locks.c

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		return (-EINVAL);
	}
	
	return (posix_lock_file(filp, &file_lock, cmd == F_SETLKW));
}

/* This function is called when the file is closed.
 */
void locks_remove_locks(struct task_struct *task, struct file *filp)
{
	struct file_lock *fl;

	/* For POSIX locks we free all locks on this file for the given task.
	 * For FLOCK we only free locks on this *open* file if it is the last
	 * close on that file.
	 */
	if ((fl = filp->f_inode->i_flock) != NULL) {
		if (fl->fl_flags & FL_POSIX)
			posix_remove_locks(&filp->f_inode->i_flock, task);
		else
			flock_remove_locks(&filp->f_inode->i_flock, filp);
	}

	return;
}

static void posix_remove_locks(struct file_lock **before, struct task_struct *task)
{
	struct file_lock *fl;

	while ((fl = *before) != NULL) {
		if (fl->fl_owner == task)
			locks_delete_lock(before, 0);
		else
			before = &fl->fl_next;
	}

	return;
}

static void flock_remove_locks(struct file_lock **before, struct file *filp)
{
	struct file_lock *fl;

 	while ((fl = *before) != NULL) {
		if ((fl->fl_file == filp) && (filp->f_count == 1))
 			locks_delete_lock(before, 0);
 		else
 			before = &fl->fl_next;
	}

	return;
}

int locks_verify_locked(struct inode *inode)
{
	/* Candidates for mandatory locking have the setgid bit set
	 * but no group execute bit -  an otherwise meaningless combination.
	 */
	if (IS_MANDLOCK(inode) &&
	    (inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID)
		return (locks_mandatory_locked(inode));
	return (0);
}

int locks_verify_area(int read_write, struct inode *inode, struct file *filp,
		      unsigned int offset, unsigned int count)
{
	/* Candidates for mandatory locking have the setgid bit set
	 * but no group execute bit -  an otherwise meaningless combination.
	 */
	if (IS_MANDLOCK(inode) &&
	    (inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID)
		return (locks_mandatory_area(read_write, inode, filp, offset,
					     count));
	return (0);
}

int locks_mandatory_locked(struct inode *inode)
{
	struct file_lock *fl;

	/* If there are no FL_POSIX locks then go ahead. */
	if (!(fl = inode->i_flock) || !(fl->fl_flags & FL_POSIX))
		return (0);

	/* Search the lock list for this inode for any POSIX locks.
	 */
	while (fl != NULL) {
		if (fl->fl_owner != current)
			return (-EAGAIN);
		fl = fl->fl_next;
	}
	return (0);
}

int locks_mandatory_area(int read_write, struct inode *inode,
			 struct file *filp, unsigned int offset,
			 unsigned int count)
{
	struct file_lock *fl;
	struct file_lock tfl;

	memset(&tfl, 0, sizeof(tfl));

	tfl.fl_file = filp;
	tfl.fl_flags = FL_POSIX | FL_ACCESS;
	tfl.fl_owner = current;
	tfl.fl_type = (read_write == FLOCK_VERIFY_WRITE) ? F_WRLCK : F_RDLCK;
	tfl.fl_start = offset;
	tfl.fl_end = offset + count - 1;

repeat:
	/* If there are no FL_POSIX locks then go ahead. */
	if (!(fl = inode->i_flock) || !(fl->fl_flags & FL_POSIX))
		return (0);

	/* Search the lock list for this inode for locks that conflict with
	 * the proposed read/write.
	 */
	while (fl != NULL) {
		/* Block for writes against a "read" lock,
		 * and both reads and writes against a "write" lock.
		 */
		if (posix_locks_conflict(fl, &tfl)) {
			if (filp && (filp->f_flags & O_NONBLOCK))
				return (-EAGAIN);
			if (current->signal & ~current->blocked)
				return (-ERESTARTSYS);
			if (posix_locks_deadlock(current, fl->fl_owner))
				return (-EDEADLK);

			locks_insert_block(fl, &tfl);
			interruptible_sleep_on(&tfl.fl_wait);
			locks_delete_block(fl, &tfl);

			if (current->signal & ~current->blocked)
				return (-ERESTARTSYS);
			/* If we've been sleeping someone might have
			 * changed the permissions behind our back.
			 */
			if ((inode->i_mode & (S_ISGID | S_IXGRP)) != S_ISGID)
				break;
			goto repeat;
		}
		fl = fl->fl_next;
	}
	return (0);
}

/* Verify a "struct flock" and copy it to a "struct file_lock" as a POSIX
 * style lock.
 */
static int posix_make_lock(struct file *filp, struct file_lock *fl,
			   struct flock *l)
{
	off_t start;

	memset(fl, 0, sizeof(*fl));
	
	fl->fl_flags = FL_POSIX;

	switch (l->l_type) {
	case F_RDLCK:
	case F_WRLCK:
	case F_UNLCK:
		fl->fl_type = l->l_type;
		break;
	case F_SHLCK :
		fl->fl_type = F_RDLCK;
		fl->fl_flags |= FL_BROKEN;
		break;
	case F_EXLCK :
		fl->fl_type = F_WRLCK;
		fl->fl_flags |= FL_BROKEN;
		break;
	default:
		return (0);
	}

	switch (l->l_whence) {
	case 0: /*SEEK_SET*/
		start = 0;
		break;
	case 1: /*SEEK_CUR*/
		start = filp->f_pos;
		break;
	case 2: /*SEEK_END*/
		start = filp->f_inode->i_size;
		break;
	default:
		return (0);
	}

	if (((start += l->l_start) < 0) || (l->l_len < 0))
		return (0);
	fl->fl_start = start;	/* we record the absolute position */
	if ((l->l_len == 0) || ((fl->fl_end = start + l->l_len - 1) < 0))
		fl->fl_end = OFFSET_MAX;
	
	fl->fl_file = filp;
	fl->fl_owner = current;

	return (1);
}

/* Verify a call to flock() and fill in a file_lock structure with
 * an appropriate FLOCK lock.
 */
static int flock_make_lock(struct file *filp, struct file_lock *fl,
			   unsigned int cmd)
{
	memset(fl, 0, sizeof(*fl));

	if (!filp->f_inode)	/* just in case */
		return (0);

	switch (cmd & ~LOCK_NB) {
	case LOCK_SH:
		fl->fl_type = F_RDLCK;
		break;
	case LOCK_EX:
		fl->fl_type = F_WRLCK;
		break;
	case LOCK_UN:
		fl->fl_type = F_UNLCK;
		break;
	default:
		return (0);
	}

	fl->fl_flags = FL_FLOCK;
	fl->fl_start = 0;
	fl->fl_end = OFFSET_MAX;
	fl->fl_file = filp;
	fl->fl_owner = NULL;
	
	return (1);
}

/* Determine if lock sys_fl blocks lock caller_fl. POSIX specific
 * checking before calling the locks_conflict().
 */
static int posix_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
{
	/* POSIX locks owned by the same process do not conflict with
	 * each other.
	 */
	if (caller_fl->fl_owner == sys_fl->fl_owner)
		return (0);

	return (locks_conflict(caller_fl, sys_fl));
}

/* Determine if lock sys_fl blocks lock caller_fl. FLOCK specific
 * checking before calling the locks_conflict().
 */
static int flock_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
{
	/* FLOCK locks referring to the same filp do not conflict with
	 * each other.
	 */
	if (caller_fl->fl_file == sys_fl->fl_file)
		return (0);

	return (locks_conflict(caller_fl, sys_fl));
}

/* Determine if lock sys_fl blocks lock caller_fl. Common functionality
 * checks for overlapping locks and shared/exclusive status.
 */
static int locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
{
	if (!locks_overlap(caller_fl, sys_fl))
		return (0);

	switch (caller_fl->fl_type) {
	case F_RDLCK:
		return (sys_fl->fl_type == F_WRLCK);
		
	case F_WRLCK:
		return (1);

	default:
		printk("locks_conflict(): impossible lock type - %d\n",
		       caller_fl->fl_type);
		break;
	}
	return (0);	/* This should never happen */
}

/* This function tests for deadlock condition before putting a process to
 * sleep. The detection scheme is no longer recursive. Recursive was neat,
 * but dangerous - we risked stack corruption if the lock data was bad, or
 * if the recursion was too deep for any other reason.
 *
 * We rely on the fact that a task can only be on one lock's wait queue
 * at a time. When we find blocked_task on a wait queue we can re-search
 * with blocked_task equal to that queue's owner, until either blocked_task
 * isn't found, or blocked_task is found on a queue owned by my_task.
 */
static int posix_locks_deadlock(struct task_struct *my_task,
				struct task_struct *blocked_task)
{
	struct file_lock *fl;
	struct file_lock *bfl;

next_task:
	if (my_task == blocked_task)
		return (1);
	for (fl = file_lock_table; fl != NULL; fl = fl->fl_nextlink) {
		if (fl->fl_owner == NULL || fl->fl_nextblock == NULL)
			continue;
		for (bfl = fl->fl_nextblock; bfl != fl; bfl = bfl->fl_nextblock) {
			if (bfl->fl_owner == blocked_task) {
				if (fl->fl_owner == my_task) {
					return (1);
				}
				blocked_task = fl->fl_owner;
				goto next_task;
			}
		}
	}
	return (0);
}

/* Try to create a FLOCK lock on filp. We always insert new FLOCK locks at
 * the head of the list, but that's secret knowledge known only to the next
 * two functions.
 */
static int flock_lock_file(struct file *filp, struct file_lock *caller,
			   unsigned int wait)
{
	struct file_lock *fl;
	struct file_lock *new_fl = NULL;
	struct file_lock **before;
	int error;
	int change;
	int unlock = (caller->fl_type == F_UNLCK);

	/*
	 * If we need a new lock, get it in advance to avoid races.
	 */
	if (!unlock) {
		error = -ENOLCK;
		new_fl = locks_alloc_lock(caller);
		if (!new_fl)
			goto out;
	}


	error = 0;
search:
	change = 0;

	before = &filp->f_inode->i_flock;

	if ((fl = *before) && (fl->fl_flags & FL_POSIX)) {
		error = -EBUSY;
		goto out;
	}

	while ((fl = *before) != NULL) {
		if (caller->fl_file == fl->fl_file) {
			if (caller->fl_type == fl->fl_type)
				goto out;
			change = 1;
			break;
		}
		before = &fl->fl_next;
	}
	/* change means that we are changing the type of an existing lock, or
	 * or else unlocking it.
	 */
	if (change) {
		/* N.B. What if the wait argument is false? */
		locks_delete_lock(before, !unlock);
		/*
		 * If we waited, another lock may have been added ...
		 */
		if (!unlock)
			goto search;
	}
	if (unlock)
		goto out;

repeat:
	/* Check signals each time we start */
	error = -ERESTARTSYS;
	if (current->signal & ~current->blocked)
		goto out;