fs/romfs/storage.c

   1 /* RomFS storage access routines
   2  *
   3  * Copyright © 2007 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the License, or (at your option) any later version.
  10  */
  11
  12 #include <linux/fs.h>
  13 #include <linux/mtd/super.h>
  14 #include <linux/buffer_head.h>
  15 #include "internal.h"
  16
  17 #if !defined(CONFIG_ROMFS_ON_MTD) && !defined(CONFIG_ROMFS_ON_BLOCK)
  18 #error no ROMFS backing store interface configured
  19 #endif
  20
  21 #ifdef CONFIG_ROMFS_ON_MTD
  22 #define ROMFS_MTD_READ(sb, ...) mtd_read((sb)->s_mtd, ##__VA_ARGS__)
  23
  24 /*
  25  * read data from an romfs image on an MTD device
  26  */
  27 static int romfs_mtd_read(struct super_block *sb, unsigned long pos,
  28                           void *buf, size_t buflen)
  29 {
  30         size_t rlen;
  31         int ret;
  32
  33         ret = ROMFS_MTD_READ(sb, pos, buflen, &rlen, buf);
  34         return (ret < 0 || rlen != buflen) ? -EIO : 0;
  35 }
  36
  37 /*
  38  * determine the length of a string in a romfs image on an MTD device
  39  */
  40 static ssize_t romfs_mtd_strnlen(struct super_block *sb,
  41                                  unsigned long pos, size_t maxlen)
  42 {
  43         ssize_t n = 0;
  44         size_t segment;
  45         u_char buf[16], *p;
  46         size_t len;
  47         int ret;
  48
  49         /* scan the string up to 16 bytes at a time */
  50         while (maxlen > 0) {
  51                 segment = min_t(size_t, maxlen, 16);
  52                 ret = ROMFS_MTD_READ(sb, pos, segment, &len, buf);
  53                 if (ret < 0)
  54                         return ret;
  55                 p = memchr(buf, 0, len);
  56                 if (p)
  57                         return n + (p - buf);
  58                 maxlen -= len;
  59                 pos += len;
  60                 n += len;
  61         }
  62
  63         return n;
  64 }
  65
  66 /*
  67  * compare a string to one in a romfs image on MTD
  68  * - return 1 if matched, 0 if differ, -ve if error
  69  */
  70 static int romfs_mtd_strcmp(struct super_block *sb, unsigned long pos,
  71                             const char *str, size_t size)
  72 {
  73         u_char buf[17];
  74         size_t len, segment;
  75         int ret;
  76
  77         /* scan the string up to 16 bytes at a time, and attempt to grab the
  78          * trailing NUL whilst we're at it */
  79         buf[0] = 0xff;
  80
  81         while (size > 0) {
  82                 segment = min_t(size_t, size + 1, 17);
  83                 ret = ROMFS_MTD_READ(sb, pos, segment, &len, buf);
  84                 if (ret < 0)
  85                         return ret;
  86                 len--;
  87                 if (memcmp(buf, str, len) != 0)
  88                         return 0;
  89                 buf[0] = buf[len];
  90                 size -= len;
  91                 pos += len;
  92                 str += len;
  93         }
  94
  95         /* check the trailing NUL was */
  96         if (buf[0])
  97                 return 0;
  98
  99         return 1;
 100 }
 101 #endif /* CONFIG_ROMFS_ON_MTD */
 102
 103 #ifdef CONFIG_ROMFS_ON_BLOCK
 104 /*
 105  * read data from an romfs image on a block device
 106  */
 107 static int romfs_blk_read(struct super_block *sb, unsigned long pos,
 108                           void *buf, size_t buflen)
 109 {
 110         struct buffer_head *bh;
 111         unsigned long offset;
 112         size_t segment;
 113
 114         /* copy the string up to blocksize bytes at a time */
 115         while (buflen > 0) {
 116                 offset = pos & (ROMBSIZE - 1);
 117                 segment = min_t(size_t, buflen, ROMBSIZE - offset);
 118                 bh = sb_bread(sb, pos >> ROMBSBITS);
 119                 if (!bh)
 120                         return -EIO;
 121                 memcpy(buf, bh->b_data + offset, segment);
 122                 brelse(bh);
 123                 buf += segment;
 124                 buflen -= segment;
 125                 pos += segment;
 126         }
 127
 128         return 0;
 129 }
 130
 131 /*
 132  * determine the length of a string in romfs on a block device
 133  */
 134 static ssize_t romfs_blk_strnlen(struct super_block *sb,
 135                                  unsigned long pos, size_t limit)
 136 {
 137         struct buffer_head *bh;
 138         unsigned long offset;
 139         ssize_t n = 0;
 140         size_t segment;
 141         u_char *buf, *p;
 142
 143         /* scan the string up to blocksize bytes at a time */
 144         while (limit > 0) {
 145                 offset = pos & (ROMBSIZE - 1);
 146                 segment = min_t(size_t, limit, ROMBSIZE - offset);
 147                 bh = sb_bread(sb, pos >> ROMBSBITS);
 148                 if (!bh)
 149                         return -EIO;
 150                 buf = bh->b_data + offset;
 151                 p = memchr(buf, 0, segment);
 152                 brelse(bh);
 153                 if (p)
 154                         return n + (p - buf);
 155                 limit -= segment;
 156                 pos += segment;
 157                 n += segment;
 158         }
 159
 160         return n;
 161 }
 162
 163 /*
 164  * compare a string to one in a romfs image on a block device
 165  * - return 1 if matched, 0 if differ, -ve if error
 166  */
 167 static int romfs_blk_strcmp(struct super_block *sb, unsigned long pos,
 168                             const char *str, size_t size)
 169 {
 170         struct buffer_head *bh;
 171         unsigned long offset;
 172         size_t segment;
 173         bool matched, terminated = false;
 174
 175         /* compare string up to a block at a time */
 176         while (size > 0) {
 177                 offset = pos & (ROMBSIZE - 1);
 178                 segment = min_t(size_t, size, ROMBSIZE - offset);
 179                 bh = sb_bread(sb, pos >> ROMBSBITS);
 180                 if (!bh)
 181                         return -EIO;
 182                 matched = (memcmp(bh->b_data + offset, str, segment) == 0);
 183
 184                 size -= segment;
 185                 pos += segment;
 186                 str += segment;
 187                 if (matched && size == 0 && offset + segment < ROMBSIZE) {
 188                         if (!bh->b_data[offset + segment])
 189                                 terminated = true;
 190                         else
 191                                 matched = false;
 192                 }
 193                 brelse(bh);
 194                 if (!matched)
 195                         return 0;
 196         }
 197
 198         if (!terminated) {
 199                 /* the terminating NUL must be on the first byte of the next
 200                  * block */
 201                 BUG_ON((pos & (ROMBSIZE - 1)) != 0);
 202                 bh = sb_bread(sb, pos >> ROMBSBITS);
 203                 if (!bh)
 204                         return -EIO;
 205                 matched = !bh->b_data[0];
 206                 brelse(bh);
 207                 if (!matched)
 208                         return 0;
 209         }
 210
 211         return 1;
 212 }
 213 #endif /* CONFIG_ROMFS_ON_BLOCK */
 214
 215 /*
 216  * read data from the romfs image
 217  */
 218 int romfs_dev_read(struct super_block *sb, unsigned long pos,
 219                    void *buf, size_t buflen)
 220 {
 221         size_t limit;
 222
 223         limit = romfs_maxsize(sb);
 224         if (pos >= limit || buflen > limit - pos)
 225                 return -EIO;
 226
 227 #ifdef CONFIG_ROMFS_ON_MTD
 228         if (sb->s_mtd)
 229                 return romfs_mtd_read(sb, pos, buf, buflen);
 230 #endif
 231 #ifdef CONFIG_ROMFS_ON_BLOCK
 232         if (sb->s_bdev)
 233                 return romfs_blk_read(sb, pos, buf, buflen);
 234 #endif
 235         return -EIO;
 236 }
 237
 238 /*
 239  * determine the length of a string in romfs
 240  */
 241 ssize_t romfs_dev_strnlen(struct super_block *sb,
 242                           unsigned long pos, size_t maxlen)
 243 {
 244         size_t limit;
 245
 246         limit = romfs_maxsize(sb);
 247         if (pos >= limit)
 248                 return -EIO;
 249         if (maxlen > limit - pos)
 250                 maxlen = limit - pos;
 251
 252 #ifdef CONFIG_ROMFS_ON_MTD
 253         if (sb->s_mtd)
 254                 return romfs_mtd_strnlen(sb, pos, maxlen);
 255 #endif
 256 #ifdef CONFIG_ROMFS_ON_BLOCK
 257         if (sb->s_bdev)
 258                 return romfs_blk_strnlen(sb, pos, maxlen);
 259 #endif
 260         return -EIO;
 261 }
 262
 263 /*
 264  * compare a string to one in romfs
 265  * - the string to be compared to, str, may not be NUL-terminated; instead the
 266  *   string is of the specified size
 267  * - return 1 if matched, 0 if differ, -ve if error
 268  */
 269 int romfs_dev_strcmp(struct super_block *sb, unsigned long pos,
 270                      const char *str, size_t size)
 271 {
 272         size_t limit;
 273
 274         limit = romfs_maxsize(sb);
 275         if (pos >= limit)
 276                 return -EIO;
 277         if (size > ROMFS_MAXFN)
 278                 return -ENAMETOOLONG;
 279         if (size + 1 > limit - pos)
 280                 return -EIO;
 281
 282 #ifdef CONFIG_ROMFS_ON_MTD
 283         if (sb->s_mtd)
 284                 return romfs_mtd_strcmp(sb, pos, str, size);
 285 #endif
 286 #ifdef CONFIG_ROMFS_ON_BLOCK
 287         if (sb->s_bdev)
 288                 return romfs_blk_strcmp(sb, pos, str, size);
 289 #endif
 290         return -EIO;
 291 }