【内核源码】linux UDP实现
创建udp socket
在socket()创建的时候，会设置对应协议的操作集。 inet_dgram_ops是系统调用层直接调用的操作。udp_prot是底层协议的处理。
可以看到相比TCP，UDP不用accept(),listen(). 但是可以bind(), connect().
直接通过sendto()等发送数据即可
int __sock_create(struct net *net, int family, int type, int protocol,
struct socket **res, int kern)
{
...
pf = rcu_dereference(net_families[family]); // inet_family_ops
err = pf->create(net, sock, protocol, kern); // inet_create
...
}
static int inet_create(struct net *net, struct socket *sock, int protocol,
int kern)
{
...
list_for_each_entry_rcu(answer, &inetsw[sock->type], list) { //inet_init->inet_register_protosw, inetsw_array
err = 0;
/* Check the non-wild match. */
if (protocol == answer->protocol) {
if (protocol != IPPROTO_IP)
break;
} else {
..
}
}
...
sock->ops = answer->ops; //inet_dgram_ops
answer_prot = answer->prot; //udp_prot
...
}
static struct inet_protosw inetsw_array[] =
{
...
{
.type = SOCK_DGRAM,
.protocol = IPPROTO_UDP,
.prot = &udp_prot,
.ops = &inet_dgram_ops,
.flags = INET_PROTOSW_PERMANENT,
},
...
};
const struct proto_ops inet_dgram_ops = {
.family = PF_INET,
.owner = THIS_MODULE,
.release = inet_release,
.bind = inet_bind,
.connect = inet_dgram_connect,
.socketpair = sock_no_socketpair,
.accept = sock_no_accept,
.getname = inet_getname,
.poll = udp_poll,
.ioctl = inet_ioctl,
.listen = sock_no_listen,
.shutdown = inet_shutdown,
.setsockopt = sock_common_setsockopt,
.getsockopt = sock_common_getsockopt,
.sendmsg = inet_sendmsg,
.recvmsg = inet_recvmsg,
.mmap = sock_no_mmap,
.sendpage = inet_sendpage,
.set_peek_off = sk_set_peek_off,
#ifdef CONFIG_COMPAT
.compat_setsockopt = compat_sock_common_setsockopt,
.compat_getsockopt = compat_sock_common_getsockopt,
.compat_ioctl = inet_compat_ioctl,
#endif
};
struct proto udp_prot = {
.name = "UDP",
.owner = THIS_MODULE,
.close = udp_lib_close,
.connect = ip4_datagram_connect,
.disconnect = udp_disconnect,
.ioctl = udp_ioctl,
.destroy = udp_destroy_sock,
.setsockopt = udp_setsockopt,
.getsockopt = udp_getsockopt,
.sendmsg = udp_sendmsg,
.recvmsg = udp_recvmsg,
.sendpage = udp_sendpage,
.backlog_rcv = __udp_queue_rcv_skb,
.release_cb = ip4_datagram_release_cb,
.hash = udp_lib_hash,
.unhash = udp_lib_unhash,
.rehash = udp_v4_rehash,
.get_port = udp_v4_get_port,
.memory_allocated = &udp_memory_allocated,
.sysctl_mem = sysctl_udp_mem,
.sysctl_wmem = &sysctl_udp_wmem_min,
.sysctl_rmem = &sysctl_udp_rmem_min,
.obj_size = sizeof(struct udp_sock),
.h.udp_table = &udp_table,
#ifdef CONFIG_COMPAT
.compat_setsockopt = compat_udp_setsockopt,
.compat_getsockopt = compat_udp_getsockopt,
#endif
.diag_destroy = udp_abort,
};
bind()
bind()->inet_bind()->udp_v4_get_port()
int inet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
{
...
lock_sock(sk);
inet->inet_rcv_saddr = inet->inet_saddr = addr->sin_addr.s_addr; //绑定地址
/* Make sure we are allowed to bind here. */
if ((snum || !inet->bind_address_no_port) &&
sk->sk_prot->get_port(sk, snum)) { // udp_v4_get_port 绑定端口
inet->inet_saddr = inet->inet_rcv_saddr = 0;
err = -EADDRINUSE;
goto out_release_sock;
}
if (inet->inet_rcv_saddr)
sk->sk_userlocks |= SOCK_BINDADDR_LOCK;
if (snum)
sk->sk_userlocks |= SOCK_BINDPORT_LOCK;
inet->inet_sport = htons(inet->inet_num);
inet->inet_daddr = 0;
inet->inet_dport = 0;
sk_dst_reset(sk);
err = 0;
out_release_sock:
release_sock(sk);
out:
return err;
}
int udp_v4_get_port(struct sock *sk, unsigned short snum)
{
unsigned int hash2_nulladdr =
udp4_portaddr_hash(sock_net(sk), htonl(INADDR_ANY), snum);
unsigned int hash2_partial =
udp4_portaddr_hash(sock_net(sk), inet_sk(sk)->inet_rcv_saddr, 0);
/* precompute partial secondary hash */
udp_sk(sk)->udp_portaddr_hash = hash2_partial;
return udp_lib_get_port(sk, snum, ipv4_rcv_saddr_equal, hash2_nulladdr);
}
int udp_lib_get_port(struct sock *sk, unsigned short snum,
int (*saddr_comp)(const struct sock *sk1,
const struct sock *sk2,
bool match_wildcard),
unsigned int hash2_nulladdr)
{
struct udp_hslot *hslot, *hslot2;
struct udp_table *udptable = sk->sk_prot->h.udp_table;
if (!snum) { //sendto的时候自动bind， 查找一个可用端口
...
} else {
hslot = udp_hashslot(udptable, net, snum);
spin_lock_bh(&hslot->lock);
if (hslot->count > 10) { // 超过10个要检查hash2
int exist;
unsigned int slot2 = udp_sk(sk)->udp_portaddr_hash ^ snum; //udp_portaddr_hash之前只对inet_rcv_saddr做过hash
slot2 &= udptable->mask;
hash2_nulladdr &= udptable->mask;
hslot2 = udp_hashslot2(udptable, slot2);
if (hslot->count < hslot2->count) //检查较短的那个hash链表
goto scan_primary_hash;
exist = udp_lib_lport_inuse2(net, snum, hslot2, //判断hash2是否有该端口正在被使用
sk, saddr_comp);
if (!exist && (hash2_nulladdr != slot2)) {
hslot2 = udp_hashslot2(udptable, hash2_nulladdr);
exist = udp_lib_lport_inuse2(net, snum, hslot2, //再判断通配地址的情况
sk, saddr_comp);
}
if (exist)
goto fail_unlock;
else
goto found;
}
scan_primary_hash:
if (udp_lib_lport_inuse(net, snum, hslot, NULL, sk,
saddr_comp, 0))
goto fail_unlock;
}
found:
inet_sk(sk)->inet_num = snum;
udp_sk(sk)->udp_port_hash = snum;
udp_sk(sk)->udp_portaddr_hash ^= snum; //地址+端口 hash
if (sk_unhashed(sk)) { //未添加过hash表中
if (sk->sk_reuseport &&
udp_reuseport_add_sock(sk, hslot, saddr_comp)) { //添加到sk_reuseport_cb
inet_sk(sk)->inet_num = 0;
udp_sk(sk)->udp_port_hash = 0;
udp_sk(sk)->udp_portaddr_hash ^= snum;
goto fail_unlock;
}
sk_add_node_rcu(sk, &hslot->head); //根据net+端口的hash，添加到hash1
hslot->count++;
sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
hslot2 = udp_hashslot2(udptable, udp_sk(sk)->udp_portaddr_hash); //根据地址+端口hash，添加到hash2
spin_lock(&hslot2->lock);
if (IS_ENABLED(CONFIG_IPV6) && sk->sk_reuseport &&
sk->sk_family == AF_INET6)
hlist_add_tail_rcu(&udp_sk(sk)->udp_portaddr_node,
&hslot2->head);
else
hlist_add_head_rcu(&udp_sk(sk)->udp_portaddr_node,
&hslot2->head);
hslot2->count++;
spin_unlock(&hslot2->lock);
}
sock_set_flag(sk, SOCK_RCU_FREE);
error = 0;
fail_unlock:
spin_unlock_bh(&hslot->lock);
fail:
return error;
}
bind()会设置inet_rcv_saddr接收地址，以及通过udp_lib_get_port绑定到特定端口， 如果可以绑定，会在hash1和hash2两个hash表的对应链表中都添加
- 为什么使用两个hash? 两个hash的key为什么不同?
最初的时候只有一个hash表，hash key为本地端口，当使用了大量ip地址的情况下，有可能导致单个链表的上有很多socket，导致查询慢
添加第二个hash表，使用地址和端口作为key， 来应对上述情况。 查询的时候只用查两个hash链表中较短的那个。
connect()
sys_connect()->inet_dgram_connect()->ip4_datagram_connect()
调用connect之后，就不需要sendto()指定目的地址了，直接调用send()即可
int ip4_datagram_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
{
int res;
lock_sock(sk);
res = __ip4_datagram_connect(sk, uaddr, addr_len);
release_sock(sk);
return res;
}
int __ip4_datagram_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
{
...
// 查找路由
rt = ip_route_connect(fl4, usin->sin_addr.s_addr, saddr,
RT_CONN_FLAGS(sk), oif,
sk->sk_protocol,
inet->inet_sport, usin->sin_port, sk);
...
//更新源地址，如果更新后需要重新hash
if (!inet->inet_saddr)
inet->inet_saddr = fl4->saddr; /* Update source address */
if (!inet->inet_rcv_saddr) {
inet->inet_rcv_saddr = fl4->saddr;
if (sk->sk_prot->rehash)
sk->sk_prot->rehash(sk);
}
inet->inet_daddr = fl4->daddr;
inet->inet_dport = usin->sin_port;
sk->sk_state = TCP_ESTABLISHED; //进入TCP_ESTABLISHED状态
sk_set_txhash(sk);
inet->inet_id = jiffies;
sk_dst_set(sk, &rt->dst);
}
sendto
sys_sendto()->sock_sendmsg()->sock_sendmsg_nosec()->inet_sendmsg()
static int inet_autobind(struct sock *sk)
{
struct inet_sock *inet;
/* We may need to bind the socket. */
lock_sock(sk);
inet = inet_sk(sk);
if (!inet->inet_num) {
if (sk->sk_prot->get_port(sk, 0)) {
release_sock(sk);
return -EAGAIN;
}
inet->inet_sport = htons(inet->inet_num);
}
release_sock(sk);
return 0;
}
int inet_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
{
struct sock *sk = sock->sk;
sock_rps_record_flow(sk);
/* We may need to bind the socket. */
if (!inet_sk(sk)->inet_num && !sk->sk_prot->no_autobind &&
inet_autobind(sk)) //如果没调用bind(), 则自动绑定一个可用端口
return -EAGAIN;
return sk->sk_prot->sendmsg(sk, msg, size); //udp_sendmsg
}
int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
{
struct inet_sock *inet = inet_sk(sk);
struct udp_sock *up = udp_sk(sk);
struct flowi4 fl4_stack;
struct flowi4 *fl4;
int ulen = len;
struct ipcm_cookie ipc;
struct rtable *rt = NULL;
int free = 0;
int connected = 0;
__be32 daddr, faddr, saddr;
__be16 dport;
u8 tos;
int err, is_udplite = IS_UDPLITE(sk);
int corkreq = up->corkflag || msg->msg_flags&MSG_MORE; //UDP_CORK或者MSG_MORE
int (*getfrag)(void *, char *, int, int, int, struct sk_buff *);
struct sk_buff *skb;
struct ip_options_data opt_copy;
if (len > 0xFFFF) //长度不能超过64k， UDP头部只有16位长度位
return -EMSGSIZE;
/*
* Check the flags.
*/
if (msg->msg_flags & MSG_OOB) /* Mirror BSD error message compatibility */
return -EOPNOTSUPP;
ipc.opt = NULL;
ipc.tx_flags = 0;
ipc.ttl = 0;
ipc.tos = -1;
getfrag = is_udplite ? udplite_getfrag : ip_generic_getfrag;
fl4 = &inet->cork.fl.u.ip4;
if (up->pending) {
/*
* There are pending frames.
* The socket lock must be held while it's corked.
*/
lock_sock(sk);
if (likely(up->pending)) {
if (unlikely(up->pending != AF_INET)) {
release_sock(sk);
return -EINVAL;
}
goto do_append_data; //有数据pending，就往后添加
}
release_sock(sk);
}
ulen += sizeof(struct udphdr); //否则开始一个新的udp包
/*
* Get and verify the address.
*/
if (msg->msg_name) {
DECLARE_SOCKADDR(struct sockaddr_in *, usin, msg->msg_name);
if (msg->msg_namelen < sizeof(*usin))
return -EINVAL;
if (usin->sin_family != AF_INET) {
if (usin->sin_family != AF_UNSPEC)
return -EAFNOSUPPORT;
}
daddr = usin->sin_addr.s_addr;
dport = usin->sin_port;
if (dport == 0)
return -EINVAL;
} else {
//已经调用connect()进入TCP_ESTABLISHED状态
if (sk->sk_state != TCP_ESTABLISHED)
return -EDESTADDRREQ;
daddr = inet->inet_daddr;
dport = inet->inet_dport;
/* Open fast path for connected socket.
Route will not be used, if at least one option is set.
*/
connected = 1;
}
ipc.sockc.tsflags = sk->sk_tsflags;
ipc.addr = inet->inet_saddr;
ipc.oif = sk->sk_bound_dev_if;
if (msg->msg_controllen) {
//处理控制信息，如IP选项
err = ip_cmsg_send(sk, msg, &ipc, sk->sk_family == AF_INET6);
if (unlikely(err)) {
kfree(ipc.opt);
return err;
}
if (ipc.opt)
free = 1;
connected = 0;
}
if (!ipc.opt) { // 如果发送数据中的控制信息中没有IP选项信息，则尝试从inet_sock结构中获取
struct ip_options_rcu *inet_opt;
rcu_read_lock();
inet_opt = rcu_dereference(inet->inet_opt);
if (inet_opt) { //如果setsockopt设置了ip选项
memcpy(&opt_copy, inet_opt,
sizeof(*inet_opt) + inet_opt->opt.optlen);
ipc.opt = &opt_copy.opt;
}
rcu_read_unlock();
}
saddr = ipc.addr;
ipc.addr = faddr = daddr; //控制信息改成目的地址
sock_tx_timestamp(sk, ipc.sockc.tsflags, &ipc.tx_flags);
if (ipc.opt && ipc.opt->opt.srr) {//设置了源路由
if (!daddr)
return -EINVAL;
faddr = ipc.opt->opt.faddr; //需要使用ip选项中的下一跳作为目的地址
connected = 0; //因为重新选择路由，清除connected
}
tos = get_rttos(&ipc, inet);
if (sock_flag(sk, SOCK_LOCALROUTE) || //设置了SO_DONTROUTE
(msg->msg_flags & MSG_DONTROUTE) ||
(ipc.opt && ipc.opt->opt.is_strictroute)) { //ip选项中设置了严格源路由
tos |= RTO_ONLINK; //此时目的地址和下一跳必然在本地网络，设置RTO_ONLINK表示后续查找时与目的地址直连，而不用通过gateway
connected = 0;
}
if (ipv4_is_multicast(daddr)) { //如果是多播，同样控制信息中不存在的话，获取setsockopt配置
if (!ipc.oif)
ipc.oif = inet->mc_index;
if (!saddr)
saddr = inet->mc_addr;
connected = 0;
} else if (!ipc.oif)
ipc.oif = inet->uc_index;
if (connected) //connect()的时候已经查找过路由
rt = (struct rtable *)sk_dst_check(sk, 0);
if (!rt) { //查找路由
struct net *net = sock_net(sk);
__u8 flow_flags = inet_sk_flowi_flags(sk);
fl4 = &fl4_stack;
flowi4_init_output(fl4, ipc.oif, sk->sk_mark, tos,
RT_SCOPE_UNIVERSE, sk->sk_protocol,
flow_flags,
faddr, saddr, dport, inet->inet_sport);
security_sk_classify_flow(sk, flowi4_to_flowi(fl4));
rt = ip_route_output_flow(net, fl4, sk);
if (IS_ERR(rt)) {
err = PTR_ERR(rt);
rt = NULL;
if (err == -ENETUNREACH)
IP_INC_STATS(net, IPSTATS_MIB_OUTNOROUTES);
goto out;
}
err = -EACCES;
if ((rt->rt_flags & RTCF_BROADCAST) &&
!sock_flag(sk, SOCK_BROADCAST))
goto out;
if (connected)
sk_dst_set(sk, dst_clone(&rt->dst));
}
if (msg->msg_flags&MSG_CONFIRM) //设置MSG_CONFIRM，表示确认ip地址到mac地址的映射不会过期，不用定时发送arp
goto do_confirm;
back_from_confirm:
saddr = fl4->saddr; //获取路由源地址
if (!ipc.addr) //如果选项中更没有指定目的地址，从路由中获取. 比如发送的时候没有指定目的地址，而在控制信息中提供严格或者宽松的源路由
daddr = ipc.addr = fl4->daddr;
//不用cork的话不需要加锁，只是创建一个skb发出去就可以了， 由ip层执行分片
/* Lockless fast path for the non-corking case. */
if (!corkreq) {
skb = ip_make_skb(sk, fl4, getfrag, msg, ulen, //创建好skb，并设置ip头
sizeof(struct udphdr), &ipc, &rt,
msg->msg_flags);
err = PTR_ERR(skb);
if (!IS_ERR_OR_NULL(skb))
err = udp_send_skb(skb, fl4); //直接发送
goto out;
}
//需要cork数据了，需要加锁
lock_sock(sk);
if (unlikely(up->pending)) {
/* The socket is already corked while preparing it. */
/* ... which is an evident application bug. --ANK */
release_sock(sk);
net_dbg_ratelimited("cork app bug 2\n");
err = -EINVAL;
goto out;
}
/*
* Now cork the socket to pend data.
*/
fl4 = &inet->cork.fl.u.ip4;
fl4->daddr = daddr;
fl4->saddr = saddr;
fl4->fl4_dport = dport;
fl4->fl4_sport = inet->inet_sport;
up->pending = AF_INET; //标记，表明正在处理
do_append_data:
up->len += ulen;
err = ip_append_data(sk, fl4, getfrag, msg, ulen,
sizeof(struct udphdr), &ipc, &rt,
corkreq ? msg->msg_flags|MSG_MORE : msg->msg_flags);
if (err)
udp_flush_pending_frames(sk); //出错就清空数据，和pending标记， 因为udp不保证可靠性
else if (!corkreq) //不需要cork
err = udp_push_pending_frames(sk); //直接发送所有数据
else if (unlikely(skb_queue_empty(&sk->sk_write_queue)))
up->pending = 0; //没有数据等待发送，则清空pendind
release_sock(sk);
out:
ip_rt_put(rt); //发送完成，减少路由缓存的引用计数
if (free)
kfree(ipc.opt);
if (!err)
return len; //发送成功，返回发送的字节数
/*
* ENOBUFS = no kernel mem, SOCK_NOSPACE = no sndbuf space. Reporting
* ENOBUFS might not be good (it's not tunable per se), but otherwise
* we don't have a good statistic (IpOutDiscards but it can be too many
* things). We could add another new stat but at least for now that
* seems like overkill.
*/
if (err == -ENOBUFS || test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
UDP_INC_STATS(sock_net(sk),
UDP_MIB_SNDBUFERRORS, is_udplite);
}
return err; //发送失败，返回错误码
do_confirm:
dst_confirm(&rt->dst);
if (!(msg->msg_flags&MSG_PROBE) || len) // 标记MSG_PROBE和MSG_CONFIRM，且长度为0，则不发送数据
goto back_from_confirm;
err = 0;
goto out;
}
对于不设置MSG_MORE和UDP_CORK的通常情况， udp_sendmsg查找路由和获取ip选项后，直接调用ip_make_skb()来创建skb，并调用udp_send_skb发送，由ip层来执行分片
对于需要cork的情况，调用ip_append_data()来添加数据到队列
ip_make_skb
struct sk_buff *ip_make_skb(struct sock *sk,
struct flowi4 *fl4,
int getfrag(void *from, char *to, int offset,
int len, int odd, struct sk_buff *skb),
void *from, int length, int transhdrlen,
struct ipcm_cookie *ipc, struct rtable **rtp,
unsigned int flags)
{
struct inet_cork cork;
struct sk_buff_head queue;
int err;
if (flags & MSG_PROBE)
return NULL;
__skb_queue_head_init(&queue);
cork.flags = 0;
cork.addr = 0;
cork.opt = NULL;
err = ip_setup_cork(sk, &cork, ipc, rtp);
if (err)
return ERR_PTR(err);
err = __ip_append_data(sk, fl4, &queue, &cork, //创建添加copy数据到skb， 并放入queue中
¤t->task_frag, getfrag,
from, length, transhdrlen, flags);
if (err) {
__ip_flush_pending_frames(sk, &queue, &cork);
return ERR_PTR(err);
}
return __ip_make_skb(sk, fl4, &queue, &cork); //把queue中所有skb都合并到一个skb及其frag_list中， 并设置好ip头
}
ip_append_data
/*
* ip_append_data() and ip_append_page() can make one large IP datagram
* from many pieces of data. Each pieces will be holded on the socket
* until ip_push_pending_frames() is called. Each piece can be a page
* or non-page data.
*
* Not only UDP, other transport protocols - e.g. raw sockets - can use
* this interface potentially.
*
* LATER: length must be adjusted by pad at tail, when it is required.
*/
int ip_append_data(struct sock *sk, struct flowi4 *fl4,
int getfrag(void *from, char *to, int offset, int len,
int odd, struct sk_buff *skb),
void *from, int length, int transhdrlen,
struct ipcm_cookie *ipc, struct rtable **rtp,
unsigned int flags)
{
struct inet_sock *inet = inet_sk(sk);
int err;
if (flags&MSG_PROBE)
return 0;
if (skb_queue_empty(&sk->sk_write_queue)) {
err = ip_setup_cork(sk, &inet->cork.base, ipc, rtp); //sk_write_queue为空，初始化cork
if (err)
return err;
} else {
transhdrlen = 0;
}
return __ip_append_data(sk, fl4, &sk->sk_write_queue, &inet->cork.base, //添加skb到sk_write_queue
sk_page_frag(sk), getfrag,
from, length, transhdrlen, flags);
}
__ip_append_data
- 如果支持UFO则调用ip_ufo_append_data
- 尝试添加到队列sk_write_queue尾部skb，如果head空间够则copy到head，否则根据是否支持sg，创建新的skb或者添加到frag中
static int __ip_append_data(struct sock *sk,
struct flowi4 *fl4,
struct sk_buff_head *queue,
struct inet_cork *cork,
struct page_frag *pfrag,
int getfrag(void *from, char *to, int offset,
int len, int odd, struct sk_buff *skb),
void *from, int length, int transhdrlen,
unsigned int flags)
{
struct inet_sock *inet = inet_sk(sk);
struct sk_buff *skb;
struct ip_options *opt = cork->opt;
int hh_len;
int exthdrlen;
int mtu;
int copy;
int err;
int offset = 0;
unsigned int maxfraglen, fragheaderlen, maxnonfragsize;
int csummode = CHECKSUM_NONE;
struct rtable *rt = (struct rtable *)cork->dst;
u32 tskey = 0;
skb = skb_peek_tail(queue);
exthdrlen = !skb ? rt->dst.header_len : 0;
mtu = cork->fragsize;
if (cork->tx_flags & SKBTX_ANY_SW_TSTAMP &&
sk->sk_tsflags & SOF_TIMESTAMPING_OPT_ID)
tskey = sk->sk_tskey++;
hh_len = LL_RESERVED_SPACE(rt->dst.dev);
fragheaderlen = sizeof(struct iphdr) + (opt ? opt->optlen : 0);
maxfraglen = ((mtu - fragheaderlen) & ~7) + fragheaderlen; //ip包长，8对齐
maxnonfragsize = ip_sk_ignore_df(sk) ? 0xFFFF : mtu;
if (cork->length + length > maxnonfragsize - fragheaderlen) { //超过最大包长
ip_local_error(sk, EMSGSIZE, fl4->daddr, inet->inet_dport,
mtu - (opt ? opt->optlen : 0));
return -EMSGSIZE;
}
/*
* transhdrlen > 0 means that this is the first fragment and we wish
* it won't be fragmented in the future.
*/
if (transhdrlen && // sizeof(struct udphdr)
length + fragheaderlen <= mtu &&
rt->dst.dev->features & (NETIF_F_HW_CSUM | NETIF_F_IP_CSUM) &&
!(flags & MSG_MORE) &&
!exthdrlen)
csummode = CHECKSUM_PARTIAL; //硬件计算校验和
cork->length += length;
if (((length > mtu) || (skb && skb_is_gso(skb))) &&
(sk->sk_protocol == IPPROTO_UDP) &&
(rt->dst.dev->features & NETIF_F_UFO) && !rt->dst.header_len &&
(sk->sk_type == SOCK_DGRAM) && !sk->sk_no_check_tx) { //支持ufo
err = ip_ufo_append_data(sk, queue, getfrag, from, length, //创建ufo skb，添加数据到frag中
hh_len, fragheaderlen, transhdrlen,
maxfraglen, flags);
if (err)
goto error;
return 0;
}
/* So, what's going on in the loop below?
*
* We use calculated fragment length to generate chained skb,
* each of segments is IP fragment ready for sending to network after
* adding appropriate IP header.
*/
//下面是不支持gso/ufo的处理
if (!skb) //队列中没有skb，则需要创建新的
goto alloc_new_skb;
while (length > 0) {
/* Check if the remaining data fits into current packet. */ //检查当前skb是否还由空间能copy
copy = mtu - skb->len;
if (copy < length)
copy = maxfraglen - skb->len;
if (copy <= 0) { //剩余空间不够，创建新的skb插入
char *data;
unsigned int datalen;
unsigned int fraglen;
unsigned int fraggap;
unsigned int alloclen;
struct sk_buff *skb_prev;
alloc_new_skb:
skb_prev = skb;
if (skb_prev)
fraggap = skb_prev->len - maxfraglen;
else
fraggap = 0;
/*
* If remaining data exceeds the mtu,
* we know we need more fragment(s).
*/
datalen = length + fraggap;
if (datalen > mtu - fragheaderlen)
datalen = maxfraglen - fragheaderlen;
fraglen = datalen + fragheaderlen;
if ((flags & MSG_MORE) &&
!(rt->dst.dev->features&NETIF_F_SG))
alloclen = mtu;
else
alloclen = fraglen;
alloclen += exthdrlen;
/* The last fragment gets additional space at tail.
* Note, with MSG_MORE we overallocate on fragments,
* because we have no idea what fragment will be
* the last.
*/
if (datalen == length + fraggap)
alloclen += rt->dst.trailer_len;
if (transhdrlen) {
skb = sock_alloc_send_skb(sk,
alloclen + hh_len + 15,
(flags & MSG_DONTWAIT), &err);
} else {
skb = NULL;
if (atomic_read(&sk->sk_wmem_alloc) <=
2 * sk->sk_sndbuf)
skb = sock_wmalloc(sk,
alloclen + hh_len + 15, 1,
sk->sk_allocation);
if (unlikely(!skb))
err = -ENOBUFS;
}
if (!skb)
goto error;
/*
* Fill in the control structures
*/
skb->ip_summed = csummode;
skb->csum = 0;
skb_reserve(skb, hh_len);
/* only the initial fragment is time stamped */
skb_shinfo(skb)->tx_flags = cork->tx_flags;
cork->tx_flags = 0;
skb_shinfo(skb)->tskey = tskey;
tskey = 0;
/*
* Find where to start putting bytes.
*/
data = skb_put(skb, fraglen + exthdrlen);
skb_set_network_header(skb, exthdrlen);
skb->transport_header = (skb->network_header +
fragheaderlen);
data += fragheaderlen + exthdrlen;
if (fraggap) {
skb->csum = skb_copy_and_csum_bits(
skb_prev, maxfraglen,
data + transhdrlen, fraggap, 0);
skb_prev->csum = csum_sub(skb_prev->csum,
skb->csum);
data += fraggap;
pskb_trim_unique(skb_prev, maxfraglen);
}
copy = datalen - transhdrlen - fraggap;
if (copy > 0 && getfrag(from, data + transhdrlen, offset, copy, fraggap, skb) < 0) {
err = -EFAULT;
kfree_skb(skb);
goto error;
}
offset += copy;
length -= datalen - fraggap;
transhdrlen = 0;
exthdrlen = 0;
csummode = CHECKSUM_NONE;
/*
* Put the packet on the pending queue.
*/
__skb_queue_tail(queue, skb); //把新的skb插入队列
continue;
}
if (copy > length)
copy = length;
if (!(rt->dst.dev->features&NETIF_F_SG)) { //不支持sg，copy数据到head区
unsigned int off;
off = skb->len;
if (getfrag(from, skb_put(skb, copy), //ip_generic_getfrag
offset, copy, off, skb) < 0) {
__skb_trim(skb, off);
err = -EFAULT;
goto error;
}
} else { //支持sg，copy数据到frag
int i = skb_shinfo(skb)->nr_frags;
err = -ENOMEM;
if (!sk_page_frag_refill(sk, pfrag))
goto error;
if (!skb_can_coalesce(skb, i, pfrag->page,
pfrag->offset)) {
err = -EMSGSIZE;
if (i == MAX_SKB_FRAGS)
goto error;
__skb_fill_page_desc(skb, i, pfrag->page,
pfrag->offset, 0);
skb_shinfo(skb)->nr_frags = ++i;
get_page(pfrag->page);
}
copy = min_t(int, copy, pfrag->size - pfrag->offset);
if (getfrag(from,
page_address(pfrag->page) + pfrag->offset,
offset, copy, skb->len, skb) < 0)
goto error_efault;
pfrag->offset += copy;
skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy);
skb->len += copy;
skb->data_len += copy;
skb->truesize += copy;
atomic_add(copy, &sk->sk_wmem_alloc);
}
offset += copy;
length -= copy;
}
return 0;
error_efault:
err = -EFAULT;
error:
cork->length -= length;
IP_INC_STATS(sock_net(sk), IPSTATS_MIB_OUTDISCARDS);
return err;
}
ip_ufo_append_data
static inline int ip_ufo_append_data(struct sock *sk,
struct sk_buff_head *queue,
int getfrag(void *from, char *to, int offset, int len,
int odd, struct sk_buff *skb),
void *from, int length, int hh_len, int fragheaderlen,
int transhdrlen, int maxfraglen, unsigned int flags)
{
struct sk_buff *skb;
int err;
/* There is support for UDP fragmentation offload by network
* device, so create one single skb packet containing complete
* udp datagram
*/
skb = skb_peek_tail(queue);
if (!skb) {
skb = sock_alloc_send_skb(sk, //分配skb空间
hh_len + fragheaderlen + transhdrlen + 20, //这部分在skb head区
(flags & MSG_DONTWAIT), &err);
if (!skb)
return err;
/* reserve space for Hardware header */
skb_reserve(skb, hh_len);
/* create space for UDP/IP header */
skb_put(skb, fragheaderlen + transhdrlen);
/* initialize network header pointer */
skb_reset_network_header(skb);
/* initialize protocol header pointer */
skb->transport_header = skb->network_header + fragheaderlen;
skb->csum = 0;
__skb_queue_tail(queue, skb); //把这个不带数据部分的skb，插入队列中
} else if (skb_is_gso(skb)) {
goto append;
}
skb->ip_summed = CHECKSUM_PARTIAL;
/* specify the length of each IP datagram fragment */
skb_shinfo(skb)->gso_size = maxfraglen - fragheaderlen;
skb_shinfo(skb)->gso_type = SKB_GSO_UDP;
append:
return skb_append_datato_frags(sk, skb, getfrag, from, //copy数据部分到frag
(length - transhdrlen));
}
int skb_append_datato_frags(struct sock *sk, struct sk_buff *skb,
int (*getfrag)(void *from, char *to, int offset,
int len, int odd, struct sk_buff *skb),
void *from, int length)
{
int frg_cnt = skb_shinfo(skb)->nr_frags;
int copy;
int offset = 0;
int ret;
struct page_frag *pfrag = ¤t->task_frag;
do {
/* Return error if we don't have space for new frag */
if (frg_cnt >= MAX_SKB_FRAGS)
return -EMSGSIZE;
if (!sk_page_frag_refill(sk, pfrag))
return -ENOMEM;
/* copy the user data to page */
copy = min_t(int, length, pfrag->size - pfrag->offset);
ret = getfrag(from, page_address(pfrag->page) + pfrag->offset, //ip_generic_getfrag
offset, copy, 0, skb);
if (ret < 0)
return -EFAULT;
/* copy was successful so update the size parameters */
skb_fill_page_desc(skb, frg_cnt, pfrag->page, pfrag->offset,
copy);
frg_cnt++;
pfrag->offset += copy;
get_page(pfrag->page);
skb->truesize += copy;
atomic_add(copy, &sk->sk_wmem_alloc);
skb->len += copy;
skb->data_len += copy;
offset += copy;
length -= copy;
} while (length > 0);
return 0;
}
int ip_generic_getfrag(void *from, char *to, int offset, int len, int odd, struct sk_buff *skb)
{
struct msghdr *msg = from;
if (skb->ip_summed == CHECKSUM_PARTIAL) {
if (copy_from_iter(to, len, &msg->msg_iter) != len)
return -EFAULT;
} else {
__wsum csum = 0;
if (csum_and_copy_from_iter(to, len, &csum, &msg->msg_iter) != len)
return -EFAULT;
skb->csum = csum_block_add(skb->csum, csum, odd);
}
return 0;
}
udp_send_skbudp_send_skb()->ip_send_skb()->ip_local_out()
static int udp_send_skb(struct sk_buff *skb, struct flowi4 *fl4)
{
/*
* Create a UDP header
*/
uh = udp_hdr(skb);
uh->source = inet->inet_sport;
uh->dest = fl4->fl4_dport;
uh->len = htons(len);
uh->check = 0;
if (is_udplite) /* UDP-Lite */
csum = udplite_csum(skb);
else if (sk->sk_no_check_tx) { /* UDP csum disabled */
skb->ip_summed = CHECKSUM_NONE;
goto send;
} else if (skb->ip_summed == CHECKSUM_PARTIAL) { /* UDP hardware csum */
udp4_hwcsum(skb, fl4->saddr, fl4->daddr);
goto send;
} else
csum = udp_csum(skb);
/* add protocol-dependent pseudo-header */
uh->check = csum_tcpudp_magic(fl4->saddr, fl4->daddr, len,
sk->sk_protocol, csum);
if (uh->check == 0)
uh->check = CSUM_MANGLED_0;
send:
err = ip_send_skb(sock_net(sk), skb);
if (err) {
if (err == -ENOBUFS && !inet->recverr) {
UDP_INC_STATS(sock_net(sk),
UDP_MIB_SNDBUFERRORS, is_udplite);
err = 0;
}
} else
UDP_INC_STATS(sock_net(sk),
UDP_MIB_OUTDATAGRAMS, is_udplite);
return err;
}
udp_recvmsg
udp_recvmsg()只要是调用__skb_recv_datagram()从sk_receive_queue取出一个skb，然后调用skb_copy_datagram_msg拷贝数据到用户态
int udp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int noblock,
int flags, int *addr_len)
{
struct inet_sock *inet = inet_sk(sk);
DECLARE_SOCKADDR(struct sockaddr_in *, sin, msg->msg_name);
struct sk_buff *skb;
unsigned int ulen, copied;
int peeked, peeking, off;
int err;
int is_udplite = IS_UDPLITE(sk);
bool checksum_valid = false;
bool slow;
if (flags & MSG_ERRQUEUE)
return ip_recv_error(sk, msg, len, addr_len); //返回sk_error_queue队列中的数据
try_again:
peeking = off = sk_peek_offset(sk, flags);
skb = __skb_recv_datagram(sk, flags | (noblock ? MSG_DONTWAIT : 0),
&peeked, &off, &err);
if (!skb)
return err;
ulen = skb->len;
copied = len;
if (copied > ulen - off)
copied = ulen - off;
else if (copied < ulen)
msg->msg_flags |= MSG_TRUNC;
/*
* If checksum is needed at all, try to do it while copying the
* data. If the data is truncated, or if we only want a partial
* coverage checksum (UDP-Lite), do it before the copy.
*/
if (copied < ulen || UDP_SKB_CB(skb)->partial_cov || peeking) {
checksum_valid = !udp_lib_checksum_complete(skb);
if (!checksum_valid)
goto csum_copy_err;
}
if (checksum_valid || skb_csum_unnecessary(skb))
err = skb_copy_datagram_msg(skb, off, msg, copied);
else {
err = skb_copy_and_csum_datagram_msg(skb, off, msg);
if (err == -EINVAL)
goto csum_copy_err;
}
if (unlikely(err)) {
trace_kfree_skb(skb, udp_recvmsg);
if (!peeked) {
atomic_inc(&sk->sk_drops);
UDP_INC_STATS(sock_net(sk),
UDP_MIB_INERRORS, is_udplite);
}
skb_free_datagram_locked(sk, skb);
return err;
}
if (!peeked)
UDP_INC_STATS(sock_net(sk),
UDP_MIB_INDATAGRAMS, is_udplite);
sock_recv_ts_and_drops(msg, sk, skb);
/* Copy the address. */
if (sin) {
sin->sin_family = AF_INET;
sin->sin_port = udp_hdr(skb)->source;
sin->sin_addr.s_addr = ip_hdr(skb)->saddr;
memset(sin->sin_zero, 0, sizeof(sin->sin_zero));
*addr_len = sizeof(*sin);
}
if (inet->cmsg_flags)
ip_cmsg_recv_offset(msg, skb, sizeof(struct udphdr), off);
err = copied;
if (flags & MSG_TRUNC)
err = ulen;
__skb_free_datagram_locked(sk, skb, peeking ? -err : err);
return err;
csum_copy_err:
slow = lock_sock_fast(sk);
if (!skb_kill_datagram(sk, skb, flags)) {
UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS, is_udplite);
UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
}
unlock_sock_fast(sk, slow);
/* starting over for a new packet, but check if we need to yield */
cond_resched();
msg->msg_flags &= ~MSG_TRUNC;
goto try_again;
}
struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags,
int *peeked, int *off, int *err)
{
struct sk_buff *skb, *last;
long timeo;
timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT);
do {
skb = __skb_try_recv_datagram(sk, flags, peeked, off, err, //从sk_receive_queue取出一个skb
&last);
if (skb)
return skb;
if (*err != -EAGAIN)
break;
} while (timeo &&
!__skb_wait_for_more_packets(sk, err, &timeo, last)); //阻塞等待
return NULL;
}
udp_rcv
在中断下半部会调用udp_rcv来进行udp协议的处理
主要是调用__udp4_lib_lookup_skb在udp hash中查找要接收该skb的socket，
然后调用udp_queue_rcv_skb把skb放到socket的sk_receive_queue中
int udp_rcv(struct sk_buff *skb)
{
return __udp4_lib_rcv(skb, &udp_table, IPPROTO_UDP);
}
int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
int proto)
{
struct sock *sk;
struct udphdr *uh;
unsigned short ulen;
struct rtable *rt = skb_rtable(skb);
__be32 saddr, daddr;
struct net *net = dev_net(skb->dev);
/*
* Validate the packet.
*/
if (!pskb_may_pull(skb, sizeof(struct udphdr)))
goto drop; /* No space for header. */
uh = udp_hdr(skb);
ulen = ntohs(uh->len);
saddr = ip_hdr(skb)->saddr;
daddr = ip_hdr(skb)->daddr;
if (ulen > skb->len)
goto short_packet;
if (proto == IPPROTO_UDP) {
/* UDP validates ulen. */
if (ulen < sizeof(*uh) || pskb_trim_rcsum(skb, ulen))
goto short_packet;
uh = udp_hdr(skb);
}
/* UDP只提供有限的校验能力，如果不计算，则发送时为全0
* 校验和初始化，若udp头部的校验和字段为0，则设置不必校验标志位，若校验由硬
* 完成，且伪首部通过校验，则同样设置不必校验标志，若以上都不满足，则将伪首
* 部的校验和给skb->csum，之后还需要对数据部分进行校验*/
if (udp4_csum_init(skb, uh, proto))
goto csum_error;
sk = skb_steal_sock(skb);
if (sk) {
struct dst_entry *dst = skb_dst(skb);
int ret;
if (unlikely(sk->sk_rx_dst != dst))
udp_sk_rx_dst_set(sk, dst);
ret = udp_queue_rcv_skb(sk, skb);
sock_put(sk);
/* a return value > 0 means to resubmit the input, but
* it wants the return to be -protocol, or 0
*/
if (ret > 0)
return -ret;
return 0;
}
if (rt->rt_flags & (RTCF_BROADCAST|RTCF_MULTICAST))
return __udp4_lib_mcast_deliver(net, skb, uh, // 组播和广播处理，所有满足条件的sk都能接收
saddr, daddr, udptable, proto);
sk = __udp4_lib_lookup_skb(skb, uh->source, uh->dest, udptable); //在hash表中查找满足条件的sk
if (sk) {
int ret;
if (inet_get_convert_csum(sk) && uh->check && !IS_UDPLITE(sk))
skb_checksum_try_convert(skb, IPPROTO_UDP, uh->check,
inet_compute_pseudo);
ret = udp_queue_rcv_skb(sk, skb);
/* a return value > 0 means to resubmit the input, but
* it wants the return to be -protocol, or 0
*/
if (ret > 0)
return -ret;
return 0;
}
//没有满足条件的sk
if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb))
goto drop;
nf_reset(skb);
//对数据包进行校验和，如果校验失败则安静地丢弃
/* No socket. Drop packet silently, if checksum is wrong */
if (udp_lib_checksum_complete(skb))
goto csum_error;
//校验成功，发送端口不可达ICMP
__UDP_INC_STATS(net, UDP_MIB_NOPORTS, proto == IPPROTO_UDPLITE);
icmp_send(skb, ICMP_DEST_UNREACH, ICMP_PORT_UNREACH, 0);
/*
* Hmm. We got an UDP packet to a port to which we
* don't wanna listen. Ignore it.
*/
kfree_skb(skb);
return 0;
short_packet:
net_dbg_ratelimited("UDP%s: short packet: From %pI4:%u %d/%d to %pI4:%u\n",
proto == IPPROTO_UDPLITE ? "Lite" : "",
&saddr, ntohs(uh->source),
ulen, skb->len,
&daddr, ntohs(uh->dest));
goto drop;
csum_error:
/*
* RFC1122: OK. Discards the bad packet silently (as far as
* the network is concerned, anyway) as per 4.1.3.4 (MUST).
*/
net_dbg_ratelimited("UDP%s: bad checksum. From %pI4:%u to %pI4:%u ulen %d\n",
proto == IPPROTO_UDPLITE ? "Lite" : "",
&saddr, ntohs(uh->source), &daddr, ntohs(uh->dest),
ulen);
__UDP_INC_STATS(net, UDP_MIB_CSUMERRORS, proto == IPPROTO_UDPLITE);
drop:
__UDP_INC_STATS(net, UDP_MIB_INERRORS, proto == IPPROTO_UDPLITE);
kfree_skb(skb);
return 0;
}
static int __udp4_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
struct udphdr *uh,
__be32 saddr, __be32 daddr,
struct udp_table *udptable,
int proto)
{
struct sock *sk, *first = NULL;
unsigned short hnum = ntohs(uh->dest);
struct udp_hslot *hslot = udp_hashslot(udptable, net, hnum);
unsigned int hash2 = 0, hash2_any = 0, use_hash2 = (hslot->count > 10);
unsigned int offset = offsetof(typeof(*sk), sk_node);
int dif = skb->dev->ifindex;
struct hlist_node *node;
struct sk_buff *nskb;
if (use_hash2) {
hash2_any = udp4_portaddr_hash(net, htonl(INADDR_ANY), hnum) &
udptable->mask;
hash2 = udp4_portaddr_hash(net, daddr, hnum) & udptable->mask;
start_lookup:
hslot = &udptable->hash2[hash2];
offset = offsetof(typeof(*sk), __sk_common.skc_portaddr_node);
}
sk_for_each_entry_offset_rcu(sk, node, &hslot->head, offset) {
if (!__udp_is_mcast_sock(net, sk, uh->dest, daddr, //检查sk是否满足接收条件，并判断组播是否允许通过
uh->source, saddr, dif, hnum))
continue;
if (!first) {
first = sk;
continue;
}
nskb = skb_clone(skb, GFP_ATOMIC);
if (unlikely(!nskb)) {
atomic_inc(&sk->sk_drops);
__UDP_INC_STATS(net, UDP_MIB_RCVBUFERRORS,
IS_UDPLITE(sk));
__UDP_INC_STATS(net, UDP_MIB_INERRORS,
IS_UDPLITE(sk));
continue;
}
if (udp_queue_rcv_skb(sk, nskb) > 0) //所有满足条件的sk都能接收
consume_skb(nskb);
}
/* Also lookup *:port if we are using hash2 and haven't done so yet. */
if (use_hash2 && hash2 != hash2_any) { //再遍历INADDR_ANY的情况
hash2 = hash2_any;
goto start_lookup;
}
if (first) {
if (udp_queue_rcv_skb(first, skb) > 0) //第一个sk使用原始skb，不用clone了
consume_skb(skb);
} else {// 说明没有满足条件的sk，直接丢弃
kfree_skb(skb);
__UDP_INC_STATS(net, UDP_MIB_IGNOREDMULTI,
proto == IPPROTO_UDPLITE);
}
return 0;
}
__udp4_lib_lookup_skb
__udp4_lib_lookup_skb在两个udp hash中，较短的那个链表中查找。
查找的时候跟tcp一样通过compute_score来打分，最高分数的socket来进行接收。 如果是reuseport，则使用reuseport对应的算法来选择sock
struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr,
__be16 sport, __be32 daddr, __be16 dport,
int dif, struct udp_table *udptable, struct sk_buff *skb)
{
struct sock *sk, *result;
unsigned short hnum = ntohs(dport);
unsigned int hash2, slot2, slot = udp_hashfn(net, hnum, udptable->mask); //根据目的端口和net来hash1
struct udp_hslot *hslot2, *hslot = &udptable->hash[slot];
int score, badness, matches = 0, reuseport = 0;
u32 hash = 0;
if (hslot->count > 10) { //超过10个， 在hash2中查找
hash2 = udp4_portaddr_hash(net, daddr, hnum);
slot2 = hash2 & udptable->mask;
hslot2 = &udptable->hash2[slot2];
if (hslot->count < hslot2->count) //哪个链表短查哪个
goto begin;
result = udp4_lib_lookup2(net, saddr, sport, //跟begin相同的逻辑
daddr, hnum, dif,
hslot2, skb);
if (!result) {
unsigned int old_slot2 = slot2;
hash2 = udp4_portaddr_hash(net, htonl(INADDR_ANY), hnum); //再差INADDR_ANY的情况
slot2 = hash2 & udptable->mask;
/* avoid searching the same slot again. */
if (unlikely(slot2 == old_slot2))
return result;
hslot2 = &udptable->hash2[slot2];
if (hslot->count < hslot2->count)
goto begin;
result = udp4_lib_lookup2(net, saddr, sport,
daddr, hnum, dif,
hslot2, skb);
}
return result;
}
begin:
result = NULL;
badness = 0;
sk_for_each_rcu(sk, &hslot->head) {
score = compute_score(sk, net, saddr, sport,
daddr, hnum, dif);
if (score > badness) {
reuseport = sk->sk_reuseport;
if (reuseport) {
hash = udp_ehashfn(net, daddr, hnum,
saddr, sport);
result = reuseport_select_sock(sk, hash, skb,
sizeof(struct udphdr)); //根据reuseport算法选择一个sock直接返回
if (result)
return result;
matches = 1;
}
result = sk; //使用最大分数的sk作为结果返回
badness = score;
} else if (score == badness && reuseport) { //和最大分数相等，并且最大分数的sk是reuseport
matches++;
if (reciprocal_scale(hash, matches) == 0) // 判断当前sk能否作为结果
result = sk;
hash = next_pseudo_random32(hash);
}
}
return result;
}
static inline struct sock *__udp4_lib_lookup_skb(struct sk_buff *skb,
__be16 sport, __be16 dport,
struct udp_table *udptable)
{
const struct iphdr *iph = ip_hdr(skb);
return __udp4_lib_lookup(dev_net(skb->dev), iph->saddr, sport,
iph->daddr, dport, inet_iif(skb),
udptable, skb);
}
udp_queue_rcv_skb
/* returns:
* -1: error
* 0: success
* >0: "udp encap" protocol resubmission
*
* Note that in the success and error cases, the skb is assumed to
* have either been requeued or freed.
*/
int udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
{
struct udp_sock *up = udp_sk(sk);
int rc;
int is_udplite = IS_UDPLITE(sk);
/*
* Charge it to the socket, dropping if the queue is full.
*/
if (!xfrm4_policy_check(sk, XFRM_POLICY_IN, skb))
goto drop;
nf_reset(skb);
if (static_key_false(&udp_encap_needed) && up->encap_type) { //udp tunnel处理
int (*encap_rcv)(struct sock *sk, struct sk_buff *skb);
/*
* This is an encapsulation socket so pass the skb to
* the socket's udp_encap_rcv() hook. Otherwise, just
* fall through and pass this up the UDP socket.
* up->encap_rcv() returns the following value:
* =0 if skb was successfully passed to the encap
* handler or was discarded by it.
* >0 if skb should be passed on to UDP.
* <0 if skb should be resubmitted as proto -N
*/
/* if we're overly short, let UDP handle it */
encap_rcv = ACCESS_ONCE(up->encap_rcv);
if (encap_rcv) {
int ret;
/* Verify checksum before giving to encap */
if (udp_lib_checksum_complete(skb)) //校验
goto csum_error;
ret = encap_rcv(sk, skb);
if (ret <= 0) {
__UDP_INC_STATS(sock_net(sk),
UDP_MIB_INDATAGRAMS,
is_udplite);
return -ret;
}
}
/* FALLTHROUGH -- it's a UDP Packet */
}
/*
* UDP-Lite specific tests, ignored on UDP sockets
*/
if ((is_udplite & UDPLITE_RECV_CC) && UDP_SKB_CB(skb)->partial_cov) { //udplite处理
...
}
if (rcu_access_pointer(sk->sk_filter) &&
udp_lib_checksum_complete(skb))
goto csum_error;
if (sk_filter_trim_cap(sk, skb, sizeof(struct udphdr)))
goto drop;
udp_csum_pull_header(skb);
if (sk_rcvqueues_full(sk, sk->sk_rcvbuf)) { //接收缓存满了
__UDP_INC_STATS(sock_net(sk), UDP_MIB_RCVBUFERRORS,
is_udplite);
goto drop;
}
rc = 0;
ipv4_pktinfo_prepare(sk, skb);
bh_lock_sock(sk);
if (!sock_owned_by_user(sk))
rc = __udp_queue_rcv_skb(sk, skb); //应用程序没在使用，添加到sk_receive_queue队列
else if (sk_add_backlog(sk, skb, sk->sk_rcvbuf)) { //应用程序在使用，添加到backlog中，等release_lock的是否处理
bh_unlock_sock(sk);
goto drop;
}
bh_unlock_sock(sk);
return rc;
csum_error:
__UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS, is_udplite);
drop:
__UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
atomic_inc(&sk->sk_drops);
kfree_skb(skb);
return -1;
}
由上可知，udp非常简单，只有两个hash表，一个backlog队列，以及sk_receive_queue和sk_write_queue。
本文作者： bhpike65
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