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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 inodes in filesystem */
               fsfilcnt_t f_ffree;   /* Free inodes 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 */

       The following filesystem types may appear in f_type:

           ADFS_SUPER_MAGIC      0xadf5
           AFFS_SUPER_MAGIC      0xadff
           AFS_SUPER_MAGIC       0x5346414f
           ANON_INODE_FS_MAGIC   0x09041934 /* Anonymous inode FS (for
                                               pseudofiles that have no name;
                                               e.g., epoll, signalfd, bpf) */
           AUTOFS_SUPER_MAGIC    0x0187
           BDEVFS_MAGIC          0x62646576
           BEFS_SUPER_MAGIC      0x42465331
           BFS_MAGIC             0x1badface
           BINFMTFS_MAGIC        0x42494e4d
           BPF_FS_MAGIC          0xcafe4a11
           BTRFS_SUPER_MAGIC     0x9123683e
           BTRFS_TEST_MAGIC      0x73727279
           CGROUP_SUPER_MAGIC    0x27e0eb   /* Cgroup pseudo FS */
           CGROUP2_SUPER_MAGIC   0x63677270 /* Cgroup v2 pseudo FS */
           CIFS_MAGIC_NUMBER     0xff534d42
           CODA_SUPER_MAGIC      0x73757245
           COH_SUPER_MAGIC       0x012ff7b7
           CRAMFS_MAGIC          0x28cd3d45
           DEBUGFS_MAGIC         0x64626720
           DEVFS_SUPER_MAGIC     0x1373     /* Linux 2.6.17 and earlier */
           DEVPTS_SUPER_MAGIC    0x1cd1
           ECRYPTFS_SUPER_MAGIC  0xf15f
           EFIVARFS_MAGIC        0xde5e81e4
           EFS_SUPER_MAGIC       0x00414a53
           EXT_SUPER_MAGIC       0x137d     /* Linux 2.0 and earlier */
           EXT2_OLD_SUPER_MAGIC  0xef51
           EXT2_SUPER_MAGIC      0xef53
           EXT3_SUPER_MAGIC      0xef53
           EXT4_SUPER_MAGIC      0xef53
           F2FS_SUPER_MAGIC      0xf2f52010
           FUSE_SUPER_MAGIC      0x65735546
           FUTEXFS_SUPER_MAGIC   0xbad1dea  /* Unused */
           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     /* original minix FS */
           MINIX_SUPER_MAGIC2    0x138f     /* 30 char minix FS */
           MINIX2_SUPER_MAGIC    0x2468     /* minix V2 FS */
           MINIX2_SUPER_MAGIC2   0x2478     /* minix V2 FS, 30 char names */
           MINIX3_SUPER_MAGIC    0x4d5a     /* minix V3 FS, 60 char names */
           MQUEUE_MAGIC          0x19800202 /* POSIX message queue FS */
           MSDOS_SUPER_MAGIC     0x4d44
           MTD_INODE_FS_MAGIC    0x11307854
           NCP_SUPER_MAGIC       0x564c
           NFS_SUPER_MAGIC       0x6969
           NILFS_SUPER_MAGIC     0x3434
           NSFS_MAGIC            0x6e736673
           NTFS_SB_MAGIC         0x5346544e
           OCFS2_SUPER_MAGIC     0x7461636f
           OPENPROM_SUPER_MAGIC  0x9fa1
           OVERLAYFS_SUPER_MAGIC 0x794c7630
           PIPEFS_MAGIC          0x50495045
           PROC_SUPER_MAGIC      0x9fa0     /* /proc FS */
           PSTOREFS_MAGIC        0x6165676c
           QNX4_SUPER_MAGIC      0x002f
           QNX6_SUPER_MAGIC      0x68191122
           RAMFS_MAGIC           0x858458f6
           REISERFS_SUPER_MAGIC  0x52654973
           ROMFS_MAGIC           0x7275
           SECURITYFS_MAGIC      0x73636673
           SELINUX_MAGIC         0xf97cff8c
           SMACK_MAGIC           0x43415d53
           SMB_SUPER_MAGIC       0x517b
           SMB2_MAGIC_NUMBER     0xfe534d42
           SOCKFS_MAGIC          0x534f434b
           SQUASHFS_MAGIC        0x73717368
           SYSFS_MAGIC           0x62656572
           SYSV2_SUPER_MAGIC     0x012ff7b6
           SYSV4_SUPER_MAGIC     0x012ff7b5
           TMPFS_MAGIC           0x01021994
           TRACEFS_MAGIC         0x74726163
           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 /* Linux 2.0 and earlier */

       Most  of  these  MAGIC  constants  are defined in /usr/include/linux/magic.h, and some are
       hardcoded in kernel sources.

       The f_flags field is a bit mask indicating mount options for the filesystem.  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

       ST_NOSYMFOLLOW (since Linux 5.10)
              Symbolic links are not followed when resolving paths; see mount(2).

       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 to indicate the


       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  The call was interrupted by a signal; see signal(7).

       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(3)
       and fstatvfs(3) 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(3), path_resolution(7)


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