      VMS Notes for Info-ZIP Zip 3.0 and UnZip 6.0
      ============================================

   This document describes some VMS-specific behavior and implementation
details of the Info-ZIP Zip and UnZip programs.

   Last modified: 2007-03-16.


   Building with the LIST option using MMK or MMS
   ----------------------------------------------

   Currently, building with MMK or MMS using the LIST option (as in
"/MACRO = LIST=1") may cause a failure for some old versions of the DEC
C compiler.  The LIST option currently adds "/show = (all, nomessages)"
to the CC command line, and some old DEC C compilers do not support the
"nomessages" keyword.  When VAX C is used, this keyword is omitted, but
the builder does not distinguish between the various DEC/Compaq/HP C
versions.  The work-arounds are to use BUILD_[UN]ZIP.COM, or edit
[.VMS]DESCRIP_SRC.MMS to remove the troublesome keyword.


   Command-line Case
   -----------------

   Zip and UnZip now include code which can preserve the case of
command-line parameters and options, which obviates quoting upper-case
options like "-V" or "-Z".  This works on non-VAX systems with a
sufficiently recent C RTL, and SET PROCESS /PARSE_STYLE = EXTENDED.
(Sufficiently recent here means __CRTL_VER >= 70301000, which includes
VMS V7.3-1 with a C Run Time Library ECO, or V7.3-2 or newer.)   This
code uses the decc$feature_set_value() function to enable the
DECC$ARGV_PARSE_STYLE feature.  There is a small range of C RTL versions
where this function is unavailable, but where manually setting the
logical name DECC$ARGV_PARSE_STYLE to "ENABLE" will work.   HELP CRTL
leads to some additional information on these features.


   File I/O Performance
   --------------------

   When compiled using DEC/Compaq/HP C (not GNU C or VAX C), the Zip and
UnZip file I/O code now includes open callback functions which are used
to try to set some RMS parameters to non-default values, with the
intention of improving file I/O speed.  This affects reading an archive
file in UnZip and writing one in Zip.  (Reading and writing the
individual data files are handled in more exotic ways, making these
parameters less important for them.)

   Currently, the built-in default parameters enable read-ahead and
write-behind, using a multi-buffer count of 2, and a multi-block count
of 127 (the maximum).  For writing the archive, the default extend
quantity is 16384 blocks (8MB), with truncation enabled.  This
combination is believed to be, at worst, fairly harmless for most
situations, and, in most cases, to provide a substantial speed
improvement, especially with large archives.

   This code allows SET RMS_DEFAULT parameters to override the built-in
default values.  On some old VMS versions, sys$getjpi() can not provide
the SET RMS_DEFAULT values, and in this situation, the callback function
will not try to use its improved parameter values.  Users on such old
VMS versions who seek improved I/O speed may wish to bypass this check,
which requires changing the code in the get_rms_defaults() function in
[.VMS]VMS.C.  The "-v" option on both programs enables diagnostic
messages which show the operation of the callback function.  A message
showing a failure status from sys$getjpi() indicates this problem.

   Sample results (UnZip shown, Zip similar):

   VMS VAX V5.4, VAX C.  Callback code disabled, no messages:
      WIMP $ unzip -tvv TESTMAKE.ZIP
      Archive:  SYS$SYSDEVICE:[UTILITY.SOURCE.ZIP.UNZIP60C]TESTMAKE.ZIP;1
      [...]

   VMS VAX V5.5-2, DEC C.  SYS$GETJPI() fails (%SYSTEM-F-BADPARAM):
      WEAK $ unzip -tvv TESTMAKE.ZIP
      Get RMS defaults.  getjpi sts = %x00000014.
      Archive:  DUA1:[UTILITY.SOURCE.ZIP.UNZIP60C]TESTMAKE.ZIP;1
      [...]

   VMS VAX V7.3, DEC/Compaq C.  Callback code works:
      WUSS $ unzip -tvv TESTMAKE.ZIP
      Get RMS defaults.  getjpi sts = %x00000001.
                     Default: deq =      0, mbc =   0, mbf =   0.
      Open callback.  ID = 1, deq =  16384, mbc = 127, mbf =   2.
      Archive:  ALP$DKA0:[UTILITY.SOURCE.ZIP.UNZIP60C]TESTMAKE.ZIP;1
      [...]

   VMSV5.5-2 is too old.  V7.3 is new enough.  Anyone with more precise
information is invited to contribute it.

   Users who find other parameter sets more beneficial, or who find
particular problems with this set are welcome to comment.

   In this version, as in previous versions, when UnZip expands a -V
archive, it allocates the entire extent of a data file before writing
any of its data.  In some previous versions, this could cause the
destination disk to be locked for a considerable time (minutes).  Now,
the FAB "sequential access only" flag (or equivalent) is set, which
prevents this troublesome disk locking.

   In some previous versions, when UnZip expanded a non-V archive, it
did no pre-allocation, and used the default extension quantity.  This
could slow file creation significantly for large files.  Now, space for
extracted files is pre-allocated, and the same "sequential access only"
flag is set, as with a -V archive.


   Changes to the "-V" (/VMS) Option
   ---------------------------------

   The intent of the "-V" (/VMS) option was to store VMS RMS file
attributes in a Zip archive, allowing UnZip to extract an exact copy of
a file on a VMS system, including all its RMS attributes.

   In Zip before version 2.31, using the "-V" (/VMS) option created an
archive which usually contained data from beyond the EOF (End-of-File)
marker in a data file, but generally not all the disk blocks allocated
for the file.  When extracted on a VMS system, the result was usually
acceptable (because the data from beyond the EOF marker were usually
ignored).  However, when extracted on a non-VMS system, the resulting
file was usually corrupted by being NUL-padded to the next larger 16KB
multiple in size.

   Now (Zip 2.31 and later), with "-V" (/VMS), Zip truncates a data file
at EOF, and portable-format files (Stream_LF, fixed-512) should be
extracted properly on a non-VMS system.  On a VMS system, well-formed
files (that is, those with no valid data beyond EOF) should also be
restored correctly.

   With the new "-VV" (/VMS = ALL) option, the archive includes all
allocated blocks for the file (including those beyond EOF).  When
extracted on a VMS system, the original file should be reproduced with
as much fidelity as possible, but on a non-VMS system, most files will
be seen as corrupt because of the data from beyond EOF.


   Changes to Program Exit Status Values
   -------------------------------------

   Zip and UnZip exit with 32-bit VMS status values which are formed
from their internal OS-independent status values.  In previous program
versions, this was done by converting the internal success code (0) into
%x00000001 (SS$_NORMAL), and converting the other internal warning and
error codes using an artificial control/facility code, 0x7FFF (which
includes some reserved bits), and a severity value which was determined
according to rules specified in the VMS-specific exit function.
Curiously, the internal status codes were left-shifted by 4 bits instead
of 3, so all the resulting VMS message codes (bits 13:3) were even.

   Zip and UnZip now have facility names and codes assigned by HP
(UnZip: IZ_UNZIP, 1954; Zip: IZ_ZIP, 1955).  Now, by default, the
programs exit with standard 32-bit VMS status values which differ from
the old ones in several ways: The official facility code is used, and
the facility-specific bit is set.  (For compatibility with older
versions, the internal status codes are still left-shifted by 4 bits.)
The builders also create non-executable message files (UNZIP_MSG.EXE and
ZIP_MSG.EXE) so that, after a suitable SET MESSAGE command, the program
messages will be available from DCL.  For example:

      $ SET MESSAGE dev:[dir]ZIP_MSG.EXE
      $ ZIP FRED.ZIP no_such_file
        zip warning: name not matched: no_such_file

      zip error: Nothing to do!
      (dev:[dir]FRED.ZIP;)

      ALP $ WRITE SYS$OUTPUT F$MESSAGE( $STATUS)
      %IZ_ZIP-W-NONE, Nothing to do

The message files may be copied into SYS$MESSAGE to make them generally
available, although this could cause some confusion if multiple versions
of the programs are used on the system, and their error message source
files differ.  Each different destination directory will get its own
UNZIP_MSG.EXE or ZIP_MSG.EXE ([.ALPHA], [.ALPHAL], [.VAX], and so on),
but all of the same-architecture files are equivalent to each other.
That is, on an Alpha system, any of the [.ALPHA*]ZIP_MSG.EXE files could
be used; on an IA64 system, any of the [.IA64*]ZIP_MSG.EXE files could
be used; and on a VAX system, any of the [.VAX*]ZIP_MSG.EXE files could
be used.  (Similar for UNZIP_MSG.EXE, of course.)

   If desired, the programs may be built to use the old exit status values
by defining a C macro with the old facility value:
"CTL_FAC_IZ_UNZIP=0x7FFF" (UnZip) or "CTL_FAC_IZ_ZIP=0x7FFF" (Zip).
(See comments in the builder regarding LOCAL_UNZIP or LOCAL_ZIP, as
appropriate.)  This will maintain compatibility with older program
versions, but will make the programs incompatible with the new error
message files.


   Symbolic Links
   --------------

   VMS V8.3 offers support for symbolic links (symlinks) on ODS5 disks.
In previous Zip and UnZip versions, the generic code for symlinks was
disabled, and there was no VMS-specific code for symlinks.  Now, by
default, Zip and UnZip attempt to support symlinks wherever the C
headers and C run-time library include the functions needed for symlink
support.  This means non-VAX systems with __CRTL_VER >= 70301000, so
this includes VMS V7.3-1 and up, and thus symlink-capable Zip and UnZip
programs may be built on systems which do not themselves offer symlink
support.  (Various run-time failures may be expected if symlinks are
encountered on pre-V8.3 systems, either in a file system or in a Zip
archive.)

   Symlink support can be disabled at build-time, if desired, by
defining the C macro NO_SYMLINKS.  (See comments in the builder
regarding LOCAL_UNZIP or LOCAL_ZIP, as appropriate.)  For example, using
MMS to build UnZip:

      MMS /DESCRIP = [.VMS] /MACRO = ("LOCAL_UNZIP=NO_SYMLINKS=1")

or, using the command procedure to build Zip:

      LOCAL_ZIP == "NO_SYMLINKS=1"
      @ [.VMS]BUILD_ZIP.COM
      DELETE /SYMBOL /GLOBAL LOCAL_ZIP



   GNU C
   -----

   Zip and UnZip have been built using GNU C (VAX) version 2.3, mostly
for fun, but serious users are encouraged to report any interest in
continuing this activity.  The GNU C 2.3 header files were missing some
things, including definitions of SEEK_CUR, SEEK_END, and SEEK_SET.  The
VMS-specific code now expects to find unixio.h and unixlib.h, which were
absent from the GNU C 2.3 distribution.

   To work around these difficulties, the Zip and UnZip kits include
some emergency replacement unixio.h and unixlib.h files which appear to
work for these programs, at least.  To install them, use commands like
the following:

      COPY [.VMS]UNIXIO_GCC.H GNU_CC_INCLUDE:[000000]UNIXIO.H
      COPY [.VMS]UNIXLIB_GCC.H GNU_CC_INCLUDE:[000000]UNIXLIB.H
      SET PROTECTION W:RE GNU_CC_INCLUDE:[000000]UNIXIO.H, UNIXLIB.H

   There may be an error in the GNU C header file ATRDEF.H which can
cause Zip to fail, when making a "-V" archive, with a spurious "could
not open for reading" error message, followed by more bad behavior.  It
probably also causes trouble of some kind in UnZip.  To check the
questionable macro definition, use a command like the following:

      SEARCH GNU_CC_INCLUDE:[000000]ATRDEF.H ATR$S_JOURNAL

This should show something equivalent to this:

      #define ATR$S_JOURNAL           0x001

If you see "0x002" (or equivalent) instead of "0x001" (or equivalent),
then this value must be corrected in the file before building Zip or
UnZip.

   You may also see several warnings from the compiler caused by other
defects in the GNU C header files, such as:

<various>: warning: passing arg 4 of `qsort' from incompatible pointer type

[...]rab.h:134: warning: unnamed struct/union that defines no instances
[...]rab.h:143: warning: unnamed struct/union that defines no instances

These warnings appear to be harmless.

