skipcpio/skipcpio.c

   1 /* dracut-install.c  -- install files and executables
   2
   3    Copyright (C) 2012 Harald Hoyer
   4    Copyright (C) 2012 Red Hat, Inc.  All rights reserved.
   5
   6    This program is free software: you can redistribute it and/or modify
   7    under the terms of the GNU Lesser General Public License as published by
   8    the Free Software Foundation; either version 2.1 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful, but
  12    WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public License
  17    along with this program; If not, see <http://www.gnu.org/licenses/>.
  18 */
  19
  20 #define PROGRAM_VERSION_STRING "1"
  21
  22 #ifndef _GNU_SOURCE
  23 #define _GNU_SOURCE
  24 #endif
  25
  26 #include <stdio.h>
  27 #include <stdlib.h>
  28 #include <string.h>
  29
  30 #define CPIO_MAGIC "070701"
  31 #define CPIO_END "TRAILER!!!"
  32 #define CPIO_ENDLEN (sizeof(CPIO_END) - 1)
  33
  34 #define CPIO_ALIGNMENT 4
  35
  36 struct cpio_header {
  37         char c_magic[6];
  38         char c_ino[8];
  39         char c_mode[8];
  40         char c_uid[8];
  41         char c_gid[8];
  42         char c_nlink[8];
  43         char c_mtime[8];
  44         char c_filesize[8];
  45         char c_dev_maj[8];
  46         char c_dev_min[8];
  47         char c_rdev_maj[8];
  48         char c_rdev_min[8];
  49         char c_namesize[8];
  50         char c_chksum[8];
  51 } __attribute__((packed));
  52
  53 struct buf_struct {
  54         struct cpio_header h;
  55         char filename[CPIO_ENDLEN];
  56 } __attribute__((packed));
  57
  58 union buf_union {
  59         struct buf_struct cpio;
  60         char copy_buffer[2048];
  61 };
  62
  63 static union buf_union buf;
  64
  65 #define ALIGN_UP(n, a) (((n) + (a) - 1) & (~((a) - 1)))
  66
  67 int main(int argc, char **argv)
  68 {
  69         FILE *f;
  70         size_t s;
  71
  72         if (argc != 2) {
  73                 fprintf(stderr, "Usage: %s <file>\n", argv[0]);
  74                 exit(1);
  75         }
  76
  77         f = fopen(argv[1], "r");
  78
  79         if (f == NULL) {
  80                 fprintf(stderr, "Cannot open file '%s'\n", argv[1]);
  81                 exit(1);
  82         }
  83
  84         s = fread(&buf.cpio, sizeof(buf.cpio), 1, f);
  85         if (s <= 0) {
  86                 fprintf(stderr, "Read error from file '%s'\n", argv[1]);
  87                 fclose(f);
  88                 exit(1);
  89         }
  90         fseek(f, 0, SEEK_SET);
  91
  92         /* check, if this is a cpio archive */
  93         if (memcmp(buf.cpio.h.c_magic, CPIO_MAGIC, 6) == 0) {
  94
  95                 long pos = 0;
  96
  97                 unsigned long filesize;
  98                 unsigned long filename_length;
  99
 100                 do {
 101                         // zero string, spilling into next unused field, to use strtol
 102                         buf.cpio.h.c_chksum[0] = 0;
 103                         filename_length = strtoul(buf.cpio.h.c_namesize, NULL, 16);
 104                         pos = ALIGN_UP(pos + sizeof(struct cpio_header) + filename_length, CPIO_ALIGNMENT);
 105
 106                         // zero string, spilling into next unused field, to use strtol
 107                         buf.cpio.h.c_dev_maj[0] = 0;
 108                         filesize = strtoul(buf.cpio.h.c_filesize, NULL, 16);
 109                         pos = ALIGN_UP(pos + filesize, CPIO_ALIGNMENT);
 110
 111                         if (filename_length == (CPIO_ENDLEN + 1)
 112                             && strncmp(buf.cpio.filename, CPIO_END, CPIO_ENDLEN) == 0) {
 113                                 fseek(f, pos, SEEK_SET);
 114                                 break;
 115                         }
 116
 117                         if (fseek(f, pos, SEEK_SET) != 0) {
 118                                 perror("fseek");
 119                                 exit(1);
 120                         }
 121
 122                         if (fread(&buf.cpio, sizeof(buf.cpio), 1, f) != 1) {
 123                                 perror("fread");
 124                                 exit(1);
 125                         }
 126
 127                         if (memcmp(buf.cpio.h.c_magic, CPIO_MAGIC, 6) != 0) {
 128                                 fprintf(stderr, "Corrupt CPIO archive!\n");
 129                                 exit(1);
 130                         }
 131                 } while (!feof(f));
 132
 133                 if (feof(f)) {
 134                         /* CPIO_END not found, just cat the whole file */
 135                         fseek(f, 0, SEEK_SET);
 136                 } else {
 137                         /* skip zeros */
 138                         do {
 139                                 size_t i;
 140
 141                                 s = fread(buf.copy_buffer, 1, sizeof(buf.copy_buffer) - 1, f);
 142                                 if (s <= 0)
 143                                         break;
 144
 145                                 for (i = 0; (i < s) && (buf.copy_buffer[i] == 0); i++) ;
 146
 147                                 if (buf.copy_buffer[i] != 0) {
 148                                         pos += i;
 149
 150                                         fseek(f, pos, SEEK_SET);
 151                                         break;
 152                                 }
 153
 154                                 pos += s;
 155                         } while (!feof(f));
 156                 }
 157         }
 158         /* cat out the rest */
 159         while (!feof(f)) {
 160                 s = fread(buf.copy_buffer, 1, sizeof(buf.copy_buffer), f);
 161                 if (s <= 0)
 162                         break;
 163
 164                 s = fwrite(buf.copy_buffer, 1, s, stdout);
 165                 if (s <= 0)
 166                         break;
 167         }
 168         fclose(f);
 169
 170         return EXIT_SUCCESS;
 171 }