/* RomFS storage access routines
   *
   * Copyright © 2007 Red Hat, Inc. All Rights Reserved.
   * Written by David Howells (dhowells@redhat.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 <linux/fs.h>
  #include <linux/mtd/super.h>
  #include <linux/buffer_head.h>
  #include "internal.h"
  
  #if !defined(CONFIG_ROMFS_ON_MTD) && !defined(CONFIG_ROMFS_ON_BLOCK)
  #error no ROMFS backing store interface configured
  #endif
  
  #ifdef CONFIG_ROMFS_ON_MTD
  #define ROMFS_MTD_READ(sb, ...) mtd_read((sb)->s_mtd, ##__VA_ARGS__)
  
  /*
   * read data from an romfs image on an MTD device
   */
  static int romfs_mtd_read(struct super_block *sb, unsigned long pos,
  			  void *buf, size_t buflen)
  {
  	size_t rlen;
  	int ret;
  
  	ret = ROMFS_MTD_READ(sb, pos, buflen, &rlen, buf);
  	return (ret < 0 || rlen != buflen) ? -EIO : 0;
  }
  
  /*
   * determine the length of a string in a romfs image on an MTD device
   */
  static ssize_t romfs_mtd_strnlen(struct super_block *sb,
  				 unsigned long pos, size_t maxlen)
  {
  	ssize_t n = 0;
  	size_t segment;
  	u_char buf[16], *p;
  	size_t len;
  	int ret;
  
  	/* scan the string up to 16 bytes at a time */
  	while (maxlen > 0) {
  		segment = min_t(size_t, maxlen, 16);
  		ret = ROMFS_MTD_READ(sb, pos, segment, &len, buf);
  		if (ret < 0)
  			return ret;
  		p = memchr(buf, 0, len);
  		if (p)
  			return n + (p - buf);
  		maxlen -= len;
  		pos += len;
  		n += len;
  	}
  
  	return n;
  }
  
  /*
   * compare a string to one in a romfs image on MTD
   * - return 1 if matched, 0 if differ, -ve if error
   */
  static int romfs_mtd_strcmp(struct super_block *sb, unsigned long pos,
  			    const char *str, size_t size)
  {
  	u_char buf[17];
  	size_t len, segment;
  	int ret;
  
  	/* scan the string up to 16 bytes at a time, and attempt to grab the
  	 * trailing NUL whilst we're at it */
  	buf[0] = 0xff;
  
  	while (size > 0) {
  		segment = min_t(size_t, size + 1, 17);
  		ret = ROMFS_MTD_READ(sb, pos, segment, &len, buf);
  		if (ret < 0)
  			return ret;
  		len--;
  		if (memcmp(buf, str, len) != 0)
  			return 0;
  		buf[0] = buf[len];
  		size -= len;
  		pos += len;
  		str += len;
  	}
  
  	/* check the trailing NUL was */
  	if (buf[0])
  		return 0;
  
  	return 1;
  }
  #endif /* CONFIG_ROMFS_ON_MTD */
  
  #ifdef CONFIG_ROMFS_ON_BLOCK
  /*
   * read data from an romfs image on a block device
   */
  static int romfs_blk_read(struct super_block *sb, unsigned long pos,
  			  void *buf, size_t buflen)
  {
  	struct buffer_head *bh;
  	unsigned long offset;
  	size_t segment;
  
  	/* copy the string up to blocksize bytes at a time */
  	while (buflen > 0) {
  		offset = pos & (ROMBSIZE - 1);
  		segment = min_t(size_t, buflen, ROMBSIZE - offset);
  		bh = sb_bread(sb, pos >> ROMBSBITS);
  		if (!bh)
  			return -EIO;
  		memcpy(buf, bh->b_data + offset, segment);
  		brelse(bh);
  		buf += segment;
  		buflen -= segment;
  		pos += segment;
  	}
  
  	return 0;
  }
  
  /*
   * determine the length of a string in romfs on a block device
   */
  static ssize_t romfs_blk_strnlen(struct super_block *sb,
  				 unsigned long pos, size_t limit)
  {
  	struct buffer_head *bh;
  	unsigned long offset;
  	ssize_t n = 0;
  	size_t segment;
  	u_char *buf, *p;
  
  	/* scan the string up to blocksize bytes at a time */
  	while (limit > 0) {
  		offset = pos & (ROMBSIZE - 1);
  		segment = min_t(size_t, limit, ROMBSIZE - offset);
  		bh = sb_bread(sb, pos >> ROMBSBITS);
  		if (!bh)
  			return -EIO;
  		buf = bh->b_data + offset;
  		p = memchr(buf, 0, segment);
  		brelse(bh);
  		if (p)
  			return n + (p - buf);
  		limit -= segment;
  		pos += segment;
  		n += segment;
  	}
  
  	return n;
  }
  
  /*
   * compare a string to one in a romfs image on a block device
   * - return 1 if matched, 0 if differ, -ve if error
   */
  static int romfs_blk_strcmp(struct super_block *sb, unsigned long pos,
  			    const char *str, size_t size)
  {
  	struct buffer_head *bh;
  	unsigned long offset;
  	size_t segment;
  	bool matched, terminated = false;
  
  	/* compare string up to a block at a time */
  	while (size > 0) {
  		offset = pos & (ROMBSIZE - 1);
  		segment = min_t(size_t, size, ROMBSIZE - offset);
  		bh = sb_bread(sb, pos >> ROMBSBITS);
  		if (!bh)
  			return -EIO;
  		matched = (memcmp(bh->b_data + offset, str, segment) == 0);
  
  		size -= segment;
  		pos += segment;
  		str += segment;
  		if (matched && size == 0 && offset + segment < ROMBSIZE) {
  			if (!bh->b_data[offset + segment])
  				terminated = true;
  			else
  				matched = false;
  		}
  		brelse(bh);
  		if (!matched)
  			return 0;
  	}
  
  	if (!terminated) {
  		/* the terminating NUL must be on the first byte of the next
  		 * block */
  		BUG_ON((pos & (ROMBSIZE - 1)) != 0);
  		bh = sb_bread(sb, pos >> ROMBSBITS);
  		if (!bh)
  			return -EIO;
  		matched = !bh->b_data[0];
  		brelse(bh);
  		if (!matched)
  			return 0;
  	}
  
  	return 1;
  }
  #endif /* CONFIG_ROMFS_ON_BLOCK */
  
  /*
   * read data from the romfs image
   */
  int romfs_dev_read(struct super_block *sb, unsigned long pos,
  		   void *buf, size_t buflen)
  {
  	size_t limit;
  
  	limit = romfs_maxsize(sb);
  	if (pos >= limit)
  		return -EIO;
  	if (buflen > limit - pos)
  		buflen = limit - pos;
  
  #ifdef CONFIG_ROMFS_ON_MTD
  	if (sb->s_mtd)
  		return romfs_mtd_read(sb, pos, buf, buflen);
  #endif
  #ifdef CONFIG_ROMFS_ON_BLOCK
  	if (sb->s_bdev)
  		return romfs_blk_read(sb, pos, buf, buflen);
  #endif
  	return -EIO;
  }
  
  /*
   * determine the length of a string in romfs
   */
  ssize_t romfs_dev_strnlen(struct super_block *sb,
  			  unsigned long pos, size_t maxlen)
  {
  	size_t limit;
  
  	limit = romfs_maxsize(sb);
  	if (pos >= limit)
  		return -EIO;
  	if (maxlen > limit - pos)
  		maxlen = limit - pos;
  
  #ifdef CONFIG_ROMFS_ON_MTD
  	if (sb->s_mtd)
  		return romfs_mtd_strnlen(sb, pos, maxlen);
  #endif
  #ifdef CONFIG_ROMFS_ON_BLOCK
  	if (sb->s_bdev)
  		return romfs_blk_strnlen(sb, pos, maxlen);
  #endif
  	return -EIO;
  }
  
  /*
   * compare a string to one in romfs
   * - the string to be compared to, str, may not be NUL-terminated; instead the
   *   string is of the specified size
   * - return 1 if matched, 0 if differ, -ve if error
   */
  int romfs_dev_strcmp(struct super_block *sb, unsigned long pos,
  		     const char *str, size_t size)
  {
  	size_t limit;
  
  	limit = romfs_maxsize(sb);
  	if (pos >= limit)
  		return -EIO;
  	if (size > ROMFS_MAXFN)
  		return -ENAMETOOLONG;
  	if (size + 1 > limit - pos)
  		return -EIO;
  
  #ifdef CONFIG_ROMFS_ON_MTD
  	if (sb->s_mtd)
  		return romfs_mtd_strcmp(sb, pos, str, size);
  #endif
  #ifdef CONFIG_ROMFS_ON_BLOCK
  	if (sb->s_bdev)
  		return romfs_blk_strcmp(sb, pos, str, size);
  #endif
  	return -EIO;
  }