lib/libminlib/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_VALUE_EXT2        0xef53
  28
  29 static int check_super(off_t offset, unsigned short magic)
  30 {
  31   return (memcmp(super + offset, &magic, sizeof(magic)) == 0) ? 1 : 0;
  32 }
  33
  34 int fsversion(dev, prog)
  35 char *dev, *prog;
  36 {
  37   int 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   close(fd);
  55
  56   /* first check MFS, a valid MFS may look like EXT but not vice versa */
  57   if (check_super(MAGIC_OFFSET_MFS, SUPER_MAGIC))       return FSVERSION_MFS1;
  58   if (check_super(MAGIC_OFFSET_MFS, SUPER_V2))          return FSVERSION_MFS2;
  59   if (check_super(MAGIC_OFFSET_MFS, SUPER_V3))          return FSVERSION_MFS3;
  60   if (check_super(MAGIC_OFFSET_EXT, MAGIC_VALUE_EXT2))  return FSVERSION_EXT2;
  61
  62   return(-1);
  63 }