On Thu, Apr 20, 2017 at 02:01:49AM +0200, Daniel Borkmann wrote:
> On 04/20/2017 12:20 AM, Johannes Berg wrote:
> >On Wed, 2017-04-19 at 23:31 +0200, Johannes Berg wrote:
> >>Hi Alexei, Daniel,
> >>
> >>I'm looking at adding the __wifi_sk_buff I talked about, and I notice
> >>that it uses CB space to store data_end. Unfortunately, in a lot of
> >>cases, we don't have any CB space to spare in wifi.
> >
> >I guess I can work around this, would this seem reasonable?
> >
> > struct bpf_skb_data_end {
> > struct qdisc_skb_cb qdisc_cb;
> >- void *data_end;
> >+ /*
> >+ * The alignment here is for mac80211, since that doesn't use
> >+ * a pointer but a u64 value and needs to save/restore that
> >+ * across running its BPF programs.
> >+ */
> >+ void *data_end __aligned(sizeof(u64));
> > };
>
> Yeah, should work as well for the 32 bit archs, on 64 bit we
> have this effectively already:
>
> struct bpf_skb_data_end {
> struct qdisc_skb_cb qdisc_cb; /* 0 28 */
>
> /* XXX 4 bytes hole, try to pack */
>
> void * data_end; /* 32 8 */
>
> /* size: 40, cachelines: 1, members: 2 */
> /* sum members: 36, holes: 1, sum holes: 4 */
> /* last cacheline: 40 bytes */
> };
>
> Can you elaborate on why this works for mac80211? It uses cb
> only up to that point from where you invoke the prog?
+1
also didn't we discuss that wifi has crazy non-linear skb?
this data/data_end is used by cls_bpf with headlen only
for direct packet access where performance matters.
Since wifi skbs have only eth in headlen, there is not much
pointing adding support for data/data_end to wifi.
Just use ld_abs/ld_ind instructions and load_bytes() helper.
