One way of protecting access to an address space is to require that the system check that the EAX of a program is a certain value. The two times that the system might check this EAX value are when your program tries to

• Add an entry to an access list for the address space
• Access the address space through that access list entry.

If the address space does not need the protection that the EAX offers, a program in supervisor state or PSW key 0 - 7 can use the CHKEAX and ACCESS parameters on ALESERV ADD when it adds the address space entry to the access list:

• CHKEAX=NO tells the system not to check the EAX value of the program that is adding the entry to the access list.
• ACCESS=PUBLIC tells the system not to check the EAX value of a program trying to access data in the address space.

In the following example, a supervisor state or PSW key 0 - 7 program adds an entry to its DU-AL. It asks the system not to check any EAX values, either when it adds the entry or when any instruction accesses data in the address space. The program can have any EAX, including 0. The address space (represented by the STOKEN at location ASTOKENN) is non-swappable. It could have been created by the ASCRE service, which returns a STOKEN at the time of the address space creation.

         ALESERV ADD,ALET=ASALET,STOKEN=ASTOKENN,CHKEAX=NO,            X
               AL=WORKUNIT,ACCESS=PUBLIC
         .
*  PROGRAMS CAN NOW ACCESS THE ADDRESS SPACE USING THE ALET, ASALET
         .
ASALET   DS    F                       ALET FOR MVS ADDRESS SPACE
ASTOKENN DS    CL8                     STOKEN FOR MVS ADDRESS SPACE

Note that, by using the ALESERV defaults, the program could have issued the following:

         ALESERV ADD,ALET=ASALET,STOKEN=ASTOKENN,CHKEAX=NO