netdev - Re: [PATCH net-next v2 4/4] net: hdlc_fr: Add support for any Ethertype

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Date:   Thu, 29 Oct 2020 16:53:02 -0700
From:   Xie He <xie.he.0141@...il.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Krzysztof Halasa <khc@...waw.pl>
Subject: Re: [PATCH net-next v2 4/4] net: hdlc_fr: Add support for any Ethertype

On Thu, Oct 29, 2020 at 10:24 AM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> > Also add skb_reset_mac_header before we pass an skb (received on normal
> > PVC devices) to upper layers. Because we don't use header_ops for normal
> > PVC devices, we should hide the header from upper layer code in this case.
>
> This should probably be a separate commit

OK. I'll make it a separate commit in the next version of the series. Thanks!

> Does it make sense to define a struct snap_hdr instead of manually
> casting all these bytes?

> And macros or constant integers to self document these kinds of fields.

Yes, we can define a struct snap_hdr, like this:

struct snap_hdr {
        u8 oui[3];
        __be16 pid;
} __packed;

And then the fr_snap_parse function could be like this:

static int fr_snap_parse(struct sk_buff *skb, struct pvc_device *pvc)
{
       struct snap_hdr *hdr = (struct snap_hdr *)skb->data;

       if (hdr->oui[0] == OUI_ETHERTYPE_1 &&
           hdr->oui[1] == OUI_ETHERTYPE_2 &&
           hdr->oui[2] == OUI_ETHERTYPE_3) {
               if (!pvc->main)
                       return -1;
               skb->dev = pvc->main;
               skb->protocol = hdr->pid; /* Ethertype */
               skb_pull(skb, 5);
               skb_reset_mac_header(skb);
               return 0;

       } else if (hdr->oui[0] == OUI_802_1_1 &&
                  hdr->oui[1] == OUI_802_1_2 &&
                  hdr->oui[2] == OUI_802_1_3) {
               if (hdr->pid == htons(PID_ETHER_WO_FCS)) {

Would this look cleaner?