splice_from_pipe

/**
 * splice_from_pipe_next - wait for some data to splice from
 * @pipe:   pipe to splice from
 * @sd:     information about the splice operation
 *
 * Description:
 *    This function will wait for some data and return a positive
 *    value (one) if pipe buffers are available.  It will return zero
 *    or -errno if no more data needs to be spliced.
 */
static int splice_from_pipe_next(struct pipe_inode_info *pipe, struct splice_desc *sd)
{
    /*
     * Check for signal early to make process killable when there are
     * always buffers available
     */
    if (signal_pending(current))
        return -ERESTARTSYS;
 
    while (pipe_empty(pipe->head, pipe->tail)) {
        if (!pipe->writers)
            return 0;
 
        if (sd->num_spliced)
            return 0;
 
        if (sd->flags & SPLICE_F_NONBLOCK)
            return -EAGAIN;
 
        if (signal_pending(current))
            return -ERESTARTSYS;
 
        if (sd->need_wakeup) {
            wakeup_pipe_writers(pipe);
            sd->need_wakeup = false;
        }
 
        pipe_wait(pipe);
    }
 
    return 1;
}
函数源码
