.TH LOCKERS 7 "6 March 1998"
.ds ]W MIT Athena
.SH NAME
lockers - description of Athena locker organization conventions
.SH DESCRIPTION

There are many possible ways to provide binaries for multiple
architectures in some organization under a single filesystem. Athena
suggests and supports a particular convention for doing this.

The primary purpose of this convention is to provide a standard way of
separating machine dependent binaries into different directories for
ease of use and maintenance. Generality, backwards compatibility, and
neatness also count.

.SH MACHINE DEPENDENT FILES

In order to avoid any sort of clutter in the top level directory of a
locker, all machine dependent directories are placed under a directory
called \fIarch\fR. Under \fIarch\fR is one directory, for each
supported platform, named after the AFS "@sys" values (pmax_ul4,
sun4m_53, etc.). Under each of these directories are directories
containing a specific type of machine dependent data, such as binaries
or libraries (bin, lib, etc.).

For example, a locker containing libraries and binaries might look
like:

/mit/locker/arch/
                 pmax_ul4/
                          bin/
                          lib/
                 rs_aix32/
                          bin/
                          lib/
                 sgi_52/
                        bin/
                        lib/
                 sun4m_53/
                          bin/
                          lib/

Possibilities for data subdirectories include bin, lib, etc, man, and
build.

Note that due to the fact there is binary compatibility across
multiple AFS "@sys" values, there will also be many symbolic links:

/mit/locker/arch/
                 sun4c_51 -> sun4m_53
                 sun4c_53 -> sun4m_53
                 sun4m_51 -> sun4m_53

Note also that the string "@sys" should never be used literally,
except in convenience symlinks described below; the string
"$ATHENA_SYS" should be used instead. Continue reading for more
details.

.SH MACHINE INDEPENDENT FILES

Many files, such as manual pages or data files, may be the same for
all machine architectures. Currently, the only defined convention for
such files applies only to manual pages. That convention is simply
that, in the top level directory of a locker there is a directory
called "man" that follows the conventions for manual directories
followed by most flavors of Unix.

Note that the \fIadd\fR command also supports the possibility of
machine specific manual pages when modifying the MANPATH, in that it
first checks for the existence of the directory arch/@sys/man prior
to falling back on man itself.

.SH CONVENIENCE SYMLINKS

While the \fIadd\fR command deals for the user with finding the
appropriate binary directory for their platform, some users sometimes
do not use \fIadd\fR, instead typing explicit paths on their own.
This could become tedious when they need to type "cd
/mit/lockername/arch/pmax_ul4/bin." For the user's convenience then,
we suggest that you make a link "bin -> arch/@sys/bin" and possibly
others (for lib, etc.) as it makes sense. This is the \fIonly\fR case
where we suggest using the explicit string "@sys." See the end of the
section \fIUSER SUPPORT\fR, below, for the reasons.

.SH BACKWARDS COMPATIBILITY AND BINARY LAYOUT

The previous file layout conventions included only standards for
binary and manual directories, and no suggestions for hierarchies to
avoid clutter or other general hints. The main convention was that the
output from \fImachtype\fR(1) be used to generate a binary directory
for a given platform, e.g. `machtype`bin (decmipsbin, sun4bin, etc.).
Because of the inflexibility of the shell \fIbindir\fR variable, we
cannot simply tell everyone to begin using arch/@sys/bin for their
binary directories. Old lockers may still be using `machtype`bin and
not the new convention, and there is no practical way to update the
entire world simultaneously. Therefore, lockers should contain
structures such as

/mit/locker/
            arch/pmax_ul4/bin
            decmipsbin -> arch/pmax_ul4/bin

That is, there should be compatibility symlinks provided from the old
convention to the new convention, for such platforms as were supported
under the old convention. Those platforms are vax, rt, decmips, sun4,
and rsaix. New platforms, such as SGI, need not provide these symlinks
as they don't have an old bindir value to worry about.

.SH USER SUPPORT

There are four forms of support provided to the user for handling
locker conventions: the \fIadd\fR command, the \fIathdir\fR command,
the \fIbindir\fR C shell variable, and the \fIATHENA_SYS\fR
environment variable.

The \fIadd\fR command (see \fIadd\fR(1) for details on use), for
binary directories, initially checks for the existence of the new
style binary directory. If it finds it, it adds that to the user's
search path. If not, it falls back to the old \fImachtype\fR based
convention. Similiarly, in order to more easily support machine
dependent manual pages, it checks for an arch/@sys/man directory
before falling back to the traditional man directory.

The \fIathdir\fR command is in some ways a generalization of the
\fIadd\fR command. The most important functionality it provides is as
a replacement for the use of the /mit/locker/`machtype`bin string.
`athdir /mit/locker` should now be used instead, and will work
correctly whether old or new directory conventions are in use in
that locker. \fIathdir\fR is also potentially useful for finding
library or include directories from inside of makefiles. See
\fIathdir\fR(1) for details.

The \fIbindir\fR variable, on older platforms, is set to the value
`machtype`bin. On newer platforms, it is set to arch/@sys/bin. Note
that it is not set literally to arch/@sys/bin, but to arch/(the value
of @sys)/bin; the literal string @sys should never be used except in
convenience symlinks.

The \fIATHENA_SYS\fR environment variable is used lieu of the AFS
string @sys. In all cases, it should be equal to what @sys resolves to
for any particular platform. So in shell scripts, makefiles, etc., one
should never attempt to find one's libraries with a string such as
"arch/@sys/lib" but rather "arch/$ATHENA_SYS/lib." It is usually
preferable to use \fIathdir\fR, however.

\fIATHENA_SYS\fR is derived in the global cshrc from the output of
``machtype -S''.

Avoidance of the literal string ``@sys'' is done in order to keep the
locker conventions filesystem independent. If for some reason a locker
is copied to (or is maintained in) NFS space, it will still work
correctly.  If AFS is translated through some other medium which does
not magically know how to cope with the "@sys" string properly, it
will also still work correctly. If Athena migrates to another kind of
filesystem that does not support the use of "@sys," nothing will need
to be done to update lockers and everything will still work.

.SH OPERATING SYSTEM COMPATIBILITY SUPPORT

As mentioned above, a given operating system may have the ability to
run binaries from various @sys values. For example, a sun4x_56 system
can run binaries from sun4x_55 and sun4m_54. In part to ease the
transition of machines to new operating systems, where ordinarily they
would find no support initially for their @sys values in lockers,
there is the environment variable \fIATHENA_SYS_COMPAT\fR. This
variable is a colon separated list of fallback @sys values which are
known to be generally compatible with the current system. So in the
above example, this variable might be set to sun4x_55:sun4m_54 to
enable lockers that have not yet been updated for the new operating
system to continue to function. Both \fIadd\fR(1) and \fIathdir\fR(1)
support this variable.

.SH MAINTENANCE SUPPORT

The \fIlockers\fR locker contains tools to aid in the maintenance of
lockers. "add lockers; man lockertools" for more information.

.SH SUGGESTIONS ON CONFIGURING SOFTWARE

Many software packages use autoconf-generated configure scripts.
These packages can generally be configured for a locker with a command
like "./configure --prefix=/mit/lockername
--exec-prefix=/mit/lockername/arch/$ATHENA_SYS".  This command will
configure the program to install its shared data files directly under
/mit/lockername, and to install architecture-dependent materials under
the appropriate arch directory.

Alternatively, one could configure with simply "./configure
--prefix=/mit/lockername/arch/$ATHENA_SYS" to install all materials
under the appropriate arch directory.  This option may waste space,
but may also be more resistant to flaws in the package (e.g. the
package might install architecture-dependent materials under the
prefix instead of the exec-prefix, or an installation of a newer
version of the package might break an older installation for an older
platform by overwriting the shared data area).

Some software in lockers is configured to use the full AFS path as a
prefix instead of /mit/lockername.  This practice is not recommended
because it is incompatible with the local-lockers framework.  It is
also not recommended to use arch/@sys (instead of arch/$ATHENA_SYS) in
the prefix, since that can fail when the software is used via
\fIATHENA_SYS_COMPAT\fR.

.SH SEE ALSO

add(1), athdir(1), machtype(1), athena-ws discuss meeting, txns
1932-1961 more or less, /etc/athena/local-lockers.conf