[apue]作为daemon启动,UnixDomainSocket侦听失败?

Z时代
2024-01-10
分类：综合

前段时间写一个传递文件句柄的小 demo，有 server 端、有 client 端，之间通过 Unix Domain Socket 通讯。

在普通模式下，双方可以正常建立连接，当server端作为daemon启动时，则第一次启动成功，之后再启动， listen 会连接报 ENOTSUPP 错误，导致启动失败。

spipe.c

 1int cli_conn(constchar *name)
 2{
 3int fd, len, err, rval; 
 4struct sockaddr_un un; 
 5
 6if ((fd = socket (AF_UNIX, SOCK_STREAM, 0)) < 0) { 
 7         printf ("create socket failed
"); 
 8return -1; 
 9    }
10
11     printf ("create socket ok
"); 
12     memset (&un, 0, sizeof (un)); 
13     un.sun_family = AF_UNIX; 
14    strcpy (un.sun_path, name); 
15     len = offsetof (struct sockaddr_un, sun_path) + strlen (name); 
16if (connect (fd, (struct sockaddr *)&un, len) < 0) {
17         err = errno; 
18         printf ("connect failed
"); 
19         rval = -4; 
20goto errout; 
21    }
22
23     printf ("connect to server ok
"); 
24return fd;
25errout:
26    close (fd); 
27     errno = err; 
28return rval;
29}
30
31
32int serv_listen (constchar *name)
33{
34int fd, len, err, rval; 
35struct sockaddr_un un; 
36
37if ((fd = socket (AF_UNIX, SOCK_STREAM, 0)) < 0) {
38         printf ("socket failed
"); 
39return -1; 
40    }
41
42     printf ("create socket ok
"); 
43    unlink (name); 
44     memset (&un, 0, sizeof(un)); 
45     un.sun_family = AF_UNIX; 
46    strcpy (un.sun_path, name); 
47     len = offsetof (struct sockaddr_un, sun_path) + strlen (name); 
48
49if (bind (fd, (struct sockaddr *)&un, len) < 0) {
50         err = errno; 
51         printf ("bind failed
");  
52         rval = -2; 
53goto errout; 
54    }
55
56     printf ("bind socket to path ok
"); 
57if (listen (fd, QLEN) < 0) { 
58         err = errno; 
59         printf ("listen failed, errno %d
", errno); 
60         rval = -3; 
61goto errout; 
62    }
63
64     printf ("start listen on socket ok
"); 
65return fd; 
66errout:
67    close (fd); 
68     errno = err; 
69return rval; 
70}
71
72int serv_accept (int listenfd, uid_t *uidptr)
73{
74int clifd, err, rval; 
75    time_t staletime; 
76struct sockaddr_un un; 
77struct stat statbuf; 
78
79     size_t len = sizeof (un); 
80if ((clifd = accept (listenfd, (struct sockaddr *)&un, &len)) < 0) { 
81         printf ("accept failed
"); 
82return -1; 
83    }
84
85     len -= offsetof (struct sockaddr_un, sun_path); 
86     un.sun_path[len] = 0; 
87     printf ("accept %s ok
", un.sun_path); 
88
89    unlink (un.sun_path); 
90return clifd; 
91
92errout:
93    close (clifd); 
94     errno = err; 
95return rval; 
96 }

出错的位置在 serv_listen (line 57) 处，出错时的 server 端输出为：

Jan 17 00:24:44 localhost opend: create socket ok

Jan 17 00:24:44 localhost opend: bind socket to path ok

Jan 17 00:24:44 localhost opend: listen failed, errno 95

Jan 17 00:24:44 localhost opend: serv_listen error: Operation not supported

errno 95 为 ENOTSUPP。不以 daemon 运行时正常的输出如下：

create socket ok

bind socket to path ok

start listen on socket ok

accept ok

new connection: uid 0, fd 4

可能细心的读者会觉得，以 daemon 方式运行 printf 怎么还可以输出呢，是有以下宏定义做了处理：

1#ifdef USE_APUE
2 #include "../apue.h"
3#define printf log_msg
4#endif

以 daemon 运行时会定义 USE_APUE 宏，从而将 printf 重定义为 log_msg 输出到 syslog。

下面是 server 端的代码：

csopend2.c

 1int main (int argc, char *argv[])
 2{
 3int c = 0; 
 4     log_open ("open.serv", LOG_PID, LOG_USER); 
 5
 6     opterr = 0; // don"t want getopt() writting to stderr !
 7while ((c = getopt (argc, argv, "d")) != EOF) {
 8switch (c) { 
 9case"d":
10                 debug = log_to_stderr = 1; 
11break; 
12case"?":
13                 err_quit ("unrecongnized option: -%c", optopt); 
14        }
15    }
16
17if (debug == 0)
18    {
19         log_to_stderr = 0; 
20         daemonize ("opend");
21    }
22
23    loop (); 
24return0; 
25 }

不使用 -d 时表示 daemon 运行(与常识相反?)，上面标黄的代码就是。

对应的 client 端代码：

csopenc.c

一开始怀疑是用于 listen 的本地 socket 文件已经存在，于是去 /tmp 目录看了下，果然有 opend 这个文件，删除之，再运行，不行；

然后怀疑是没有复用端口(?)所致，于是在 listen 之前添加了以下代码段：

1int opt = 1; 
2if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, (constvoid *)&opt, sizeof(opt)) < 0) {
3         err = errno; 
4         printf ("setsockopt failed
"); 
5         rval = -3; 
6goto errout; 
7     }