (for now)
> 
> Other helpers use just "0" in that case, but I do not really mind.
> Out of curiosity, do you have anything specific in mind for changing the
> return value here in the future?

I don't expect this is to change, so I should just "0".

> 
> > + *
> > + * int bpf_rc_repeat(void *ctx)
> > + *	Description
> > + *		Repeat the last decoded scancode; some IR protocols like
> > + *		NEC have a special IR message for repeat last button,
> 
> s/repeat/repeating/?
> 
> > + *		in case user is holding a button down; the scancode is
> > + *		not repeated.
> > + *
> > + *		*ctx* pointer to bpf_rawir_event.
> 
> Please use a complete sentence here as well, if you do not mind.
> 
> > + *
> > + *     Return
> > + *		Always return 0 (for now)
> >   */
> Thanks,
> Quentin