Validate the library

The goal of the function "Validate library" is to return a return code indicating whether the library can be supported by the exit.

The key return codes are:

0

Library supported by this exit.

120

Library not supported. File Manager should try other access methods to try to read the data in the library.

(other)

Some other error occurred.

The sample COBOL exit validates a PDS by checking to see if it contains a member named $$FMN$$. If $$FMN$$ exists, the exit returns rc=0. If not, it returns rc=120.

There is a performance enhancement included in the sample code: if the library has already been validated, the validation is not repeated. This can only safely be done if the previous return code was 0 or 120. If it was some other value, the validation must be repeated. For example, if the previous validation found that the data set was in use, the validation must be repeated.

To support a customer LMS, you can replace the USER-REPOS-VALIDATE paragraph and leave the remaining code unchanged.