Node and Host Name Sizes on HP-UX: Using the Expanded Capabilities of HP-UX

Arrays Dimensioned by UTSLEN, SYS_NMLN, SNLEN, or MAXHOSTNAMELEN

A program might use one of the symbolic constant interfaces (UTSLEN, SYS_NMLN, SNLEN, or

MAXHOSTNAMELEN) to declare the size of array buffers to hold the node or host name. If not rebuilt

with the compiler option –D_HPUX_API_LEVEL=20040821, the program’s buffer is not large

enough to hold the entire node or host name.

In most cases, when recompiling to use the expanded version, these symbol references adapt cleanly

to the expanded values. However, developers need to validate this for their code.

Because UTSLEN, SYS_NMLN, and SNLEN are used in conjunction with uname(2), and because

the program must be rebuilt to use the expanded uname(2) function version, the recompile is usually

the best approach. However, with MAXHOSTNAMELEN, it is possible to simply not use it, and have the

program simply define its own buffer sizes to pass along to gethostname(2). See “Building for

Execution on Multiple Releases”. Rebuilding the program is still required, but there is more flexibility

in compilation environment and in deployment.

Arrays Dimensioned by Constant 8, 9, 15, or 64

Some programs do not use the symbolic constants but instead use hard-coded integer constants to

declare arrays that ultimately hold values returned by uname(2) or gethostname(2). Strictly

speaking, this is a violation of the specification.

These programs must be modified to use the symbolic constants before recompiling to use the

expanded interface version. (Better yet, use sysconf(_SC_HOST_NAME_MAX) to obtain the

maximum size, and dynamically allocate buffers to hold the host name. For a sample code fragment

see “Dynamic Buffer Sizing”.)

Embedded utsname Structure or Node/Host Name Constants

Some programs use the utsname structure or one of the node name or host name constants

(SYS_NMLN, SNLEN, UTSLEN, or MAXHOSTNAMELEN) in the definition of their own data

structures. That is, the utsname structure might be a substructure of a program data structure.

Alternatively, one of the listed constants (or their literal equivalents) might be used to declare an array

within a data structure. For the purpose of this discussion, we say one interface is “embedded”

within another.

The concern about node and host name interfaces embedded within a program data structure

depends on the program’s use of that data structure.

Embedded in Internal-Only Data Structures

The node/host name structure/constant interfaces may be embedded inside program private

structures. Generally, such programs can be updated for expanded names simply by recompiling with

the option –D_HPUX_API_LEVEL=20040821. The alternative approach for MAXHOSTNAMELEN

described in “Building for Execution on Multiple Releases” is also acceptable.

Embedded in Storage Formats

Sometimes the node/host name structure/constant interfaces are embedded in storage formats (such

as files, tapes, and so on). Recompiling the program to use the expanded version has two problems.

First, the program can no longer read files created with the prior version of the program. To remedy