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 /**
  17  * define a new mutex
  18  *
  19  * \return the identifier for the new mutex on success, \a -E_SEM_GET
  20  * on errors.
  21  *
  22  * \sa semget(2)
  23  */
  24 int mutex_new(void)
  25 {
  26         int ret = semget(IPC_PRIVATE, 1, IPC_CREAT | 0666);
  27         return ret < 0?  -E_SEM_GET : ret;
  28 }
  29
  30 /**
  31  * destroy a mutex
  32  *
  33  * \param id the identifier of the mutex to be destroyed
  34  *
  35  * \return Positive on success, \a -E_SEM_REMOVE on errors.
  36  *
  37  * \sa semctl(2)
  38  */
  39 int mutex_destroy(int id)
  40 {
  41         int ret = semctl(id, 0, IPC_RMID);
  42         return ret < 0? -E_SEM_REMOVE : 1;
  43 }
  44
  45 static void para_semop(int id, struct sembuf *sops, int num)
  46 {
  47         do {
  48                 if (semop(id, sops, num) >= 0)
  49                         return;
  50         } while (errno == EINTR);
  51         if (errno == EIDRM) {
  52                 PARA_NOTICE_LOG("semaphore set %d was removed\n", id);
  53                 return;
  54         }
  55         PARA_EMERG_LOG("fatal semop error %s: pid %d\n", strerror(errno), getpid());
  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 }