Open System Services Programmer's Guide

Common and Unique Characteristics
The OSS file system looks like a typical UNIX file system, but there are a few important differences.
Features Common to the UNIX and OSS File Systems
The OSS file system conforms to the POSIX.1 specification. There is no major difference between
the OSS file system and most UNIX file systems. There are some differences in the particulars of
some functions. These differences are summarized for each function in Table 8 (page 91) and
explained in detail in the reference pages, which can be found online and in the Open System
Services System Calls Reference Manual and the Open System Services Library Calls Reference
Manual.
Features Unique to the OSS File System
The OSS file system has the following unique features:
• Administration through the Guardian environment and nonstandard information displays. For
example, ownership is displayed in the groupname.username format rather than the
standard username format. For additional information, refer to the Open System Services
User’s Guide.
• The /G directory, which is the OSS window into the Guardian file system on your local NonStop
node. All Guardian disk files on a node have a name in the /G directory.
• The /E directory, which is the OSS window into file systems on remote NonStop nodes.
• OSS file caching.
• Common Completion.
Accessing Files From the OSS API
In the OSS environment, you access OSS files in the same way that you would in any
POSIX-compliant UNIX programming environment. OSS functions are tailored to the OSS
environment and work more efficiently than Guardian procedures on OSS files.
You can access up to four types of Guardian files on physical disk volumes with OSS function calls:
• Odd-unstructured Format 1 files (file codes 0, 100, and 180). These files permit reading and
writing of both even and odd byte counts and positioning to both even and odd byte addresses.
Unstructured files do not have a built-in record structure.
• EDIT files (file type 101). These files are unstructured. You can access them only for reading.
• Telnet processes.
• For J-series RVUs, H06.06 and later RVUs, and G06.29 and later G-series RVUs,
odd-unstructured Format 2 files (file codes 0, 100, and 180). These files permit reading and
writing of both even and odd byte counts and positioning to both even and odd byte addresses.
Unstructured files do not have a built-in record structure. For detailed information about
accessing these files, see “Accessing OSS Files Larger Than 2 GB” (page 78).
You cannot access:
• Files on logical disk volumes administered through the Storage Management Foundation (SMF)
on systems that are running either J-series RVUs prior to J06.15 or H-series RVUs prior to
H06.26. (For details of accessing files on SMF logical disk volumes on systems with later
J-series or H-series RVUs, see “Accessing Files on SMF Logical Disk Volumes” (page 68)).
• A volume, a subvolume, or a process other than a TTY simulation process (/G/vol,
/G/vol/subvol, or /G/process, respectively)
• A file within a subvolume with a reserved name beginning with ZYQ (for example:
/G/vol2/zyq00004/z000002x)
Common and Unique Characteristics 65