lib/libminlib/fsversion.c
/* This procedure examines a file system and figures out whether it is
 * version 1 or version 2.  It returns the result as an int.  If the
 * file system is neither, it returns -1.  A typical call is:
 *
 *	n = fsversion("/dev/hd1", "df");
 *
 * The first argument is the special file for the file system. 
 * The second is the program name, which is used in error messages.
 */

#include <sys/types.h>
#include <minix/config.h>
#include <minix/const.h>
#include <minix/minlib.h>
#include <minix/type.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>

#include "mfs/const.h"

static char super[SUPER_BLOCK_BYTES];

#define MAGIC_OFFSET_MFS 0x18
#define MAGIC_OFFSET_EXT 0x38
#define MAGIC_VALUE_EXT2	0xef53

static int check_super(off_t offset, unsigned short magic)
{
  return (memcmp(super + offset, &magic, sizeof(magic)) == 0) ? 1 : 0;
}

int fsversion(dev, prog)
char *dev, *prog;
{
  int fd;

  if ((fd = open(dev, O_RDONLY)) < 0) {
	std_err(prog);
	std_err(" cannot open ");
	perror(dev);
	return(-1);
  }

  lseek(fd, (off_t) SUPER_BLOCK_BYTES, SEEK_SET);	/* skip boot block */
  if (read(fd, (char *) &super, sizeof(super)) != sizeof(super)) {
	std_err(prog);
	std_err(" cannot read super block on ");
	perror(dev);
	close(fd);
	return(-1);
  }
  close(fd);
  
  /* first check MFS, a valid MFS may look like EXT but not vice versa */
  if (check_super(MAGIC_OFFSET_MFS, SUPER_MAGIC))	return FSVERSION_MFS1;
  if (check_super(MAGIC_OFFSET_MFS, SUPER_V2))		return FSVERSION_MFS2;
  if (check_super(MAGIC_OFFSET_MFS, SUPER_V3))		return FSVERSION_MFS3;
  if (check_super(MAGIC_OFFSET_EXT, MAGIC_VALUE_EXT2))	return FSVERSION_EXT2;
  
  return(-1);
}
