On 04/20/2017 02:12 AM, Alexei Starovoitov wrote:
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.
bpf_skb_pull_data() helper can be used as an option to pull
in more, though, f.e. up to bpf_skb_pull_data(skb, skb->len)
in the worst case, which then results in a fully linearized
skb where data/data_end has complete access. That much may
not be needed, though, but f.e. cls_bpf can certainly expand
the available headlen for direct packet access.
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.
Afaik, the ld_abs/ld_ind are not an option due to the data
on the wire being in little endian, but the bpf_skb_load_bytes()
might be the way to go initially, agree.
