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

this, the program needs to recognize that it has encountered a nonexpanded format, and it must be

able to use the nonexpanded structure layout to read it. Updating the the stored format to the

expanded version is optional.

Second, if other programs are expected to read the expanded stored format, they must be updated to

use the expanded version. If the other programs are user programs, this can be compatibility issue if

older user programs need to be supported. One solution might be to always write two versions of the

stored data. The nonexpanded version can be used by some programs, the expanded version can be

used by enhanced user programs.

Some storage formats have flexible formats where the sizes of the data are described by metadata

stored with or alongside the actual data. It might be possible to add expanded “sections” which are

generally ignored except by programs that can recognize them. If so, the data that depends on the

node/host name structures or constants can be added to the data in an expanded section, rather than

replacing existing sections.

Embedded in IPC Communication Protocols

Node/host name structure/constants might be embedded in communication protocols. This is similar

to having them embedded in storage formats, except there is no persistent, nonexpanded, stored

data. In most cases, protocol version levels are negotiated between the parties. This leads to a natural

way for the programs to adapt to one version or another.

In many cases, simply recompiling all the programs that use the protocol is the solution.

Embedded in Shared Memory Structures

The node/host name structure/constants might be embedded in structures that are placed in shared

memory. Again, the situation is similar to that of having them embedded in storage formats.

When accessed only by multiple instantiations of a single program, updating that program to the

expanded version (that is, recompiling with the expanded version selected) is sufficient. This is

usually the case.

When accessed by different programs, the differing data layout can cause problems. Therefore, all

the programs that access the shared memory should be updated together, if possible. Since

programs evolve, changes to the shared memory format are not uncommon. This is not an unusual

situation.

Depending on the data structures used, supporting both the nonexpanded and expanded formats in

shared memory might be possible. All writers must be updated to deal with both formats. However,

readers can use either format.

If the shared memory is accessed by others (such as, by customer applications), developers must

devise a reasonable migration plan. However, this situation is highly unusual.

Embedded in Exported Interfaces (Re-exported)

Through a library, an application might export a function (or data structure) interface that includes in

its definition arrays or structures containing a node/host name structure/constant. That interface is

said to re-export the node/host name interfaces. The developer has some choices: