locks.c

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	error = -EBUSY;
	if ((fl = filp->f_inode->i_flock) && (fl->fl_flags & FL_POSIX))
		goto out;

	while (fl != NULL) {
		if (!flock_locks_conflict(new_fl, fl)) {
			fl = fl->fl_next;
			continue;
		}
		error = -EAGAIN;
		if (!wait)
			goto out;
		locks_insert_block(fl, new_fl);
		interruptible_sleep_on(&new_fl->fl_wait);
		locks_delete_block(fl, new_fl);
		goto repeat;
	}
	locks_insert_lock(&filp->f_inode->i_flock, new_fl);
	new_fl = NULL;
	error = 0;

out:
	if (new_fl)
		locks_free_lock(new_fl);
	return (error);
}

/* Add a POSIX style lock to a file.
 * We merge adjacent locks whenever possible. POSIX locks are sorted by owner
 * task, then by starting address
 *
 * Kai Petzke writes:
 * To make freeing a lock much faster, we keep a pointer to the lock before the
 * actual one. But the real gain of the new coding was, that lock_it() and
 * unlock_it() became one function.
 *
 * To all purists: Yes, I use a few goto's. Just pass on to the next function.
 */

static int posix_lock_file(struct file *filp, struct file_lock *caller,
			   unsigned int wait)
{
	struct file_lock *fl;
	struct file_lock *new_fl, *new_fl2;
	struct file_lock *left = NULL;
	struct file_lock *right = NULL;
	struct file_lock **before;
	int error;
	int added = 0;

	/*
	 * We may need two file_lock structures for this operation,
	 * so we get them in advance to avoid races.
	 */
	new_fl  = locks_empty_lock();
	new_fl2 = locks_empty_lock();
	error = -ENOLCK; /* "no luck" */
	if (!(new_fl && new_fl2))
		goto out;
 
	if (caller->fl_type != F_UNLCK) {
  repeat:
		error = -EBUSY;
		if ((fl = filp->f_inode->i_flock) && (fl->fl_flags & FL_FLOCK))
			goto out;

		while (fl != NULL) {
			if (!posix_locks_conflict(caller, fl)) {
				fl = fl->fl_next;
				continue;
			}
			error = -EAGAIN;
			if (!wait)
				goto out;
			error = -EDEADLK;
			if (posix_locks_deadlock(caller->fl_owner, fl->fl_owner))
				goto out;
			error = -ERESTARTSYS;
			if (current->signal & ~current->blocked)
				goto out;
			locks_insert_block(fl, caller);
			interruptible_sleep_on(&caller->fl_wait);
			locks_delete_block(fl, caller);
			goto repeat;
  		}
  	}

	/*
	 * We've allocated the new locks in advance, so there are no
	 * errors possible (and no blocking operations) from here on.
	 * 
	 * Find the first old lock with the same owner as the new lock.
	 */
	
	before = &filp->f_inode->i_flock;

	error = -EBUSY;
	if ((*before != NULL) && ((*before)->fl_flags & FL_FLOCK))
		goto out;

	/* First skip locks owned by other processes.
	 */
	while ((fl = *before) && (caller->fl_owner != fl->fl_owner)) {
		before = &fl->fl_next;
	}

	/* Process locks with this owner.
	 */
	while ((fl = *before) && (caller->fl_owner == fl->fl_owner)) {
		/* Detect adjacent or overlapping regions (if same lock type)
		 */
		if (caller->fl_type == fl->fl_type) {
			if (fl->fl_end < caller->fl_start - 1)
				goto next_lock;
			/* If the next lock in the list has entirely bigger
			 * addresses than the new one, insert the lock here.
			 */
			if (fl->fl_start > caller->fl_end + 1)
				break;

			/* If we come here, the new and old lock are of the
			 * same type and adjacent or overlapping. Make one
			 * lock yielding from the lower start address of both
			 * locks to the higher end address.
			 */
			if (fl->fl_start > caller->fl_start)
				fl->fl_start = caller->fl_start;
			else
				caller->fl_start = fl->fl_start;
			if (fl->fl_end < caller->fl_end)
				fl->fl_end = caller->fl_end;
			else
				caller->fl_end = fl->fl_end;
			if (added) {
				locks_delete_lock(before, 0);
				continue;
			}
			caller = fl;
			added = 1;
		}
		else {
			/* Processing for different lock types is a bit
			 * more complex.
			 */
			if (fl->fl_end < caller->fl_start)
				goto next_lock;
			if (fl->fl_start > caller->fl_end)
				break;
			if (caller->fl_type == F_UNLCK)
				added = 1;
			if (fl->fl_start < caller->fl_start)
				left = fl;
			/* If the next lock in the list has a higher end
			 * address than the new one, insert the new one here.
			 */
			if (fl->fl_end > caller->fl_end) {
				right = fl;
				break;
			}
			if (fl->fl_start >= caller->fl_start) {
				/* The new lock completely replaces an old
				 * one (This may happen several times).
				 */
				if (added) {
					locks_delete_lock(before, 0);
					continue;
				}
				/* Replace the old lock with the new one.
				 * Wake up anybody waiting for the old one,
				 * as the change in lock type might satisfy
				 * their needs.
				 */
				locks_wake_up_blocks(fl, 0);
				fl->fl_start = caller->fl_start;
				fl->fl_end = caller->fl_end;
				fl->fl_type = caller->fl_type;
				caller = fl;
				added = 1;
			}
		}
		/* Go on to next lock.
		 */
	next_lock:
		before = &fl->fl_next;
	}

	error = 0;
	if (!added) {
		if (caller->fl_type == F_UNLCK)
			goto out;
		locks_init_lock(new_fl, caller);
		locks_insert_lock(before, new_fl);
		new_fl = NULL;
	}
	if (right) {
		if (left == right) {
			/* The new lock breaks the old one in two pieces,
			 * so we have to use the second new lock (in this
			 * case, even F_UNLCK may fail!).
			 */
			left = locks_init_lock(new_fl2, right);
			locks_insert_lock(before, left);
			new_fl2 = NULL;
		}
		right->fl_start = caller->fl_end + 1;
		locks_wake_up_blocks(right, 0);
	}
	if (left) {
		left->fl_end = caller->fl_start - 1;
		locks_wake_up_blocks(left, 0);
	}
out:
	/*
	 * Free any unused locks.  (They haven't
	 * ever been used, so we use kfree().)
	 */
	if (new_fl)
		kfree(new_fl);
	if (new_fl2)
		kfree(new_fl2);
	return error;
}

/*
 * Allocate an empty lock structure. We can use GFP_KERNEL now that
 * all allocations are done in advance.
 */
static struct file_lock *locks_empty_lock(void)
{
	return ((struct file_lock *) kmalloc(sizeof(struct file_lock),
						GFP_KERNEL));
}

/*
 * Initialize a new lock from an existing file_lock structure.
 */
static struct file_lock *locks_init_lock(struct file_lock *new,
					 struct file_lock *fl)
{
	if (new) {
		memset(new, 0, sizeof(*new));
		new->fl_owner = fl->fl_owner;
		new->fl_file = fl->fl_file;
		new->fl_flags = fl->fl_flags;
		new->fl_type = fl->fl_type;
		new->fl_start = fl->fl_start;
		new->fl_end = fl->fl_end;
	}
	return new;
}

/* Insert file lock fl into an inode's lock list at the position indicated
 * by pos. At the same time add the lock to the global file lock list.
 */
static void locks_insert_lock(struct file_lock **pos, struct file_lock *fl)
{
	fl->fl_nextlink = file_lock_table;
	fl->fl_prevlink = NULL;
	if (file_lock_table != NULL)
		file_lock_table->fl_prevlink = fl;
	file_lock_table = fl;
	fl->fl_next = *pos;	/* insert into file's list */
	*pos = fl;

	return;
}

/* Delete a lock and free it.
 * First remove our lock from the active lock lists. Then call
 * locks_wake_up_blocks() to wake up processes that are blocked
 * waiting for this lock. Finally free the lock structure.
 */
static void locks_delete_lock(struct file_lock **thisfl_p, unsigned int wait)
{
	struct file_lock *thisfl;
	struct file_lock *prevfl;
	struct file_lock *nextfl;
	
	thisfl = *thisfl_p;
	*thisfl_p = thisfl->fl_next;

	prevfl = thisfl->fl_prevlink;
	nextfl = thisfl->fl_nextlink;

	if (nextfl != NULL)
		nextfl->fl_prevlink = prevfl;

	if (prevfl != NULL)
		prevfl->fl_nextlink = nextfl;
	else
		file_lock_table = nextfl;
	
	locks_wake_up_blocks(thisfl, wait);
	locks_free_lock(thisfl);

	return;
}


static char *lock_get_status(struct file_lock *fl, int id, char *pfx)
{
	static char temp[129];
	char *p = temp;
	struct inode *inode;

	inode = fl->fl_file->f_inode;

	p += sprintf(p, "%d:%s ", id, pfx);
	if (fl->fl_flags & FL_POSIX) {
		p += sprintf(p, "%6s %s ",
			     (fl->fl_flags & FL_BROKEN) ? "BROKEN" :
			     (fl->fl_flags & FL_ACCESS) ? "ACCESS" : "POSIX ",
			     (IS_MANDLOCK(inode) &&
			      (inode->i_mode & (S_IXGRP | S_ISGID)) == S_ISGID) ?
			     "MANDATORY" : "ADVISORY ");
	}
	else {
		p += sprintf(p, "FLOCK  ADVISORY  ");
	}
	p += sprintf(p, "%s ", (fl->fl_type == F_RDLCK) ? "READ " : "WRITE");
	p += sprintf(p, "%d %s:%ld %ld %ld ",
		     fl->fl_owner ? fl->fl_owner->pid : 0,
		     kdevname(inode->i_dev), inode->i_ino, fl->fl_start,
		     fl->fl_end);
	sprintf(p, "%08lx %08lx %08lx %08lx %08lx\n",
		(long)fl, (long)fl->fl_prevlink, (long)fl->fl_nextlink,
		(long)fl->fl_next, (long)fl->fl_nextblock);
	return (temp);
}

static inline int copy_lock_status(char *p, char **q, off_t pos, int len,
				   off_t offset, int length)
{
	int i;

	i = pos - offset;
	if (i > 0) {
		if (i >= length) {
			i = len + length - i;
			memcpy(*q, p, i);
			*q += i;
			return (0);
		}
		if (i < len) {
			p += len - i;
		}
		else
			i = len;
		memcpy(*q, p, i);
		*q += i;
	}
	
	return (1);
}

int get_locks_status(char *buffer, char **start, off_t offset, int length)
{
	struct file_lock *fl;
	struct file_lock *bfl;
	char *p;
	char *q = buffer;
	int i;
	int len;
	off_t pos = 0;

	for (fl = file_lock_table, i = 1; fl != NULL; fl = fl->fl_nextlink, i++) {
		p = lock_get_status(fl, i, "");
		len = strlen(p);
		pos += len;
		if (!copy_lock_status(p, &q, pos, len, offset, length))
			goto done;
		if ((bfl = fl->fl_nextblock) == NULL)
			continue;
		do {
			p = lock_get_status(bfl, i, " ->");
			len = strlen(p);
			pos += len;
			if (!copy_lock_status(p, &q, pos, len, offset, length))
				goto done;
		} while ((bfl = bfl->fl_nextblock) != fl);
	}
done:
	if (q != buffer)
		*start = buffer;
	return (q - buffer);
}