drivers/md/dm-verity-fec.h

/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
 * Copyright (C) 2015 Google, Inc.
 *
 * Author: Sami Tolvanen <samitolvanen@google.com>
 */

#ifndef DM_VERITY_FEC_H
#define DM_VERITY_FEC_H

#include "dm-verity.h"
#include <linux/rslib.h>

/* Reed-Solomon(n, k) parameters */
#define DM_VERITY_FEC_RS_N	255
#define DM_VERITY_FEC_MIN_ROOTS	2	/* RS(255, 253): ~0.8% space overhead */
#define DM_VERITY_FEC_MAX_ROOTS	24	/* RS(255, 231): ~10% space overhead */

/* buffers for deinterleaving and decoding */
#define DM_VERITY_FEC_BUF_RS_BITS	4 /* log2(RS messages per buffer) */

#define DM_VERITY_OPT_FEC_DEV		"use_fec_from_device"
#define DM_VERITY_OPT_FEC_BLOCKS	"fec_blocks"
#define DM_VERITY_OPT_FEC_START		"fec_start"
#define DM_VERITY_OPT_FEC_ROOTS		"fec_roots"

/* configuration */
struct dm_verity_fec {
	struct dm_dev *dev;	/* parity data device */
	struct dm_bufio_client *data_bufio;	/* for data dev access */
	struct dm_bufio_client *bufio;		/* for parity data access */
	size_t block_size;	/* size of data, hash, and parity blocks in bytes */
	sector_t start;		/* parity data start in blocks */
	sector_t blocks;	/* number of blocks covered */
	sector_t region_blocks; /* blocks per region: ceil(blocks / rs_k) */
	sector_t hash_blocks;	/* blocks covered after v->hash_start */
	unsigned char roots;	/* parity bytes per RS codeword, n-k of RS(n, k) */
	unsigned char rs_k;	/* message bytes per RS codeword, k of RS(n, k) */
	mempool_t fio_pool;	/* mempool for dm_verity_fec_io */
	mempool_t rs_pool;	/* mempool for fio->rs */
	mempool_t prealloc_pool;	/* mempool for preallocated buffers */
	mempool_t output_pool;	/* mempool for output */
	struct kmem_cache *cache;	/* cache for buffers */
	atomic64_t corrected; /* corrected errors */
};

/* per-bio data */
struct dm_verity_fec_io {
	struct rs_control *rs;	/* Reed-Solomon state */
	int erasures[DM_VERITY_FEC_MAX_ROOTS + 1]; /* erasures for decode_rs8 */
	u8 *output;		/* buffer for corrected output */
	unsigned int level;		/* recursion level */
	unsigned int nbufs;		/* number of buffers allocated */
	/*
	 * Buffers for deinterleaving RS codewords.  Each buffer has space for
	 * the message bytes of (1 << DM_VERITY_FEC_BUF_RS_BITS) RS codewords.
	 * The array length is fec_max_nbufs(v), and we try to allocate that
	 * many buffers.  However, in low-memory situations we may be unable to
	 * allocate all buffers.  'nbufs' holds the number actually allocated.
	 */
	u8 *bufs[];
};

#ifdef CONFIG_DM_VERITY_FEC

/* each feature parameter requires a value */
#define DM_VERITY_OPTS_FEC	8

/* Returns true if forward error correction is enabled. */
static inline bool verity_fec_is_enabled(struct dm_verity *v)
{
	return v->fec && v->fec->dev;
}

extern int verity_fec_decode(struct dm_verity *v, struct dm_verity_io *io,
			     enum verity_block_type type, const u8 *want_digest,
			     sector_t block, u8 *dest);

extern unsigned int verity_fec_status_table(struct dm_verity *v, unsigned int sz,
					char *result, unsigned int maxlen);

extern void __verity_fec_finish_io(struct dm_verity_io *io);
static inline void verity_fec_finish_io(struct dm_verity_io *io)
{
	if (unlikely(io->fec_io))
		__verity_fec_finish_io(io);
}

static inline void verity_fec_init_io(struct dm_verity_io *io)
{
	io->fec_io = NULL;
}

extern bool verity_is_fec_opt_arg(const char *arg_name);
extern int verity_fec_parse_opt_args(struct dm_arg_set *as,
				     struct dm_verity *v, unsigned int *argc,
				     const char *arg_name);

extern void verity_fec_dtr(struct dm_verity *v);

extern int verity_fec_ctr_alloc(struct dm_verity *v);
extern int verity_fec_ctr(struct dm_verity *v);

#else /* !CONFIG_DM_VERITY_FEC */

#define DM_VERITY_OPTS_FEC	0

static inline bool verity_fec_is_enabled(struct dm_verity *v)
{
	return false;
}

static inline int verity_fec_decode(struct dm_verity *v,
				    struct dm_verity_io *io,
				    enum verity_block_type type,
				    const u8 *want_digest,
				    sector_t block, u8 *dest)
{
	return -EOPNOTSUPP;
}

static inline unsigned int verity_fec_status_table(struct dm_verity *v,
					       unsigned int sz, char *result,
					       unsigned int maxlen)
{
	return sz;
}

static inline void verity_fec_finish_io(struct dm_verity_io *io)
{
}

static inline void verity_fec_init_io(struct dm_verity_io *io)
{
}

static inline bool verity_is_fec_opt_arg(const char *arg_name)
{
	return false;
}

static inline int verity_fec_parse_opt_args(struct dm_arg_set *as,
					    struct dm_verity *v,
					    unsigned int *argc,
					    const char *arg_name)
{
	return -EINVAL;
}

static inline void verity_fec_dtr(struct dm_verity *v)
{
}

static inline int verity_fec_ctr_alloc(struct dm_verity *v)
{
	return 0;
}

static inline int verity_fec_ctr(struct dm_verity *v)
{
	return 0;
}

#endif /* CONFIG_DM_VERITY_FEC */

#endif /* DM_VERITY_FEC_H */