RE: [EXT] [PATCH] mwifiex: set needed_headroom, not hard_header_len

[Ganapathi Bhat]

Hi Brian,
 
> hard_header_len provides limitations for things like AF_PACKET, such that
> we don't allow transmitting packets smaller than this.


OK; However, are we not supposed to mention hard_header_len also?

> 
> needed_headroom provides a suggested minimum headroom for SKBs, so
> that we can trivally add our headers to the front.
> 
> The latter is the correct field to use in this case, while the former mostly just
> prevents sending small AF_PACKET frames.
> 
> In any case, mwifiex already does its own bounce buffering [1] if we don't
> have enough headroom, so hints (not hard limits) are all that are needed.
> 
> This is the essentially the same bug (and fix) that brcmfmac had, fixed in
> commit cb39288fd6bb ("brcmfmac: use ndev->needed_headroom to reserve
> additional header space").

OK; I read this commit:

"... According to definition of LL_RESERVED_SPACE() and hard_header_len, we should use hard_header_len to reserve for L2 header, like ethernet header(ETH_HLEN) in our case and use needed_headroom for the additional headroom needed by hardware..."

So, does it mean, hard_header_len is already considered by upper layer?


Regards,
Ganapathi