text: /*
   * Copyright (C) 2015 Google, Inc.
   *
   * Author: Sami Tolvanen <samitolvanen@google.com>
   *
   * This program is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License as published by the Free
   * Software Foundation; either version 2 of the License, or (at your option)
   * any later version.
   */
  
  #include "dm-verity-fec.h"
  #include <linux/math64.h>
  
  #define DM_MSG_PREFIX	"verity-fec"
  
  /*
   * If error correction has been configured, returns true.
   */
  bool verity_fec_is_enabled(struct dm_verity *v)
  {
  	return v->fec && v->fec->dev;
  }
  
  /*
   * Return a pointer to dm_verity_fec_io after dm_verity_io and its variable
   * length fields.
   */
  static inline struct dm_verity_fec_io *fec_io(struct dm_verity_io *io)
  {
  	return (struct dm_verity_fec_io *) verity_io_digest_end(io->v, io);
  }
  
  /*
   * Return an interleaved offset for a byte in RS block.
   */
  static inline u64 fec_interleave(struct dm_verity *v, u64 offset)
  {
  	u32 mod;
  
  	mod = do_div(offset, v->fec->rsn);
  	return offset + mod * (v->fec->rounds << v->data_dev_block_bits);
  }
  
  /*
   * Decode an RS block using Reed-Solomon.
   */
  static int fec_decode_rs8(struct dm_verity *v, struct dm_verity_fec_io *fio,
  			  u8 *data, u8 *fec, int neras)
  {
  	int i;
  	uint16_t par[DM_VERITY_FEC_RSM - DM_VERITY_FEC_MIN_RSN];
  
  	for (i = 0; i < v->fec->roots; i++)
  		par[i] = fec[i];
  
  	return decode_rs8(fio->rs, data, par, v->fec->rsn, NULL, neras,
  			  fio->erasures, 0, NULL);
  }
  
  /*
   * Read error-correcting codes for the requested RS block. Returns a pointer
   * to the data block. Caller is responsible for releasing buf.
   */
  static u8 *fec_read_parity(struct dm_verity *v, u64 rsb, int index,
  			   unsigned *offset, struct dm_buffer **buf)
  {
  	u64 position, block;
  	u8 *res;
  
  	position = (index + rsb) * v->fec->roots;
  	block = position >> v->data_dev_block_bits;
  	*offset = (unsigned)(position - (block << v->data_dev_block_bits));
  
  	res = dm_bufio_read(v->fec->bufio, v->fec->start + block, buf);
  	if (unlikely(IS_ERR(res))) {
  		DMERR("%s: FEC %llu: parity read failed (block %llu): %ld",
  		      v->data_dev->name, (unsigned long long)rsb,
  		      (unsigned long long)(v->fec->start + block),
  		      PTR_ERR(res));
  		*buf = NULL;
  	}
  
  	return res;
  }
  
  /* Loop over each preallocated buffer slot. */
  #define fec_for_each_prealloc_buffer(__i) \
  	for (__i = 0; __i < DM_VERITY_FEC_BUF_PREALLOC; __i++)
  
  /* Loop over each extra buffer slot. */
  #define fec_for_each_extra_buffer(io, __i) \
  	for (__i = DM_VERITY_FEC_BUF_PREALLOC; __i < DM_VERITY_FEC_BUF_MAX; __i++)
  
  /* Loop over each allocated buffer. */
  #define fec_for_each_buffer(io, __i) \
  	for (__i = 0; __i < (io)->nbufs; __i++)
  
  /* Loop over each RS block in each allocated buffer. */
  #define fec_for_each_buffer_rs_block(io, __i, __j) \
  	fec_for_each_buffer(io, __i) \
  		for (__j = 0; __j < 1 << DM_VERITY_FEC_BUF_RS_BITS; __j++)
  
  /*
   * Return a pointer to the current RS block when called inside
   * fec_for_each_buffer_rs_block.
   */
  static inline u8 *fec_buffer_rs_block(struct dm_verity *v,
  				      struct dm_verity_fec_io *fio,
  				      unsigned i, unsigned j)
  {
  	return &fio->bufs[i][j * v->fec->rsn];
  }
  
  /*
   * Return an index to the current RS block when called inside
   * fec_for_each_buffer_rs_block.
   */
  static inline unsigned fec_buffer_rs_index(unsigned i, unsigned j)
  {
  	return (i << DM_VERITY_FEC_BUF_RS_BITS) + j;
  }
  
  /*
   * Decode all RS blocks from buffers and copy corrected bytes into fio->output
   * starting from block_offset.
   */
  static int fec_decode_bufs(struct dm_verity *v, struct dm_verity_fec_io *fio,
  			   u64 rsb, int byte_index, unsigned block_offset,
  			   int neras)
  {
  	int r, corrected = 0, res;
  	struct dm_buffer *buf;
  	unsigned n, i, offset;
  	u8 *par, *block;
  
  	par = fec_read_parity(v, rsb, block_offset, &offset, &buf);
  	if (IS_ERR(par))
  		return PTR_ERR(par);
  
  	/*
  	 * Decode the RS blocks we have in bufs. Each RS block results in
  	 * one corrected target byte and consumes fec->roots parity bytes.
  	 */
  	fec_for_each_buffer_rs_block(fio, n, i) {
  		block = fec_buffer_rs_block(v, fio, n, i);
  		res = fec_decode_rs8(v, fio, block, &par[offset], neras);
  		if (res < 0) {
  			dm_bufio_release(buf);
  
  			r = res;
  			goto error;
  		}
  
  		corrected += res;
  		fio->output[block_offset] = block[byte_index];
  
  		block_offset++;
  		if (block_offset >= 1 << v->data_dev_block_bits)
  			goto done;
  
  		/* read the next block when we run out of parity bytes */
  		offset += v->fec->roots;
  		if (offset >= 1 << v->data_dev_block_bits) {
  			dm_bufio_release(buf);
  
  			par = fec_read_parity(v, rsb, block_offset, &offset, &buf);
  			if (unlikely(IS_ERR(par)))
  				return PTR_ERR(par);
  		}
  	}
  done:
  	r = corrected;
  error:
  	if (r < 0 && neras)
  		DMERR_LIMIT("%s: FEC %llu: failed to correct: %d",
  			    v->data_dev->name, (unsigned long long)rsb, r);
  	else if (r > 0)
  		DMWARN_LIMIT("%s: FEC %llu: corrected %d errors",
  			     v->data_dev->name, (unsigned long long)rsb, r);
  
  	return r;
  }
  
  /*
   * Locate data block erasures using verity hashes.
   */
  static int fec_is_erasure(struct dm_verity *v, struct dm_verity_io *io,
  			  u8 *want_digest, u8 *data)
  {
  	if (unlikely(verity_hash(v, verity_io_hash_desc(v, io),
  				 data, 1 << v->data_dev_block_bits,
  				 verity_io_real_digest(v, io))))
  		return 0;
  
  	return memcmp(verity_io_real_digest(v, io), want_digest,
  		      v->digest_size) != 0;
  }
  
  /*
   * Read data blocks that are part of the RS block and deinterleave as much as
   * fits into buffers. Check for erasure locations if @neras is non-NULL.
   */
  static int fec_read_bufs(struct dm_verity *v, struct dm_verity_io *io,
  			 u64 rsb, u64 target, unsigned block_offset,
  			 int *neras)
  {
  	bool is_zero;
  	int i, j, target_index = -1;
  	struct dm_buffer *buf;
  	struct dm_bufio_client *bufio;
  	struct dm_verity_fec_io *fio = fec_io(io);
  	u64 block, ileaved;
  	u8 *bbuf, *rs_block;
  	u8 want_digest[v->digest_size];
  	unsigned n, k;
  
  	if (neras)
  		*neras = 0;
  
  	/*
  	 * read each of the rsn data blocks that are part of the RS block, and
  	 * interleave contents to available bufs
  	 */
  	for (i = 0; i < v->fec->rsn; i++) {
  		ileaved = fec_interleave(v, rsb * v->fec->rsn + i);
  
  		/*
  		 * target is the data block we want to correct, target_index is
  		 * the index of this block within the rsn RS blocks
  		 */
  		if (ileaved == target)
  			target_index = i;
  
  		block = ileaved >> v->data_dev_block_bits;
  		bufio = v->fec->data_bufio;
  
  		if (block >= v->data_blocks) {
  			block -= v->data_blocks;
  
  			/*
  			 * blocks outside the area were assumed to contain
  			 * zeros when encoding data was generated
  			 */
  			if (unlikely(block >= v->fec->hash_blocks))
  				continue;
  
  			block += v->hash_start;
  			bufio = v->bufio;
  		}
  
  		bbuf = dm_bufio_read(bufio, block, &buf);
  		if (unlikely(IS_ERR(bbuf))) {
  			DMWARN_LIMIT("%s: FEC %llu: read failed (%llu): %ld",
  				     v->data_dev->name,
  				     (unsigned long long)rsb,
  				     (unsigned long long)block, PTR_ERR(bbuf));
  
  			/* assume the block is corrupted */
  			if (neras && *neras <= v->fec->roots)
  				fio->erasures[(*neras)++] = i;
  
  			continue;
  		}
  
  		/* locate erasures if the block is on the data device */
  		if (bufio == v->fec->data_bufio &&
  		    verity_hash_for_block(v, io, block, want_digest,
  					  &is_zero) == 0) {
  			/* skip known zero blocks entirely */
  			if (is_zero)
  				continue;
  
  			/*
  			 * skip if we have already found the theoretical
  			 * maximum number (i.e. fec->roots) of erasures
  			 */
  			if (neras && *neras <= v->fec->roots &&
  			    fec_is_erasure(v, io, want_digest, bbuf))
  				fio->erasures[(*neras)++] = i;
  		}
  
  		/*
  		 * deinterleave and copy the bytes that fit into bufs,
  		 * starting from block_offset
  		 */
  		fec_for_each_buffer_rs_block(fio, n, j) {
  			k = fec_buffer_rs_index(n, j) + block_offset;
  
  			if (k >= 1 << v->data_dev_block_bits)
  				goto done;
  
  			rs_block = fec_buffer_rs_block(v, fio, n, j);
  			rs_block[i] = bbuf[k];
  		}
  done:
  		dm_bufio_release(buf);
  	}
  
  	return target_index;
  }
  
  /*
   * Allocate RS control structure and FEC buffers from preallocated mempools,
   * and attempt to allocate as many extra buffers as available.
   */
  static int fec_alloc_bufs(struct dm_verity *v, struct dm_verity_fec_io *fio)
  {
  	unsigned n;
  
  	if (!fio->rs) {
  		fio->rs = mempool_alloc(v->fec->rs_pool, 0);
  		if (unlikely(!fio->rs)) {
  			DMERR("failed to allocate RS");
  			return -ENOMEM;
  		}
  	}
  
  	fec_for_each_prealloc_buffer(n) {
  		if (fio->bufs[n])
  			continue;
  
  		fio->bufs[n] = mempool_alloc(v->fec->prealloc_pool, GFP_NOIO);
  		if (unlikely(!fio->bufs[n])) {
  			DMERR("failed to allocate FEC buffer");
  			return -ENOMEM;
  		}
  	}
  
  	/* try to allocate the maximum number of buffers */
  	fec_for_each_extra_buffer(fio, n) {
  		if (fio->bufs[n])
  			continue;
  
  		fio->bufs[n] = mempool_alloc(v->fec->extra_pool, GFP_NOIO);
  		/* we can manage with even one buffer if necessary */
  		if (unlikely(!fio->bufs[n]))
  			break;
  	}
  	fio->nbufs = n;
  
  	if (!fio->output) {
  		fio->output = mempool_alloc(v->fec->output_pool, GFP_NOIO);
  
  		if (!fio->output) {
  			DMERR("failed to allocate FEC page");
  			return -ENOMEM;
  		}
  	}
  
  	return 0;
  }
  
  /*
   * Initialize buffers and clear erasures. fec_read_bufs() assumes buffers are
   * zeroed before deinterleaving.
   */
  static void fec_init_bufs(struct dm_verity *v, struct dm_verity_fec_io *fio)
  {
  	unsigned n;
  
  	fec_for_each_buffer(fio, n)
  		memset(fio->bufs[n], 0, v->fec->rsn << DM_VERITY_FEC_BUF_RS_BITS);
  
  	memset(fio->erasures, 0, sizeof(fio->erasures));
  }
  
  /*
   * Decode all RS blocks in a single data block and return the target block
   * (indicated by @offset) in fio->output. If @use_erasures is non-zero, uses
   * hashes to locate erasures.
   */
  static int fec_decode_rsb(struct dm_verity *v, struct dm_verity_io *io,
  			  struct dm_verity_fec_io *fio, u64 rsb, u64 offset,
  			  bool use_erasures)
  {
  	int r, neras = 0;
  	unsigned pos;
  
  	r = fec_alloc_bufs(v, fio);
  	if (unlikely(r < 0))
  		return r;
  
  	for (pos = 0; pos < 1 << v->data_dev_block_bits; ) {
  		fec_init_bufs(v, fio);
  
  		r = fec_read_bufs(v, io, rsb, offset, pos,
  				  use_erasures ? &neras : NULL);
  		if (unlikely(r < 0))
  			return r;
  
  		r = fec_decode_bufs(v, fio, rsb, r, pos, neras);
  		if (r < 0)
  			return r;
  
  		pos += fio->nbufs << DM_VERITY_FEC_BUF_RS_BITS;
  	}
  
  	/* Always re-validate the corrected block against the expected hash */
  	r = verity_hash(v, verity_io_hash_desc(v, io), fio->output,
  			1 << v->data_dev_block_bits,
  			verity_io_real_digest(v, io));
  	if (unlikely(r < 0))
  		return r;
  
  	if (memcmp(verity_io_real_digest(v, io), verity_io_want_digest(v, io),
  		   v->digest_size)) {
  		DMERR_LIMIT("%s: FEC %llu: failed to correct (%d erasures)",
  			    v->data_dev->name, (unsigned long long)rsb, neras);
  		return -EILSEQ;
  	}
  
  	return 0;
  }
  
  static int fec_bv_copy(struct dm_verity *v, struct dm_verity_io *io, u8 *data,
  		       size_t len)
  {
  	struct dm_verity_fec_io *fio = fec_io(io);
  
  	memcpy(data, &fio->output[fio->output_pos], len);
  	fio->output_pos += len;
  
  	return 0;
  }
  
  /*
   * Correct errors in a block. Copies corrected block to dest if non-NULL,
   * otherwise to a bio_vec starting from iter.
   */
  int verity_fec_decode(struct dm_verity *v, struct dm_verity_io *io,
  		      enum verity_block_type type, sector_t block, u8 *dest,
  		      struct bvec_iter *iter)
  {
  	int r;
  	struct dm_verity_fec_io *fio = fec_io(io);
  	u64 offset, res, rsb;
  
  	if (!verity_fec_is_enabled(v))
  		return -EOPNOTSUPP;
  
  	if (type == DM_VERITY_BLOCK_TYPE_METADATA)
  		block += v->data_blocks;
  
  	/*
  	 * For RS(M, N), the continuous FEC data is divided into blocks of N
  	 * bytes. Since block size may not be divisible by N, the last block
  	 * is zero padded when decoding.
  	 *
  	 * Each byte of the block is covered by a different RS(M, N) code,
  	 * and each code is interleaved over N blocks to make it less likely
  	 * that bursty corruption will leave us in unrecoverable state.
  	 */
  
  	offset = block << v->data_dev_block_bits;
  	res = div64_u64(offset, v->fec->rounds << v->data_dev_block_bits);
  
  	/*
  	 * The base RS block we can feed to the interleaver to find out all
  	 * blocks required for decoding.
  	 */
  	rsb = offset - res * (v->fec->rounds << v->data_dev_block_bits);
  
  	/*
  	 * Locating erasures is slow, so attempt to recover the block without
  	 * them first. Do a second attempt with erasures if the corruption is
  	 * bad enough.
  	 */
  	r = fec_decode_rsb(v, io, fio, rsb, offset, false);
  	if (r < 0) {
  		r = fec_decode_rsb(v, io, fio, rsb, offset, true);
  		if (r < 0)
  			return r;
  	}
  
  	if (dest)
  		memcpy(dest, fio->output, 1 << v->data_dev_block_bits);
  	else if (iter) {
  		fio->output_pos = 0;
  		r = verity_for_bv_block(v, io, iter, fec_bv_copy);
  	}
  
  	return r;
  }
  
  /*
   * Clean up per-bio data.
   */
  void verity_fec_finish_io(struct dm_verity_io *io)
  {
  	unsigned n;
  	struct dm_verity_fec *f = io->v->fec;
  	struct dm_verity_fec_io *fio = fec_io(io);
  
  	if (!verity_fec_is_enabled(io->v))
  		return;
  
  	mempool_free(fio->rs, f->rs_pool);
  
  	fec_for_each_prealloc_buffer(n)
  		mempool_free(fio->bufs[n], f->prealloc_pool);
  
  	fec_for_each_extra_buffer(fio, n)
  		mempool_free(fio->bufs[n], f->extra_pool);
  
  	mempool_free(fio->output, f->output_pool);
  }
  
  /*
   * Initialize per-bio data.
   */
  void verity_fec_init_io(struct dm_verity_io *io)
  {
  	struct dm_verity_fec_io *fio = fec_io(io);
  
  	if (!verity_fec_is_enabled(io->v))
  		return;
  
  	fio->rs = NULL;
  	memset(fio->bufs, 0, sizeof(fio->bufs));
  	fio->nbufs = 0;
  	fio->output = NULL;
  }
  
  /*
   * Append feature arguments and values to the status table.
   */
  unsigned verity_fec_status_table(struct dm_verity *v, unsigned sz,
  				 char *result, unsigned maxlen)
  {
  	if (!verity_fec_is_enabled(v))
  		return sz;
  
  	DMEMIT(" " DM_VERITY_OPT_FEC_DEV " %s "
  	       DM_VERITY_OPT_FEC_BLOCKS " %llu "
  	       DM_VERITY_OPT_FEC_START " %llu "
  	       DM_VERITY_OPT_FEC_ROOTS " %d",
  	       v->fec->dev->name,
  	       (unsigned long long)v->fec->blocks,
  	       (unsigned long long)v->fec->start,
  	       v->fec->roots);
  
  	return sz;
  }
  
  void verity_fec_dtr(struct dm_verity *v)
  {
  	struct dm_verity_fec *f = v->fec;
  
  	if (!verity_fec_is_enabled(v))
  		goto out;
  
  	mempool_destroy(f->rs_pool);
  	mempool_destroy(f->prealloc_pool);
  	mempool_destroy(f->extra_pool);
  	kmem_cache_destroy(f->cache);
  
  	if (f->data_bufio)
  		dm_bufio_client_destroy(f->data_bufio);
  	if (f->bufio)
  		dm_bufio_client_destroy(f->bufio);
  
  	if (f->dev)
  		dm_put_device(v->ti, f->dev);
  out:
  	kfree(f);
  	v->fec = NULL;
  }
  
  static void *fec_rs_alloc(gfp_t gfp_mask, void *pool_data)
  {
  	struct dm_verity *v = (struct dm_verity *)pool_data;
  
  	return init_rs(8, 0x11d, 0, 1, v->fec->roots);
  }
  
  static void fec_rs_free(void *element, void *pool_data)
  {
  	struct rs_control *rs = (struct rs_control *)element;
  
  	if (rs)
  		free_rs(rs);
  }
  
  bool verity_is_fec_opt_arg(const char *arg_name)
  {
  	return (!strcasecmp(arg_name, DM_VERITY_OPT_FEC_DEV) ||
  		!strcasecmp(arg_name, DM_VERITY_OPT_FEC_BLOCKS) ||
  		!strcasecmp(arg_name, DM_VERITY_OPT_FEC_START) ||
  		!strcasecmp(arg_name, DM_VERITY_OPT_FEC_ROOTS));
  }
  
  int verity_fec_parse_opt_args(struct dm_arg_set *as, struct dm_verity *v,
  			      unsigned *argc, const char *arg_name)
  {
  	int r;
  	struct dm_target *ti = v->ti;
  	const char *arg_value;
  	unsigned long long num_ll;
  	unsigned char num_c;
  	char dummy;
  
  	if (!*argc) {
  		ti->error = "FEC feature arguments require a value";
  		return -EINVAL;
  	}
  
  	arg_value = dm_shift_arg(as);
  	(*argc)--;
  
  	if (!strcasecmp(arg_name, DM_VERITY_OPT_FEC_DEV)) {
  		r = dm_get_device(ti, arg_value, FMODE_READ, &v->fec->dev);
  		if (r) {
  			ti->error = "FEC device lookup failed";
  			return r;
  		}
  
  	} else if (!strcasecmp(arg_name, DM_VERITY_OPT_FEC_BLOCKS)) {
  		if (sscanf(arg_value, "%llu%c", &num_ll, &dummy) != 1 ||
  		    ((sector_t)(num_ll << (v->data_dev_block_bits - SECTOR_SHIFT))
  		     >> (v->data_dev_block_bits - SECTOR_SHIFT) != num_ll)) {
  			ti->error = "Invalid " DM_VERITY_OPT_FEC_BLOCKS;
  			return -EINVAL;
  		}
  		v->fec->blocks = num_ll;
  
  	} else if (!strcasecmp(arg_name, DM_VERITY_OPT_FEC_START)) {
  		if (sscanf(arg_value, "%llu%c", &num_ll, &dummy) != 1 ||
  		    ((sector_t)(num_ll << (v->data_dev_block_bits - SECTOR_SHIFT)) >>
  		     (v->data_dev_block_bits - SECTOR_SHIFT) != num_ll)) {
  			ti->error = "Invalid " DM_VERITY_OPT_FEC_START;
  			return -EINVAL;
  		}
  		v->fec->start = num_ll;
  
  	} else if (!strcasecmp(arg_name, DM_VERITY_OPT_FEC_ROOTS)) {
  		if (sscanf(arg_value, "%hhu%c", &num_c, &dummy) != 1 || !num_c ||
  		    num_c < (DM_VERITY_FEC_RSM - DM_VERITY_FEC_MAX_RSN) ||
  		    num_c > (DM_VERITY_FEC_RSM - DM_VERITY_FEC_MIN_RSN)) {
  			ti->error = "Invalid " DM_VERITY_OPT_FEC_ROOTS;
  			return -EINVAL;
  		}
  		v->fec->roots = num_c;
  
  	} else {
  		ti->error = "Unrecognized verity FEC feature request";
  		return -EINVAL;
  	}
  
  	return 0;
  }
  
  /*
   * Allocate dm_verity_fec for v->fec. Must be called before verity_fec_ctr.
   */
  int verity_fec_ctr_alloc(struct dm_verity *v)
  {
  	struct dm_verity_fec *f;
  
  	f = kzalloc(sizeof(struct dm_verity_fec), GFP_KERNEL);
  	if (!f) {
  		v->ti->error = "Cannot allocate FEC structure";
  		return -ENOMEM;
  	}
  	v->fec = f;
  
  	return 0;
  }
  
  /*
   * Validate arguments and preallocate memory. Must be called after arguments
   * have been parsed using verity_fec_parse_opt_args.
   */
  int verity_fec_ctr(struct dm_verity *v)
  {
  	struct dm_verity_fec *f = v->fec;
  	struct dm_target *ti = v->ti;
  	u64 hash_blocks;
  
  	if (!verity_fec_is_enabled(v)) {
  		verity_fec_dtr(v);
  		return 0;
  	}
  
  	/*
  	 * FEC is computed over data blocks, possible metadata, and
  	 * hash blocks. In other words, FEC covers total of fec_blocks
  	 * blocks consisting of the following:
  	 *
  	 *  data blocks | hash blocks | metadata (optional)
  	 *
  	 * We allow metadata after hash blocks to support a use case
  	 * where all data is stored on the same device and FEC covers
  	 * the entire area.
  	 *
  	 * If metadata is included, we require it to be available on the
  	 * hash device after the hash blocks.
  	 */
  
  	hash_blocks = v->hash_blocks - v->hash_start;
  
  	/*
  	 * Require matching block sizes for data and hash devices for
  	 * simplicity.
  	 */
  	if (v->data_dev_block_bits != v->hash_dev_block_bits) {
  		ti->error = "Block sizes must match to use FEC";
  		return -EINVAL;
  	}
  
  	if (!f->roots) {
  		ti->error = "Missing " DM_VERITY_OPT_FEC_ROOTS;
  		return -EINVAL;
  	}
  	f->rsn = DM_VERITY_FEC_RSM - f->roots;
  
  	if (!f->blocks) {
  		ti->error = "Missing " DM_VERITY_OPT_FEC_BLOCKS;
  		return -EINVAL;
  	}
  
  	f->rounds = f->blocks;
  	if (sector_div(f->rounds, f->rsn))
  		f->rounds++;
  
  	/*
  	 * Due to optional metadata, f->blocks can be larger than
  	 * data_blocks and hash_blocks combined.
  	 */
  	if (f->blocks < v->data_blocks + hash_blocks || !f->rounds) {
  		ti->error = "Invalid " DM_VERITY_OPT_FEC_BLOCKS;
  		return -EINVAL;
  	}
  
  	/*
  	 * Metadata is accessed through the hash device, so we require
  	 * it to be large enough.
  	 */
  	f->hash_blocks = f->blocks - v->data_blocks;
  	if (dm_bufio_get_device_size(v->bufio) < f->hash_blocks) {
  		ti->error = "Hash device is too small for "
  			DM_VERITY_OPT_FEC_BLOCKS;
  		return -E2BIG;
  	}
  
  	f->bufio = dm_bufio_client_create(f->dev->bdev,
  					  1 << v->data_dev_block_bits,
  					  1, 0, NULL, NULL);
  	if (IS_ERR(f->bufio)) {
  		ti->error = "Cannot initialize FEC bufio client";
  		return PTR_ERR(f->bufio);
  	}
  
  	if (dm_bufio_get_device_size(f->bufio) <
  	    ((f->start + f->rounds * f->roots) >> v->data_dev_block_bits)) {
  		ti->error = "FEC device is too small";
  		return -E2BIG;
  	}
  
  	f->data_bufio = dm_bufio_client_create(v->data_dev->bdev,
  					       1 << v->data_dev_block_bits,
  					       1, 0, NULL, NULL);
  	if (IS_ERR(f->data_bufio)) {
  		ti->error = "Cannot initialize FEC data bufio client";
  		return PTR_ERR(f->data_bufio);
  	}
  
  	if (dm_bufio_get_device_size(f->data_bufio) < v->data_blocks) {
  		ti->error = "Data device is too small";
  		return -E2BIG;
  	}
  
  	/* Preallocate an rs_control structure for each worker thread */
  	f->rs_pool = mempool_create(num_online_cpus(), fec_rs_alloc,
  				    fec_rs_free, (void *) v);
  	if (!f->rs_pool) {
  		ti->error = "Cannot allocate RS pool";
  		return -ENOMEM;
  	}
  
  	f->cache = kmem_cache_create("dm_verity_fec_buffers",
  				     f->rsn << DM_VERITY_FEC_BUF_RS_BITS,
  				     0, 0, NULL);
  	if (!f->cache) {
  		ti->error = "Cannot create FEC buffer cache";
  		return -ENOMEM;
  	}
  
  	/* Preallocate DM_VERITY_FEC_BUF_PREALLOC buffers for each thread */
  	f->prealloc_pool = mempool_create_slab_pool(num_online_cpus() *
  						    DM_VERITY_FEC_BUF_PREALLOC,
  						    f->cache);
  	if (!f->prealloc_pool) {
  		ti->error = "Cannot allocate FEC buffer prealloc pool";
  		return -ENOMEM;
  	}
  
  	f->extra_pool = mempool_create_slab_pool(0, f->cache);
  	if (!f->extra_pool) {
  		ti->error = "Cannot allocate FEC buffer extra pool";
  		return -ENOMEM;
  	}
  
  	/* Preallocate an output buffer for each thread */
  	f->output_pool = mempool_create_kmalloc_pool(num_online_cpus(),
  						     1 << v->data_dev_block_bits);
  	if (!f->output_pool) {
  		ti->error = "Cannot allocate FEC output pool";
  		return -ENOMEM;
  	}
  
  	/* Reserve space for our per-bio data */
  	ti->per_io_data_size += sizeof(struct dm_verity_fec_io);
  
  	return 0;
  }
  