nginx 异常长连接快速断开
最近碰到了一个问题，设备端上挂载的nginx服务通过c版fcgi提供服务，其中的长连接API经常连接的设备断网后其他设备无法连接上。
初步查看源代码调试日志发现网络断了nginx未检测到，这时就想到给nginx添加保活检测，配置中listen加上了，写模块给connection也加上，均发现无效果，半天摸不清头脑。先写个小小的测试程序测试保活特性吧，开始我测试的是服务端只收不发，客户端只发不收，居然达到了我要的效果，短短几秒之后端口就关闭了。后面测试了收发同时跑的时候，死活都达不到效果，这就郁闷了。
listen保活检测配置:
listen 80 so_keepalive=1:1:1;
//so_keepalive= tcp_keepidle:tcp_keepintvl:tcp_keepcnt经过抓包后发现这两种情况的不同之处，请看截图：
这是只收不发的抓包截图，Keep-Alive严格按照设定走。
这是收发同时跑的抓包截图，Keep-Alive一个都没有，多出了TCP Retransmission，这个是超时重传的包。后面查了下为啥保活没激活，仔细瞧了下保活注解后注意到了 （ 如果2小时内在此套接口的任一方向都没有数据交换 ） 这是重点。在后面这种情况下需要去处理超时重发，但是超时重发貌似只能调整系统设置（暂时未找到怎么通过设置socket调整超时重发参数，知道的希望告诉我下）。
改系统中的设定如下，可以达到了效果。
echo "net.ipv4.tcp_retries2=5" >> /etc/sysctl.conf
sysctl -p但是改系统参数配置影响范围有点大，这个是能是没有办法之后的方法了。之后翻找了下nginx中fastcgi流程，与源码对照的看了下，发现可以这么操作：
1.清零 SO_SNDBUF，，通过listen 80 sndbuf=0; 参数修改
2.降低fastcgi缓冲区大小，避免太多次的缓冲区操作导致超时延后
3.设置send_timeout 1
ps：1,2两点为了使协议栈和用户发送缓冲能尽快的装满，走入发送超时检测流程。
具体配置如下：
listen 80 sndbuf=0;
...
location ~ \.push$ {
send_timeout 1;
fastcgi_buffer_size 200;
fastcgi_buffers 2 200;
fastcgi_busy_buffers_size 200;
...
}nginx结构流程图.vsdx
nginx保活模块：https://pan.baidu.com/s/1EGLmNg5S9uXZloeLCvPOFQ
测试用c版代码:
server.c
#include
#include
#include
#ifdef _WIN32
#define WIN32 1
#endif
#ifdef WIN32
#include
#include
#include
#define close closesocket
#else
#include
#include
#include
#include
#include
#include
#include
#include
#include
typedef int SOCKET;
#endif
#define LOGS_FULL(OPTION,ERRNO) \
printf("(%s %d %s) %s errno:%d",__FILE__,__LINE__,__FUNCTION__,OPTION,ERRNO);
#define LOGS(OPTION,ERRNO) \
printf("%s errno:%d",OPTION,ERRNO);
#define ERRORS(OPTION,ERRNO) LOGS(OPTION,ERRNO)
#ifdef WIN32
int initNetwork()
{
WSADATA wsaData;
int ret = WSAStartup(MAKEWORD(2,2), &wsaData);
if (ret != 0) return 1;
return 0;
}
int setnonblocking(SOCKET sock)
{
unsigned long ul=1;
int ret=ioctlsocket(sock,FIONBIO,(unsigned long *)&ul);
if(ret==SOCKET_ERROR)
{
}
return ret;
}
int socket_keepalive(SOCKET socket)
{
int keep_alive = 1;
int ret = setsockopt(socket, SOL_SOCKET, SO_KEEPALIVE, (char*)&keep_alive, sizeof(keep_alive));
if (ret == SOCKET_ERROR)
{
printf("SO_KEEPALIVE failed:%d\n", WSAGetLastError());
return -1;
}
struct tcp_keepalive in_keep_alive = {0};
unsigned long ul_in_len = sizeof(struct tcp_keepalive);
struct tcp_keepalive out_keep_alive = {0};
unsigned long ul_out_len = sizeof(struct tcp_keepalive);
unsigned long ul_bytes_return = 0;
in_keep_alive.onoff = 1;
in_keep_alive.keepaliveinterval = 5000;
in_keep_alive.keepalivetime = 1000;
ret = WSAIoctl(socket, SIO_KEEPALIVE_VALS, (LPVOID)&in_keep_alive, ul_in_len,
(LPVOID)&out_keep_alive, ul_out_len, &ul_bytes_return, NULL, NULL);
if (ret == SOCKET_ERROR)
{
printf("WSAIoctl KEEPALIVE failed:%d\n", WSAGetLastError());
return -1;
}
return 0;
}
#else
int setnonblocking(SOCKET sock)
{
int opts = fcntl(sock,F_GETFL);
if (opts < 0 )
{
printf( "fcntl(sock,GETFL) " );
return -1;
}
opts = opts | O_NONBLOCK;
if (fcntl(sock,F_SETFL,opts) < 0 )
{
printf( "fcntl(sock,SETFL,opts) " );
return -1;
}
return 0;
}
int socket_keepalive(SOCKET socket)
{
int optval;
socklen_t optlen = sizeof(int);
optval = 1;
int ret = setsockopt(socket, SOL_SOCKET, SO_KEEPALIVE, &optval, optlen);
if(ret != 0)
{
printf("SO_KEEPALIVE set failed:%d\n",errno);
return -1;
}
#ifdef SOL_TCP
//重复检查次数
optval = 5;
ret = setsockopt(socket, SOL_TCP, TCP_KEEPCNT, &optval, optlen);
if(ret != 0)
{
printf("SO_KEEPALIVE set failed:%d\n",errno);
return -1;
}
//检查空闲
optval = 1;
ret = setsockopt(socket, SOL_TCP, TCP_KEEPIDLE, &optval, optlen);
if(ret != 0)
{
printf("SO_KEEPALIVE set failed:%d\n",errno);
return -1;
}
//检查间隔
optval = 1;
ret = setsockopt(socket, SOL_TCP, TCP_KEEPINTVL, &optval, optlen);
if(ret != 0)
{
printf("SO_KEEPALIVE set failed:%d\n",errno);
return -1;
}
#endif
return 0;
}
int socket_sendbuf(SOCKET socket,int size){
return setsockopt(socket,SOL_SOCKET,SO_SNDBUF,(const char*)&size,sizeof(int));
}
int socket_recvbuf(SOCKET socket,int size){
return setsockopt(socket,SOL_SOCKET,SO_RCVBUF,(const char*)&size,sizeof(int));
}
int socket_linger(SOCKET socket,int onoff,int linger){
struct linger l;
l.l_onoff = onoff;
l.l_linger = linger;
return setsockopt(socket, SOL_SOCKET, SO_LINGER,(const void *) &l, sizeof(struct linger));
}
int socket_sendtimeout(SOCKET socket, int timeout){
return setsockopt(socket,SOL_SOCKET,SO_SNDTIMEO,&timeout,sizeof(timeout));
}
int socket_recvtimeout(SOCKET socket, int timeout){
return setsockopt(socket,SOL_SOCKET,SO_RCVTIMEO,&timeout,sizeof(timeout));
}
uint64_t time_microsecond(){
struct timeval tv;
gettimeofday(&tv,NULL);
return tv.tv_sec*1000000 + tv.tv_usec;
}
uint64_t time_millisecond(){
struct timeval tv;
gettimeofday(&tv,NULL);
return tv.tv_sec*1000 + tv.tv_usec/1000;
}
long time_second(){
struct timeval tv;
gettimeofday(&tv,NULL);
return tv.tv_sec;
}
double time_secondD(){
struct timeval tv;
gettimeofday(&tv,NULL);
double usec = (double)tv.tv_usec;
return tv.tv_sec + usec/1000000;
}
#endif
void init()
{
#ifdef WIN32
initNetwork();
#endif
}
int main(int argc,char *argv[])
{
init();
SOCKET fd = socket(AF_INET,SOCK_STREAM,0);
struct sockaddr_in server = {0};
server.sin_family = AF_INET;
server.sin_addr.s_addr = inet_addr(argv[1]);
server.sin_port = htons(atoi(argv[2]));
int ret = bind(fd,&server,sizeof(struct sockaddr_in));
if(ret < 0)
{
printf("bind %d errno:%d\n",ret,errno);
return -1;
}
// socket_keepalive(fd);
// socket_sendbuf(fd,0);
// socket_linger(fd,1,0);
ret = listen(fd,100);
if(ret == -1)
{
printf("listen %d errno:%d\n",ret,errno);
close(fd);
return -1;
}
int nfds = fd;
fd_set readfds_cache;
fd_set writefds_cache;
FD_ZERO(&readfds_cache);
FD_ZERO(&writefds_cache);
FD_SET(fd,&readfds_cache);
fd_set readfds;
fd_set writefds;
FD_ZERO(&readfds);
FD_ZERO(&writefds);
struct timeval timeout;
timeout.tv_sec = 1;
timeout.tv_usec = 0;
printf("begin run...\n");
int fd_count = 1;
int no_recv = 0;
int no_send = 0;
fd_set * ptrRecv = &readfds;
fd_set * ptrSend = &writefds;
while(1)
{
readfds = readfds_cache;
writefds = writefds_cache;
if(no_recv == 1)
{
// ptrRecv = NULL;
}
if(no_send == 1)
{
ptrSend = NULL;
}
int ret = select(nfds + 1,ptrRecv,ptrSend,NULL,&timeout);
if(ret == -1)
{
if (errno == EINTR)
continue;
printf("select error:%d\n",errno);
break;
}
if(ret == 0)
{
continue;
}
printf("%d select %d.\n",time_second(),ret);
if(ptrRecv != NULL && FD_ISSET(fd,ptrRecv))
{
printf("accept connection\n");
struct sockaddr_in client = {0};
socklen_t client_len = sizeof(struct sockaddr_in);
SOCKET cfd = accept(fd,&client,&client_len);
if(cfd == -1)
{
ERRORS("accept",errno);
}else{
printf("accept %d\n",cfd);
setnonblocking(cfd);
socket_keepalive(cfd);
// socket_sendbuf(cfd,0);
// socket_linger(fd,1,0);
if(!no_recv){
FD_SET(cfd,&readfds_cache);
}
if(!no_send){
FD_SET(cfd,&writefds_cache);
}
nfds = nfds>cfd?nfds:cfd;
fd_count++;
printf("accept end.\n");
}
}
int i = 0;
for (; i <= nfds; i++)
{
if( i == fd)
{
continue;
}
if(ptrRecv != NULL && no_recv == 0)
{
if (FD_ISSET(i, ptrRecv))
{
printf("recv %d check...\n",i);
char peek;
ret = recv(i,&peek,1,MSG_PEEK);
if(ret != 1)
{
if(ret == 0 || (ret != 0 && EAGAIN != errno) )
{
printf("recv %d check close.%d\n",i,errno);
FD_CLR(i,&readfds_cache);
FD_CLR(i,&writefds_cache);
close(i);
printf("check close %d.\n",i);
fd_count--;
continue;
}
printf("recv %d check :%d errno:%d\n",i,ret,errno);
}else{
printf("recv %d ...\n",i);
char buffer[65536];
ret = recv(i,buffer,65535,0);
if(ret == -1)
{
if(EAGAIN != errno)
{
printf("recv %d close.%d\n",i,errno);
FD_CLR(i,&readfds_cache);
FD_CLR(i,&writefds_cache);
close(i);
printf("close %d.\n",i);
fd_count--;
continue;
}
}else if(ret == 0)
{
printf("recv %d close.\n",i);
FD_CLR(i,&readfds_cache);
FD_CLR(i,&writefds_cache);
close(i);
printf("close %d.\n",i);
fd_count--;
continue;
}else{
buffer[ret] = 0x00;
// printf("%s\n",buffer);
printf("recv %i %d\n",i,ret);
}
}
}
}
if(ptrSend != NULL && no_send == 0)
{
if(FD_ISSET(i, ptrSend))
{
printf("send %d ...\n",i);
ret = send(i,"client",6,0);
if(ret == -1)
{
if(EAGAIN != errno)
{
printf("send %d close.%d\n",i,errno);
FD_CLR(i,&readfds_cache);
FD_CLR(i,&writefds_cache);
close(i);
printf("close %d.\n",i);
fd_count--;
}
}else{
printf("send %d %d\n",i,ret);
}
}
}
}
}
return -1;
}
client:
#include
#include
#include
#ifdef _WIN32
#define WIN32 1
#endif
#ifdef WIN32
#include
#include
#include
#define close closesocket
#else
#include
#include
#include
#include
#include
#include
#include
#include
#include
typedef int SOCKET;
#endif
#define LOGS_FULL(OPTION,ERRNO) \
printf("(%s %d %s) %s errno:%d",__FILE__,__LINE__,__FUNCTION__,OPTION,ERRNO);
#define LOGS(OPTION,ERRNO) \
printf("%s errno:%d",OPTION,ERRNO);
#define ERRORS(OPTION,ERRNO) LOGS(OPTION,ERRNO)
#ifdef WIN32
int initNetwork()
{
WSADATA wsaData;
int ret = WSAStartup(MAKEWORD(2,2), &wsaData);
if (ret != 0) return 1;
return 0;
}
int setnonblocking(SOCKET sock)
{
unsigned long ul=1;
int ret=ioctlsocket(sock,FIONBIO,(unsigned long *)&ul);
if(ret==SOCKET_ERROR)
{
}
return ret;
}
int socket_keepalive(SOCKET socket)
{
int keep_alive = 1;
int ret = setsockopt(socket, SOL_SOCKET, SO_KEEPALIVE, (char*)&keep_alive, sizeof(keep_alive));
if (ret == SOCKET_ERROR)
{
printf("SO_KEEPALIVE failed:%d\n", WSAGetLastError());
return -1;
}
struct tcp_keepalive in_keep_alive = {0};
unsigned long ul_in_len = sizeof(struct tcp_keepalive);
struct tcp_keepalive out_keep_alive = {0};
unsigned long ul_out_len = sizeof(struct tcp_keepalive);
unsigned long ul_bytes_return = 0;
in_keep_alive.onoff = 1;
in_keep_alive.keepaliveinterval = 5000;
in_keep_alive.keepalivetime = 1000;
ret = WSAIoctl(socket, SIO_KEEPALIVE_VALS, (LPVOID)&in_keep_alive, ul_in_len,
(LPVOID)&out_keep_alive, ul_out_len, &ul_bytes_return, NULL, NULL);
if (ret == SOCKET_ERROR)
{
printf("WSAIoctl KEEPALIVE failed:%d\n", WSAGetLastError());
return -1;
}
return 0;
}
#else
int setnonblocking(SOCKET sock)
{
int opts = fcntl(sock,F_GETFL);
if (opts < 0 )
{
printf( "fcntl(sock,GETFL) " );
return -1;
}
opts = opts | O_NONBLOCK;
if (fcntl(sock,F_SETFL,opts) < 0 )
{
printf( "fcntl(sock,SETFL,opts) " );
return -1;
}
return 0;
}
int socket_keepalive(SOCKET socket)
{
int optval;
socklen_t optlen = sizeof(int);
optval = 1;
int ret = setsockopt(socket, SOL_SOCKET, SO_KEEPALIVE, &optval, optlen);
if(ret != 0)
{
printf("SO_KEEPALIVE set failed:%d\n",errno);
return -1;
}
#ifdef SOL_TCP
//重复检查次数
optval = 5;
ret = setsockopt(socket, SOL_TCP, TCP_KEEPCNT, &optval, optlen);
if(ret != 0)
{
printf("SO_KEEPALIVE set failed:%d\n",errno);
return -1;
}
//检查空闲
optval = 1;
ret = setsockopt(socket, SOL_TCP, TCP_KEEPIDLE, &optval, optlen);
if(ret != 0)
{
printf("SO_KEEPALIVE set failed:%d\n",errno);
return -1;
}
//检查间隔
optval = 1;
ret = setsockopt(socket, SOL_TCP, TCP_KEEPINTVL, &optval, optlen);
if(ret != 0)
{
printf("SO_KEEPALIVE set failed:%d\n",errno);
return -1;
}
#endif
return 0;
}
int socket_sendbuf(SOCKET socket,int size){
return setsockopt(socket,SOL_SOCKET,SO_SNDBUF,(const char*)&size,sizeof(int));
}
int socket_recvbuf(SOCKET socket,int size){
return setsockopt(socket,SOL_SOCKET,SO_RCVBUF,(const char*)&size,sizeof(int));
}
int socket_linger(SOCKET socket,int onoff,int linger){
struct linger l;
l.l_onoff = onoff;
l.l_linger = linger;
return setsockopt(socket, SOL_SOCKET, SO_LINGER,(const void *) &l, sizeof(struct linger));
}
int socket_sendtimeout(SOCKET socket, int timeout){
return setsockopt(socket,SOL_SOCKET,SO_SNDTIMEO,&timeout,sizeof(timeout));
}
int socket_recvtimeout(SOCKET socket, int timeout){
return setsockopt(socket,SOL_SOCKET,SO_RCVTIMEO,&timeout,sizeof(timeout));
}
uint64_t time_microsecond(){
struct timeval tv;
gettimeofday(&tv,NULL);
return tv.tv_sec*1000000 + tv.tv_usec;
}
uint64_t time_millisecond(){
struct timeval tv;
gettimeofday(&tv,NULL);
return tv.tv_sec*1000 + tv.tv_usec/1000;
}
long time_second(){
struct timeval tv;
gettimeofday(&tv,NULL);
return tv.tv_sec;
}
double time_secondD(){
struct timeval tv;
gettimeofday(&tv,NULL);
double usec = (double)tv.tv_usec;
return tv.tv_sec + usec/1000000;
}
#endif
void init()
{
#ifdef WIN32
initNetwork();
#endif
}
int main(int argc,char *argv[])
{
init();
SOCKET fd = socket(AF_INET,SOCK_STREAM,0);
struct sockaddr_in server = {0};
server.sin_family = AF_INET;
server.sin_addr.s_addr = inet_addr(argv[1]);
server.sin_port = htons(atoi(argv[2]));
int ret = connect(fd,&server,sizeof(struct sockaddr_in));
if(ret != 0)
{
printf("connect error:%d\n",errno);
return -1;
}
int nfds = fd;
fd_set readfds_cache;
fd_set writefds_cache;
FD_ZERO(&readfds_cache);
FD_ZERO(&writefds_cache);
FD_SET(fd,&readfds_cache);
FD_SET(fd,&writefds_cache);
fd_set readfds;
fd_set writefds;
FD_ZERO(&readfds);
FD_ZERO(&writefds);
struct timeval timeout;
timeout.tv_sec = 1;
timeout.tv_usec = 0;
int fd_count = 1;
int last_nfds = nfds;
printf("begin run...\n");
int no_recv = 0;
int no_send = 0;
fd_set * ptrRecv = &readfds;
fd_set * ptrSend = &writefds;
while(1)
{
if(fd_count <= 0){
break;
}
nfds = last_nfds;
readfds = readfds_cache;
writefds = writefds_cache;
ptrRecv = &readfds;
ptrSend = &writefds;
if(no_recv == 1)
{
ptrRecv = NULL;
}
if(no_send == 1)
{
ptrSend = NULL;
}
int ret = select(nfds + 1,ptrRecv,ptrSend,NULL,&timeout);
if(ret == -1)
{
if (errno == EINTR)
continue;
printf("select error:%d\n",errno);
break;
}
if(ret == 0)
{
continue;
}
printf("%d select %d.\n",time_second(),ret);
int i = 0;
for (; i <= nfds; i++)
{
if(ptrRecv != NULL && no_recv == 0)
{
if (FD_ISSET(i, ptrRecv))
{
printf("recv %d check...\n",i);
char peek;
ret = recv(i,&peek,1,MSG_PEEK);
if(ret != 1)
{
if(ret == 0 || (ret != 0 && EAGAIN != errno) )
{
printf("recv %d check close.%d\n",i,errno);
FD_CLR(i,&readfds_cache);
FD_CLR(i,&writefds_cache);
close(i);
printf("check close %d.\n",i);
fd_count--;
continue;
}
printf("recv %d check :%d errno:%d\n",i,ret,errno);
}else{
printf("recv %d ...\n",i);
char buffer[65536];
ret = recv(i,buffer,65535,0);
if(ret == -1)
{
if(EAGAIN != errno)
{
printf("recv %d close.%d\n",i,errno);
FD_CLR(i,&readfds_cache);
FD_CLR(i,&writefds_cache);
close(i);
printf("close %d.\n",i);
fd_count--;
continue;
}
}else if(ret == 0)
{
printf("recv %d close.\n",i);
FD_CLR(i,&readfds_cache);
FD_CLR(i,&writefds_cache);
close(i);
printf("close %d.\n",i);
fd_count--;
continue;
}else{
buffer[ret] = 0x00;
// printf("%s\n",buffer);
printf("recv %i %d\n",i,ret);
}
}
}
}
if(ptrSend != NULL && no_send == 0)
{
if(FD_ISSET(i, ptrSend))
{
printf("send %d ...\n",i);
ret = send(i,"client",6,0);
if(ret == -1)
{
if(EAGAIN != errno)
{
printf("send %d close.%d\n",i,errno);
FD_CLR(i,&readfds_cache);
FD_CLR(i,&writefds_cache);
close(i);
printf("close %d.\n",i);
fd_count--;
}
}else{
printf("send %d %d\n",i,ret);
}
}
}
}
}
return -1;
}
Makefile
CORSS_PREFIX :=
SYSROOT :=
$(warning $(CORSS_PREFIX))
$(warning $(SYSROOT))
CC = $(CORSS_PREFIX)gcc
AR = $(CORSS_PREFIX)ar
RM = rm -rf
#原始目录
SRC_PATH :=.
MODULES :=
#目标名
TARGET :=
#源文件
MODULES += $(wildcard $(SRC_PATH)/src/*.c)
MODULES += $(wildcard $(SRC_PATH)/*.c)
SRCS += $(MODULES)
#中间文件
OBJS := $(SRCS:.c=.o)
TARGET =
MODULE_OBJS := $(MODULES:.c=.o)
OBJ_TEST=win32/server.o
OBJS_TEST=$(MODULE_OBJS) $(OBJ_TEST)
TARGET_TEST=server
OBJ_INFO=win32/client.o
OBJS_INFO=$(MODULE_OBJS) $(OBJ_INFO)
TARGET_INFO=client
ALL_OBJS=$(OBJS) $(OBJS_TEST) $(OBJ_INFO)
#动态库
LIBS := pthread
#模块库文件
MOULE_LIBRARY_PATH = $(SYSROOT)/usr/lib/ $(SYSROOT)/usr/local/lib/
#头文件路径
INCLUDE_PATH :=.
#动态库路径
LIBRARY_PATH :=
INCLUDE_PATH += $(SYSROOT)/usr/include
INCLUDE_PATH += ./include
INCLUDE_PATH += ./src
INCLUDE_PATH += ./test
INCLUDE_PATH += ./win32
LIBRARY_PATH += $(MOULE_LIBRARY_PATH)
LIBRARY_PATH += ./
RELEASE = 1
BITS =
#ifeq ( 1 , ${DBG_ENABLE} )
# CFLAGS += -D_DEBUG -O0 -g -DDEBUG=1
#endif
CFLAGS = -Wall -DMAIN_TEST -DUSE_BOOL
LFLAGS =
#头文件
CFLAGS += $(foreach dir,$(INCLUDE_PATH),-I$(dir))
#库路径
LDFLAGS += $(foreach lib,$(LIBRARY_PATH),-L$(lib))
#库名
LDFLAGS += $(foreach lib,$(LIBS),-l$(lib))
#检查版本
ifeq ($(RELEASE),0)
#debug
CFLAGS += -g
else
#release
CFLAGS += -O3 -DNDEBUG
endif
#检查位宽
ifeq ($(BITS),32)
CFLAGS += -m32
LFLAGS += -m32
else
ifeq ($(BITS),64)
CFLAGS += -m64
LFLAGS += -m64
else
endif
endif
$(warning $(OBJS))
#操作命令
all:clean build
$(ALL_OBJS):%.o:%.c
$(CC) $(CFLAGS) -c $^ -o $@
build_static:$(OBJS)
# $(AR) -cru $(TARGET) $(OBJS)
build_test:build_static $(OBJ_TEST)
$(CC) $(CFLAGS) $(LFLAGS) -o $(TARGET_TEST) $(OBJ_TEST) $(LDFLAGS)
build_info:build_static $(OBJ_INFO)
$(CC) $(CFLAGS) $(LFLAGS) -o $(TARGET_INFO) $(OBJ_INFO) $(LDFLAGS)
build:build_test build_info
$(RM) $(ALL_OBJS)
clean:
echo $(SRCS)
$(RM) $(ALL_OBJS) $(TARGET) $(TARGET_TEST) $(TARGET_INFO)
makefile中CORSS_PREFIX和 SYSROOT是为了跨平台编译才增加的。
CORSS_PREFIX ：跨平台编译工具路径
SYSROOT：跨平台环境头文件及库路径
跨平台编译时需要配置如下:
#编译
make SYSROOT=/。。。/root CORSS_PREFIX=/。。。/prebuilts/toolschain/usr/bin/arm-linux-