GNU Info
(libc.info)fstab
The `fstab' file
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The internal representation for entries of the file is
`struct fstab', defined in `fstab.h'.
- Data Type: struct fstab
This structure is used with the `getfsent', `getfsspec', and
`getfsfile' functions.
`char *fs_spec'
This element describes the device from which the filesystem
is mounted. Normally this is the name of a special device,
such as a hard disk partition, but it could also be a more or
less generic string. For "NFS" it would be a hostname and
directory name combination.
Even though the element is not declared `const' it shouldn't
be modified. The missing `const' has historic reasons, since
this function predates ISO C. The same is true for the other
string elements of this structure.
`char *fs_file'
This describes the mount point on the local system. I.e.,
accessing any file in this filesystem has implicitly or
explicitly this string as a prefix.
`char *fs_vfstype'
This is the type of the filesystem. Depending on what the
underlying kernel understands it can be any string.
`char *fs_mntops'
This is a string containing options passed to the kernel with
the `mount' call. Again, this can be almost anything. There
can be more than one option, separated from the others by a
comma. Each option consists of a name and an optional value
part, introduced by an `=' character.
If the value of this element must be processed it should
ideally be done using the `getsubopt' function; see Note:
Suboptions.
`const char *fs_type'
This name is poorly chosen. This element points to a string
(possibly in the `fs_mntops' string) which describes the
modes with which the filesystem is mounted. `fstab' defines
five macros to describe the possible values:
`FSTAB_RW'
The filesystems gets mounted with read and write enabled.
`FSTAB_RQ'
The filesystems gets mounted with read and write
enabled. Write access is restricted by quotas.
`FSTAB_RO'
The filesystem gets mounted read-only.
`FSTAB_SW'
This is not a real filesystem, it is a swap device.
`FSTAB_XX'
This entry from the `fstab' file is totally ignored.
Testing for equality with these value must happen using
`strcmp' since these are all strings. Comparing the pointer
will probably always fail.
`int fs_freq'
This element describes the dump frequency in days.
`int fs_passno'
This element describes the pass number on parallel dumps. It
is closely related to the `dump' utility used on Unix systems.
To read the entire content of the of the `fstab' file the GNU libc
contains a set of three functions which are designed in the usual way.
- Function: int setfsent (void)
This function makes sure that the internal read pointer for the
`fstab' file is at the beginning of the file. This is done by
either opening the file or resetting the read pointer.
Since the file handle is internal to the libc this function is not
thread-safe.
This function returns a non-zero value if the operation was
successful and the `getfs*' functions can be used to read the
entries of the file.
- Function: void endfsent (void)
This function makes sure that all resources acquired by a prior
call to `setfsent' (explicitly or implicitly by calling
`getfsent') are freed.
- Function: struct fstab * getfsent (void)
This function returns the next entry of the `fstab' file. If this
is the first call to any of the functions handling `fstab' since
program start or the last call of `endfsent', the file will be
opened.
The function returns a pointer to a variable of type `struct
fstab'. This variable is shared by all threads and therefore this
function is not thread-safe. If an error occurred `getfsent'
returns a `NULL' pointer.
- Function: struct fstab * getfsspec (const char *NAME)
This function returns the next entry of the `fstab' file which has
a string equal to NAME pointed to by the `fs_spec' element. Since
there is normally exactly one entry for each special device it
makes no sense to call this function more than once for the same
argument. If this is the first call to any of the functions
handling `fstab' since program start or the last call of
`endfsent', the file will be opened.
The function returns a pointer to a variable of type `struct
fstab'. This variable is shared by all threads and therefore this
function is not thread-safe. If an error occurred `getfsent'
returns a `NULL' pointer.
- Function: struct fstab * getfsfile (const char *NAME)
This function returns the next entry of the `fstab' file which has
a string equal to NAME pointed to by the `fs_file' element. Since
there is normally exactly one entry for each mount point it makes
no sense to call this function more than once for the same
argument. If this is the first call to any of the functions
handling `fstab' since program start or the last call of
`endfsent', the file will be opened.
The function returns a pointer to a variable of type `struct
fstab'. This variable is shared by all threads and therefore this
function is not thread-safe. If an error occurred `getfsent'
returns a `NULL' pointer.
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