大家都知道TCP是面向stream，而UDP是面向datagram的。

那，到底什么是stream呢？

我们来看一下以下代码

/* Now we need to check if we have a half built packet. */

if ((skb = tcp_dequeue_partial(sk)) != NULL) {

int hdrlen;

/* IP header + TCP header */

hdrlen = ((unsigned long)skb->h.th - (unsigned long)skb->data)

+ sizeof(struct tcphdr);

/* Add more stuff to the end of skb->len */

if (!(flags & MSG_OOB)) {

copy = min(sk->mss - (skb->len - hdrlen), len);

/* FIXME: this is really a bug. */

if (copy <= 0) {

printk("TCP: **bug**: "copy" <= 0!!

");

copy = 0;

}

memcpy_fromfs(skb->data + skb->len, from, copy);

skb->len += copy;

from += copy;

copied += copy;

len -= copy;

sk->write_seq += copy;

}

if ((skb->len - hdrlen) >= sk->mss ||

(flags & MSG_OOB) ||

!sk->packets_out)

tcp_send_skb(sk, skb);

else

tcp_enqueue_partial(skb, sk);

continue;

}

明白了吧？