Re: [PATCH] mac80211: Populate radiotap header with MCS info for tx'ed frames

[Johannes Berg <johannes@sipsolutions.net>]

On Tue, 2011-10-11 at 13:48 +0200, Helmut Schaa wrote:
> On Tue, Oct 11, 2011 at 1:35 PM, Johannes Berg
> <johannes@sipsolutions.net> wrote:
> > So using something like
> > this would allow us to save some space as well:
> >
> > struct ieee80211_tx_status_rtap_hdr {
> >        struct ieee80211_radiotap_header hdr;
> >        union {
> >                struct {
> >                        u8 rate;
> >                        u8 padding_for_rate;
> >                        __le16 tx_flags;
> >                        u8 data_retries;
> >                } non_mcs;
> >                struct {
> >                        __le16 tx_flags;
> >                        u8 data_retries;
> >                        u8 mcs_known, mcs_flags, mcs;
> >                } mcs;
> >        }
> > } __packed;
> 
> I thought about the same but this means we have to fill in
> different fields (non_mcs.tx_flags vs mcs.tx_flags) for the MCS
> vs legacy path and set the radiotap header len differently in
> both cases.

Good point.

> Or should we just get rid of the whole struct and fill in the
> rtap header dynamically like it is done in the rx path and
> drop the build-bug-on thing?

I wouldn't mind that either, but we'll want to have a WARN_ON_ONCE()
somewhere if we run out of space.

johannes