linux/net/tipc/ref.c

/*
 * net/tipc/ref.c: TIPC object registry code
 *
 * Copyright (c) 1991-2006, Ericsson AB
 * Copyright (c) 2004-2007, Wind River Systems
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the names of the copyright holders nor the names of its
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * Alternatively, this software may be distributed under the terms of the
 * GNU General Public License ("GPL") version 2 as published by the Free
 * Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include "core.h"
#include "ref.h"
#include "port.h"
#include "subscr.h"
#include "name_distr.h"
#include "name_table.h"
#include "config.h"
#include "discover.h"
#include "bearer.h"
#include "node.h"
#include "bcast.h"

/**
 * struct reference - TIPC object reference entry
 * @object: pointer to object associated with reference entry
 * @lock: spinlock controlling access to object
 * @data: reference value associated with object (or link to next unused entry)
 */

struct reference {
	void *object;
	spinlock_t lock;
	union {
		u32 next_plus_upper;
		u32 reference;
	} data;
};

/**
 * struct tipc_ref_table - table of TIPC object reference entries
 * @entries: pointer to array of reference entries
 * @index_mask: bitmask for array index portion of reference values
 * @first_free: array index of first unused object reference entry
 * @last_free: array index of last unused object reference entry
 */

struct ref_table {
	struct reference *entries;
	u32 index_mask;
	u32 first_free;
	u32 last_free;
};

/*
 * Object reference table consists of 2**N entries.
 *
 * A used entry has object ptr != 0, reference == XXXX|own index
 *				     (XXXX changes each time entry is acquired)
 * A free entry has object ptr == 0, reference == YYYY|next free index
 *				     (YYYY is one more than last used XXXX)
 *
 * Free list is initially chained from entry (2**N)-1 to entry 1.
 * Entry 0 is not used to allow index 0 to indicate the end of the free list.
 *
 * Note: Any accidental reference of the form XXXX|0--0 won't match entry 0
 * because entry 0's reference field has the form XXXX|1--1.
 */

static struct ref_table tipc_ref_table = { NULL };

static DEFINE_RWLOCK(ref_table_lock);

/**
 * tipc_ref_table_init - create reference table for objects
 */

int tipc_ref_table_init(u32 requested_size, u32 start)
{
	struct reference *table;
	u32 sz = 1 << 4;
	u32 index_mask;
	int i;

	while (sz < requested_size) {
		sz <<= 1;
	}
	table = vmalloc(sz * sizeof(*table));
	if (table == NULL)
		return -ENOMEM;

	write_lock_bh(&ref_table_lock);
	index_mask = sz - 1;
	for (i = sz - 1; i >= 0; i--) {
		table[i].object = NULL;
		spin_lock_init(&table[i].lock);
		table[i].data.next_plus_upper = (start & ~index_mask) + i - 1;
	}
	tipc_ref_table.entries = table;
	tipc_ref_table.index_mask = index_mask;
	tipc_ref_table.first_free = sz - 1;
	tipc_ref_table.last_free = 1;
	write_unlock_bh(&ref_table_lock);
	return TIPC_OK;
}

/**
 * tipc_ref_table_stop - destroy reference table for objects
 */

void tipc_ref_table_stop(void)
{
	if (!tipc_ref_table.entries)
		return;

	vfree(tipc_ref_table.entries);
	tipc_ref_table.entries = NULL;
}

/**
 * tipc_ref_acquire - create reference to an object
 *
 * Return a unique reference value which can be translated back to the pointer
 * 'object' at a later time.  Also, pass back a pointer to the lock protecting
 * the object, but without locking it.
 */

u32 tipc_ref_acquire(void *object, spinlock_t **lock)
{
	struct reference *entry;
	u32 index;
	u32 index_mask;
	u32 next_plus_upper;
	u32 reference = 0;

	if (!object) {
		err("Attempt to acquire reference to non-existent object\n");
		return 0;
	}
	if (!tipc_ref_table.entries) {
		err("Reference table not found during acquisition attempt\n");
		return 0;
	}

	write_lock_bh(&ref_table_lock);
	if (tipc_ref_table.first_free) {
		index = tipc_ref_table.first_free;
		entry = &(tipc_ref_table.entries[index]);
		index_mask = tipc_ref_table.index_mask;
		/* take lock in case a previous user of entry still holds it */
		spin_lock_bh(&entry->lock);
		next_plus_upper = entry->data.next_plus_upper;
		tipc_ref_table.first_free = next_plus_upper & index_mask;
		reference = (next_plus_upper & ~index_mask) + index;
		entry->data.reference = reference;
		entry->object = object;
		if (lock != NULL)
			*lock = &entry->lock;
		spin_unlock_bh(&entry->lock);
	}
	write_unlock_bh(&ref_table_lock);
	return reference;
}

/**
 * tipc_ref_discard - invalidate references to an object
 *
 * Disallow future references to an object and free up the entry for re-use.
 * Note: The entry's spin_lock may still be busy after discard
 */

void tipc_ref_discard(u32 ref)
{
	struct reference *entry;
	u32 index;
	u32 index_mask;

	if (!ref) {
		err("Attempt to discard reference 0\n");
		return;
	}
	if (!tipc_ref_table.entries) {
		err("Reference table not found during discard attempt\n");
		return;
	}

	write_lock_bh(&ref_table_lock);
	index_mask = tipc_ref_table.index_mask;
	index = ref & index_mask;
	entry = &(tipc_ref_table.entries[index]);

	if (!entry->object) {
		err("Attempt to discard reference to non-existent object\n");
		goto exit;
	}
	if (entry->data.reference != ref) {
		err("Attempt to discard non-existent reference\n");
		goto exit;
	}

	/* mark entry as unused */
	entry->object = NULL;
	if (tipc_ref_table.first_free == 0)
		tipc_ref_table.first_free = index;
	else
		/* next_plus_upper is always XXXX|0--0 for last free entry */
		tipc_ref_table.entries[tipc_ref_table.last_free].
			data.next_plus_upper |= index;
	tipc_ref_table.last_free = index;

	/* increment upper bits of entry to invalidate subsequent references */
	entry->data.next_plus_upper = (ref & ~index_mask) + (index_mask + 1);
exit:
	write_unlock_bh(&ref_table_lock);
}

/**
 * tipc_ref_lock - lock referenced object and return pointer to it
 */

void *tipc_ref_lock(u32 ref)
{
	if (likely(tipc_ref_table.entries)) {
		struct reference *r;

		r = &tipc_ref_table.entries[ref & tipc_ref_table.index_mask];
		spin_lock_bh(&r->lock);
		if (likely(r->data.reference == ref))
			return r->object;
		spin_unlock_bh(&r->lock);
	}
	return NULL;
}

/**
 * tipc_ref_unlock - unlock referenced object
 */

void tipc_ref_unlock(u32 ref)
{
	if (likely(tipc_ref_table.entries)) {
		struct reference *r;

		r = &tipc_ref_table.entries[ref & tipc_ref_table.index_mask];
		if (likely(r->data.reference == ref))
			spin_unlock_bh(&r->lock);
		else
			err("tipc_ref_unlock() invoked using "
			    "obsolete reference\n");
	}
}

/**
 * tipc_ref_deref - return pointer referenced object (without locking it)
 */

void *tipc_ref_deref(u32 ref)
{
	if (likely(tipc_ref_table.entries)) {
		struct reference *r;

		r = &tipc_ref_table.entries[ref & tipc_ref_table.index_mask];
		if (likely(r->data.reference == ref))
			return r->object;
	}
	return NULL;
}