io/bufio.c

   1 /* bufio.c - buffered io access */
   2 /*
   3  *  GRUB  --  GRand Unified Bootloader
   4  *  Copyright (C) 2008  Free Software Foundation, Inc.
   5  *
   6  *  GRUB is free software: you can redistribute it and/or modify
   7  *  it under the terms of the GNU General Public License as published by
   8  *  the Free Software Foundation, either version 3 of the License, or
   9  *  (at your option) any later version.
  10  *
  11  *  GRUB is distributed in the hope that it will be useful,
  12  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  *  GNU General Public License for more details.
  15  *
  16  *  You should have received a copy of the GNU General Public License
  17  *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
  18  */
  19
  20 #include <grub/err.h>
  21 #include <grub/types.h>
  22 #include <grub/mm.h>
  23 #include <grub/misc.h>
  24 #include <grub/fs.h>
  25 #include <grub/bufio.h>
  26
  27 #define GRUB_BUFIO_DEF_SIZE     8192
  28 #define GRUB_BUFIO_MAX_SIZE     1048576
  29
  30 struct grub_bufio
  31 {
  32   grub_file_t file;
  33   grub_size_t block_size;
  34   grub_size_t buffer_len;
  35   char buffer[0];
  36 };
  37 typedef struct grub_bufio *grub_bufio_t;
  38
  39 static struct grub_fs grub_bufio_fs;
  40
  41 grub_file_t
  42 grub_bufio_open (grub_file_t io, int size)
  43 {
  44   grub_file_t file;
  45   grub_bufio_t bufio = 0;
  46
  47   file = (grub_file_t) grub_malloc (sizeof (*file));
  48   if (! file)
  49     return 0;
  50
  51   if (size == 0)
  52     size = GRUB_BUFIO_DEF_SIZE;
  53   else if (size > GRUB_BUFIO_MAX_SIZE)
  54     size = GRUB_BUFIO_MAX_SIZE;
  55
  56   if ((size < 0) || ((unsigned) size > io->size))
  57     size = ((io->size > GRUB_BUFIO_MAX_SIZE) ? GRUB_BUFIO_MAX_SIZE :
  58             io->size);
  59
  60   bufio = grub_malloc (sizeof (struct grub_bufio) + size);
  61   if (! bufio)
  62     {
  63       grub_free (file);
  64       return 0;
  65     }
  66
  67   bufio->file = io;
  68   bufio->block_size = size;
  69   bufio->buffer_len = 0;
  70
  71   file->device = io->device;
  72   file->offset = 0;
  73   file->size = io->size;
  74   file->data = bufio;
  75   file->read_hook = 0;
  76   file->fs = &grub_bufio_fs;
  77
  78   return file;
  79 }
  80
  81 grub_file_t
  82 grub_buffile_open (const char *name, int size)
  83 {
  84   grub_file_t io, file;
  85
  86   io = grub_file_open (name);
  87   if (! io)
  88     return 0;
  89
  90   file = grub_bufio_open (io, size);
  91   if (! file)
  92     {
  93       grub_file_close (io);
  94       return 0;
  95     }
  96
  97   return file;
  98 }
  99
 100 static grub_ssize_t
 101 grub_bufio_read (grub_file_t file, char *buf, grub_size_t len)
 102 {
 103   grub_size_t res = len;
 104   grub_bufio_t bufio = file->data;
 105   grub_uint32_t pos;
 106
 107   if ((file->offset >= bufio->file->offset) &&
 108       (file->offset < bufio->file->offset + bufio->buffer_len))
 109     {
 110       grub_size_t n;
 111
 112       pos = file->offset - bufio->file->offset;
 113       n = bufio->buffer_len - pos;
 114       if (n > len)
 115         n = len;
 116
 117       grub_memcpy (buf, &bufio->buffer[pos], n);
 118       len -= n;
 119       if (! len)
 120         return res;
 121
 122       buf += n;
 123       bufio->file->offset += bufio->buffer_len;
 124       pos = 0;
 125     }
 126   else
 127     {
 128       bufio->file->offset = grub_divmod64 (file->offset, bufio->block_size,
 129                                            &pos);
 130       bufio->file->offset *= bufio->block_size;
 131     }
 132
 133   if (pos + len >= bufio->block_size)
 134     {
 135       if (pos)
 136         {
 137           grub_size_t n;
 138
 139           bufio->file->fs->read (bufio->file, bufio->buffer,
 140                                  bufio->block_size);
 141           if (grub_errno)
 142             return -1;
 143
 144           n = bufio->block_size - pos;
 145           grub_memcpy (buf, &bufio->buffer[pos], n);
 146           len -= n;
 147           buf += n;
 148           bufio->file->offset += bufio->block_size;
 149           pos = 0;
 150         }
 151
 152       while (len >= bufio->block_size)
 153         {
 154           bufio->file->fs->read (bufio->file, buf, bufio->block_size);
 155           if (grub_errno)
 156             return -1;
 157
 158           len -= bufio->block_size;
 159           buf += bufio->block_size;
 160           bufio->file->offset += bufio->block_size;
 161         }
 162
 163       if (! len)
 164         {
 165           bufio->buffer_len = 0;
 166           return res;
 167         }
 168     }
 169
 170   bufio->buffer_len = bufio->file->size - bufio->file->offset;
 171   if (bufio->buffer_len > bufio->block_size)
 172     bufio->buffer_len = bufio->block_size;
 173
 174   bufio->file->fs->read (bufio->file, bufio->buffer, bufio->buffer_len);
 175   if (grub_errno)
 176     return -1;
 177
 178   grub_memcpy (buf, &bufio->buffer[pos], len);
 179
 180   return res;
 181 }
 182
 183 static grub_err_t
 184 grub_bufio_close (grub_file_t file)
 185 {
 186   grub_bufio_t bufio = file->data;
 187
 188   grub_file_close (bufio->file);
 189   grub_free (bufio);
 190
 191   file->device = 0;
 192
 193   return grub_errno;
 194 }
 195
 196 static struct grub_fs grub_bufio_fs =
 197   {
 198     .name = "bufio",
 199     .dir = 0,
 200     .open = 0,
 201     .read = grub_bufio_read,
 202     .close = grub_bufio_close,
 203     .label = 0,
 204     .next = 0
 205   };