Open System Services Programmer's Guide

Interoperability
Opening OSS Files
Applications running on systems that do not include support for OSS large files can use either OSS
or Enscribe APIs to open any OSS file smaller than approximately 2 GB, even if that file is on a
system that includes support for OSS large files.
HP does not support OSS opens of OSS files larger than approximately 2 GB on systems that do
not include support for OSS large files. However, because Enscribe has long understood Guardian
Format 2 files, a program running on a system that does not support large files can use Enscribe
with 64-bit elections to open an OSS file that resides on a system that supports large files. If the
file is smaller than approximately 2 GB, the file size limit for that open is approximately 2 GB. If
the file is larger than approximately 2 GB, the file size limit for that open is the size of the volume.
The actual size limits depend on the API used and how the file was created. For detailed information
about size limits when opening files, see the Open System Services Management and Operations
Guide.
Opening Guardian C Files
For J-series RVUs, H06.06 and later H-series RVUs, and G06.29 and later G-series RVUs, OSS
can use the creat64() and open64() functions to create Guardian files in the /G name space.
The resulting files, regardless of size, are Guardian Format 2 files with file code 180. If a program
running on any RVU attempts to open this type of file using FILE_OPEN_ without 64-bit elections,
the open succeeds if the file is smaller than approximately 4 GB and fails if the file is larger than
4 GB.
If the open call includes 64-bit elections and is issued on J-series RVUs, H06.06 or later H-series
RVUs, or G06.29 or a later G-series RVUs, the open succeeds regardless of file size.
If an application running on an RVU earlier than G06.29 or H06.06 invokes FILE_OPEN_ with
64-bit elections, the open succeeds. However, if the file size is smaller than 4 GB, the file size limit
for that open is 4 GB. If the file size is larger than 4 GB, the file size limit for that open is the limit
defined at file-creation time.
For detailed information about size limits when opening files, see the Open System Services
Management and Operations Guide.
Compatibility Issue For Guardian Files Created by OSS APIs
For RVUs before G06.29 and H06.06, OSS files always had an underlying Guardian file format
of Format 1. For J-series RVUs, H06.06 and later H-series RVUs, and G06.29 and later G-series
RVUs, OSS files can have an underlying Guardian file format of Format 1 or Format 2. For
applications using OSS APIs to access OSS files, the underlying Guardian file format is not visible
and there are no known compatibility issues. For applications using Enscribe APIs to access
Guardian files created by OSS APIs, there is a known compatibility issue.
Before to the G06.29 and H06.06 RVUs, Guardian files created by OSS APIs were always
Format 1 with a maximum size of 175 megabytes. For J-series RVUs, H06.06 and later H-series
RVUs, and G06.29 and later G-series RVUs, Guardian files created by the open() and creat()
APIs are Guardian Format 1 with a maximum size of approximately 2 GB, and Guardian files
created by the open64() and creat64() APIs are Guardian Format 2 with a maximum size of
approximately 26 GB.
The standard OSS utilities, such as cp, pax and pinstall, now use the open64() and
creat64() functions and create a Guardian Format 2 file when given a /G output file name. For
example:
cp myfile /G/disk/subvol/myfile
Guardian applications that use file attributes such as file format and maximum size might fail when
unexpected values are returned (such as Format 2 if only Format 1 is expected).
82 Managing Files