include/linux/dm-bht.h

/*
 * Copyright (C) 2011 The Chromium OS Authors <chromium-os-dev chromium org>
 *
 * Device-Mapper block hash tree interface.
 * See Documentation/device-mapper/dm-bht.txt for details.
 *
 * This file is released under the GPLv2.
 */
#ifndef __LINUX_DM_BHT_H
#define __LINUX_DM_BHT_H

#include <linux/compiler.h>
#include <linux/crypto.h>
#include <linux/types.h>

/* To avoid allocating memory for digest tests, we just setup a
 * max to use for now.
 */
#define DM_BHT_MAX_DIGEST_SIZE 128  /* 1k hashes are unlikely for now */
#define DM_BHT_SALT_SIZE       32   /* 256 bits of salt is a lot */

/* UNALLOCATED, PENDING, READY, and VERIFIED are valid states. All other
 * values are entry-related return codes.
 */
#define DM_BHT_ENTRY_VERIFIED 8  /* 'nodes' has been checked against parent */
#define DM_BHT_ENTRY_READY 4  /* 'nodes' is loaded and available */
#define DM_BHT_ENTRY_PENDING 2  /* 'nodes' is being loaded */
#define DM_BHT_ENTRY_UNALLOCATED 0 /* untouched */
#define DM_BHT_ENTRY_ERROR -1 /* entry is unsuitable for use */
#define DM_BHT_ENTRY_ERROR_IO -2 /* I/O error on load */

/* Additional possible return codes */
#define DM_BHT_ENTRY_ERROR_MISMATCH -3 /* Digest mismatch */

/* dm_bht_entry
 * Contains dm_bht->node_count tree nodes at a given tree depth.
 * state is used to transactionally assure that data is paged in
 * from disk.  Unless dm_bht kept running crypto contexts for each
 * level, we need to load in the data for on-demand verification.
 */
struct dm_bht_entry {
	atomic_t state; /* see defines */
	/* Keeping an extra pointer per entry wastes up to ~33k of
	 * memory if a 1m blocks are used (or 66 on 64-bit arch)
	 */
	void *io_context;  /* Reserve a pointer for use during io */
	/* data should only be non-NULL if fully populated. */
	void *nodes;  /* The hash data used to verify the children.
		       * Guaranteed to be page-aligned.
		       */
};

/* dm_bht_level
 * Contains an array of entries which represent a page of hashes where
 * each hash is a node in the tree at the given tree depth/level.
 */
struct dm_bht_level {
	struct dm_bht_entry *entries;  /* array of entries of tree nodes */
	unsigned int count;  /* number of entries at this level */
	sector_t sector;  /* starting sector for this level */
};

/* opaque context, start, databuf, sector_count */
typedef int(*dm_bht_callback)(void *,  /* external context */
			      sector_t,  /* start sector */
			      u8 *,  /* destination page */
			      sector_t,  /* num sectors */
			      struct dm_bht_entry *);
/* dm_bht - Device mapper block hash tree
 * dm_bht provides a fixed interface for comparing data blocks
 * against a cryptographic hashes stored in a hash tree. It
 * optimizes the tree structure for storage on disk.
 *
 * The tree is built from the bottom up.  A collection of data,
 * external to the tree, is hashed and these hashes are stored
 * as the blocks in the tree.  For some number of these hashes,
 * a parent node is created by hashing them.  These steps are
 * repeated.
 *
 * TODO(wad): All hash storage memory is pre-allocated and freed once an
 * entire branch has been verified.
 */
struct dm_bht {
	/* Configured values */
	int depth;  /* Depth of the tree including the root */
	unsigned int block_count;  /* Number of blocks hashed */
	unsigned int block_size;  /* Size of a hash block */
	char hash_alg[CRYPTO_MAX_ALG_NAME];
	unsigned char salt[DM_BHT_SALT_SIZE];

	/* Computed values */
	unsigned int node_count;  /* Data size (in hashes) for each entry */
	unsigned int node_count_shift;  /* first bit set - 1 */
	/* There is one per CPU so that verified can be simultaneous. */
	struct hash_desc hash_desc[NR_CPUS];  /* Container for the hash alg */
	unsigned int digest_size;
	sector_t sectors;  /* Number of disk sectors used */

	/* bool verified;  Full tree is verified */
	u8 root_digest[DM_BHT_MAX_DIGEST_SIZE];
	struct dm_bht_level *levels;  /* in reverse order */
	/* Callback for reading from the hash device */
	dm_bht_callback read_cb;
};

/* Constructor for struct dm_bht instances. */
int dm_bht_create(struct dm_bht *bht,
		  unsigned int block_count,
		  unsigned int block_size,
		  const char *alg_name);
/* Destructor for struct dm_bht instances.  Does not free @bht */
void dm_bht_destroy(struct dm_bht *bht);

/* Basic accessors for struct dm_bht */
int dm_bht_set_root_hexdigest(struct dm_bht *bht, const u8 *hexdigest);
int dm_bht_root_hexdigest(struct dm_bht *bht, u8 *hexdigest, int available);
void dm_bht_set_salt(struct dm_bht *bht, const char *hexsalt);
int dm_bht_salt(struct dm_bht *bht, char *hexsalt);

/* Functions for loading in data from disk for verification */
bool dm_bht_is_populated(struct dm_bht *bht, unsigned int block);
int dm_bht_populate(struct dm_bht *bht, void *read_cb_ctx,
		    unsigned int block);
int dm_bht_verify_block(struct dm_bht *bht, unsigned int block,
			struct page *pg, unsigned int offset);
void dm_bht_read_completed(struct dm_bht_entry *entry, int status);

/* Functions for converting indices to nodes. */

static inline unsigned int dm_bht_get_level_shift(struct dm_bht *bht,
						  int depth)
{
	return (bht->depth - depth) * bht->node_count_shift;
}

/* For the given depth, this is the entry index.  At depth+1 it is the node
 * index for depth.
 */
static inline unsigned int dm_bht_index_at_level(struct dm_bht *bht,
							int depth,
							unsigned int leaf)
{
	return leaf >> dm_bht_get_level_shift(bht, depth);
}

static inline struct dm_bht_entry *dm_bht_get_entry(struct dm_bht *bht,
						    int depth,
						    unsigned int block)
{
	unsigned int index = dm_bht_index_at_level(bht, depth, block);
	struct dm_bht_level *level = &bht->levels[depth];

	return &level->entries[index];
}

static inline void *dm_bht_get_node(struct dm_bht *bht,
				  struct dm_bht_entry *entry,
				  int depth,
				  unsigned int block)
{
	unsigned int index = dm_bht_index_at_level(bht, depth, block);
	unsigned int node_index = index % bht->node_count;

	return entry->nodes + (node_index * bht->digest_size);
}
#endif  /* __LINUX_DM_BHT_H */