/*
 * Cleancache frontend
 *
 * This code provides the generic "frontend" layer to call a matching
 * "backend" driver implementation of cleancache.  See
 * Documentation/vm/cleancache.txt for more information.
 *
 * Copyright (C) 2009-2010 Oracle Corp. All rights reserved.
 * Author: Dan Magenheimer
 *
 * This work is licensed under the terms of the GNU GPL, version 2.
 */

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/exportfs.h>
#include <linux/mm.h>
#include <linux/debugfs.h>
#include <linux/cleancache.h>

/*
 * cleancache_ops is set by cleancache_register_ops to contain the pointers
 * to the cleancache "backend" implementation functions.
 */
static struct cleancache_ops *cleancache_ops __read_mostly;

/*
 * Counters available via /sys/kernel/debug/cleancache (if debugfs is
 * properly configured.  These are for information only so are not protected
 * against increment races.
 */
static u64 cleancache_succ_gets;
static u64 cleancache_failed_gets;
static u64 cleancache_puts;
static u64 cleancache_invalidates;

static void cleancache_register_ops_sb(struct super_block *sb, void *unused)
{
	switch (sb->cleancache_poolid) {
	case CLEANCACHE_NO_BACKEND:
		__cleancache_init_fs(sb);
		break;
	case CLEANCACHE_NO_BACKEND_SHARED:
		__cleancache_init_shared_fs(sb);
		break;
	}
}

/*
 * Register operations for cleancache. Returns 0 on success.
 */
int cleancache_register_ops(struct cleancache_ops *ops)
{
	if (cmpxchg(&cleancache_ops, NULL, ops))
		return -EBUSY;

	/*
	 * A cleancache backend can be built as a module and hence loaded after
	 * a cleancache enabled filesystem has called cleancache_init_fs. To
	 * handle such a scenario, here we call ->init_fs or ->init_shared_fs
	 * for each active super block. To differentiate between local and
	 * shared filesystems, we temporarily initialize sb->cleancache_poolid
	 * to CLEANCACHE_NO_BACKEND or CLEANCACHE_NO_BACKEND_SHARED
	 * respectively in case there is no backend registered at the time
	 * cleancache_init_fs or cleancache_init_shared_fs is called.
	 *
	 * Since filesystems can be mounted concurrently with cleancache
	 * backend registration, we have to be careful to guarantee that all
	 * cleancache enabled filesystems that has been mounted by the time
	 * cleancache_register_ops is called has got and all mounted later will
	 * get cleancache_poolid. This is assured by the following statements
	 * tied together:
	 *
	 * a) iterate_supers skips only those super blocks that has started
	 *    ->kill_sb
	 *
	 * b) if iterate_supers encounters a super block that has not finished