trafficserver的DNS初始化源码分析三

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这个函数的功能是设置DNSHandler的handler为DNSHandler::mainEvent，并定时调用该函数，然后打开到DNSserver的链接
main()--->DNSProcessor::start()--->DNSProcessor::open()--->DNSHandler::startEvent()
int
DNSHandler::startEvent(int/* event ATS_UNUSED */,Event
*e)
{
Debug("dns","DNSHandler::startEvent:
on thread%d\n", e->ethread->id);
this->validate_ip();
if(!dns_handler_initialized) {
dns_handler_initialized = 1;
//设置DNSHandler的handler为DNSHandler::mainEvent
SET_HANDLER(&DNSHandler::mainEvent);
//如果开启round_robin功能，想所有DNSserver发起链接
if(dns_ns_rr) {
intmax_nscount =
m_res->nscount;
if(max_nscount > MAX_NAMED)
max_nscount = MAX_NAMED;
n_con= 0;
for(inti = 0; i < max_nscount; i++) {
ip_port_text_bufferbuff;
sockaddr*sa = &m_res->nsaddr_list[i].sa;
if(ats_is_ip(sa)) {
open_con(sa,
false,n_con);
++n_con;
Debug("dns_pas","opened connection to %s, n_con =%d",
ats_ip_nptop(sa, buff,sizeof(buff)),
n_con
);
}
}
dns_ns_rr_init_down = 0;
//没有开启round_robin功能，指向一个DNSserver发起链接
}else{
open_con(0);

n_con= 1;
}
//定时调用DNSHandler::mainEvent
e->ethread->schedule_every(this,DNS_PERIOD);
returnEVENT_CONT;
}else{
ink_assert(false);
// I.e. this should neverreally happen
returnEVENT_DONE;
}
}
向一个DNSserver发起链接
main()--->DNSProcessor::start()--->DNSProcessor::open()--->DNSHandler::startEvent()--->DNSHandler::open_con()
void
DNSHandler::open_con(sockaddrconst*target,
boolfailed,
inticon)
{
ip_port_text_bufferip_text;
PollDescriptor*pd = get_PollDescriptor(dnsProcessor.thread);
if(!icon && target) {
ats_ip_copy(&ip,target);
}elseif(!target) {
target = &ip.sa;
}
Debug("dns","open_con:
opening connection %s",ats_ip_nptop(target, ip_text,
sizeofip_text));
if(con[icon].fd!= NO_FD) { //
Remove old FD from epollfd
con[icon].eio.stop();
con[icon].close();
}
//向DNSserver发起链接
if(con[icon].connect(
target,
DNSConnection::Options()
.setNonBlockingConnect(true)
.setNonBlockingIo(true)
.setUseTcp(false)
.setBindRandomPort(true)
.setLocalIpv6(&local_ipv6.sa)
.setLocalIpv4(&local_ipv4.sa)
)< 0) {
Debug("dns","opening
connection %s FAILED for%d", ip_text, icon);
if(!failed) {
if(dns_ns_rr)
rr_failure(icon);
else
failover();
}
return;
}else{
ns_down[icon]= 0;
//让NET模块能接受该DNS请求的响应，留到NET模块再做分析
if(con[icon].eio.start(pd,&con[icon],EVENTIO_READ)
< 0) {
Error("[iocore_dns]open_con: Failed to add %d server to
epolllist\n", icon);
}else{
con[icon].num= icon;
Debug("dns","opening
connection %s SUCCEEDEDfor %d", ip_text, icon);
}
}
}
这个函数的功能一是接收DNS响应，二是从等待队列中取出DNS请求项并发送DNS请求
main()--->DNSProcessor::start()--->DNSProcessor::open()--->DNSHandler::startEvent()--->DNSHandler::mainEvent()
int
DNSHandler::mainEvent(intevent,
Event*e)
{
//接收DNSserver的响应
recv_dns(event, e);
//下面判断正常的DNSserver是否满足设置为失败的条件以及失败的DNSserver是否满足重新发起链接的条件，如果满足则设置为失败以及重新发起链接，同样分两种模式处理
//round_robin模式时的处理
if(dns_ns_rr) {
ink_hrtimet = ink_get_hrtime();
//超时了，重新想所有down的DNSserver发起链接
if(t -
last_primary_retry> DNS_PRIMARY_RETRY_PERIOD) {
for(inti = 0; i <
n_con;i++) {
if(ns_down[i]){
Debug("dns","mainEvent:
nameserver= %d is down", i);
retry_named(i, t,
true);
}
}
last_primary_retry= t;
}
//判断正常的DNSserver是否快失败了，如果是则设置为失败，否则看是否要重新发起链接
for(inti = 0; i <
n_con;i++) {
if(!ns_down[i]&& failover_soon(i)) {
Debug("dns","mainEvent:
nameserver= %d
failoversoon",
name_server);
if(failover_now(i))
rr_failure(i);
else{
Debug("dns","mainEvent:
nameserver= %d no
failovernow - retrying", i);
retry_named(i, t,
false);
++failover_soon_number[i];
}
}
}
}else{
//非round_robin模式时的处理
if(failover_soon(name_server)){
Debug("dns","mainEvent:
will failoversoon");
if(failover_now(name_server)){
Debug("dns","mainEvent:
failing over now toanother nameserver");
failover();
}
else{
try_primary_named(false);
++failover_soon_number[name_server];
}
}elseif(name_server) //
not on the primary named
try_primary_named(true);
}
//把等待队列中的DNS请求项取出发送DNS请求
if(entries.head)
write_dns(this);

returnEVENT_CONT;
}
接收DNS响应
main()--->DNSProcessor::start()--->DNSProcessor::open()--->DNSHandler::startEvent()--->DNSHandler::mainEvent()--->DNSHandler::recv_dns()
DNSHandler::recv_dns(int/*event
ATS_UNUSED */,Event*
/*e ATS_UNUSED */)
{
DNSConnection*dnsc = NULL;
ip_text_bufferipbuff1, ipbuff2;
while((dnsc = (DNSConnection*)
triggered.dequeue())){
while(1) {
IpEndpointfrom_ip;
socklen_tfrom_length =
sizeof(from_ip);
if(!hostent_cache)
hostent_cache= dnsBufAllocator.alloc();
HostEnt*buf =
hostent_cache;
//接收DNS响应
intres = socketManager.recvfrom(dnsc->fd,buf->buf,MAX_DNS_PACKET_LEN,
0, &from_ip.sa,&from_length);
//如果出错则把相应的DNSserver设置为down，如果是round_robin模式则直接设置为down即可，如果是非round_robin模式，要切换当前DNSserver，重新发起到新DNSserver的链接
if(res == -EAGAIN)
break;
if(res <= 0) {
Debug("dns","named
error: %d",res);
if(dns_ns_rr)
rr_failure(dnsc->num);
elseif(dnsc->num==
name_server)
failover();
break;
}
//判断本次响应是否和请求对应
if(!ats_ip_addr_eq(&dnsc->ip.sa,&from_ip.sa)){
Warning("unexpectedDNS response from %s (expected %s)",
ats_ip_ntop(&from_ip.sa,ipbuff1,
sizeofipbuff1),
ats_ip_ntop(&dnsc->ip.sa,ipbuff2,
sizeofipbuff2)
);
continue;
}
hostent_cache= 0;
buf->packet_size= res;
Debug("dns","received
packet size = %d",res);
//round_robin模式时的处理
if(dns_ns_rr) {
Debug("dns","round-robin:
nameserver%d DNS response code = %d",dnsc->num,get_rcode(buf));
//响应码是否正确，如果正确设置该DNSserver可可用
if(good_rcode(buf->buf)){
received_one(dnsc->num);
if(ns_down[dnsc->num]){
Warning("connectionto DNS server %s restored",
ats_ip_ntop(&m_res->nsaddr_list[dnsc->num].sa,ipbuff1,
sizeofipbuff1)
);
ns_down[dnsc->num]= 0;
}
}
}
else{
//非round_robin模式时的处理
if(!dnsc->num){
Debug("dns","primary
DNS response code = %d",get_rcode(buf));
if(good_rcode(buf->buf)){
if(name_server)
recover();
else
received_one(name_server);
}
}
}
Ptr<HostEnt>protect_hostent = make_ptr(buf);
//处理响应报文，下面分析完DNS请求的发送流程再分析接收DNS响应处理流程
if(dns_process(this,buf, res)) {
if(dnsc->num==
name_server)
received_one(name_server);
}
}
}
}
分析完dns的启动后，下面该分析hostdb的启动了
main()--->HostDBProcessor::start()
int
HostDBProcessor::start(int,size_t)
{
hostDB.alloc_mutexes();
//调用hostDB.start启动hostdb
if(hostDB.start(0) < 0)
return-1;
......
hostdb_current_interval =(unsignedint)(ink_get_based_hrtime()/ HOST_DB_TIMEOUT_INTERVAL);
HostDBContinuation*b = hostDBContAllocator.alloc();
//设置HostDBContinuation的handler为HostDBContinuation::backgroundEvent并定时调用
SET_CONTINUATION_HANDLER(b,(HostDBContHandler)&
HostDBContinuation::backgroundEvent);
b->mutex= new_ProxyMutex();
eventProcessor.schedule_every(b,HOST_DB_TIMEOUT_INTERVAL, ET_DNS);
//如果配置hostdb同步则进行同步处理
if(hostdb_sync_frequency > 0)
eventProcessor.schedule_imm(NEW(newHostDBSyncer));
return0;
}
这个函数找到hostdb存储的文件名host.db，并创建或打开该文件并初始化相关数据
main()--->HostDBProcessor::start()--->HostDBCache::start()
int
HostDBCache::start(intflags)
{
Store*hostDBStore;
Span*hostDBSpan;
charstorage_path[PATH_NAME_MAX + 1];
intstorage_size = 33554432;
// 32MB default
boolreconfigure = ((flags & PROCESSOR_RECONFIGURE) ?
true:
false);
boolfix = ((flags & PROCESSOR_FIX) ?
true:
false);
......
if(storage_path[0] !=
'/'){
Layout::relative_to(storage_path,PATH_NAME_MAX, system_root_dir, storage_path);
}
Debug("hostdb","Storage
path is %s",storage_path);
if(access(storage_path,R_OK) == -1) {
ink_strlcpy(storage_path,system_runtime_dir,
sizeof(storage_path));
if(access(storage_path,R_OK) == -1) {
Warning("Unableto access() directory '%s': %d, %s",storage_path, errno,
strerror(errno));
Warning("Please set 'proxy.config.hostdb.storage_path' or'proxy.config.local_state_dir' ");
}
}
hostDBStore = NEW(newStore);
hostDBSpan = NEW(newSpan);
hostDBSpan->init(storage_path,storage_size);
hostDBStore->add(hostDBSpan);
Debug("hostdb","Opening
%s, size=%d",hostdb_filename, hostdb_size);
if(open(hostDBStore,
"hostdb.config",hostdb_filename, hostdb_size, reconfigure, fix,
false/*
slient*/ ) < 0) {
Note("reconfiguringhost database");
charp[PATH_NAME_MAX + 1];
Layout::relative_to(p,PATH_NAME_MAX, system_runtime_dir,
"hostdb.config");
if(unlink(p)< 0)
Debug("hostdb","unable
to unlink %s",p);
deletehostDBStore;
hostDBStore = NEW(newStore);
hostDBSpan = NEW(newSpan);
hostDBSpan->init(storage_path,storage_size);
hostDBStore->add(hostDBSpan);
if(open(hostDBStore,
"hostdb.config",hostdb_filename, hostdb_size,
true,fix) < 0) {
Warning("couldnot initialize host database. Host database will be disabled");
hostdb_enable = 0;
deletehostDBStore;
return-1;
}
}
HOSTDB_SET_DYN_COUNT(hostdb_bytes_stat,totalsize);
deletehostDBStore;
return0;
}

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