.TH FMOUNT 2
.CT 2 sa
.SH NAME
fmount, funmount \- mount or remove file system
.SH SYNOPSIS
.nf
.B int fmount(type, fildes, name, flag)
.B char *name;
.PP
.B int funmount(name)
.B char *name;
.PP
.B #include <sys/label.h>
.PP
.B int fmount5(type, fildes, name, flag, ceiling)
.B char *name;
.B struct label *ceiling;
.fi
.SH DESCRIPTION
.I Fmount
mounts a file system of the named
.I type
described by the file descriptor
.I fildes
on pathname
.IR name .
The ceiling label, described under
.I fmount5,
is given a default value.
Henceforth,
references to
.I name
(the mount point)
will refer to the root file
on the newly mounted file system.
.PP
.I Name
must already exist.
Its old contents are inaccessible while the
file system is mounted.
.PP
The meaning of
.I flag
varies with the file system type.
.PP
Allowed types are
.TP
.B 0
Regular (block device) file system.
.I Fildes
should be a block special file.
If
.I flag
is nonzero,
the file system may not be written on;
this must be used with physically write-protected media
or errors will occur when access times are updated,
even if no explicit write is attempted.
The default ceiling label is lattice top with all privileges.
.TP
.B 1
Obsolete version of the
network file system.
.TP
.B 2
Process file system,
.IR proc (4).
.I Fildes
is ignored.
.TP
.B 3
Mounted stream.
.I Fildes
must refer to a stream;
future calls to
.IR open (2)
on
.I name
will reopen the stream.
The mount is undone
if the other end of the stream
is closed or hung up.
.TP
.B 4
Stream (network) file system.
.I Fildes
is a stream,
whose other end is handled by a file system server,
.IR netfs (8).
The default ceiling label is lattice bottom with no privileges.
.PP
Types 5 and 6
are used internally
to close off errors
and for pipes;
these types may not be mounted.
.PP
.I Fmount5
performs the function of
.I fmount
and, on file systems of type 0 or 4, imposes a specified 
.I ceiling
label.
No file in the file system can be accessed \-
regardless of privilege \- unless the label of the file
is dominated by the file system ceiling.
Moreover, in determining capabilities during
.IR exec (2),
capability and license bits in the file label are
masked by corresponding bits in the ceiling.
.PP
Ceilings may be used to limit the labels of data
placed in file systems for export to untrusted destinations,
and to limit the acquisition
of privilege by programs in file systems of untrusted origin.
.PP
.I Funmount
removes knowledge of the file system
on which
.I name
resides.
The mount point
reverts to its previous interpretation.
.PP
Anyone may mount or unmount
process file systems
(type 3);
for other types,
these calls are restricted to the
super-user.
All require capability
.BR T_EXTERN ;
see 
.IR getplab (2).
.SH SEE ALSO
.IR labmount (2),
.IR mount (8)
.SH DIAGNOSTICS
.BR EBADF ,
.BR EBUSY ,
.BR EINVAL ,
.BR EIO ,
.BR ELAB ,
.BR ENODEV
.SH BUGS
Although
.I fildes
for type 2 file systems is ignored,
it must be a valid file descriptor.