RMTOPS(3)                                                            RMTOPS(3)


NAME
     rmtops - remote tape drive access routines

SYNOPSIS
     int rmtaccess(char *path, int amode);
     int rmtclose(int fildes);
     int rmtcreat(char *path, int mode);
     int rmtfstat(int fildes, struct stat *buf);
     int rmtioctl(int fildes, int request, int arg);
     int rmtopen(char *path, int oflag, int mode);
     int rmtread(int fildes, char *buf, unsigned int nbyte);
     int rmtwrite(int fildes, char *buf, unsigned int nbyte);

DESCRIPTION
     Rmtops provides a simple means of transparently accessing tape drives on
     remote machines over a network, via rsh(1) and rmt(1M).  This version of
     the library expects the remote rmt program to be version 2, which is
     fairly widespread.  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.  rmtaccess() always returns 0 in the remote case, since the
     protocol doesn't support this concept, deferring access errors until the
     rmtopen or rmtcreat.

     A remote tape drive file name has the form

          [user@]system:/dev/???

     where system is the remote system, /dev/??? is the particular drive on
     the remote system (raw, blocked, rewinding, non-rewinding, etc.), and the
     optional user is the login name to be used on the remote system, if
     different from the current user's login name.  This corresponds to the
     remote syntax used by rcp(1).  Note that the remote device must in fact
     be a device, and must reside below /dev on the remote system.

     The routines differentiate between local and remote file descriptors by
     adding a bias to the file descriptor of the pipe.  The programmer, if he
     must know if a file is remote, should use the isrmt function.  Up to 4
     remote devices may be in simultaneous use by one program at the same
     time.

FILES
     /usr/lib/librmt.a
          Contains the remote tape library.  To include the library with a
          program, add the flag -lrmt to the cc(1) command line.

SEE ALSO
     rcp(1), rsh(1), rmt(2), and the appropriate system calls in section 2.


DIAGNOSTICS
     Several of these routines will return -1 and set errno to EOPNOTSUPP, if
     they are given a remote file name or a file descriptor on an open remote
     file (e.g., rmtdup).

BUGS
     See diagnostics above.  It is to be hoped that true remote file systems
     will eventually appear, and eliminate the need for these routines.

     There is no way to use remote tape drives with the stdio(3) package with
     the current implementation.

     The rmt(1m) 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.

     The rmt program allows no more than 10K bytes to be transferred at one
     time.  The rmtread and rmtwrite routines will transfer data in multiple
     chunks if necessary to meet this requirement, and the rmt program on the
     remote will reassemble the data and pass it via the read and write system
     calls as a single system call.

ORIGINAL AUTHORS
     This set of routines is passed on a package posted to the Usenet group
     comp.sources.unix, circa 1989.  Further changes, particularly to the
     rmtioctl code, were made at Silicon Graphics.
     Jeff Lee (gatech!jeff) wrote the original routines for accessing tape
     drives via rmt(1m).

     Fred Fish (unisoft!fnf) redid them into a general purpose library.

     Arnold Robbins (gatech!arnold) added the ability to specify a user name
     on the remote system, this man page, and cleaned up the library a little.


                                                                        Page 2