/***************************************************************************** Excerpt from "Linux Programmer's Guide - Chapter 6" (C)opyright 1994-1995, Scott Burkett ***************************************************************************** MODULE: semtool.c ***************************************************************************** A command line tool for tinkering with SysV style Semaphore Sets *****************************************************************************/ /* * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation; either version 2 * of the License, or (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. * * See the COPYING file for license information. */ #if HAVE_CONFIG_H # include "config.h" #endif #include "common.h" #if HAVE_SYS_IPC_H # include #endif #if HAVE_SYS_SEM_H # include #endif /* cygserver doesn't define this constant where we can get it, so just use the default configuration value */ #ifndef SEMMSL # define SEMMSL 60 #endif /* arg for semctl system calls. */ union semun { int val; /* value for SETVAL */ struct semid_ds *buf; /* buffer for IPC_STAT & IPC_SET */ ushort *array; /* array for GETALL & SETALL */ struct seminfo *__buf; /* buffer for IPC_INFO */ void *__pad; }; #define SEM_RESOURCE_MAX 1 /* Initial value of all semaphores */ void opensem(int *sid, key_t key); void createsem(int *sid, key_t key, int members); void locksem(int sid, int member); void unlocksem(int sid, int member); void removesem(int sid); unsigned short get_member_count(int sid); int getval(int sid, int member); void dispval(int sid, int member); void changemode(int sid, char *mode); void usage(void); int main(int argc, char *argv[]) { key_t key; int semset_id; if(argc == 1) usage(); /* Create unique key via call to ftok() */ key = ftok(".", 's'); switch(tolower(argv[1][0])) { case 'c': if(argc != 3) usage(); createsem(&semset_id, key, atoi(argv[2])); break; case 'l': if(argc != 3) usage(); opensem(&semset_id, key); locksem(semset_id, atoi(argv[2])); break; case 'u': if(argc != 3) usage(); opensem(&semset_id, key); unlocksem(semset_id, atoi(argv[2])); break; case 'd': opensem(&semset_id, key); removesem(semset_id); break; case 'm': opensem(&semset_id, key); changemode(semset_id, argv[2]); break; default: usage(); } return(0); } void opensem(int *sid, key_t key) { /* Open the semaphore set - do not create! */ if((*sid = semget(key, 0, 0666)) == -1) { printf("Semaphore set does not exist!\n"); exit(1); } } void createsem(int *sid, key_t key, int members) { int cntr; union semun semopts; if(members > SEMMSL) { printf("Sorry, max number of semaphores in a set is %d\n", SEMMSL); exit(1); } printf("Attempting to create new semaphore set with %d members\n", members); if((*sid = semget(key, members, IPC_CREAT|IPC_EXCL|0666)) == -1) { fprintf(stderr, "Semaphore set already exists!\n"); exit(1); } semopts.val = SEM_RESOURCE_MAX; /* Initialize all members (could be done with SETALL) */ for(cntr=0; cntr(get_member_count(sid)-1)) { fprintf(stderr, "semaphore member %d out of range\n", member); return; } /* Attempt to lock the semaphore set */ if(!getval(sid, member)) { fprintf(stderr, "Semaphore resources exhausted (no lock)!\n"); exit(1); } sem_lock.sem_num = member; if((semop(sid, &sem_lock, 1)) == -1) { fprintf(stderr, "Lock failed\n"); exit(1); } else printf("Semaphore resources decremented by one (locked)\n"); dispval(sid, member); } void unlocksem(int sid, int member) { struct sembuf sem_unlock={ member, 1, IPC_NOWAIT}; int semval; if( member<0 || member>(get_member_count(sid)-1)) { fprintf(stderr, "semaphore member %d out of range\n", member); return; } /* Is the semaphore set locked? */ semval = getval(sid, member); if(semval == SEM_RESOURCE_MAX) { fprintf(stderr, "Semaphore not locked!\n"); exit(1); } sem_unlock.sem_num = member; /* Attempt to lock the semaphore set */ if((semop(sid, &sem_unlock, 1)) == -1) { fprintf(stderr, "Unlock failed\n"); exit(1); } else printf("Semaphore resources incremented by one (unlocked)\n"); dispval(sid, member); } void removesem(int sid) { union semun semopts; semopts.val = 0; semctl(sid, 0, IPC_RMID, semopts); printf("Semaphore removed\n"); } unsigned short get_member_count(int sid) { union semun semopts; struct semid_ds mysemds; semopts.buf = &mysemds; /* Return number of members in the semaphore set */ return(semopts.buf->sem_nsems); } int getval(int sid, int member) { int semval; union semun semopts; semopts.val = 0; semval = semctl(sid, member, GETVAL, semopts); return(semval); } void changemode(int sid, char *mode) { int rc; union semun semopts; struct semid_ds mysemds; /* Get current values for internal data structure */ semopts.buf = &mysemds; rc = semctl(sid, 0, IPC_STAT, semopts); if (rc == -1) { perror("semctl"); exit(1); } printf("Old permissions were %o\n", semopts.buf->sem_perm.mode); /* Change the permissions on the semaphore */ sscanf(mode, "%ho", &semopts.buf->sem_perm.mode); /* Update the internal data structure */ semctl(sid, 0, IPC_SET, semopts); printf("Updated...\n"); } void dispval(int sid, int member) { int semval; union semun semopts; semopts.val = 0; semval = semctl(sid, member, GETVAL, semopts); printf("semval for member %d is %d\n", member, semval); } void usage(void) { fprintf(stderr, "semtool - A utility for tinkering with semaphores\n"); fprintf(stderr, "\nUSAGE: semtool (c)reate \n"); fprintf(stderr, " (l)ock \n"); fprintf(stderr, " (u)nlock \n"); fprintf(stderr, " (d)elete\n"); fprintf(stderr, " (m)ode \n"); exit(1); }