ipc/shm_semaph.c

   1 /***************************************************************************
   2  * Copyright 1995, Technion, Israel Institute of Technology
   3  * Electrical Eng, Software Lab.
   4  * Author:    Michael Veksler.
   5  ***************************************************************************
   6  * File:      shm_semaph.c
   7  * Purpose:   Handle semaphores for shared memory operations.
   8  ***************************************************************************
   9  */
  10 #ifdef CONFIG_IPC
  11
  12 #define inline __inline__
  13 #include <assert.h>
  14 #include <unistd.h>
  15 #include <sys/sem.h>
  16 #include <errno.h>
  17 #include "debug.h"
  18 #include "shm_semaph.h"
  19
  20 DEFAULT_DEBUG_CHANNEL(sem)
  21 #define SEM_READ  0
  22 #define SEM_WRITE 1
  23
  24 /* IMPORTANT: Make sure that killed process will not lock everything.
  25  *            If possible, restrict usage of these functions.
  26  */
  27 void shm_read_wait(shm_sem semid)
  28 {
  29   struct sembuf sop[2];
  30   int ret;
  31
  32   TRACE(sem,"(%d)\n",semid);
  33   sop[0].sem_num=SEM_READ;
  34   sop[0].sem_op=1;                 /* add this read instance */
  35   sop[0].sem_flg=SEM_UNDO;         /* undo in case process dies */
  36
  37   sop[1].sem_num=SEM_WRITE;
  38   sop[1].sem_op=0;                 /* wait until no writing instance exists */
  39   sop[1].sem_flg=SEM_UNDO;
  40
  41   do {
  42      ret=semop (semid,sop , 2);
  43   } while (ret<0 && errno==EINTR);  /* interrupted system call? */
  44
  45   if (ret<0)
  46      WARN(sem,"(semid=%d,errno=%d): Failed semaphore lock for read\n",
  47          semid, errno);
  48 }
  49 void shm_write_wait(shm_sem semid)
  50 {
  51   struct sembuf sop[3];
  52   int ret;
  53
  54   TRACE(sem,"(%d)\n",semid);
  55   sop[0].sem_num=SEM_READ;
  56   sop[0].sem_op=0;                 /* wait until no reading instance exist */
  57   sop[0].sem_flg=SEM_UNDO;
  58
  59   sop[1].sem_num=SEM_WRITE;
  60   sop[1].sem_op=1;                 /* writing is in progress - disable read */
  61   sop[1].sem_flg=SEM_UNDO;         /* undo if process dies */
  62
  63   sop[2].sem_num=SEM_READ;
  64   sop[2].sem_op=1;                 /* disable new writes */
  65   sop[2].sem_flg=SEM_UNDO;
  66
  67   do {
  68      ret=semop (semid,sop , 3);
  69   } while (ret<0 && errno==EINTR);  /* interrupted system call? */
  70
  71   if (ret<0)                       /* test for the error */
  72      WARN(sem,"(semid=%d,errno=%d): Failed semaphore lock for write\n",
  73              semid, errno);
  74 }
  75 void shm_write_signal(shm_sem semid)
  76 {
  77   struct sembuf sop[2];
  78   int ret;
  79
  80   TRACE(sem,"(%d)\n",semid);
  81   sop[0].sem_num=SEM_READ;
  82   sop[0].sem_op=-1;
  83   sop[0].sem_flg=IPC_NOWAIT | SEM_UNDO; /* no reason to wait */
  84
  85   sop[1].sem_num=SEM_WRITE;
  86   sop[1].sem_op=-1;
  87   sop[1].sem_flg=IPC_NOWAIT | SEM_UNDO; /* no reason to wait */
  88
  89   do {
  90      ret=semop (semid,sop , 2);
  91   } while (ret<0 && errno==EINTR);  /* interrupted system call? */
  92
  93   if (ret<0)                       /* test for the error */
  94      WARN(sem,"(semid=%d,errno=%d): Failed semaphore unlock for write\n",
  95              semid, errno);
  96 }
  97
  98 void shm_read_signal(shm_sem semid)
  99 {
 100   struct sembuf sop[2];
 101   int ret;
 102
 103   TRACE(sem,"(%d)\n",semid);
 104   sop[0].sem_num=SEM_READ;
 105   sop[0].sem_op=-1;
 106   sop[0].sem_flg=IPC_NOWAIT | SEM_UNDO; /* no reason to wait */
 107
 108   do {
 109      ret=semop (semid,sop , 1);
 110   } while (ret<0 && errno==EINTR);  /* interrupted system call? */
 111
 112   if (ret<0)                       /* test for the error */
 113      WARN(sem,"(semid=%d,errno=%d): Failed semaphore unlock for read\n",
 114              semid, errno);
 115 }
 116
 117 void shm_sem_init(shm_sem *sptr)
 118 {
 119   shm_sem semid;
 120   union semun arg;
 121
 122   semid=semget (IPC_PRIVATE, 2, 0700 | IPC_CREAT);
 123
 124   arg.val=0;
 125   semctl (semid, 0, SETVAL, arg);
 126   semctl (semid, 1, SETVAL, arg);
 127   *sptr=semid;
 128 }
 129
 130 void shm_sem_done(shm_sem *semptr)
 131 {
 132   union semun arg;
 133
 134   semctl (*semptr, 0, IPC_RMID , arg);
 135   semctl (*semptr, 1, IPC_RMID , arg);
 136
 137   *semptr= -1;
 138 }
 139
 140 #endif  /* CONFIG_IPC */