On Wed, Dec 20, 2023 at 1:43 AM Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:
> Then for *this* driver I need to check for the ethertype
> ETH_P_8021Q what is inside it, one level down, and that is a
> separate helper. And I named it skb_vlan_raw_inner_ethertype()
> It will retrieve the inner type no matter
>
> include/linux/if_vlan.h
>
> +/* This determines the inner ethertype incoded into the skb data without
> + * relying on skb->protocol which is not always identical.
> + */
> +static inline u16 skb_vlan_raw_inner_ethertype(const struct sk_buff *skb)
> +{
> + struct vlan_ethhdr *vhdr;
> +
> + if (!skb_pointer_if_linear(skb, 0, VLAN_ETH_HLEN))
> + return 0x0000U;
> +
> + vhdr = vlan_eth_hdr(skb);
> + return ntohs(vhdr->h_vlan_encapsulated_proto);
> +}
>
> (We can bikeshed the name of the function. *_inner_protocol maybe.)
>
> It does not handle nested VLANs and I don't see why it should since
> the immediate siblings in if_vlan.h does not, i.e.
> vlan_eth_hdr(), skb_vlan_eth_hdr(). It's pretty clear these helpers
> all go just one level down. (We can add a *_descend_*()
> helper the day someone needs that.)
Forget this whole discussion because in <linux/if_vlan.h>
there is already vlan_get_protocol() and vlan_get_protocol_and_depth()
so this problem is already solved, just better.
Yours,
Linus Walleij
