Open System Services Programmer's Guide

2 Managing Files
You access OSS files in the OSS environment as you would access UNIX files. The OSS environment
also enables you to access files in the Guardian environment, which means that you can create
applications for NonStop systems that use data in Guardian files and that take advantage of OSS
portability and other OSS features.
In the OSS environment, sockets, pipes, FIFOs, and terminals are also files. These files are discussed
elsewhere in this guide. With respect to the OSS environment, this section discusses only directories
and regular files.
This section discusses the following topics:
ContentTopic
Differences between the two file systems, including filename
formats and mapping, and Guardian security and OSS
file-access permissions.
“The OSS and Guardian File Systems” (page 53)
Summary of the differences between the OSS and UNIX
file systems.
“Common and Unique Characteristics” (page 65)
Discussion and examples of how to access files from the
OSS API.
“Accessing Files From the OSS API” (page 65)
Discussion and examples of how to access files from the
Guardian API.
“Accessing Files From the Guardian API” (page 68)
Discussion of support for OSS files larger than
approximately 2 GB, including accessing such files from
OSS APIs and Guardian APIs, and interoperability issues.
“Accessing OSS Files Larger Than 2 GB” (page 78)
An enhancement to the Enscribe file system and the Open
System Services file system.
“Common Completion” (page 84)
Discussion of how to get optimum performance for your
application.
“Performance Considerations” (page 86)
List of each OSS file-system function with notes about its
OSS implementation and use with Guardian files.
“OSS File-System Functions” (page 90)
List of each Guardian file-system procedure that affects or
is affected by OSS files with notes about its use with OSS
files.
“Guardian File-System Procedures” (page 100)
The OSS and Guardian File Systems
This subsection describes differences between the Guardian and OSS file systems and the
implications of the differences for OSS programming.
Physical and Logical Names
Visible Guardian filenames are physical: they include the names of physical storage devices. A
fully qualified filename includes the name of a physical system (node) and the name of a physical
disk volume.
OSS pathnames are logical names: they do not include the names of storage devices. An OSS
pathname describes a path through the OSS directory tree to a file. Every OSS pathname (the
character string that identifies a file within its file system) for a disk file has a physical name in the
Guardian namespace, but that physical (Guardian) name cannot normally be used to access files.
To access OSS files, you must use OSS pathnames. For further information about OSS files and
pathnames, refer to the Open System Services User’s Guide.
The OSS and Guardian File Systems 53