标签:linux sockets nonblocking c-3 recv
我试图实现套接字recv的非阻塞,问题是我在没有数据的情况下得到了错误-1但我希望得到EAGAIN错误.
套接字肯定设置为非阻塞状态,我检查了标志= fcntl(s,F_GETFL,0)的O_NONBLOCK标志.
非常感谢提前!
#include <arpa/inet.h>
#include <linux/if_packet.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <net/if.h>
#include <netinet/ether.h>
#include <unistd.h>
#include <fcntl.h>
#include <asm-generic/errno-base.h>
#include <assert.h>
#define ETH_FRAME_LEN_MY 1400
void print(void *buf, int length)
{
int i;
for (i = 0; i < length; ++i)
putchar(((char *)buf)[i]);
printf("\n");
}
int main(){
int flags, s, r, err;
struct sockaddr_ll socket_addr;
char ifName[IFNAMSIZ] = "eth0";
struct ifreq if_idx;
struct ifreq if_mac;
s = socket(PF_PACKET, SOCK_RAW, htons(0x88b6));
if (s == -1) { perror("socket"); }
flags = fcntl(s,F_GETFL,0);
assert(flags != -1);
fcntl(s, F_SETFL, flags | O_NONBLOCK);
flags = fcntl(s, F_GETFL, 0);
if ((flags & O_NONBLOCK) == O_NONBLOCK) {
printf("it's nonblocking");
}
else {
printf("it's blocking.");
}
/* Get the index of the interface to send on */
memset(&if_idx, 0, sizeof(struct ifreq));
strncpy(if_idx.ifr_name, ifName, IFNAMSIZ-1);
if (ioctl(s, SIOCGIFINDEX, &if_idx) < 0)
{perror("SIOCGIFINDEX");}
memset(&socket_addr, 0, sizeof(socket_addr));
socket_addr.sll_ifindex = if_idx.ifr_ifindex;
socket_addr.sll_protocol = htons(0x88b5);
socket_addr.sll_family = PF_PACKET;
socket_addr.sll_pkttype = PACKET_OUTGOING;
r = bind(s, (struct sockaddr*)&socket_addr,
sizeof(socket_addr));
if ( r < 0) { perror("bind"); }
void* buffer = (void*)malloc(ETH_FRAME_LEN_MY); /*Buffer for ethernet frame*/
int length = 0; /*length of the received frame*/
while(1){
printf("1\n");
length = recv(s, buffer, ETH_FRAME_LEN_MY, 0);
printf("2\n");
if (length < 0)
{
if (length == -EAGAIN)
printf("non-blocking succeeded\n");
else printf("error code %i\n", length);
}
//printf ("buffer %s\n", buffer);
print(buffer, length);
}
return 0;
}
解决方法:
您需要检查errno,而不是长度值以获取套接字无法返回数据的原因.此外,EWOULDBLOCK是除了EAGAIN之外您应该检查的其他错误代码.更改while循环,如下所示:
while(1)
{
int err;
printf("1\n");
length = recv(s, buffer, ETH_FRAME_LEN_MY, 0);
err = errno; // save off errno, because because the printf statement might reset it
printf("2\n");
if (length < 0)
{
if ((err == EAGAIN) || (err == EWOULDBLOCK))
{
printf("non-blocking operation returned EAGAIN or EWOULDBLOCK\n");
}
else
{
printf("recv returned unrecoverable error(errno=%d)\n", err);
break;
}
}
//printf ("buffer %s\n", buffer);
print(buffer, length);
}
当然,这个无限循环会在等待数据时进入CPU浪费繁忙周期.有多种方法可以通知套接字上的数据,而无需在旋转循环中调用recv().这包括选择和轮询呼叫.
标签:linux,sockets,nonblocking,c-3,recv 来源: https://codeday.me/bug/20190718/1493665.html
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