I found that sock_alloc_send_skb() allocates a skb data area which is
aligned on a word boundary (in alloc_skb()).
So given a datagram and its outgoing device (thereby hard_header_len),
the maximum wasted space in the skb data should be 15 bytes, right?
But I am seeing more "unused" space in my skb. My skb data area has the
end : fb336620
Therefore, there is 46 bytes of headroom and 22 bytes of tailroom. Could
anybody point out why this would be caused?
1. Kernel 2.2.18
2. Implementing a virtual device which attaches a 16 byte header between
IP and Ethernet header. Hence, vdev MTU is 1500 - 16 = 1484.
3. vdev then sends the packets over the physical ethernet interface.
4. vdev hard_header_len is set to ETH_HLEN + 16 = 30 bytes
5. In the example above, skb->data points to the virtual header.
-- I'm an angel!!! Honest! The horns are just there to hold the halo up straight. ^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^ Amit Kucheria EECS Grad. Research Assistant University of Kansas @ Lawrence (R): +1-785-830-8521 ||| (C): +1-785-760-2871 ____________________________________________________
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This archive was generated by hypermail 2b29 : Tue Jul 23 2002 - 22:00:01 EST