读取未挂载的设备上的文件系统类型：char * fstype(char*device)

最近因项目需要，需要对块设备进行判断：是否有文件系统，以及文件系统的类型。

虽然linux下自带有几种命令可以知道文件系统：fdisk -l , blkid ,parted -l , df -T ,file -sL

但没有直接的函数调用来获取设备上的文件系统。

下面用C语言实现一个函数：char *  fstype(char*device); 返回 指定设备上的文件系统，没有返回NULL

 参考自mkfs.xfs的源代码

#include 
#include 
#include 
#include 
#include 
#include 
#include "fstype.h"
#undef XFS_SUPER_MAGIC

/*
 * From mount(8) source by Andries Brouwer.  Hacked for XFS by mkp.
 * Recent sync's to mount source:
 *      - util-linux-2.10o ... 06 Sep 00
 *      - util-linux-2.10r ... 06 Dec 00
 *      - util-linux-2.11g ... 02 Jul 01
 *      - util-linux-2.11u ... 24 Aug 02
 *	- util-linux-2.11z ... 13 May 03
 */

/* Including  became more and more painful.
   Below a very abbreviated version of some declarations,
   only designed to be able to check a magic number
   in case no filesystem type was given. */

#define MINIX_SUPER_MAGIC   0x137F         /* minix v1, 14 char names */
#define MINIX_SUPER_MAGIC2  0x138F         /* minix v1, 30 char names */
#define MINIX2_SUPER_MAGIC  0x2468	   /* minix v2, 14 char names */
#define MINIX2_SUPER_MAGIC2 0x2478         /* minix v2, 30 char names */
struct minix_super_block {
	char   s_dummy[16];
	char   s_magic[2];
};
#define minixmagic(s)	assemble2le(s.s_magic)

#define ISODCL(from, to) (to - from + 1)
#define ISO_STANDARD_ID "CD001"
struct iso_volume_descriptor {
	char type[ISODCL(1,1)]; /* 711 */
	char id[ISODCL(2,6)];
	char version[ISODCL(7,7)];
	char data[ISODCL(8,2048)];
};

#define HS_STANDARD_ID "CDROM"
struct  hs_volume_descriptor {
	char foo[ISODCL (  1,   8)]; /* 733 */
	char type[ISODCL (  9,   9)]; /* 711 */
	char id[ISODCL ( 10,  14)];
	char version[ISODCL ( 15,  15)]; /* 711 */
	char data[ISODCL(16,2048)];
};

#define EXT_SUPER_MAGIC 0x137D
struct ext_super_block {
	char   s_dummy[56];
	char   s_magic[2];
};
#define extmagic(s)	assemble2le(s.s_magic)

#define EXT2_PRE_02B_MAGIC  0xEF51
#define EXT2_SUPER_MAGIC    0xEF53
#define EXT3_FEATURE_COMPAT_HAS_JOURNAL 0x0004

#define EXT4_FEATURE_RO_COMPAT_HUGE_FILE	0x0008
#define EXT4_FEATURE_RO_COMPAT_GDT_CSUM		0x0010
#define EXT4_FEATURE_RO_COMPAT_DIR_NLINK	0x0020
#define EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE	0x0040

struct ext2_super_block {
	char 	s_dummy1[56];
	char 	s_magic[2];
	char	s_dummy2[34];
	char	s_feature_compat[4];
	char	s_feature_incompat[4];
	char	s_feature_ro_compat[4];
	char	s_uuid[16];
	char 	s_volume_name[16];
	char	s_dummy3[88];
	char	s_journal_inum[4];	/* ext3 only */
};
#define ext2magic(s)	assemble2le(s.s_magic)

struct reiserfs_super_block
{
	char		s_block_count[4];
	char		s_free_blocks[4];
	char		s_root_block[4];
	char		s_journal_block[4];
	char		s_journal_dev[4];
	char		s_orig_journal_size[4];
	char		s_journal_trans_max[4];
	char		s_journal_block_count[4];
	char		s_journal_max_batch[4];
	char		s_journal_max_commit_age[4];
	char		s_journal_max_trans_age[4];
	char		s_blocksize[2];
	char		s_oid_maxsize[2];
	char		s_oid_cursize[2];
	char		s_state[2];
	char		s_magic[12];
};
#define REISERFS_SUPER_MAGIC_STRING "ReIsErFs"
#define REISER2FS_SUPER_MAGIC_STRING "ReIsEr2Fs"
#define REISERFS_DISK_OFFSET_IN_BYTES (64 * 1024)
/* the spot for the super in versions 3.5 - 3.5.10 (inclusive) */
#define REISERFS_OLD_DISK_OFFSET_IN_BYTES (8 * 1024)

#define _XIAFS_SUPER_MAGIC 0x012FD16D
struct xiafs_super_block {
    char     s_boot_segment[512];     /*  1st sector reserved for boot */
    char     s_dummy[60];
    char     s_magic[4];
};
#define xiafsmagic(s)	assemble4le(s.s_magic)

/* From [email protected] Mon Mar 23 15:19:05 1998 */
#define UFS_SUPER_MAGIC_LE 0x00011954
#define UFS_SUPER_MAGIC_BE 0x54190100
struct ufs_super_block {
    char     s_dummy[0x55c];
    char     s_magic[4];
};
#define ufsmagic(s)	assemble4le(s.s_magic)

/* From [email protected] Wed Feb 24 08:05:27 1999 */
#define NTFS_SUPER_MAGIC "NTFS"
struct ntfs_super_block {
    char    s_dummy[3];
    char    s_magic[4];
};

/* From inspection of a few FAT filesystems - aeb */
/* Unfortunately I find almost the same thing on an extended partition;
   it looks like a primary has some directory entries where the extended
   has a partition table: IO.SYS, MSDOS.SYS, WINBOOT.SYS */
struct fat_super_block {
    char    s_dummy[3];
    char    s_os[8];		/* "MSDOS5.0" or "MSWIN4.0" or "MSWIN4.1" */
				/* mtools-3.9.4 writes "MTOOL394" */
    char    s_dummy2[32];
    char    s_label[11];	/* for DOS? */
    char    s_fs[8];		/* "FAT12   " or "FAT16   " or all zero   */
                                /* OS/2 BM has "FAT     " here. */
    char    s_dummy3[9];
    char    s_label2[11];	/* for Windows? */
    char    s_fs2[8];	        /* garbage or "FAT32   " */
};

#define XFS_SUPER_MAGIC "XFSB"
struct xfs_super_block {
    char    s_magic[4];
    char    s_dummy[28];
    char    s_uuid[16];
    char    s_dummy2[60];
    char    s_fname[12];
};

#define CRAMFS_SUPER_MAGIC 0x28cd3d45
#define CRAMFS_SUPER_MAGIC_BE 0x453dcd28
struct cramfs_super_block {
	char    s_magic[4];
	char    s_dummy[12];
	char    s_id[16];
};
#define cramfsmagic(s)	assemble4le(s.s_magic)

#define HFS_SUPER_MAGIC 0x4244
#define HFSPLUS_SUPER_MAGIC 0x482B
#define HFSPLUS_SUPER_VERSION 0x004
struct hfs_super_block {
	char    s_magic[2];
	char    s_version[2];
};
#define hfsmagic(s)	assemble2le(s.s_magic)
#define hfsversion(s)	assemble2le(s.s_version)

#define HPFS_SUPER_MAGIC 0xf995e849
struct hpfs_super_block {
	char    s_magic[4];
	char    s_magic2[4];
};
#define hpfsmagic(s)	assemble4le(s.s_magic)

struct adfs_super_block {
	char    s_dummy[448];
	char    s_blksize[1];
	char    s_dummy2[62];
	char    s_checksum[1];
};
#define adfsblksize(s)	((uint) s.s_blksize[0])

/* found in first 4 bytes of block 1 */
struct vxfs_super_block {
	char	s_magic[4];
};
#define vxfsmagic(s)	assemble4le(s.s_magic)
#define VXFS_SUPER_MAGIC 0xa501FCF5

struct jfs_super_block {
	char	s_magic[4];
	char	s_version[4];
	char	s_dummy1[93];
	char	s_fpack[11];
	char	s_dummy2[24];
	char	s_uuid[16];
	char	s_label[16];
};
#define JFS_SUPER1_OFF 0x8000
#define JFS_MAGIC "JFS1"

struct sysv_super_block {
	char  s_dummy1[504];
	char  s_magic[4];
	char  type[4];
};
#define sysvmagic(s)		assemble4le(s.s_magic)
#define SYSV_SUPER_MAGIC	0xfd187e20

struct mdp_super_block {
	char	md_magic[4];
};
#define MD_SB_MAGIC	0xa92b4efc
#define mdsbmagic(s)	assemble4le(s.md_magic)

struct ocfs_volume_header {
	char  minor_version[4];
	char  major_version[4];
	char  signature[128];
};

struct ocfs_volume_label {
	char  disk_lock[48];
	char  label[64];
	char  label_len[2];
};

#define ocfslabellen(o)	assemble2le(o.label_len)
#define OCFS_MAGIC	"OracleCFS"

/* Common gfs/gfs2 constants: */
#define GFS_MAGIC               0x01161970
#define GFS_DEFAULT_BSIZE       4096
#define GFS_SUPERBLOCK_OFFSET	(0x10 * GFS_DEFAULT_BSIZE)
#define GFS_LOCKNAME_LEN        64

/* gfs1 constants: */
#define GFS_FORMAT_FS           1309
#define GFS_FORMAT_MULTI        1401
/* gfs2 constants: */
#define GFS2_FORMAT_FS          1801
#define GFS2_FORMAT_MULTI       1900

struct gfs2_meta_header {
	char mh_magic[4];
	char mh_type[4];
	char __pad0[8];          /* Was generation number in gfs1 */
	char mh_format[4];
	char __pad1[4];          /* Was incarnation number in gfs1 */
};

struct gfs2_inum {
	char no_formal_ino[8];
	char no_addr[8];
};

struct gfs2_sb {
	struct gfs2_meta_header sb_header;

	char sb_fs_format[4];
	char sb_multihost_format[4];
	char  __pad0[4];  /* Was superblock flags in gfs1 */

	char sb_bsize[4];
	char sb_bsize_shift[4];
	char __pad1[4];   /* Was journal segment size in gfs1 */

	struct gfs2_inum sb_master_dir; /* Was jindex dinode in gfs1 */
	struct gfs2_inum __pad2; /* Was rindex dinode in gfs1 */
	struct gfs2_inum sb_root_dir;

	char sb_lockproto[GFS_LOCKNAME_LEN];
	char sb_locktable[GFS_LOCKNAME_LEN];
	/* In gfs1, quota and license dinodes followed */
};

#define gfsmagic(s)		assemble4be(s.sb_header.mh_magic)
#define gfsformat(s)		assemble4be(s.sb_fs_format)
#define gfsmultiformat(s)	assemble4be(s.sb_multihost_format)

/* btrfs constants */
#define BTRFS_SUPER_INFO_OFFSET (64 * 1024)

/* 32 bytes in various csum fields */
#define BTRFS_CSUM_SIZE 32

#define BTRFS_FSID_SIZE 16

#define BTRFS_MAGIC "_BHRfS_M"

/*
 * the super block basically lists the main trees of the FS
 * it currently lacks any block count etc etc
 */
struct btrfs_super_block {
	char csum[BTRFS_CSUM_SIZE];
	/* the first 3 fields must match struct btrfs_header */
	char fsid[BTRFS_FSID_SIZE];    /* FS specific uuid */
	char bytenr[8]; /* this block number */
	char flags[8];
	/* allowed to be different from the btrfs_header from here own down */
	char magic[8];
	/* more follows but this is all our libdisk cares about*/
} __attribute__ ((__packed__));

static inline unsigned short assemble2le(char *p) {
	return (unsigned short)(p[0] | (p[1] << 8));
}

static inline int assemble4le(char *p) {
	return (p[0] | (p[1] << 8) | (p[2] << 16) | (p[3] << 24));
}

static inline int assemble4be(char *p) {
	return (p[3] | (p[2] << 8) | (p[1] << 16) | (p[0] << 24));
}

/*
 * From mount(8) source by Andries Brouwer.  Hacked for XFS by mkp.
 * Recent sync's to mount source:
 *	- util-linux-2.10o ... 06 Sep 00
 *	- util-linux-2.10r ... 06 Dec 00
 *	- util-linux-2.11g ... 02 Jul 01
 *	- util-linux-2.11u ... 24 Aug 02
 *	- util-linux-2.11z ... 13 May 03
 */

#define SIZE(a) (sizeof(a)/sizeof(a[0]))

/* Most file system types can be recognized by a `magic' number
   in the superblock.  Note that the order of the tests is
   significant: by coincidence a filesystem can have the
   magic numbers for several file system types simultaneously.
   For example, the romfs magic lives in the 1st sector;
   xiafs does not touch the 1st sector and has its magic in
   the 2nd sector; ext2 does not touch the first two sectors. */

static inline unsigned short  swapped(unsigned short a) {
     return (a>>8) | (a<<8);
}

/*
    Probes the device and attempts to determine the type of filesystem
    contained within.

    Original routine by ; made into a function
    for mount(8) by Mike Grupenhoff .
    Corrected the test for xiafs - aeb
    Read the superblock only once - aeb
    Added a very weak heuristic for vfat - aeb
    Added iso9660, minix-v2, romfs, qnx4, udf, vxfs, swap - aeb
    Added a test for high sierra (iso9660) - [email protected]
    Added ufs from a patch by jj. But maybe there are several types of ufs?
    Added ntfs from a patch by Richard Russon.
    Added xfs - 2000-03-21 Martin K. Petersen 
    Added cramfs, hfs, hpfs, adfs - Sepp Wijnands 
    Added ext3 - Andrew Morton
    Added jfs - Christoph Hellwig
    Added sysv - Tim Launchbury
    Added udf - Bryce Nesbitt
    Added gfs/gfs2, btrfs - Eric Sandeen
*/

/*
 * udf magic - I find that trying to mount garbage as an udf fs
 * causes a very large kernel delay, almost killing the machine.
 * So, we do not try udf unless there is positive evidence that it
 * might work. Strings below taken from ECMA 167.
 */
/*
 * It seems that before udf 2.00 the volume descriptor was not well
 * defined.  For 2.00 you're supposed to keep scanning records until
 * you find one NOT in this list.  (See ECMA 2/8.3.1).
 */
static char
*udf_magic[] = { "BEA01", "BOOT2", "CD001", "CDW02", "NSR02","NSR03", "TEA01" };
static int may_be_udf(const char *id) {
    char **m;
    for (m = udf_magic; m - udf_magic < SIZE(udf_magic); m++)
       if (!strncmp(*m, id, 5))
	  return 1;
    return 0;
}
/* we saw "CD001" - may be iso9660 or udf - Bryce Nesbitt */
static int is_really_udf(int fd) {
	int j, bs;
	struct iso_volume_descriptor isosb;
	/* determine the block size by scanning in 2K increments
	   (block sizes larger than 2K will be null padded) */
	for (bs = 1; bs < 16; bs++) {
		lseek(fd, bs*2048+32768, SEEK_SET);
		if (read(fd, (char *)&isosb, sizeof(isosb)) != sizeof(isosb))
			return 0;
		if (isosb.id[0])
			break;
	}
	/* Scan up to another 64 blocks looking for additional VSD's */
	for (j = 1; j < 64; j++) {
		if (j > 1) {
			lseek(fd, j*bs*2048+32768, SEEK_SET);
			if (read(fd, (char *)&isosb, sizeof(isosb))
			    != sizeof(isosb))
				return 0;
		}
		/* If we find NSR0x then call it udf:
		   NSR01 for UDF 1.00
		   NSR02 for UDF 1.50
		   NSR03 for UDF 2.00 */
		if (!strncmp(isosb.id, "NSR0", 4))
			return 1;
		if (!may_be_udf(isosb.id))
			return 0;
	}
	return 0;
}

static int may_be_swap(const char *s) {
	return (strncmp(s-10, "SWAP-SPACE", 10) == 0 ||
		strncmp(s-10, "SWAPSPACE2", 10) == 0);
}
/* rather weak necessary condition */
static int may_be_adfs(const struct adfs_super_block *sb) {
	char *p;
	int sum;
	p = (char *)sb->s_checksum;
	sum = 0;
	while(--p != (char *)sb)
		sum = (sum >> 8) + (sum & 0xff) + *p;
	return (sum & 0xff) == sb->s_checksum[0];
}
static int is_reiserfs_magic_string (struct reiserfs_super_block * rs)
{
    return (!strncmp (rs->s_magic, REISERFS_SUPER_MAGIC_STRING, 
		      strlen ( REISERFS_SUPER_MAGIC_STRING)) ||
	    !strncmp (rs->s_magic, REISER2FS_SUPER_MAGIC_STRING, 
		      strlen ( REISER2FS_SUPER_MAGIC_STRING)));
}
char * fstype(const char *device) {  //获取设备的文件系统类型，没有则为NULL
    int fd;
    char *type = NULL;
    union {
    	struct minix_super_block ms;
    	struct ext_super_block es;
    	struct ext2_super_block e2s;
    	struct vxfs_super_block vs;
    	struct hfs_super_block hs;
    } sb;			/* stuff at 1024 */
    union {
    	struct xiafs_super_block xiasb;
    	char romfs_magic[8];
    	char qnx4fs_magic[10];	/* ignore first 4 bytes */
    	unsigned int bfs_magic;
    	struct ntfs_super_block ntfssb;
    	struct fat_super_block fatsb;
    	struct xfs_super_block xfsb;
    	struct cramfs_super_block cramfssb;
    } xsb;
    struct ufs_super_block ufssb;
    union {
    	struct iso_volume_descriptor iso;
    	struct hs_volume_descriptor hs;
    } isosb;
    struct reiserfs_super_block reiserfssb;	/* block 64 or 8 */
    struct jfs_super_block jfssb;		/* block 32 */
    struct hpfs_super_block hpfssb;
    struct adfs_super_block adfssb;
    struct sysv_super_block svsb;
    struct gfs2_sb gfs2sb;
    struct btrfs_super_block btrfssb;
    struct stat statbuf;

    /* opening and reading an arbitrary unknown path can have
       undesired side effects - first check that `device' refers
       to a block device or ordinary file */
    if (stat (device, &statbuf) ||
	!(S_ISBLK(statbuf.st_mode) || S_ISREG(statbuf.st_mode)))
      return NULL;

    fd = open(device, O_RDONLY);
    if (fd < 0)
      return NULL;

    /* do seeks and reads in disk order, otherwise a very short
       partition may cause a failure because of read error */

    if (!type) {
	 /* block 0 */
	 if (lseek(fd, 0, SEEK_SET) != 0
	     || read(fd, (char *) &xsb, sizeof(xsb)) != sizeof(xsb))
	      goto try_iso9660;
	 /* Gyorgy Kovesdi: none of my photocds has a readable block 0 */

	 if (xiafsmagic(xsb.xiasb) == _XIAFS_SUPER_MAGIC)
	      type = "xiafs";
	 else if(!strncmp(xsb.romfs_magic, "-rom1fs-", 8))
	      type = "romfs";
	 else if(!strncmp(xsb.xfsb.s_magic, XFS_SUPER_MAGIC, 4))
	      type = "xfs";
	 else if(!strncmp(xsb.qnx4fs_magic+4, "QNX4FS", 6))
	      type = "qnx4";
	 else if(xsb.bfs_magic == 0x1badface)
	      type = "bfs";
	 else if(!strncmp(xsb.ntfssb.s_magic, NTFS_SUPER_MAGIC,
			  sizeof(xsb.ntfssb.s_magic)))
	      type = "ntfs";
	 else if(cramfsmagic(xsb.cramfssb) == CRAMFS_SUPER_MAGIC ||
		 cramfsmagic(xsb.cramfssb) == CRAMFS_SUPER_MAGIC_BE)
	      type = "cramfs";
	 else if ((!strncmp(xsb.fatsb.s_os, "MSDOS", 5) ||
		   !strncmp(xsb.fatsb.s_os, "MSWIN", 5) ||
		   !strncmp(xsb.fatsb.s_os, "MTOOL", 5) ||
		   !strncmp(xsb.fatsb.s_os, "mkdosfs", 7) ||
		   !strncmp(xsb.fatsb.s_os, "kmkdosfs", 8) ||
		   /* Michal Svec: created by fdformat, old msdos utility for
		      formatting large (1.7) floppy disks. */
		   !strncmp(xsb.fatsb.s_os, "CH-FOR18", 8))
		  && (!strncmp(xsb.fatsb.s_fs, "FAT12   ", 8) ||
		      !strncmp(xsb.fatsb.s_fs, "FAT16   ", 8) ||
		      !strncmp(xsb.fatsb.s_fs2, "FAT32   ", 8)))
	      type = "vfat";	/* only guessing - might as well be fat or umsdos */
    }

    if (!type) {
	    /* sector 1 */
	    if (lseek(fd, 512 , SEEK_SET) != 512
		|| read(fd, (char *) &svsb, sizeof(svsb)) != sizeof(svsb))
		    goto io_error;
	    if (sysvmagic(svsb) == SYSV_SUPER_MAGIC )
		    type = "sysv";
    }

    if (!type) {
	/* block 1 */
	if (lseek(fd, 1024, SEEK_SET) != 1024 ||
	    read(fd, (char *) &sb, sizeof(sb)) != sizeof(sb))
		goto io_error;

	/* ext2 has magic in little-endian on disk, so "swapped" is
	   superfluous; however, there have existed strange byteswapped
	   PPC ext2 systems */
	if (ext2magic(sb.e2s) == EXT2_SUPER_MAGIC ||
	    ext2magic(sb.e2s) == EXT2_PRE_02B_MAGIC ||
	    ext2magic(sb.e2s) == swapped(EXT2_SUPER_MAGIC)) {
		type = "ext2";

	     /* maybe even ext3? */
	     if ((assemble4le(sb.e2s.s_feature_compat)
		  & EXT3_FEATURE_COMPAT_HAS_JOURNAL) &&
		 assemble4le(sb.e2s.s_journal_inum) != 0)
		     type = "ext3";	/* "ext3,ext2" */

		  if(assemble4le(sb.e2s.s_feature_ro_compat)&(EXT4_FEATURE_RO_COMPAT_HUGE_FILE|EXT4_FEATURE_RO_COMPAT_GDT_CSUM|
	      EXT4_FEATURE_RO_COMPAT_DIR_NLINK|
	      EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE))
	            type="ext4";
	}

	else if (minixmagic(sb.ms) == MINIX_SUPER_MAGIC ||
		 minixmagic(sb.ms) == MINIX_SUPER_MAGIC2 ||
		 minixmagic(sb.ms) == swapped(MINIX_SUPER_MAGIC2) ||
		 minixmagic(sb.ms) == MINIX2_SUPER_MAGIC ||
		 minixmagic(sb.ms) == MINIX2_SUPER_MAGIC2)
		type = "minix";

	else if (extmagic(sb.es) == EXT_SUPER_MAGIC)
		type = "ext";

	else if (vxfsmagic(sb.vs) == VXFS_SUPER_MAGIC)
		type = "vxfs";

	else if (hfsmagic(sb.hs) == swapped(HFS_SUPER_MAGIC) ||
		(hfsmagic(sb.hs) == swapped(HFSPLUS_SUPER_MAGIC) &&
		 hfsversion(sb.hs) == swapped(HFSPLUS_SUPER_VERSION)))
		type = "hfs";
    }

    if (!type) {
	/* block 3 */
        if (lseek(fd, 0xc00, SEEK_SET) != 0xc00
            || read(fd, (char *) &adfssb, sizeof(adfssb)) != sizeof(adfssb))
             goto io_error;

	/* only a weak test */
        if (may_be_adfs(&adfssb)
            && (adfsblksize(adfssb) >= 8 &&
                adfsblksize(adfssb) <= 10))
             type = "adfs";
    }

    if (!type) {
	 int mag;

	 /* block 8 */
	 if (lseek(fd, 8192, SEEK_SET) != 8192
	     || read(fd, (char *) &ufssb, sizeof(ufssb)) != sizeof(ufssb))
	      goto io_error;

	 mag = ufsmagic(ufssb);
	 if (mag == UFS_SUPER_MAGIC_LE || mag == UFS_SUPER_MAGIC_BE)
	      type = "ufs";
    }

    if (!type) {
	/* block 8 */
	if (lseek(fd, REISERFS_OLD_DISK_OFFSET_IN_BYTES, SEEK_SET) !=
				REISERFS_OLD_DISK_OFFSET_IN_BYTES
	    || read(fd, (char *) &reiserfssb, sizeof(reiserfssb)) !=
		sizeof(reiserfssb))
	    goto io_error;
	if (is_reiserfs_magic_string(&reiserfssb))
	    type = "reiserfs";
    }

    if (!type) {
	/* block 8 */
        if (lseek(fd, 0x2000, SEEK_SET) != 0x2000
            || read(fd, (char *) &hpfssb, sizeof(hpfssb)) != sizeof(hpfssb))
             goto io_error;

        if (hpfsmagic(hpfssb) == HPFS_SUPER_MAGIC)
             type = "hpfs";
    }

    if (!type) {
	 /* block 32 */
	 if (lseek(fd, JFS_SUPER1_OFF, SEEK_SET) != JFS_SUPER1_OFF
	     || read(fd, (char *) &jfssb, sizeof(jfssb)) != sizeof(jfssb))
	      goto io_error;
	 if (!strncmp(jfssb.s_magic, JFS_MAGIC, 4))
	      type = "jfs";
    }

    if (!type) {
	 /* block 32 */
    try_iso9660:
	 if (lseek(fd, 0x8000, SEEK_SET) != 0x8000
	     || read(fd, (char *) &isosb, sizeof(isosb)) != sizeof(isosb))
	      goto io_error;

	 if (strncmp(isosb.hs.id, HS_STANDARD_ID, sizeof(isosb.hs.id)) == 0) {
		 /* "CDROM" */
		 type = "iso9660";
	 } else if (strncmp(isosb.iso.id, ISO_STANDARD_ID,
			  sizeof(isosb.iso.id)) == 0) {
		 /* CD001 */
		 type = "iso9660";
		 if (is_really_udf(fd))
			 type = "udf";
	 } else if (may_be_udf(isosb.iso.id))
		 type = "udf";
    }

    if (!type) {
	/* block 64 */
	if (lseek(fd, REISERFS_DISK_OFFSET_IN_BYTES, SEEK_SET) !=
		REISERFS_DISK_OFFSET_IN_BYTES
	    || read(fd, (char *) &reiserfssb, sizeof(reiserfssb)) !=
		sizeof(reiserfssb))
	    goto io_error;
	if (is_reiserfs_magic_string(&reiserfssb))
	    type = "reiserfs";
    }

    if (!type) {
	/* block 64 */
	if (lseek(fd, GFS_SUPERBLOCK_OFFSET, SEEK_SET) != GFS_SUPERBLOCK_OFFSET
	    || read(fd, (char *) &gfs2sb, sizeof(gfs2sb)) != sizeof(gfs2sb))
	    goto io_error;
	if (gfsmagic(gfs2sb)) {
		if (gfsformat(gfs2sb) == GFS_FORMAT_FS &&
		    gfsmultiformat(gfs2sb) == GFS_FORMAT_MULTI)
			type = "gfs";
		else if (gfsformat(gfs2sb) == GFS2_FORMAT_FS &&
			 gfsmultiformat(gfs2sb) == GFS2_FORMAT_MULTI)
			type = "gfs2";
	}
    }

    if (!type) {
	/* block 64 */
	if (lseek(fd, BTRFS_SUPER_INFO_OFFSET, SEEK_SET) != BTRFS_SUPER_INFO_OFFSET 
	    || read(fd, (char *) &btrfssb, sizeof(btrfssb)) != sizeof(btrfssb))
	    goto io_error;
	if (!strncmp((char *)(btrfssb.magic), BTRFS_MAGIC,
                    sizeof(btrfssb.magic))) {
		type = "btrfs";
	}
    }

    if (!type) {
	    /* perhaps the user tries to mount the swap space
	       on a new disk; warn her before she does mkfs on it */
	    int pagesize = getpagesize();
	    int rd;
	    char buf[128 * 1024];	/* 64k is current max pagesize */

	    if (pagesize > sizeof(buf))
		    abort();

	    rd = pagesize;
	    if (rd < 8192)
		    rd = 8192;
	    if (rd > sizeof(buf))
		    rd = sizeof(buf);
	    if (lseek(fd, 0, SEEK_SET) != 0
		|| read(fd, buf, rd) != rd)
		    goto io_error;
	    if (may_be_swap(buf+pagesize) ||
		may_be_swap(buf+4096) || may_be_swap(buf+8192))
		    type = "swap";
    }

    close (fd);
    return(type);

io_error:
    close(fd);
    return NULL;
}

int check_ismounted(char *devname){  //检查设备是否已经挂载
		struct ustat	ust[2];
		struct stat	st;
		if(access(devname,F_OK)!=0)
			return -1;
		if (stat(devname, &st) < 0)
			return -1;
		if ((st.st_mode & S_IFMT) != S_IFBLK)
			return -1;
		if (ustat(st.st_rdev, ust) >= 0) {
			return 1;   //mounted
		}
		return 0;  // can mkfs
}