Man page 9 : skb_seq_read

skb_seq_read - Sequentially read skb data

unsigned int skb_seq_read(unsigned int  consumed , const u8 **  data , struct skb_seq_state *  st );

consumed
    number of bytes consumed by the caller so far

data
    destination pointer for data to be returned

st
    state variable

Reads a block of skb data at consumed relative to the lower offset specified to skb_prepare_seq_read. Assigns the head of the data block to data and returns the length of the block or 0 if the end of the skb data or the upper offset has been reached.

The caller is not required to consume all of the data returned, i.e. consumed is typically set to the number of bytes already consumed and the next call to skb_seq_read will return the remaining part of the block.

The size of each block of data returned can be arbitrary, this limitation is the cost for zerocopy seqeuental reads of potentially non linear data.

Fragment lists within fragments are not implemented at the moment, state->root_skb could be replaced with a stack for this purpose.