ipc: Prefer key_t over int for System V IPC keys.
[dss.git] / ipc.c
1 #include <sys/wait.h>
2 #include <stdio.h>
3 #include <inttypes.h>
4 #include <stdlib.h>
5 #include <unistd.h>
6 #include <errno.h>
7 #include <sys/types.h>
8 #include <sys/ipc.h>
9 #include <sys/sem.h>
10 #include <string.h>
11 #include <assert.h>
12 #include <sys/stat.h>
13 #include <stddef.h>
14 #include <limits.h>
15 #include <sys/param.h>
16 #include <stdbool.h>
17
18 #include "gcc-compat.h"
19 #include "str.h"
20 #include "log.h"
21 #include "gcc-compat.h"
22 #include "err.h"
23 #include "ipc.h"
24
25 static key_t get_key(const char *config_file)
26 {
27 key_t ret;
28
29 assert(config_file);
30 ret = ftok(config_file, 'D');
31 if (ret >= 0)
32 return ret;
33 /*
34 * This happens if the user did not specify a config file, and the
35 * default config file does not exist. Another (unlikely) possibility
36 * is that the config file was removed between startup and this call.
37 * We don't care about these corner cases too much and just return a
38 * fixed key in this case.
39 */
40 return 0x0D55; /* no magic, this number just looks a bit like DSS */
41 }
42
43 static int mutex_get(key_t key, int flags)
44 {
45 int ret;
46
47 DSS_DEBUG_LOG(("getting semaphore 0x%lx\n", (long)key));
48 ret = semget(key, 2, flags);
49 if (ret < 0)
50 return -ERRNO_TO_DSS_ERROR(errno);
51 return ret;
52 }
53
54 static int do_semop(int id, struct sembuf *sops, int num)
55 {
56 int ret;
57
58 DSS_DEBUG_LOG(("calling semop\n"));
59 do {
60 ret = semop(id, sops, num);
61 if (ret >= 0)
62 return 1;
63 } while (errno == EINTR);
64 return -ERRNO_TO_DSS_ERROR(errno);
65 }
66
67 static int mutex_lock(int id)
68 {
69 struct sembuf sops[4];
70
71 DSS_DEBUG_LOG(("locking\n"));
72
73 sops[0].sem_num = 0;
74 sops[0].sem_op = 0;
75 sops[0].sem_flg = SEM_UNDO | IPC_NOWAIT;
76
77 sops[1].sem_num = 0;
78 sops[1].sem_op = 1;
79 sops[1].sem_flg = SEM_UNDO | IPC_NOWAIT;
80
81 sops[2].sem_num = 1;
82 sops[2].sem_op = 0;
83 sops[2].sem_flg = SEM_UNDO | IPC_NOWAIT;
84
85 sops[3].sem_num = 1;
86 sops[3].sem_op = 1;
87 sops[3].sem_flg = SEM_UNDO | IPC_NOWAIT;
88
89 return do_semop(id, sops, 4);
90 }
91
92 static bool mutex_is_locked(int id)
93 {
94 struct sembuf sops;
95 int ret;
96
97 DSS_DEBUG_LOG(("trying to lock\n"));
98
99 sops.sem_num = 0;
100 sops.sem_op = 0;
101 sops.sem_flg = SEM_UNDO | IPC_NOWAIT;
102
103 ret = do_semop(id, &sops, 1);
104 if (ret < 0)
105 return true;
106 return false;
107 }
108
109 int lock_dss(char *config_file)
110 {
111 int ret;
112 key_t key = get_key(config_file);
113
114 ret = mutex_get(key, IPC_CREAT | 0600);
115 if (ret < 0)
116 return ret;
117 return mutex_lock(ret);
118 }
119
120 int get_dss_pid(char *config_file, pid_t *pid)
121 {
122 int ret, semid;
123 key_t key = get_key(config_file);
124
125 if (pid)
126 *pid = 0;
127 ret = mutex_get(key, 0);
128 if (ret < 0)
129 return ret;
130 semid = ret;
131 ret = semctl(semid, 1, GETPID);
132 if (ret < 0)
133 return -E_NOT_RUNNING;
134 if (pid)
135 *pid = ret;
136 return mutex_is_locked(semid)? 1 : -E_NOT_RUNNING;
137 }