Re: patch idea for wfx

[Stefano Brivio <sbrivio@redhat.com>]

On Thu, 31 Mar 2022 17:47:33 -0400
Jaehee Park <jhpark1013@gmail.com> wrote:

> [...]
>
> Ok so my understanding is: vif is an instance of the struct
> ieee80211_vif which is from the /net/mac80211.h in the linux kernel
> code and so the compiler knows the offset of drv_priv because it's
> defined within this generic struct.

Correct! Well, it's not an instance, it's just a reference to an
instance -- note that it's a pointer. Usually by "instance" one refers
to something more concrete (such as the storage for a given struct).

	struct ieee80211_vif vif <- instance!

	struct ieee80211_vif *vif -> hmm, you could call it an
				     instance, but might cause confusion

> This makes is so much clearer in my head; Thank you so much!! I
> didn't know about pahole. Such a neat tool!

You're welcome, I'm glad it's clear now!

> [...]
>
> Thank you Stefano for explanining contain_of() so clearly! To
> implement it, I think I need to implement work_struct from
> linux/workqueue.h because I see it's being used in container_of()
> defined in functions: wfx_cooling_timeout_work, wfx_beacon_loss_work,
> wfx_update_tim_work.

Hah, no, forget about that! It's just the very same construct but it
has little to do with what you want to change.

Take wfx_update_tim_work(): struct wfx_vif here is like struct
ieee80211_vif because it carries a struct work_struct, here, which is
like your struct wfx_wif:

	struct wfx_vif *wvif = container_of(work, struct wfx_vif, update_tim_work);

meaning:

- struct wfx_vif contains a struct work_struct, and you have a pointer
  to the inner struct ("work")

- "update_tim_work" is the name of the instance of struct work_struct
  inside struct wfx_vif

- from "work", take a pointer to the struct wfx_vif which contains it

> I'm not totally sure of my questions / what to ask here - maybe how
> does the kernel know that there is work and what work to queue?

http://www.makelinux.net/ldd3/chp-7-sect-6.shtml

...but it's unrelated with the issue at hand. :)

-- 
Stefano