Man page 9 : generic_splice_sendpage

generic_splice_sendpage - splice data from a pipe to a socket

ssize_t generic_splice_sendpage(struct pipe_inode_info *  pipe , struct file *  out , loff_t *  ppos , size_t  len , unsigned int  flags );

pipe
    pipe to splice from

out
    socket to write to

ppos
    position in out

len
    number of bytes to splice

flags
    splice modifier flags

Will send len bytes from the pipe to a network socket. No data copying is involved.