On Mon Jul 27 2020, Petr Machata wrote: > So this looks good, and works, but I'm wondering about one thing.
Thanks for testing.
>
> Your code (and evidently most drivers as well) use a different check
> than mlxsw, namely skb->len + ETH_HLEN < X. When I print_hex_dump()
> skb_mac_header(skb), skb->len in mlxsw with some test packet, I get e.g.
> this:
>
> 00000000259a4db7: 01 00 5e 00 01 81 00 02 c9 a4 e4 e1 08 00 45 00
> ..^...........E.
> 000000005f29f0eb: 00 48 0d c9 40 00 01 11 c8 59 c0 00 02 01 e0 00
> .H..@....Y......
> 00000000f3663e9e: 01 81 01 3f 01 3f 00 34 9f d3 00 02 00 2c 00 00
> ...?.?.4.....,..
> ^sp^^ ^dp^^ ^len^ ^cks^ ^len^
> 00000000b3914606: 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 02
> ................
> 000000002e7828ea: c9 ff fe a4 e4 e1 00 01 09 fa 00 00 00 00 00 00
> ................
> 000000000b98156e: 00 00 00 00 00 00 ......
>
> Both UDP and PTP length fields indicate that the payload ends exactly at
> the end of the dump. So apparently skb->len contains all the payload
> bytes, including the Ethernet header.
>
> Is that the case for other drivers as well? Maybe mlxsw is just missing
> some SKB magic in the driver.
So I run some tests (on other hardware/drivers) and it seems like that
the skb->len usually doesn't include the ETH_HLEN. Therefore, it is
added to the check.
Looking at the driver code:
|static void mlxsw_sp_rx_sample_listener(struct sk_buff *skb, u8 local_port,
| void *trap_ctx)
|{
| [...]
| /* The sample handler expects skb->data to point to the start of the
| * Ethernet header.
| */
| skb_push(skb, ETH_HLEN);
| mlxsw_sp_sample_receive(mlxsw_sp, skb, local_port);
|}
Maybe that's the issue here?
I was also wondering about something else in that driver driver: The
parsing code allows for ptp v1, but the message type was always fetched
from offset 0 in the header. Is that indented?
Thanks,
Kurt
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