rxrpc_jumbo_header
struct rxrpc_jumbo_header jhdr;
capacity += sizeof(struct rxrpc_jumbo_header); /* First subpacket has main hdr, not jumbo */
capacity /= sizeof(struct rxrpc_jumbo_header) + RXRPC_JUMBO_DATALEN;
struct rxrpc_jumbo_header *jumbo = txb->data - sizeof(*jumbo);
jumbo = max_data + sizeof(struct rxrpc_jumbo_header);
#define RXRPC_JUMBO_SUBPKTLEN (RXRPC_JUMBO_DATALEN + sizeof(struct rxrpc_jumbo_header))
size_t total, doff, jsize = sizeof(struct rxrpc_jumbo_header);