Merge /fml/ag-raetsch/home/maan/scm/paraslash_meins/paraslash
[paraslash.git] / ipc.c
1 /*
2 * Copyright (C) 2006-2007 Andre Noll <maan@systemlinux.org>
3 *
4 * Licensed under the GPL v2. For licencing details see COPYING.
5 */
6
7 /** \file ipc.c interprocess communication and shared memory helpers */
8
9 #include "para.h"
10 #include "error.h"
11 #include "ipc.h"
12 #include <sys/ipc.h>
13 #include <sys/shm.h>
14 #include <sys/sem.h>
15
16 /** abort if semget() failed that many times */
17 #define MAX_SEMOP_RETRIES 500
18
19 /**
20 * define a new mutex
21 *
22 * \return the identifier for the new mutex on success, \a -E_SEM_GET
23 * on errors.
24 *
25 * \sa semget(2)
26 */
27 int mutex_new(void)
28 {
29 int ret = semget(IPC_PRIVATE, 1, IPC_CREAT | 0666);
30 return ret < 0? -E_SEM_GET : ret;
31 }
32
33 /**
34 * destroy a mutex
35 *
36 * \param id the identifier of the mutex to be destroyed
37 *
38 * \return Positive on success, \a -E_SEM_REMOVE on errors.
39 *
40 * \sa semctl(2)
41 */
42 int mutex_destroy(int id)
43 {
44 int ret = semctl(id, 0, IPC_RMID);
45 return ret < 0? -E_SEM_REMOVE : 1;
46 }
47
48 static void para_semop(int id, struct sembuf *sops, unsigned num)
49 {
50 int i;
51
52 for (i = 0; i < MAX_SEMOP_RETRIES; i++)
53 if (semop(id, sops, num) >= 0)
54 return;
55 PARA_EMERG_LOG("semop failed %d times, aborting\n", MAX_SEMOP_RETRIES);
56 exit(EXIT_FAILURE);
57 }
58
59 /**
60 * lock the given mutex
61 *
62 * \param id of the shared memory area to lock
63 *
64 * This function either succeeds or aborts.
65 *
66 * \sa semop(2), struct misc_meta_data
67 */
68 void mutex_lock(int id)
69 {
70 struct sembuf sops[2] = {
71 {
72 .sem_num = 0,
73 .sem_op = 0,
74 .sem_flg = SEM_UNDO
75 },
76 {
77 .sem_num = 0,
78 .sem_op = 1,
79 .sem_flg = SEM_UNDO
80 }
81 };
82 para_semop(id, sops, 2);
83 }
84
85 /**
86 * unlock a mutex
87 *
88 * \param id the identifier of the mutex
89 *
90 * This function either succeeds or aborts.
91 *
92 * \sa semop(2), struct misc_meta_data
93 */
94 void mutex_unlock(int id)
95 {
96 struct sembuf sops[1] = {
97 {
98 .sem_num = 0,
99 .sem_op = -1,
100 .sem_flg = SEM_UNDO
101 },
102 };
103 para_semop(id, sops, 1);
104 }
105
106 /**
107 * create a new shared memory area of given size
108 *
109 * \param size the size of the shared memory area to create
110 *
111 * \return The id of the shared memory areay on success, \a -E_SHM_GET on errors.
112 *
113 * \sa shmget(2)
114 */
115 int shm_new(size_t size)
116 {
117 int ret = shmget(IPC_PRIVATE, size, IPC_CREAT | IPC_EXCL | 0600);
118 return ret < 0 ? -E_SHM_GET : ret;
119 }
120
121 /**
122 * destroy the given shared memory area
123 *
124 * \param id the shared memory id
125 *
126 * \return The return value of the underlying shmctl() call on success,
127 * \a -E_SHM_DESTROY on errors.
128 *
129 * \sa shmctl(2)
130 */
131 int shm_destroy(int id)
132 {
133 struct shmid_ds shm_desc;
134 int ret = shmctl(id, IPC_RMID, &shm_desc);
135 return ret < 0? -E_SHM_DESTROY : ret;
136 }
137
138 /**
139 * attach a shared memory segment
140 *
141 * \param id the identifier of the shared memory segment to attach
142 * \param mode either ATTACH_RO (read only) or ATTACH_RW (read/write)
143 * \param result points to the attached area just attached
144 *
145 * \return positive on success, \a -E_SHM_ATTACH on errors.
146 *
147 * \sa shmat(2)
148 */
149 int shm_attach(int id, enum shm_attach_mode mode, void **result)
150 {
151 if (mode == ATTACH_RW) {
152 *result = shmat(id, NULL, 0);
153 return *result? 1 : -E_SHM_ATTACH;
154 }
155 *result = shmat(id, NULL, SHM_RDONLY);
156 return *result? 1 : -E_SHM_ATTACH;
157 }
158
159 /**
160 * detach a shared memory segment
161 *
162 * \param addr the address of the attached segment
163 *
164 * \return positive on success, \a -E_SHM_DETACH on errors.
165 *
166 * \sa shmdt(2)
167 */
168 int shm_detach(void *addr)
169 {
170 int ret = shmdt(addr);
171 return ret < 0? -E_SHM_DETACH : 1;
172 }