sem.c

在linux下的进程间通信的源代码

		goto out_free;
	}
	case SETALL:
	{
		int i;
		struct sem_undo *un;

		sem_unlock(semid);

		if(nsems > SEMMSL_FAST) {
			sem_io = ipc_alloc(sizeof(ushort)*nsems);
			if(sem_io == NULL)
				return -ENOMEM;
		}

		if (copy_from_user (sem_io, arg.array, nsems*sizeof(ushort))) {
			err = -EFAULT;
			goto out_free;
		}

		for (i = 0; i < nsems; i++) {
			if (sem_io[i] > SEMVMX) {
				err = -ERANGE;
				goto out_free;
			}
		}
		err = sem_revalidate(semid, sma, nsems, S_IWUGO);
		if(err)
			goto out_free;

		for (i = 0; i < nsems; i++)
			sma->sem_base[i].semval = sem_io[i];
		for (un = sma->undo; un; un = un->id_next)
			for (i = 0; i < nsems; i++)
				un->semadj[i] = 0;
		sma->sem_ctime = CURRENT_TIME;
		/* maybe some queued-up processes were waiting for this */
		update_queue(sma);
		err = 0;
		goto out_unlock;
	}
	case IPC_STAT:
	{
		struct semid64_ds tbuf;
		memset(&tbuf,0,sizeof(tbuf));
		kernel_to_ipc64_perm(&sma->sem_perm, &tbuf.sem_perm);
		tbuf.sem_otime  = sma->sem_otime;
		tbuf.sem_ctime  = sma->sem_ctime;
		tbuf.sem_nsems  = sma->sem_nsems;
		sem_unlock(semid);
		if (copy_semid_to_user (arg.buf, &tbuf, version))
			return -EFAULT;
		return 0;
	}
	/* GETVAL, GETPID, GETNCTN, GETZCNT, SETVAL: fall-through */
	}
	err = -EINVAL;
	if(semnum < 0 || semnum >= nsems)
		goto out_unlock;

	curr = &sma->sem_base[semnum];

	switch (cmd) {
	case GETVAL:
		err = curr->semval;
		goto out_unlock;
	case GETPID:
		err = curr->sempid & 0xffff;
		goto out_unlock;
	case GETNCNT:
		err = count_semncnt(sma,semnum);
		goto out_unlock;
	case GETZCNT:
		err = count_semzcnt(sma,semnum);
		goto out_unlock;
	case SETVAL:
	{
		int val = arg.val;
		struct sem_undo *un;
		err = -ERANGE;
		if (val > SEMVMX || val < 0)
			goto out_unlock;

		for (un = sma->undo; un; un = un->id_next)
			un->semadj[semnum] = 0;
		curr->semval = val;
		sma->sem_ctime = CURRENT_TIME;
		/* maybe some queued-up processes were waiting for this */
		update_queue(sma);
		err = 0;
		goto out_unlock;
	}
	}
out_unlock:
	sem_unlock(semid);
out_free:
	if(sem_io != fast_sem_io)
		ipc_free(sem_io, sizeof(ushort)*nsems);
	return err;
}

struct sem_setbuf {
	uid_t	uid;
	gid_t	gid;
	mode_t	mode;
};

static inline unsigned long copy_semid_from_user(struct sem_setbuf *out, void *buf, int version)
{
	switch(version) {
	case IPC_64:
	    {
		struct semid64_ds tbuf;

		if(copy_from_user(&tbuf, buf, sizeof(tbuf)))
			return -EFAULT;

		out->uid	= tbuf.sem_perm.uid;
		out->gid	= tbuf.sem_perm.gid;
		out->mode	= tbuf.sem_perm.mode;

		return 0;
	    }
	case IPC_OLD:
	    {
		struct semid_ds tbuf_old;

		if(copy_from_user(&tbuf_old, buf, sizeof(tbuf_old)))
			return -EFAULT;

		out->uid	= tbuf_old.sem_perm.uid;
		out->gid	= tbuf_old.sem_perm.gid;
		out->mode	= tbuf_old.sem_perm.mode;

		return 0;
	    }
	default:
		return -EINVAL;
	}
}

int semctl_down(int semid, int semnum, int cmd, int version, union semun arg)
{
	struct sem_array *sma;
	int err;
	struct sem_setbuf setbuf;
	struct kern_ipc_perm *ipcp;

	if(cmd == IPC_SET) {
		if(copy_semid_from_user (&setbuf, arg.buf, version))
			return -EFAULT;
	}
	sma = sem_lock(semid);
	if(sma==NULL)
		return -EINVAL;

	if (sem_checkid(sma,semid)) {
		err=-EIDRM;
		goto out_unlock;
	}	
	ipcp = &sma->sem_perm;
	
	if (current->euid != ipcp->cuid && 
	    current->euid != ipcp->uid && !capable(CAP_SYS_ADMIN)) {
	    	err=-EPERM;
		goto out_unlock;
	}

	switch(cmd){
	case IPC_RMID:
		freeary(semid);
		err = 0;
		break;
	case IPC_SET:
		ipcp->uid = setbuf.uid;
		ipcp->gid = setbuf.gid;
		ipcp->mode = (ipcp->mode & ~S_IRWXUGO)
				| (setbuf.mode & S_IRWXUGO);
		sma->sem_ctime = CURRENT_TIME;
		sem_unlock(semid);
		err = 0;
		break;
	default:
		sem_unlock(semid);
		err = -EINVAL;
		break;
	}
	return err;

out_unlock:
	sem_unlock(semid);
	return err;
}

asmlinkage long sys_semctl (int semid, int semnum, int cmd, union semun arg)
{
	int err = -EINVAL;
	int version;

	if (semid < 0)
		return -EINVAL;

	version = ipc_parse_version(&cmd);

	switch(cmd) {
	case IPC_INFO:
	case SEM_INFO:
	case SEM_STAT:
		err = semctl_nolock(semid,semnum,cmd,version,arg);
		return err;
	case GETALL:
	case GETVAL:
	case GETPID:
	case GETNCNT:
	case GETZCNT:
	case IPC_STAT:
	case SETVAL:
	case SETALL:
		err = semctl_main(semid,semnum,cmd,version,arg);
		return err;
	case IPC_RMID:
	case IPC_SET:
		down(&sem_ids.sem);
		err = semctl_down(semid,semnum,cmd,version,arg);
		up(&sem_ids.sem);
		return err;
	default:
		return -EINVAL;
	}
}

static struct sem_undo* freeundos(struct sem_array *sma, struct sem_undo* un)
{
	struct sem_undo* u;
	struct sem_undo** up;

	for(up = &current->semundo;(u=*up);up=&u->proc_next) {
		if(un==u) {
			un=u->proc_next;
			*up=un;
			kfree(u);
			return un;
		}
	}
	printk ("freeundos undo list error id=%d\n", un->semid);
	return un->proc_next;
}

/* returns without sem_lock on error! */
static int alloc_undo(struct sem_array *sma, struct sem_undo** unp, int semid, int alter)
{
	int size, nsems, error;
	struct sem_undo *un;

	nsems = sma->sem_nsems;
	size = sizeof(struct sem_undo) + sizeof(short)*nsems;
	sem_unlock(semid);

	un = (struct sem_undo *) kmalloc(size, GFP_KERNEL);
	if (!un)
		return -ENOMEM;

	memset(un, 0, size);
	error = sem_revalidate(semid, sma, nsems, alter ? S_IWUGO : S_IRUGO);
	if(error) {
		kfree(un);
		return error;
	}

	un->semadj = (short *) &un[1];
	un->semid = semid;
	un->proc_next = current->semundo;
	current->semundo = un;
	un->id_next = sma->undo;
	sma->undo = un;
	*unp = un;
	return 0;
}

asmlinkage long sys_semop (int semid, struct sembuf *tsops, unsigned nsops)
{
	int error = -EINVAL;
	struct sem_array *sma;
	struct sembuf fast_sops[SEMOPM_FAST];
	struct sembuf* sops = fast_sops, *sop;
	struct sem_undo *un;
	int undos = 0, decrease = 0, alter = 0;
	struct sem_queue queue;

	if (nsops < 1 || semid < 0)
		return -EINVAL;
	if (nsops > sc_semopm)
		return -E2BIG;
	if(nsops > SEMOPM_FAST) {
		sops = kmalloc(sizeof(*sops)*nsops,GFP_KERNEL);
		if(sops==NULL)
			return -ENOMEM;
	}
	if (copy_from_user (sops, tsops, nsops * sizeof(*tsops))) {
		error=-EFAULT;
		goto out_free;
	}
	sma = sem_lock(semid);
	error=-EINVAL;
	if(sma==NULL)
		goto out_free;
	error = -EIDRM;
	if (sem_checkid(sma,semid))
		goto out_unlock_free;
	error = -EFBIG;
	for (sop = sops; sop < sops + nsops; sop++) {
		if (sop->sem_num >= sma->sem_nsems)
			goto out_unlock_free;
		if (sop->sem_flg & SEM_UNDO)
			undos++;
		if (sop->sem_op < 0)
			decrease = 1;
		if (sop->sem_op > 0)
			alter = 1;
	}
	alter |= decrease;

	error = -EACCES;
	if (ipcperms(&sma->sem_perm, alter ? S_IWUGO : S_IRUGO))
		goto out_unlock_free;
	if (undos) {
		/* Make sure we have an undo structure
		 * for this process and this semaphore set.
		 */
		un=current->semundo;
		while(un != NULL) {
			if(un->semid==semid)
				break;
			if(un->semid==-1)
				un=freeundos(sma,un);
			 else
				un=un->proc_next;
		}
		if (!un) {
			error = alloc_undo(sma,&un,semid,alter);
			if(error)
				goto out_free;
		}
	} else
		un = NULL;

	error = try_atomic_semop (sma, sops, nsops, un, current->pid, 0);
	if (error <= 0)
		goto update;

	/* We need to sleep on this operation, so we put the current
	 * task into the pending queue and go to sleep.
	 */
		
	queue.sma = sma;
	queue.sops = sops;
	queue.nsops = nsops;
	queue.undo = un;
	queue.pid = current->pid;
	queue.alter = decrease;
	queue.id = semid;
	if (alter)
		append_to_queue(sma ,&queue);
	else
		prepend_to_queue(sma ,&queue);
	current->semsleeping = &queue;

	for (;;) {
		struct sem_array* tmp;
		queue.status = -EINTR;
		queue.sleeper = current;
		current->state = TASK_INTERRUPTIBLE;
		sem_unlock(semid);

		schedule();

		tmp = sem_lock(semid);
		if(tmp==NULL) {
			if(queue.status != -EIDRM)
				BUG();
			current->semsleeping = NULL;
			error = -EIDRM;
			goto out_free;
		}
		/*
		 * If queue.status == 1 we where woken up and
		 * have to retry else we simply return.
		 * If an interrupt occurred we have to clean up the
		 * queue
		 *
		 */
		if (queue.status == 1)
		{
			error = try_atomic_semop (sma, sops, nsops, un,
						  current->pid,0);
			if (error <= 0) 
				break;
		} else {
			error = queue.status;
			if (queue.prev) /* got Interrupt */
				break;
			/* Everything done by update_queue */
			current->semsleeping = NULL;
			goto out_unlock_free;
		}
	}
	current->semsleeping = NULL;
	remove_from_queue(sma,&queue);
update:
	if (alter)
		update_queue (sma);
out_unlock_free:
	sem_unlock(semid);
out_free:
	if(sops != fast_sops)
		kfree(sops);
	return error;
}

/*
 * add semadj values to semaphores, free undo structures.
 * undo structures are not freed when semaphore arrays are destroyed
 * so some of them may be out of date.
 * IMPLEMENTATION NOTE: There is some confusion over whether the
 * set of adjustments that needs to be done should be done in an atomic
 * manner or not. That is, if we are attempting to decrement the semval
 * should we queue up and wait until we can do so legally?
 * The original implementation attempted to do this (queue and wait).
 * The current implementation does not do so. The POSIX standard
 * and SVID should be consulted to determine what behavior is mandated.
 */
void sem_exit (void)
{
	struct sem_queue *q;
	struct sem_undo *u, *un = NULL, **up, **unp;
	struct sem_array *sma;
	int nsems, i;

	/* If the current process was sleeping for a semaphore,
	 * remove it from the queue.
	 */
	if ((q = current->semsleeping)) {
		int semid = q->id;
		sma = sem_lock(semid);
		current->semsleeping = NULL;

		if (q->prev) {
			if(sma==NULL)
				BUG();
			remove_from_queue(q->sma,q);
		}
		if(sma!=NULL)
			sem_unlock(semid);
	}

	for (up = &current->semundo; (u = *up); *up = u->proc_next, kfree(u)) {
		int semid = u->semid;
		if(semid == -1)
			continue;
		sma = sem_lock(semid);
		if (sma == NULL)
			continue;

		if (u->semid == -1)
			goto next_entry;

		if (sem_checkid(sma,u->semid))
			goto next_entry;

		/* remove u from the sma->undo list */
		for (unp = &sma->undo; (un = *unp); unp = &un->id_next) {
			if (u == un)
				goto found;
		}
		printk ("sem_exit undo list error id=%d\n", u->semid);
		goto next_entry;
found:
		*unp = un->id_next;
		/* perform adjustments registered in u */
		nsems = sma->sem_nsems;
		for (i = 0; i < nsems; i++) {
			struct sem * sem = &sma->sem_base[i];
			sem->semval += u->semadj[i];
			if (sem->semval < 0)
				sem->semval = 0; /* shouldn't happen */
			sem->sempid = current->pid;
		}
		sma->sem_otime = CURRENT_TIME;
		/* maybe some queued-up processes were waiting for this */
		update_queue(sma);
next_entry:
		sem_unlock(semid);
	}
	current->semundo = NULL;
}

#ifdef CONFIG_PROC_FS
static int sysvipc_sem_read_proc(char *buffer, char **start, off_t offset, int length, int *eof, void *data)
{
	off_t pos = 0;
	off_t begin = 0;
	int i, len = 0;

	len += sprintf(buffer, "       key      semid perms      nsems   uid   gid  cuid  cgid      otime      ctime\n");
	down(&sem_ids.sem);

	for(i = 0; i <= sem_ids.max_id; i++) {
		struct sem_array *sma;
		sma = sem_lock(i);
		if(sma) {
			len += sprintf(buffer + len, "%10d %10d  %4o %10lu %5u %5u %5u %5u %10lu %10lu\n",
				sma->sem_perm.key,
				sem_buildid(i,sma->sem_perm.seq),
				sma->sem_perm.mode,
				sma->sem_nsems,
				sma->sem_perm.uid,
				sma->sem_perm.gid,
				sma->sem_perm.cuid,
				sma->sem_perm.cgid,
				sma->sem_otime,
				sma->sem_ctime);
			sem_unlock(i);

			pos += len;
			if(pos < offset) {
				len = 0;
	    			begin = pos;
			}
			if(pos > offset + length)
				goto done;
		}
	}
	*eof = 1;
done:
	up(&sem_ids.sem);
	*start = buffer + (offset - begin);
	len -= (offset - begin);
	if(len > length)
		len = length;
	if(len < 0)
		len = 0;
	return len;
}
#endif