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, unsigned 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 }