NETdev driver question xxxx_type_trans()

[Russell McGuire]

All,

A general and specific question on the behavior of netdev devices before
received sk_buff(s) get passed up to the kernel.

I am almost done creating / testing an HDLC device driver for the 83xx.

I have it working at a low level and was printing out skb_bufs before and
after TX and RX, to ensure data integrity.

Due to me having the print_skbbuf, AFTER the hdlc_type_trans(skb, ndev).
I thought I was continuously losing 14 bytes of data, after a little digging
I realized that the hdlc_type_trans() call
was shifting the skb->data pointer forward by 14 bytes. ????????

Is this corresponding to a 14 byte pad that the kernel stack adds before it
sends it down?
And why isn't the data length being shortened as a result after I call
hdlc_type_trans?

Anyway. I guess I am confused as to what this function was intended for, I
see there are other calls for eth_type_trans, so I imagine their usage is
similar. 

When are they needed?

-Russ

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