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       statfs, fstatfs - get filesystem statistics


       #include <sys/vfs.h>    /* or <sys/statfs.h> */

       int statfs(const char *path, struct statfs *buf);
       int fstatfs(int fd, struct statfs *buf);


       The  statfs()  system  call  returns  information about a mounted filesystem.  path is the
       pathname of any file within the  mounted  filesystem.   buf  is  a  pointer  to  a  statfs
       structure defined approximately as follows:

           struct statfs {
               __fsword_t f_type;    /* Type of filesystem (see below) */
               __fsword_t f_bsize;   /* Optimal transfer block size */
               fsblkcnt_t f_blocks;  /* Total data blocks in filesystem */
               fsblkcnt_t f_bfree;   /* Free blocks in filesystem */
               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 filesystem */
               fsid_t     f_fsid;    /* Filesystem ID */
               __fsword_t f_namelen; /* Maximum length of filenames */
               __fsword_t f_frsize;  /* Fragment size (since Linux 2.6) */
               __fsword_t f_flags;   /* Mount flags of filesystem
                                        (since Linux 2.6.36) */
               __fsword_t f_spare[xxx];
                               /* Padding bytes reserved for future use */

           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
              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
              OCFS2_SUPER_MAGIC     0x7461636f
              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, and some are
       hardcoded in kernel sources.

       The f_flags is a bit mask indicating mount options for the file system.  It contains  zero
       or more of the following bits:

              Mandatory locking is permitted on the filesystem (see fcntl(2)).

              Do not update access times; see mount(2).

              Disallow access to device special files on this filesystem.

              Do not update directory access times; see mount(2).

              Execution of programs is disallowed on this filesystem.

              The  set-user-ID  and set-group-ID bits are ignored by exec(3) for executable files
              on this filesystem

              This filesystem is mounted read-only.

              Update atime relative to mtime/ctime; see mount(2).

              Writes are synched to the filesystem immediately (see the description of O_SYNC  in

       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.


       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.


       EACCES (statfs())  Search permission is denied for a component of the path prefix of path.
              (See also path_resolution(7).)

       EBADF  (fstatfs()) fd is not a valid open file descriptor.

       EFAULT buf or path points to an invalid address.

       EINTR  This call was interrupted by a signal.

       EIO    An I/O error occurred while reading from the filesystem.

       ELOOP  (statfs()) Too many symbolic links were encountered in translating path.

              (statfs()) path is too long.

       ENOENT (statfs()) The file referred to by path does not exist.

       ENOMEM Insufficient kernel memory was available.

       ENOSYS The filesystem does not support this call.

              (statfs()) A component of the path prefix of path is not a directory.

              Some values were too large to be represented in the returned struct.


       Linux-specific.  The Linux statfs() was inspired by the 4.4BSD one (but they  do  not  use
       the same structure).


       The  __fsword_t type used for various fields in the statfs structure definition is a glibc
       internal type, not intended for public use.  This leaves the programmer  in  a  bit  of  a
       conundrum  when  trying  to  copy or compare these fields to local variables in a program.
       Using unsigned int for such variables suffices on most systems.

       The original Linux statfs() and fstatfs() system calls were not  designed  with  extremely
       large  file  sizes  in mind.  Subsequently, Linux 2.6 added new statfs64() and fstatfs64()
       system calls that employ a new structure, statfs64.  The new structure contains  the  same
       fields as the original statfs structure, but the sizes of various fields are increased, to
       accommodate large  file  sizes.   The  glibc  statfs()  and  fstatfs()  wrapper  functions
       transparently deal with the kernel differences.

       Some  systems  have  only  <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 f_fsid field
       Solaris,  Irix  and  POSIX  have  a  system  call statvfs(2) that returns a struct statvfs
       (defined in <sys/statvfs.h>) containing an unsigned long  f_fsid.   Linux,  SunOS,  HP-UX,
       4.4BSD  have  a system call statfs() that returns a struct statfs (defined in <sys/vfs.h>)
       containing a fsid_t f_fsid, where fsid_t is defined as struct { int val[2]; }.   The  same
       holds for FreeBSD, except that it uses the include file <sys/mount.h>.

       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.


       From  Linux  2.6.38  up to and including Linux 3.1, fstatfs() failed with the error ENOSYS
       for file descriptors created by pipe(2).


       stat(2), statvfs(2), path_resolution(7)


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