.\"	$NetBSD: rmtops.3,v 1.17 2022/12/04 11:25:09 uwe Exp $
.\"
.Dd October 16, 2001
.Dt RMTOPS 3
.Os
.Sh NAME
.Nm rmtops
.Nd access tape drives on remote machines
.Sh LIBRARY
Remote Magnetic Tape Library (librmt, -lrmt)
.Sh SYNOPSIS
.In rmt.h
.In sys/stat.h
.Ft int
.Fn isrmt "int fd"
.Ft int
.Fn rmtaccess "char *file" "int mode"
.Ft int
.Fn rmtclose "int fd"
.Ft int
.Fn rmtcreat "char *file" "int mode"
.Ft int
.Fn rmtdup "int fd"
.Ft int
.Fn rmtfcntl "int fd" "int cmd" "int arg"
.Ft int
.Fn rmtfstat "int fd" "struct stat *buf"
.Ft int
.Fn rmtioctl "int fd" "int request" "char *argp"
.Ft int
.Fn rmtisatty "int fd"
.Ft long
.Fn rmtlseek "int fd" "long offset" "int whence"
.Ft int
.Fn rmtlstat "char *file" "struct stat *buf"
.Ft int
.Fn rmtopen "char *file" "int flags" "int mode"
.Ft int
.Fn rmtread "int fd" "char *buf" "int nbytes"
.Ft int
.Fn rmtstat "char *file" "struct stat *buf"
.Ft int
.Fn rmtwrite "int fd" "char *buf" "int nbytes"
.Sh DESCRIPTION
The
.Nm
library provides a simple means of transparently accessing tape drives
on remote machines via
.Xr rsh 1
and
.Xr rmt 8 .
These routines are used like their corresponding system calls, but
allow the user to open up a tape drive on a remote system on which he
or she has an account and the appropriate remote permissions.
.Pp
A remote tape drive file name has the form
.Dl [user@]hostname:/dev/???
where
.Em system
is the remote system,
.Em /dev/???
is the particular drive on the remote system (raw, blocked, rewinding,
non-rewinding, etc.), and the optional
.Em user
is the login name to be used on the remote system, if different from
the current user's login name.
.\" .Pp
.\" The library source code may be optionally compiled to recognize the
.\" old
.\" .Bx 4.2 ,
.\" remote syntax
.\" .sp
.\" 	hostname[.user]:/dev/???
.\" .sp
.\" By default, only the first form (introduced in
.\" .Bx 4.3 )
.\" is recognized.
.Pp
For transparency, the user should include the file
.In rmt.h ,
which has the following defines in it:
.Bd -literal
#define access	rmtaccess
#define close	rmtclose
#define creat	rmtcreat
#define dup	rmtdup
#define fcntl	rmtfcntl
#define fstat	rmtfstat
#define ioctl	rmtioctl
#define isatty	rmtisatty
#define lseek	rmtlseek
#define lstat	rmtlstat
#define open	rmtopen
#define read	rmtread
#define stat	rmtstat
#define write	rmtwrite
.Ed
.Pp
This allows the programmer to use
.Xr open 2 ,
.Xr close 2 ,
.Xr read 2 ,
.Xr write 2 ,
etc. in their normal fashion, with the
.Nm
routines taking care of differentiating between local and remote files.
This file should be included
.Em before
including the file
.Pa <sys/stat.h> ,
since it redefines the identifier ``stat'' which is used to declare
objects of type
.Em "struct stat" .
.Pp
The routines differentiate between local and remote file descriptors
by adding a bias (currently 128) to the file descriptor of the pipe.
The programmer, if he or she must know if a file is remote, should use
.Fn isrmt .
.Sh ENVIRONMENT
The RCMD_CMD environment variable can be set to the name or pathname
of a program to use, instead of
.Pa /usr/bin/rsh ,
and must have the same calling conventions as
.Xr rsh 1 .
.Sh FILES
.Bl -tag -width /usr/lib/librmt.a -compact
.It Pa /usr/lib/librmt.a
remote tape library
.El
.Sh RETURN VALUES
Several of these routines will return \-1 and set
.Va errno
to
.Er EOPNOTSUPP ,
if they are given a remote file name or a file descriptor
on an open remote file (e.g.,
.Fn rmtdup ) .
.Sh SEE ALSO
.Xr rcp 1 ,
.Xr rsh 1 ,
.Xr rmt 8
.Pp
And the appropriate system calls in section 2.
.\" .Sh CONFIGURATION OPTIONS
.\" The library may be compiled to allow the use of
.\" .Bx 4.2 -style
.\" remote file names.  This is not recommended.
.\" .Pp
.\" By default, the library opens two pipes to
.\" .Xr rsh 1 .
.\" It may optionally be compiled to use
.\" .Xr rexec 3 ,
.\" instead.  Doing so requires the use of a
.\" .Em .netrc
.\" file in the user's home directory, or that the application designer be
.\" willing to have
.\" .Xr rexec 3
.\" prompt the user for a login name and password on the remote host.
.Sh AUTHORS
Jeff Lee wrote the original routines for accessing tape drives via
.Xr rmt 8 .
.Pp
Fred Fish redid them into a general purpose library.
.Pp
Arnold Robbins added the ability to specify a user name on the remote
system, the
.Pa <rmt.h>
include file, this man page, cleaned up the library a little, and made
the appropriate changes for
.Bx 4.3 .
.Pp
Dan Kegel contributed the code to use the
.Xr rexec 3
library routine.
.Sh BUGS
There is no way to use remote tape drives with
.Xr stdio 3 ,
short of recompiling it entirely to use these routines.
.Pp
The
.Xr rmt 8
protocol is not very capable.
In particular, it relies on TCP/IP sockets for error
free transmission, and does no data validation of its own.