ipc.c

   1 /*
   2  * Copyright (C) 2006-2008 Andre Noll <maan@systemlinux.org>
   3  *
   4  * Licensed under the GPL v2. For licencing details see COPYING.
   5  */
   6
   7 /** \file ipc.c Inter-process 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),
  56                 (int)getpid());
  57         exit(EXIT_FAILURE);
  58 }
  59
  60 /**
  61  * Lock the given mutex.
  62  *
  63  * \param id The identifier of the shared memory area to lock.
  64  *
  65  * This function either succeeds or aborts.
  66  *
  67  * \sa semop(2), struct misc_meta_data.
  68  */
  69 void mutex_lock(int id)
  70 {
  71         struct sembuf sops[2] = {
  72                 {
  73                         .sem_num = 0,
  74                         .sem_op = 0,
  75                         .sem_flg = SEM_UNDO
  76                 },
  77                 {
  78                         .sem_num = 0,
  79                         .sem_op = 1,
  80                         .sem_flg = SEM_UNDO
  81                 }
  82         };
  83         para_semop(id, sops, 2);
  84 }
  85
  86 /**
  87  * Unlock a mutex.
  88  *
  89  * \param id The identifier of the mutex.
  90  *
  91  * This function either succeeds or aborts.
  92  *
  93  * \sa semop(2), struct misc_meta_data.
  94  */
  95 void mutex_unlock(int id)
  96 {
  97         struct sembuf sops[1] = {
  98                 {
  99                         .sem_num = 0,
 100                         .sem_op = -1,
 101                         .sem_flg = SEM_UNDO
 102                 },
 103         };
 104         para_semop(id, sops, 1);
 105 }
 106
 107 /**
 108  * Create a new shared memory area of given size.
 109  *
 110  * \param size The size of the shared memory area to create.
 111  *
 112  * \return The id of the shared memory areay on success, \a -E_SHM_GET on errors.
 113  *
 114  * \sa shmget(2).
 115  */
 116 int shm_new(size_t size)
 117 {
 118         int ret = shmget(IPC_PRIVATE, size, IPC_CREAT | IPC_EXCL | 0600);
 119         return ret < 0 ? -E_SHM_GET : ret;
 120 }
 121
 122 /**
 123  * Destroy the given shared memory area.
 124  *
 125  * \param id The shared memory identifier.
 126  *
 127  * \return The return value of the underlying shmctl() call on success,
 128  * \a -E_SHM_DESTROY on errors.
 129  *
 130  * \sa shmctl(2).
 131  */
 132 int shm_destroy(int id)
 133 {
 134         struct shmid_ds shm_desc;
 135         int ret = shmctl(id, IPC_RMID, &shm_desc);
 136         return ret < 0? -E_SHM_DESTROY : ret;
 137 }
 138
 139 /**
 140  * Attach a shared memory segment.
 141  *
 142  * \param id The identifier of the shared memory segment to attach.
 143  * \param mode either ATTACH_RO (read only) or ATTACH_RW (read/write).
 144  * \param result points to the attached area just attached.
 145  *
 146  * \return positive on success, \a -E_SHM_ATTACH on errors.
 147  *
 148  * \sa shmat(2).
 149  */
 150 int shm_attach(int id, enum shm_attach_mode mode, void **result)
 151 {
 152         if (mode == ATTACH_RW) {
 153                 *result = shmat(id, NULL, 0);
 154                 return *result? 1 : -E_SHM_ATTACH;
 155         }
 156         *result = shmat(id, NULL, SHM_RDONLY);
 157         return *result? 1 : -E_SHM_ATTACH;
 158 }
 159
 160 /**
 161  * Detach a shared memory segment.
 162  *
 163  * \param addr The address of the attached segment.
 164  *
 165  * \return Positive on success, \a -E_SHM_DETACH on errors.
 166  *
 167  * \sa shmdt(2).
 168  */
 169 int shm_detach(void *addr)
 170 {
 171         int ret = shmdt(addr);
 172         return ret < 0? -E_SHM_DETACH : 1;
 173 }