ipc.c

   1 /*
   2  * Copyright (C) 2006 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
  27 /** abort if semget() failed that many times */
  28 #define MAX_SEMOP_RETRIES 500
  29
  30 /**
  31  * define a new mutex
  32  *
  33  * \return the identifier for the new mutex on success, -E_SEM_GET
  34  * on errors.
  35  *
  36  * \sa semget(2)
  37  */
  38 int mutex_new(void)
  39 {
  40         int ret = semget(IPC_PRIVATE, 1, IPC_CREAT | 0666);
  41         return ret < 0?  -E_SEM_GET : ret;
  42 }
  43
  44 /**
  45  * destroy a mutex
  46  *
  47  * \para, id the identifier of the mutex to be destroyed
  48  *
  49  * \returns Positive on success, -E_SEM_REMOVE on errors.
  50  *
  51  * \sa semctl(2)
  52  */
  53 int mutex_destroy(int id)
  54 {
  55         int ret = semctl(id, 0, IPC_RMID);
  56         return ret < 0? -E_SEM_REMOVE : 1;
  57 }
  58
  59 static void para_semop(int id, struct sembuf *sops, int num)
  60 {
  61         int i;
  62
  63         for (i = 0; i < MAX_SEMOP_RETRIES; i++)
  64                 if (semop(id, sops, num) >= 0)
  65                         return;
  66         PARA_EMERG_LOG("semop failed %d times, aborting\n", MAX_SEMOP_RETRIES);
  67         exit(EXIT_FAILURE);
  68 }
  69
  70 /**
  71  * lock the given mutex
  72  *
  73  * This function either succeeds or aborts.
  74  *
  75  * \sa semop(2), struct misc_meta_data
  76  */
  77 void mutex_lock(int id)
  78 {
  79         struct sembuf sops[2] = {
  80                 {
  81                         .sem_num = 0,
  82                         .sem_op = 0,
  83                         .sem_flg = SEM_UNDO
  84                 },
  85                 {
  86                         .sem_num = 0,
  87                         .sem_op = 1,
  88                         .sem_flg = SEM_UNDO
  89                 }
  90         };
  91         para_semop(id, sops, 2);
  92 }
  93
  94 /**
  95  * unlock a mutex
  96  *
  97  * \param id the identifier of the mutex
  98  *
  99  * This function either succeeds or aborts.
 100  *
 101  * \sa semop(2), struct misc_meta_data
 102  */
 103 void mutex_unlock(int id)
 104 {
 105         struct sembuf sops[1] = {
 106                 {
 107                         .sem_num = 0,
 108                         .sem_op = -1,
 109                         .sem_flg = SEM_UNDO
 110                 },
 111         };
 112         para_semop(id, sops, 1);
 113 }
 114
 115 /**
 116  * create a new shared memory area of given size
 117  *
 118  * \sa shmget(2)
 119  */
 120 int shm_new(size_t size)
 121 {
 122         int ret = shmget(IPC_PRIVATE, size, IPC_CREAT | IPC_EXCL | 0600);
 123         return ret < 0 ? -E_SHM_GET : ret;
 124 }
 125
 126 /**
 127  * destroy the given shared memory area
 128  * \sa shmctl(2)
 129  **/
 130 int shm_destroy(int id)
 131 {
 132         struct shmid_ds shm_desc;
 133         int ret = shmctl(id, IPC_RMID, &shm_desc);
 134         return ret < 0? -E_SHM_DESTROY : ret;
 135 }
 136
 137 /**
 138  * attach a shared memory segment
 139  *
 140  * \param id the identifier of the shared memory segment to attach
 141  * \param mode either ATTACH_RO (read only) or ATTACH_RW (read/write)
 142  * \param result points to the attached arer which to the
 143  *
 144  * \returns positive on success, -E_SHM_ATTACH on errrors.
 145  *
 146  * \sa shmat(2)
 147  */
 148 int shm_attach(int id, enum shm_attach_mode mode, void **result)
 149 {
 150         if (mode == ATTACH_RW) {
 151                 *result = shmat(id, NULL, 0);
 152                 return *result? 1 : -E_SHM_ATTACH;
 153         }
 154         *result = shmat(id, NULL, SHM_RDONLY);
 155         return *result? 1 : -E_SHM_ATTACH;
 156 }
 157
 158 /**
 159  * detach a shared memory segment
 160  *
 161  * \param addr the address of the attached segment
 162  *
 163  * \returns positive on success, -E_SHM_DETACH on errors.
 164  *
 165  * \sa shmdt(2)
 166  */
 167 int shm_detach(void *addr)
 168 {
 169         int ret = shmdt(addr);
 170         return ret < 0? -E_SHM_DETACH : 1;
 171 }