command.c: simplify handle_connect()
[paraslash.git] / ipc.c
1 /*
2 * Copyright (C) 2006-2007 Andre Noll <maan@systemlinux.org>
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111, USA.
17 */
18
19 /** \file ipc.c interprocess communication and shared memory helpers */
20
21 #include "para.h"
22 #include "error.h"
23 #include "ipc.h"
24 #include <sys/ipc.h>
25 #include <sys/shm.h>
26 #include <sys/sem.h>
27
28 /** abort if semget() failed that many times */
29 #define MAX_SEMOP_RETRIES 500
30
31 /**
32 * define a new mutex
33 *
34 * \return the identifier for the new mutex on success, \a -E_SEM_GET
35 * on errors.
36 *
37 * \sa semget(2)
38 */
39 int mutex_new(void)
40 {
41 int ret = semget(IPC_PRIVATE, 1, IPC_CREAT | 0666);
42 return ret < 0? -E_SEM_GET : ret;
43 }
44
45 /**
46 * destroy a mutex
47 *
48 * \param id the identifier of the mutex to be destroyed
49 *
50 * \return Positive on success, \a -E_SEM_REMOVE on errors.
51 *
52 * \sa semctl(2)
53 */
54 int mutex_destroy(int id)
55 {
56 int ret = semctl(id, 0, IPC_RMID);
57 return ret < 0? -E_SEM_REMOVE : 1;
58 }
59
60 static void para_semop(int id, struct sembuf *sops, int num)
61 {
62 int i;
63
64 for (i = 0; i < MAX_SEMOP_RETRIES; i++)
65 if (semop(id, sops, num) >= 0)
66 return;
67 PARA_EMERG_LOG("semop failed %d times, aborting\n", MAX_SEMOP_RETRIES);
68 exit(EXIT_FAILURE);
69 }
70
71 /**
72 * lock the given mutex
73 *
74 * \param id of the shared memory area to lock
75 *
76 * This function either succeeds or aborts.
77 *
78 * \sa semop(2), struct misc_meta_data
79 */
80 void mutex_lock(int id)
81 {
82 struct sembuf sops[2] = {
83 {
84 .sem_num = 0,
85 .sem_op = 0,
86 .sem_flg = SEM_UNDO
87 },
88 {
89 .sem_num = 0,
90 .sem_op = 1,
91 .sem_flg = SEM_UNDO
92 }
93 };
94 para_semop(id, sops, 2);
95 }
96
97 /**
98 * unlock a mutex
99 *
100 * \param id the identifier of the mutex
101 *
102 * This function either succeeds or aborts.
103 *
104 * \sa semop(2), struct misc_meta_data
105 */
106 void mutex_unlock(int id)
107 {
108 struct sembuf sops[1] = {
109 {
110 .sem_num = 0,
111 .sem_op = -1,
112 .sem_flg = SEM_UNDO
113 },
114 };
115 para_semop(id, sops, 1);
116 }
117
118 /**
119 * create a new shared memory area of given size
120 *
121 * \param size the size of the shared memory area to create
122 *
123 * \return The id of the shared memory areay on success, \a -E_SHM_GET on errors.
124 *
125 * \sa shmget(2)
126 */
127 int shm_new(size_t size)
128 {
129 int ret = shmget(IPC_PRIVATE, size, IPC_CREAT | IPC_EXCL | 0600);
130 return ret < 0 ? -E_SHM_GET : ret;
131 }
132
133 /**
134 * destroy the given shared memory area
135 *
136 * \param id the shared memory id
137 *
138 * \return The return value of the underlying shmctl() call on success,
139 * \a -E_SHM_DESTROY on errors.
140 *
141 * \sa shmctl(2)
142 */
143 int shm_destroy(int id)
144 {
145 struct shmid_ds shm_desc;
146 int ret = shmctl(id, IPC_RMID, &shm_desc);
147 return ret < 0? -E_SHM_DESTROY : ret;
148 }
149
150 /**
151 * attach a shared memory segment
152 *
153 * \param id the identifier of the shared memory segment to attach
154 * \param mode either ATTACH_RO (read only) or ATTACH_RW (read/write)
155 * \param result points to the attached area just attached
156 *
157 * \return positive on success, \a -E_SHM_ATTACH on errors.
158 *
159 * \sa shmat(2)
160 */
161 int shm_attach(int id, enum shm_attach_mode mode, void **result)
162 {
163 if (mode == ATTACH_RW) {
164 *result = shmat(id, NULL, 0);
165 return *result? 1 : -E_SHM_ATTACH;
166 }
167 *result = shmat(id, NULL, SHM_RDONLY);
168 return *result? 1 : -E_SHM_ATTACH;
169 }
170
171 /**
172 * detach a shared memory segment
173 *
174 * \param addr the address of the attached segment
175 *
176 * \return positive on success, \a -E_SHM_DETACH on errors.
177 *
178 * \sa shmdt(2)
179 */
180 int shm_detach(void *addr)
181 {
182 int ret = shmdt(addr);
183 return ret < 0? -E_SHM_DETACH : 1;
184 }