src/ipc/semtool.c

   1 /*****************************************************************************
   2  Excerpt from "Linux Programmer's Guide - Chapter 6"
   3  (C)opyright 1994-1995, Scott Burkett
   4  *****************************************************************************
   5  MODULE: semtool.c
   6  *****************************************************************************
   7  A command line tool for tinkering with SysV style Semaphore Sets
   8
   9  *****************************************************************************/
  10 /*
  11  * This program is free software; you can redistribute it and/or
  12  * modify it under the terms of the GNU General Public License
  13  * as published by the Free Software Foundation; either version 2
  14  * of the License, or (at your option) any later version.
  15  *
  16  * This program is distributed in the hope that it will be useful,
  17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19  * GNU General Public License for more details.
  20  *
  21  * You should have received a copy of the GNU General Public License
  22  * along with this program; if not, write to the Free Software
  23  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  24  *
  25  * See the COPYING file for license information.
  26  */
  27
  28 #if HAVE_CONFIG_H
  29 # include "config.h"
  30 #endif
  31
  32 #include "common.h"
  33
  34 #if HAVE_SYS_IPC_H
  35 # include <sys/ipc.h>
  36 #endif
  37 #if HAVE_SYS_SEM_H
  38 # include <sys/sem.h>
  39 #endif
  40
  41 /* cygserver doesn't define this constant where we
  42    can get it, so just use the default configuration
  43    value */
  44 #ifndef SEMMSL
  45 # define SEMMSL 60
  46 #endif
  47
  48 /* arg for semctl system calls. */
  49 union semun
  50 {
  51   int val;                      /* value for SETVAL */
  52   struct semid_ds *buf;         /* buffer for IPC_STAT & IPC_SET */
  53   ushort *array;                /* array for GETALL & SETALL */
  54   struct seminfo *__buf;        /* buffer for IPC_INFO */
  55   void *__pad;
  56 };
  57
  58 #define SEM_RESOURCE_MAX        1       /* Initial value of all semaphores */
  59
  60 void opensem (int *sid, key_t key);
  61 void createsem (int *sid, key_t key, int members);
  62 void locksem (int sid, int member);
  63 void unlocksem (int sid, int member);
  64 void removesem (int sid);
  65 unsigned short get_member_count (int sid);
  66 int getval (int sid, int member);
  67 void dispval (int sid, int member);
  68 void changemode (int sid, char *mode);
  69 void usage (void);
  70
  71 int
  72 main (int argc, char *argv[])
  73 {
  74   key_t key;
  75   int semset_id;
  76
  77   if (argc == 1)
  78     usage ();
  79
  80   /* Create unique key via call to ftok() */
  81   key = ftok (".", 's');
  82
  83   switch (tolower (argv[1][0]))
  84     {
  85     case 'c':
  86       if (argc != 3)
  87         usage ();
  88       createsem (&semset_id, key, atoi (argv[2]));
  89       break;
  90     case 'l':
  91       if (argc != 3)
  92         usage ();
  93       opensem (&semset_id, key);
  94       locksem (semset_id, atoi (argv[2]));
  95       break;
  96     case 'u':
  97       if (argc != 3)
  98         usage ();
  99       opensem (&semset_id, key);
 100       unlocksem (semset_id, atoi (argv[2]));
 101       break;
 102     case 'd':
 103       opensem (&semset_id, key);
 104       removesem (semset_id);
 105       break;
 106     case 'm':
 107       opensem (&semset_id, key);
 108       changemode (semset_id, argv[2]);
 109       break;
 110     default:
 111       usage ();
 112
 113     }
 114
 115   return (0);
 116 }
 117
 118 void
 119 opensem (int *sid, key_t key)
 120 {
 121   /* Open the semaphore set - do not create! */
 122
 123   if ((*sid = semget (key, 0, 0666)) == -1)
 124     {
 125       printf ("Semaphore set does not exist!\n");
 126       exit (1);
 127     }
 128
 129 }
 130
 131 void
 132 createsem (int *sid, key_t key, int members)
 133 {
 134   int cntr;
 135   union semun semopts;
 136
 137   if (members > SEMMSL)
 138     {
 139       printf ("Sorry, max number of semaphores in a set is %d\n", SEMMSL);
 140       exit (1);
 141     }
 142
 143   printf ("Attempting to create new semaphore set with %d members\n",
 144           members);
 145
 146   if ((*sid = semget (key, members, IPC_CREAT | IPC_EXCL | 0666)) == -1)
 147     {
 148       fprintf (stderr, "Semaphore set already exists!\n");
 149       exit (1);
 150     }
 151
 152   semopts.val = SEM_RESOURCE_MAX;
 153
 154   /* Initialize all members (could be done with SETALL) */
 155   for (cntr = 0; cntr < members; cntr++)
 156     semctl (*sid, cntr, SETVAL, semopts);
 157 }
 158
 159 void
 160 locksem (int sid, int member)
 161 {
 162   struct sembuf sem_lock = { 0, -1, IPC_NOWAIT };
 163
 164   if (member < 0 || member > (get_member_count (sid) - 1))
 165     {
 166       fprintf (stderr, "semaphore member %d out of range\n", member);
 167       return;
 168     }
 169
 170   /* Attempt to lock the semaphore set */
 171   if (!getval (sid, member))
 172     {
 173       fprintf (stderr, "Semaphore resources exhausted (no lock)!\n");
 174       exit (1);
 175     }
 176
 177   sem_lock.sem_num = member;
 178
 179   if ((semop (sid, &sem_lock, 1)) == -1)
 180     {
 181       fprintf (stderr, "Lock failed\n");
 182       exit (1);
 183     }
 184   else
 185     printf ("Semaphore resources decremented by one (locked)\n");
 186
 187   dispval (sid, member);
 188 }
 189
 190 void
 191 unlocksem (int sid, int member)
 192 {
 193   struct sembuf sem_unlock = { member, 1, IPC_NOWAIT };
 194   int semval;
 195
 196   if (member < 0 || member > (get_member_count (sid) - 1))
 197     {
 198       fprintf (stderr, "semaphore member %d out of range\n", member);
 199       return;
 200     }
 201
 202   /* Is the semaphore set locked? */
 203   semval = getval (sid, member);
 204   if (semval == SEM_RESOURCE_MAX)
 205     {
 206       fprintf (stderr, "Semaphore not locked!\n");
 207       exit (1);
 208     }
 209
 210   sem_unlock.sem_num = member;
 211
 212   /* Attempt to lock the semaphore set */
 213   if ((semop (sid, &sem_unlock, 1)) == -1)
 214     {
 215       fprintf (stderr, "Unlock failed\n");
 216       exit (1);
 217     }
 218   else
 219     printf ("Semaphore resources incremented by one (unlocked)\n");
 220
 221   dispval (sid, member);
 222 }
 223
 224 void
 225 removesem (int sid)
 226 {
 227   union semun semopts;
 228   semopts.val = 0;
 229
 230   semctl (sid, 0, IPC_RMID, semopts);
 231   printf ("Semaphore removed\n");
 232 }
 233
 234 unsigned short
 235 get_member_count (int sid)
 236 {
 237   union semun semopts;
 238   struct semid_ds mysemds;
 239
 240   semopts.buf = &mysemds;
 241
 242   /* Return number of members in the semaphore set */
 243   return (semopts.buf->sem_nsems);
 244 }
 245
 246 int
 247 getval (int sid, int member)
 248 {
 249   int semval;
 250   union semun semopts;
 251   semopts.val = 0;
 252
 253   semval = semctl (sid, member, GETVAL, semopts);
 254   return (semval);
 255 }
 256
 257 void
 258 changemode (int sid, char *mode)
 259 {
 260   int rc;
 261   union semun semopts;
 262   struct semid_ds mysemds;
 263
 264   /* Get current values for internal data structure */
 265   semopts.buf = &mysemds;
 266
 267   rc = semctl (sid, 0, IPC_STAT, semopts);
 268
 269   if (rc == -1)
 270     {
 271       perror ("semctl");
 272       exit (1);
 273     }
 274
 275   printf ("Old permissions were %o\n", semopts.buf->sem_perm.mode);
 276
 277   /* Change the permissions on the semaphore */
 278   sscanf (mode, "%ho", &semopts.buf->sem_perm.mode);
 279
 280   /* Update the internal data structure */
 281   semctl (sid, 0, IPC_SET, semopts);
 282
 283   printf ("Updated...\n");
 284
 285 }
 286
 287 void
 288 dispval (int sid, int member)
 289 {
 290   int semval;
 291   union semun semopts;
 292   semopts.val = 0;
 293
 294   semval = semctl (sid, member, GETVAL, semopts);
 295   printf ("semval for member %d is %d\n", member, semval);
 296 }
 297
 298 void
 299 usage (void)
 300 {
 301   fprintf (stderr, "semtool - A utility for tinkering with semaphores\n");
 302   fprintf (stderr, "\nUSAGE:  semtool  (c)reate <semcount>\n");
 303   fprintf (stderr, "                 (l)ock <sem #>\n");
 304   fprintf (stderr, "                 (u)nlock <sem #>\n");
 305   fprintf (stderr, "                 (d)elete\n");
 306   fprintf (stderr, "                 (m)ode <mode>\n");
 307   exit (1);
 308 }