PSTAT Interfaces

• For more information on how to use pstat interfaces please refer to the source code of

freeware application lsof at ftp://vic.cc.purdue.edu/pub/tools/unix/lsof

2. Overview

In the early days of UNIX, programmers and system administrators were required to write

their own tools to monitor and manage the system. In order to facilitate access to the internals of

the kernel implementation, UNIX provided the /dev/kmem and /dev/mem pseudo devices. This

was a reasonable thing to do in those days, as release-to-release binary compatibility was not an

issue. Modern UNIX systems now provide the application programmers with a rich set of

standard APIs. Writing applications that depend on kernel internals is no longer a recommended

practice. In fact, exposure to kernel internals creates serious binary compatibility problems for

user applications. The availability of many commercial applications for HP-UX makes the

release-to-release binary compatibility a very important feature.

Even today many system management and measurement tools read kernel data structures

through unsupported interfaces, such as /dev/kmem pseudo driver, to get information about open

files, resource usage, process activity, etc. Because kernel data structures change from release to

release, this access method is fragile, incurring a high maintenance cost. To insulate these

applications from the release-to-release variability in private kernel data structures, HP-UX

provides the pstat() system call and a set of wrappers. Pstat is a supported API that provides

many of the HP-UX system contexts. It provides a number of wrappers (pstat_get*) and

corresponding structures (struct pst_*) to get information from the kernel. These interfaces are

designed in such a way to allow future expansion of the interface, while preserving source and

binary compatibility for programs written using the pstat interfaces. Pstat interfaces are available

in both 64-bit and 32-bit versions. Replacing the /dev/kmem access with pstat wrappers will

eliminate the need to re-release these applications with each new HP-UX release.

3. Summary of Available Contexts

The general framework for pstat() interface is that the user programs call the libc

wrappers with required parameters. The wrappers then call the pstat() system call, passing the

required parameters. pstat() collects the required information and places it in the user’s buffer.

The pstat wrappers return information about various system contexts. The contents of the various

associated data structures are described in the Appendix. The following contexts of information

are returned by pstat wrappers: Static, Dynamic, Virtual Memory (VM), Inter Process

Communication (IPC), Stable Store, Crash Dumps, Processor, Disk, Swap Areas, Dump Areas,

Node (ccNUMA), Process, Light Weight Process (LWP), Process Region, Logical Volume

Manager Volume, Semaphore Set, Message Queue, Shared Memory, Open File, Open Socket,

Open Stream, and Dynamic Name Lookup Cache (DNLC). The following table summarizes the

various contexts.

Context Structure Routine Instances Short

Cut?

Static

Dynamic

pst_static

pst_dynamic

pst_vminfo

pstat_getstatic()

pstat_getdynamic()

pstat_getvminfo