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| /**
* sock_sendpage - Socket发送页面（零拷贝）
* @sock: Socket结构
* @page: 要发送的页面
* @offset: 页面内偏移
* @size: 发送大小
* @flags: 发送标志
*
* 通过零拷贝技术发送页面数据
* 返回值：发送的字节数或错误码
*/
ssize_t sock_sendpage(struct socket *sock, struct page *page, int offset,
size_t size, int flags)
{
ssize_t res;
struct msghdr msg = {.msg_flags = flags};
struct kvec iov;
char *kaddr = kmap(page);
iov.iov_base = kaddr + offset;
iov.iov_len = size;
iov_iter_kvec(&msg.msg_iter, WRITE, &iov, 1, size);
res = sock_sendmsg(sock, &msg);
/*
* 如果这失败了，我们应该返回实际的错误码，但是
* 某些应用程序可能依赖返回的正字节数
*/
kunmap(page);
return res;
}
/**
* tcp_sendpage_locked - TCP锁定发送页面
* @sk: TCP套接字
* @page: 页面
* @offset: 偏移
* @size: 大小
* @flags: 标志
*
* 在已持有套接字锁的情况下发送页面
* 返回值：发送字节数或错误码
*/
ssize_t tcp_sendpage_locked(struct sock *sk, struct page *page, int offset,
size_t size, int flags)
{
struct tcp_sock *tp = tcp_sk(sk);
int mss_now, size_goal;
int err;
ssize_t copied = 0;
/* 检查连接状态 */
if (flags & MSG_OOB) {
err = tcp_send_urg_data(sk, page, offset, size, flags);
goto out_err;
}
/* 如果连接已关闭，返回错误 */
if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN))
goto out_err;
mss_now = tcp_send_mss(sk, &size_goal, flags);
copied = 0;
err = -EPIPE;
if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN))
goto out_err;
while (size > 0) {
struct sk_buff *skb;
size_t copy, i;
bool can_coalesce;
if (!tcp_send_head(sk) || (copy = size_goal - tcp_send_head(sk)->len) <= 0) {
new_segment:
if (!sk_stream_memory_free(sk))
goto wait_for_sndbuf;
skb = sk_stream_alloc_skb(sk, 0, sk->sk_allocation,
tcp_rtx_and_write_queues_empty(sk));
if (!skb)
goto wait_for_memory;
/*
* 检查是否需要插入TSO选项和时间戳选项
*/
skb_entail(sk, skb);
copy = size_goal;
}
if (copy > size)
copy = size;
i = skb_shinfo(skb)->nr_frags;
can_coalesce = skb_can_coalesce(skb, i, page, offset);
if (!can_coalesce && i >= sysctl_max_skb_frags) {
tcp_mark_push(tp, skb);
goto new_segment;
}
if (!sk_wmem_schedule(sk, copy))
goto wait_for_memory;
if (can_coalesce) {
skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy);
} else {
get_page(page);
skb_fill_page_desc(skb, i, page, offset, copy);
}
if (!(flags & MSG_NO_SHARED_FRAGS))
skb_shinfo(skb)->flags |= SKBFL_SHARED_FRAG;
skb->len += copy;
skb->data_len += copy;
skb->truesize += copy;
sk_wmem_queued_add(sk, copy);
sk_mem_charge(sk, copy);
skb->ip_summed = CHECKSUM_PARTIAL;
WRITE_ONCE(tp->write_seq, tp->write_seq + copy);
TCP_SKB_CB(skb)->end_seq += copy;
tcp_skb_pcount_set(skb, 0);
if (!copied)
TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_PSH;
copied += copy;
offset += copy;
size -= copy;
if (!size)
goto out;
if (skb->len < size_goal || (flags & MSG_OOB) || unlikely(tp->repair))
continue;
if (forced_push(tp)) {
tcp_mark_push(tp, skb);
__tcp_push_pending_frames(sk, mss_now, TCP_NAGLE_PUSH);
} else if (skb == tcp_send_head(sk))
tcp_push_one(sk, mss_now);
continue;
wait_for_sndbuf:
set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
wait_for_memory:
tcp_push(sk, flags & ~MSG_MORE, mss_now,
TCP_NAGLE_PUSH, size_goal);
err = sk_stream_wait_memory(sk, &timeo);
if (err != 0)
goto do_error;
mss_now = tcp_send_mss(sk, &size_goal, flags);
}
out:
if (copied) {
tcp_tx_timestamp(sk, sk->sk_tsflags);
if (!(flags & MSG_SENDPAGE_NOTLAST))
tcp_push(sk, flags, mss_now, tp->nonagle, size_goal);
}
return copied;
do_error:
tcp_remove_empty_skb(sk, tcp_write_queue_tail(sk));
if (copied)
goto out;
out_err:
/* 确保我们返回一个连接错误 */
if (sk->sk_err)
err = -sk->sk_err;
else if (sk->sk_shutdown & SEND_SHUTDOWN)
err = -EPIPE;
else if (sk->sk_state == TCP_CLOSE)
err = -ENOTCONN;
return err;
}
|