Man page 9 : skb_partial_csum_set

skb_partial_csum_set - set up and verify partial csum values for packet

bool skb_partial_csum_set(struct sk_buff *  skb , u16  start , u16  off );

skb
    the skb to set

start
    the number of bytes after skb->data to start checksumming.

off
    the offset from start to place the checksum.

For untrusted partially-checksummed packets, we need to make sure the values for skb->csum_start and skb->csum_offset are valid so we donAqt oops.

This function checks and sets those values and skb->ip_summed: if this returns false you should drop the packet.