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    /*
     * 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 const 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(const 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
    	 *    ->mount yet, it waits until it is finished
    	 *
    	 * c) cleancache_init_fs is called from ->mount and
    	 *    cleancache_invalidate_fs is called from ->kill_sb
    	 *
    	 * d) we call iterate_supers after cleancache_ops has been set
    	 *
    	 * From a) it follows that if iterate_supers skips a super block, then
    	 * either the super block is already dead, in which case we do not need
    	 * to bother initializing cleancache for it, or it was mounted after we
    	 * initiated iterate_supers. In the latter case, it must have seen
    	 * cleancache_ops set according to d) and initialized cleancache from
    	 * ->mount by itself according to c). This proves that we call
    	 * ->init_fs at least once for each active super block.
    	 *
    	 * From b) and c) it follows that if iterate_supers encounters a super
    	 * block that has already started ->init_fs, it will wait until ->mount
    	 * and hence ->init_fs has finished, then check cleancache_poolid, see
    	 * that it has already been set and therefore do nothing. This proves
    	 * that we call ->init_fs no more than once for each super block.
    	 *
    	 * Combined together, the last two paragraphs prove the function
    	 * correctness.
    	 *
    	 * Note that various cleancache callbacks may proceed before this
    	 * function is called or even concurrently with it, but since
    	 * CLEANCACHE_NO_BACKEND is negative, they will all result in a noop
    	 * until the corresponding ->init_fs has been actually called and
    	 * cleancache_ops has been set.
    	 */
    	iterate_supers(cleancache_register_ops_sb, NULL);
    	return 0;
    }
    EXPORT_SYMBOL(cleancache_register_ops);
    
    /* Called by a cleancache-enabled filesystem at time of mount */
    void __cleancache_init_fs(struct super_block *sb)
    {
    	int pool_id = CLEANCACHE_NO_BACKEND;
    
    	if (cleancache_ops) {
    		pool_id = cleancache_ops->init_fs(PAGE_SIZE);
    		if (pool_id < 0)
    			pool_id = CLEANCACHE_NO_POOL;
    	}
    	sb->cleancache_poolid = pool_id;
    }
    EXPORT_SYMBOL(__cleancache_init_fs);
    
    /* Called by a cleancache-enabled clustered filesystem at time of mount */
    void __cleancache_init_shared_fs(struct super_block *sb)
    {
    	int pool_id = CLEANCACHE_NO_BACKEND_SHARED;
    
    	if (cleancache_ops) {
    		pool_id = cleancache_ops->init_shared_fs(sb->s_uuid, PAGE_SIZE);
    		if (pool_id < 0)
    			pool_id = CLEANCACHE_NO_POOL;
    	}
    	sb->cleancache_poolid = pool_id;
    }
    EXPORT_SYMBOL(__cleancache_init_shared_fs);
    
    /*
     * If the filesystem uses exportable filehandles, use the filehandle as
     * the key, else use the inode number.
     */
    static int cleancache_get_key(struct inode *inode,
    			      struct cleancache_filekey *key)
    {
    	int (*fhfn)(struct inode *, __u32 *fh, int *, struct inode *);
    	int len = 0, maxlen = CLEANCACHE_KEY_MAX;
    	struct super_block *sb = inode->i_sb;
    
    	key->u.ino = inode->i_ino;
    	if (sb->s_export_op != NULL) {
    		fhfn = sb->s_export_op->encode_fh;
    		if  (fhfn) {
    			len = (*fhfn)(inode, &key->u.fh[0], &maxlen, NULL);
    			if (len <= FILEID_ROOT || len == FILEID_INVALID)
    				return -1;
    			if (maxlen > CLEANCACHE_KEY_MAX)
    				return -1;
    		}
    	}
    	return 0;
    }
    
    /*
     * "Get" data from cleancache associated with the poolid/inode/index
     * that were specified when the data was put to cleanache and, if
     * successful, use it to fill the specified page with data and return 0.
     * The pageframe is unchanged and returns -1 if the get fails.
     * Page must be locked by caller.
     *
     * The function has two checks before any action is taken - whether
     * a backend is registered and whether the sb->cleancache_poolid
     * is correct.
     */
    int __cleancache_get_page(struct page *page)
    {
    	int ret = -1;
    	int pool_id;
    	struct cleancache_filekey key = { .u.key = { 0 } };
    
    	if (!cleancache_ops) {
    		cleancache_failed_gets++;
    		goto out;
    	}
    
    	VM_BUG_ON_PAGE(!PageLocked(page), page);
    	pool_id = page->mapping->host->i_sb->cleancache_poolid;
    	if (pool_id < 0)
    		goto out;
    
    	if (cleancache_get_key(page->mapping->host, &key) < 0)
    		goto out;
    
    	ret = cleancache_ops->get_page(pool_id, key, page->index, page);
    	if (ret == 0)
    		cleancache_succ_gets++;
    	else
    		cleancache_failed_gets++;
    out:
    	return ret;
    }
    EXPORT_SYMBOL(__cleancache_get_page);
    
    /*
     * "Put" data from a page to cleancache and associate it with the
     * (previously-obtained per-filesystem) poolid and the page's,
     * inode and page index.  Page must be locked.  Note that a put_page
     * always "succeeds", though a subsequent get_page may succeed or fail.
     *
     * The function has two checks before any action is taken - whether
     * a backend is registered and whether the sb->cleancache_poolid
     * is correct.
     */
    void __cleancache_put_page(struct page *page)
    {
    	int pool_id;
    	struct cleancache_filekey key = { .u.key = { 0 } };
    
    	if (!cleancache_ops) {
    		cleancache_puts++;
    		return;
    	}
    
    	VM_BUG_ON_PAGE(!PageLocked(page), page);
    	pool_id = page->mapping->host->i_sb->cleancache_poolid;
    	if (pool_id >= 0 &&
    		cleancache_get_key(page->mapping->host, &key) >= 0) {
    		cleancache_ops->put_page(pool_id, key, page->index, page);
    		cleancache_puts++;
    	}
    }
    EXPORT_SYMBOL(__cleancache_put_page);
    
    /*
     * Invalidate any data from cleancache associated with the poolid and the
     * page's inode and page index so that a subsequent "get" will fail.
     *
     * The function has two checks before any action is taken - whether
     * a backend is registered and whether the sb->cleancache_poolid
     * is correct.
     */
    void __cleancache_invalidate_page(struct address_space *mapping,
    					struct page *page)
    {
    	/* careful... page->mapping is NULL sometimes when this is called */
    	int pool_id = mapping->host->i_sb->cleancache_poolid;
    	struct cleancache_filekey key = { .u.key = { 0 } };
    
    	if (!cleancache_ops)
    		return;
    
    	if (pool_id >= 0) {
    		VM_BUG_ON_PAGE(!PageLocked(page), page);
    		if (cleancache_get_key(mapping->host, &key) >= 0) {
    			cleancache_ops->invalidate_page(pool_id,
    					key, page->index);
    			cleancache_invalidates++;
    		}
    	}
    }
    EXPORT_SYMBOL(__cleancache_invalidate_page);
    
    /*
     * Invalidate all data from cleancache associated with the poolid and the
     * mappings's inode so that all subsequent gets to this poolid/inode
     * will fail.
     *
     * The function has two checks before any action is taken - whether
     * a backend is registered and whether the sb->cleancache_poolid
     * is correct.
     */
    void __cleancache_invalidate_inode(struct address_space *mapping)
    {
    	int pool_id = mapping->host->i_sb->cleancache_poolid;
    	struct cleancache_filekey key = { .u.key = { 0 } };
    
    	if (!cleancache_ops)
    		return;
    
    	if (pool_id >= 0 && cleancache_get_key(mapping->host, &key) >= 0)
    		cleancache_ops->invalidate_inode(pool_id, key);
    }
    EXPORT_SYMBOL(__cleancache_invalidate_inode);
    
    /*
     * Called by any cleancache-enabled filesystem at time of unmount;
     * note that pool_id is surrendered and may be returned by a subsequent
     * cleancache_init_fs or cleancache_init_shared_fs.
     */
    void __cleancache_invalidate_fs(struct super_block *sb)
    {
    	int pool_id;
    
    	pool_id = sb->cleancache_poolid;
    	sb->cleancache_poolid = CLEANCACHE_NO_POOL;
    
    	if (cleancache_ops && pool_id >= 0)
    		cleancache_ops->invalidate_fs(pool_id);
    }
    EXPORT_SYMBOL(__cleancache_invalidate_fs);
    
    static int __init init_cleancache(void)
    {
    #ifdef CONFIG_DEBUG_FS
    	struct dentry *root = debugfs_create_dir("cleancache", NULL);
    	if (root == NULL)
    		return -ENXIO;
    	debugfs_create_u64("succ_gets", S_IRUGO, root, &cleancache_succ_gets);
    	debugfs_create_u64("failed_gets", S_IRUGO,
    				root, &cleancache_failed_gets);
    	debugfs_create_u64("puts", S_IRUGO, root, &cleancache_puts);
    	debugfs_create_u64("invalidates", S_IRUGO,
    				root, &cleancache_invalidates);
    #endif
    	return 0;
    }
    module_init(init_cleancache)