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

However, since the expanded version of the uname(2) function and associated structure does not

exist on versions prior to HP-UX 11i v2 September 2004 Update, it is not possible to build a binary

that uses expanded uname(2) on those versions.

The solution is to employ the approach described in the previous section, and to compile the program

on the earliest HP-UX version on which it is to be run.

Again, do not use this approach for programs that re-export, via an API, the utsname structure, or

any of the symbolic constants: MAXHOSTNAMELEN, UTSLEN, SYS_NMLN, SNLEN (or equivalents).

Dynamic Buffer Sizing

Programs should avoid using the MAXHOSTNAMELEN parameter. Instead, they should query the

system for the maximum possible length by usingsysconf(_SC_HOST_NAME_MAX). The result,

after adding 1 to allow for a null terminator, should be used to allocate a buffer of that size to hold

the host name.

Because this system configuration variable is not available on all versions of HP-UX, you might want to

use conditional compilation in the following manner:

hostbufsz = 0;

#ifdef _SC_HOST_NAME_MAX

hostbufsz = sysconf(_SC_HOST_NAME_MAX) + 1;

#endif

if (hostbufsz <= 0) hostbufsz = 256;

hostbuf = malloc(hostbufsz);

retval = gethostname(hostbuf, hostbufsz);

The code fragment defaults to a host name buffer size of 256 when the sysconf() parameter is not

available.

Re-export of Node Name and Host Name Interfaces

Some software developers supply libraries of application interfaces for their customers. These

“exported” interfaces are accessible to customer applications. These interfaces might be functions or

accessible data structures.

The specification of these interfaces can include direct dependencies on the HP-UX node or host name

interfaces. If so, they are said to “re-export” those interfaces. Examples of re-exported interfaces

include:

• A structure, struct abdx, is passed into or out of some library function. A field in struct

abdx is struct utsname abdx_uts. Thus, the interface re-exports the utsname structure.

• A library function, muddle(), accepts a pointer to a buffer into which it places a string. The

specification states that the buffer should be UTSLEN bytes long. This re-exports the UTSLEN

symbol.

If the library functions are simply recompiled with -D_HPUX_API_LEVEL=20040821, they can

accommodate long host and node names. They can also allow the applications that use them to

recompile to accommodate the long names.