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

Hi Ganapathi,

On Wed, Mar 4, 2020 at 8:00 PM Ganapathi Bhat [off-list ref] wrote:

quoted

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?

No, my understanding is that we do not need to bother with
hard_header_len ourselves -- ether_setup() establishes the appropriate
L2 header parameters. I think that's covered a little better below.

quoted

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..."

Yeah, that's probably a little more verbose and accurate description,
which is partly why I referred to that commit :)

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

Right, it's set by ether_setup().

Brian