Rules for creating, deleting, and using data spaces

To protect data spaces from unauthorized use, the system uses certain rules to determine whether a program can create or delete a data space or whether it can access data in a data space. The rules for problem state programs with PSW key 8 through F differ from the rules for programs that are supervisor state or PSW key 0 through 7. The table on page Table 1 summarizes these rules and the example in Figure 1 illustrates them.

A program in supervisor state or PSW key 0-7 can:

Create a data space if its home or primary address space is the same as the intended owner's home address space.
Delete a data space if its primary or home address space is the same as the owner's home address space.
Release an area of a SCOPE=SINGLE data space if its primary or home address space is the same as the owner's home address space and its PSW key is the same as the storage key of the data space. It can release an area of a SCOPE=ALL or SCOPE=COMMON data space if its PSW key is zero or matches the storage key of the data space.
Extend the current size of any data space.
Page in and out of central storage the storage of any data space.
Establish addressability to a data space through the ALESERV macro (if the program does not already have an entry on its DU-AL or a PASN-AL) and obtain the ALET that indexes the entry. When it adds an entry, the program can specify whether it wants the entry on its DU-AL or the PASN-AL. A program can add entries:
- For a SCOPE=SINGLE data space to its DU-AL, if its home address space is the same as the owner's home address space
- For a SCOPE=SINGLE data space to its PASN-AL, if the PASN-AL belongs to the same address space as the owner
- For any SCOPE=ALL data space to its DU-AL and its PASN-AL
- For any SCOPE=COMMON data space to its PASN-AL
On the ALESERV macro, you can take the default for the ACCESS parameter. All access list entries for data spaces are public (ACCESS=PUBLIC). A public entry allows a program to access data in a data space, without having to establish EAX-authority. See Types of access list entries for more information about public entries.

Note that problem state programs with PSW key 8 - F can add entries to their PASN-ALs for the SCOPE=SINGLE data spaces they own or created. Supervisor state or PSW key 0-7 programs can add entries on behalf of problem state programs and pass ALETs to the problem state programs.
Access data in a data space
Once an entry for the data space is on its DU-AL, a program having the ALET for the entry can access the data space. Once an entry for the data space is on the PASN-AL, all programs running with that PASN-AL and having the ALET can access the data space. Note that data space storage is also subject to storage key and fetch protection.

A program can attach a subtask and pass a copy of its DU-AL to the subtask. This action allows the program and the subtask to share the data spaces that have entries on the DU-AL at the time of the attach.