Purpose
Makes
a file system available for use.
Library
Standard
C Library (libc.a)
Syntax
#include <sys/types.h>
#include <sys/vmount.h>
int vmount ( VMount, Size)
struct vmount *VMount;
int Size;
int mount
( Device, Path, Flags)
char *Device;
char *Path;
int Flags;
Description
The vmount subroutine
mounts a file system, thereby making the file available for use.
The vmount subroutine effectively creates what is known as
a virtual file system. After a file system is mounted, references
to the path name that is to be mounted over refer to the root directory
on the mounted file system.
A directory
can only be mounted over a directory, and a file can only be mounted
over a file. (The file or directory may be a symbolic link.)
Therefore, the vmount subroutine can
provide the following types of mounts:
- A local file over a local or remote file
- A local directory over a local or remote directory
- A remote file over a local or remote file
- A remote directory over a local or remote directory.
A mount to a directory or a file can be issued if the calling
process has root user authority or is in the system group and has
write access to the mount point.
To mount
a block device, remote file, or remote directory, the calling process
must also have root user authority.
The mount subroutine
only allows mounts of a block device over a local directory with
the default file system type. The mount subroutine searches
the /etc/filesystems file to find a corresponding stanza for
the desired file system.
Note: The mount subroutine interface
is provided only for compatibility with previous releases of the
operating system. The use of the mount subroutine is strongly
discouraged by normal application programs.
If the directory you are trying to mount over
has the sticky bit set to on, you must either own that directory
or be the root user for the mount to succeed. This restriction applies
only to directory-over-directory mounts.
Parameters
- Device
- A path name identifying the block device (also called a special
file) that contains the physical file system.
- Path
- A path name identifying the directory on which the file system
is to be mounted.
- Flags
- Values that define characteristics of the object to be mounted.
Currently these values are defined in the /usr/include/sys/vmount.h file:
- MNT_READONLY
- Indicates that the object to be mounted is read-only and that
write access is not allowed. If this value is not specified, writing
is permitted according to individual file accessibility.
- MNT_NOSUID
- Indicates that setuid and setgid programs referenced
through the mount should not be executable. If this value is not
specified, setuid and setgid programs referenced through
the mount may be executable.
- MNT_NODEV
- Indicates that opens of device special files referenced through
the mount should not succeed. If this value is not specified, opens
of device special files referenced through the mount may succeed.
- VMount
- A pointer to a variable-length vmount structure. This
structure is defined in the sys/vmount.h file.
The following fields of the VMount parameter
must be initialized before the call to the vmount subroutine:
- vmt_revision
- The revision code in effect when the program that created this
virtual file system was compiled. This is the value VMT_REVISION.
- vmt_length
- The total length of the structure with all its data. This must
be a multiple of the word size (4 bytes) and correspond with the Size
parameter.
- vmt_flags
- Contains the general mount characteristics. The following value
may be specified:
- MNT_READONLY
- A read-only virtual file system is to be created.
- vmt_gfstype
- The type of the generic file system underlying the VMT_OBJECT.
Values for this field are defined in the sys/vmount.h file
and include:
- MNT_JFS
- Indicates the native file system.
- MNT_NFS
- Indicates a Network File System client.
- MNT_CDROM
- Indicates a CD-ROM file system.
- vmt_data
- An array of structures that describe variable length data associated
with the vmount structure. The structure consists of the following
fields:
- vmt_off
- The offset of the data from the beginning of the vmount
structure.
- vmt_size
- The size, in bytes, of the data.
The array
consists of the following fields:
- vmt_data[VMT_OBJECT]
- Specifies he name of the device, directory, or file to be mounted.
- vmt_data[VMT_STUB]
- Specifies the name of the device, directory, or file to be mounted
over.
- vmt_data[VMT_HOST]
- Specifies the short (binary) name of the host that owns the
mounted object. This need not be specified if VMT_OBJECT is
local (that is, it has the same vmt_gfstype as / (root),
the root of all file systems).
- vmt_data[VMT_HOSTNAME]
- Specifies the long (character) name of the host that owns the
mounted object. This need not be specified if VMT_OBJECT is
local.
- vmt_data[VMT_INFO]
- Specifies binary information to be passed to the generic file-system
implementation that supports VMT_OBJECT. The interpretation
of this field is specific to the gfs_type.
- vmt_data[VMT_ARGS]
- Specifies a character string representation of VMT_INFO.
On return from the vmount subroutine,
the following additional fields of the VMount parameter are
initialized:
- vmt_fsid
- Specifies the two-word file system identifier; the interpretation
of this identifier depends on the gfs_type.
- vmt_vfsnumber
- Specifies the unique identifier of the virtual file system.
Virtual file systems do not survive the IPL; neither does this identifier.
- vmt_time
- Specifies the time at which the virtual file system was created.
- Size
- Specifies the size, in bytes, of the supplied data area.
Return Values
Upon successful completion, a value of 0 is
returned. Otherwise, a value of -1 is returned, and the errno global
variable is set to indicate the error.
Error Codes
The mount and vmount subroutines
fail and the virtual file system is not created if any of the following
is true:
Item |
Description |
EACCES |
The calling process does not have write permission on the
stub directory (the directory to be mounted over). |
EBUSY |
VMT_OBJECT specifies a device that is already mounted
or an object that is open for writing, or the kernel's mount table
is full. |
EFAULT |
The VMount parameter points to a location outside
of the allocated address space of the process. |
EFBIG |
The size of the file system is too big. |
EFORMAT |
An internal inconsistency has been detected in the file system. |
EINVAL |
The contents of the VMount parameter are unintelligible
(for example, the vmt_gfstype is unrecognizable, or the
file system implementation does not understand the VMT_INFO provided). |
ENOSYS |
The file system type requested has not been configured. |
ENOTBLK |
The object to be mounted is not a file, directory, or device. |
ENOTDIR |
The types of VMT_OBJECT and VMT_STUB are incompatible. |
EPERM |
VMT_OBJECT specifies a block device, and the calling
process does not have root user authority. |
EROFS |
An attempt has been made to mount a file system for read/write
when the file system cannot support writing. |
The mount and vmount subroutines
can also fail if additional
errors occur.