int statfs(const char *path, struct statfs *buf);
int fstatfs(int fd, struct statfs *buf);
#if __WORDSIZE == 32 /* System word size */
# define __SWORD_TYPE int
#else /* __WORDSIZE == 64 */
# define __SWORD_TYPE long int
#endif
struct statfs {
__SWORD_TYPE f_type; /* type of filesystem (see below) */
__SWORD_TYPE f_bsize; /* optimal transfer block size */
fsblkcnt_t f_blocks; /* total data blocks in filesystem */
fsblkcnt_t f_bfree; /* free blocks in fs */
fsblkcnt_t f_bavail; /* free blocks available to
unprivileged user */
fsfilcnt_t f_files; /* total file nodes in filesystem */
fsfilcnt_t f_ffree; /* free file nodes in fs */
fsid_t f_fsid; /* filesystem id */
__SWORD_TYPE f_namelen; /* maximum length of filenames */
__SWORD_TYPE f_frsize; /* fragment size (since Linux 2.6) */
__SWORD_TYPE f_spare[5];
};
Filesystem types:
ADFS_SUPER_MAGIC 0xadf5
AFFS_SUPER_MAGIC 0xADFF
BDEVFS_MAGIC 0x62646576
BEFS_SUPER_MAGIC 0x42465331
BFS_MAGIC 0x1BADFACE
BINFMTFS_MAGIC 0x42494e4d
BTRFS_SUPER_MAGIC 0x9123683E
CGROUP_SUPER_MAGIC 0x27e0eb
CIFS_MAGIC_NUMBER 0xFF534D42
CODA_SUPER_MAGIC 0x73757245
COH_SUPER_MAGIC 0x012FF7B7
CRAMFS_MAGIC 0x28cd3d45
DEBUGFS_MAGIC 0x64626720
DEVFS_SUPER_MAGIC 0x1373
DEVPTS_SUPER_MAGIC 0x1cd1
EFIVARFS_MAGIC 0xde5e81e4
EFS_SUPER_MAGIC 0x00414A53
EXT_SUPER_MAGIC 0x137D
EXT2_OLD_SUPER_MAGIC 0xEF51
EXT2_SUPER_MAGIC 0xEF53
EXT3_SUPER_MAGIC 0xEF53
EXT4_SUPER_MAGIC 0xEF53
FUSE_SUPER_MAGIC 0x65735546
FUTEXFS_SUPER_MAGIC 0xBAD1DEA
HFS_SUPER_MAGIC 0x4244
HOSTFS_SUPER_MAGIC 0x00c0ffee
HPFS_SUPER_MAGIC 0xF995E849
HUGETLBFS_MAGIC 0x958458f6
ISOFS_SUPER_MAGIC 0x9660
JFFS2_SUPER_MAGIC 0x72b6
JFS_SUPER_MAGIC 0x3153464a
MINIX_SUPER_MAGIC 0x137F /* orig. minix */
MINIX_SUPER_MAGIC2 0x138F /* 30 char minix */
MINIX2_SUPER_MAGIC 0x2468 /* minix V2 */
MINIX2_SUPER_MAGIC2 0x2478 /* minix V2, 30 char names */
MINIX3_SUPER_MAGIC 0x4d5a /* minix V3 fs, 60 char names */
MQUEUE_MAGIC 0x19800202
MSDOS_SUPER_MAGIC 0x4d44
NCP_SUPER_MAGIC 0x564c
NFS_SUPER_MAGIC 0x6969
NILFS_SUPER_MAGIC 0x3434
NTFS_SB_MAGIC 0x5346544e
OPENPROM_SUPER_MAGIC 0x9fa1
PIPEFS_MAGIC 0x50495045
PROC_SUPER_MAGIC 0x9fa0
PSTOREFS_MAGIC 0x6165676C
QNX4_SUPER_MAGIC 0x002f
QNX6_SUPER_MAGIC 0x68191122
RAMFS_MAGIC 0x858458f6
REISERFS_SUPER_MAGIC 0x52654973
ROMFS_MAGIC 0x7275
SELINUX_MAGIC 0xf97cff8c
SMACK_MAGIC 0x43415d53
SMB_SUPER_MAGIC 0x517B
SOCKFS_MAGIC 0x534F434B
SQUASHFS_MAGIC 0x73717368
SYSFS_MAGIC 0x62656572
SYSV2_SUPER_MAGIC 0x012FF7B6
SYSV4_SUPER_MAGIC 0x012FF7B5
TMPFS_MAGIC 0x01021994
UDF_SUPER_MAGIC 0x15013346
UFS_MAGIC 0x00011954
USBDEVICE_SUPER_MAGIC 0x9fa2
V9FS_MAGIC 0x01021997
VXFS_SUPER_MAGIC 0xa501FCF5
XENFS_SUPER_MAGIC 0xabba1974
XENIX_SUPER_MAGIC 0x012FF7B4
XFS_SUPER_MAGIC 0x58465342
_XIAFS_SUPER_MAGIC 0x012FD16D
Most of these MAGIC constants are defined in /usr/include/linux/magic.h some are hardcoded in kernel sources.
Nobody knows what f_fsid is supposed to contain (but see below).
Fields that are undefined for a particular filesystem are set to 0. fstatfs() returns the same information about an open file referenced by descriptor fd.
Some systems only have <sys/vfs.h>, other systems also have <sys/statfs.h>, where the former includes the latter. So it seems including the former is the best choice.
LSB has deprecated the library calls statfs() and fstatfs() and tells us to use statvfs(2) and fstatvfs(2) instead.
The general idea is that f_fsid contains some random stuff such that the pair (f_fsid,ino) uniquely determines a file. Some operating systems use (a variation on) the device number, or the device number combined with the filesystem type. Several operating systems restrict giving out the f_fsid field to the superuser only (and zero it for unprivileged users), because this field is used in the filehandle of the filesystem when NFS-exported, and giving it out is a security concern.
Under some operating systems, the fsid can be used as the second argument to the sysfs(2) system call.