minix/lib/libc/gen/fsversion.c

   1 /* This procedure examines a file system and figures out whether it is
   2  * version 1 or version 2.  It returns the result as an int.  If the
   3  * file system is neither, it returns -1.  A typical call is:
   4  *
   5  *      n = fsversion("/dev/hd1", "df");
   6  *
   7  * The first argument is the special file for the file system.
   8  * The second is the program name, which is used in error messages.
   9  */
  10
  11 #include <sys/types.h>
  12 #include <minix/config.h>
  13 #include <minix/const.h>
  14 #include <minix/minlib.h>
  15 #include <minix/type.h>
  16 #include <fcntl.h>
  17 #include <unistd.h>
  18 #include <stdio.h>
  19 #include <string.h>
  20
  21 #include "mfs/const.h"
  22
  23 static char super[SUPER_BLOCK_BYTES];
  24
  25 #define MAGIC_OFFSET_MFS        0x18
  26 #define MAGIC_OFFSET_EXT        0x38
  27 #define MAGIC_OFFSET_ISO9660    0x8000
  28 #define MAGIC_VALUE_EXT2        0xef53
  29
  30 static int check_super(off_t offset, unsigned short magic)
  31 {
  32         return (memcmp(super + offset, &magic, sizeof(magic)) == 0) ? 1 : 0;
  33 }
  34
  35 int fsversion(char *dev, char *prog)
  36 {
  37         int result = -1, fd;
  38
  39         if ((fd = open(dev, O_RDONLY)) < 0) {
  40                 std_err(prog);
  41                 std_err(" cannot open ");
  42                 perror(dev);
  43                 return(-1);
  44         }
  45
  46         lseek(fd, (off_t) SUPER_BLOCK_BYTES, SEEK_SET); /* skip boot block */
  47         if (read(fd, (char *) &super, sizeof(super)) != sizeof(super)) {
  48                 std_err(prog);
  49                 std_err(" cannot read super block on ");
  50                 perror(dev);
  51                 close(fd);
  52                 return(-1);
  53         }
  54
  55         /* first check MFS, a valid MFS may look like EXT but not vice versa */
  56         if (check_super(MAGIC_OFFSET_MFS, SUPER_MAGIC)) {
  57                 result = FSVERSION_MFS1;
  58                 goto done;
  59         }
  60         else if (check_super(MAGIC_OFFSET_MFS, SUPER_V2)) {
  61                 result = FSVERSION_MFS2;
  62                 goto done;
  63         }
  64         else if (check_super(MAGIC_OFFSET_MFS, SUPER_V3)) {
  65                 result = FSVERSION_MFS3;
  66                 goto done;
  67         }
  68
  69         /* check ext2 */
  70         if (check_super(MAGIC_OFFSET_EXT, MAGIC_VALUE_EXT2)) {
  71                 result = FSVERSION_EXT2;
  72                 goto done;
  73         }
  74
  75         /* check ISO 9660 */
  76         lseek(fd, (off_t) MAGIC_OFFSET_ISO9660, SEEK_SET);
  77         if (read(fd, (char *) &super, sizeof(super)) == sizeof(super)) {
  78                 if (memcmp(super+1, "CD001", 5) == 0) {
  79                         result = FSVERSION_ISO9660;
  80                         goto done;
  81                 }
  82         }
  83
  84 done:
  85         close(fd);
  86         return result;
  87 }