lib/dp-packet.h
/* Returns the number of bytes of headroom in 'b', that is, the number of bytes
 * of unused space in dp_packet 'b' before the data that is in use.  (Most
 * commonly, the data in a dp_packet is at its beginning, and thus the
 * dp_packet's headroom is 0.) */
Returns the number of bytes of headroom in 'b', that is, the number of bytes
of unused space in dp_packet 'b' before the data that is in use.  (Most
commonly, the data in a dp_packet is at its beginning, and thus the
dp_packet's headroom is 0.)
Returns the number of bytes of headroom in ' b ' that is the number of bytes of unused space in dp_packet ' b ' before the data that is in use . ( Most commonly the data in a dp_packet is at its beginning and thus the dp_packet ' s headroom is 0 . )
static inline size_t
dp_packet_headroom(const struct dp_packet *b)
{
    return (char *) dp_packet_data(b) - (char *) dp_packet_base(b);
}
static inline size_t dp_packet_headroom ( const struct dp_packet * b ) { return ( char * ) dp_packet_data ( b ) - ( char * ) dp_packet_base ( b ) ; }
Returns the number of bytes of headroom in 'b', that is, the number of bytes
 of unused space in dp_packet 'b' before the data that is in use.
Returns the number of bytes of headroom in ' b ' that is the number of bytes of unused space in dp_packet ' b ' before the data that is in use .