Requirement: Before an application can retrieve storage from CSM, it must be registered as a user of a CSM buffer pool. See Creating and registering buffer pools for a description.

Table 1 lists a summary of the available CSM buffer pools. CSM returns a pool token in the RETPTOKN parameter, which the application uses on subsequent buffer requests from that pool.

Applications obtain buffers from CSM by specifying the token of the pool with which they are registered and the number of buffers on the IVTCSM REQUEST=GET_BUFFER macroinstruction. CSM allocates the requested number of buffers from that pool to the application. CSM returns a buffer list. Each entry in the buffer list contains a token and other information that the application and CSM use to reference the buffers. See CSM buffer lists for more information about buffer lists in CSM.

An application can obtain buffers from CSM as they are needed or manage its own pool of buffers to be retained for multiple uses. By default, buffers are returned to CSM when the current owner issues the IVTCSM REQUEST=FREE_BUFFER macroinstruction. An application designed to manage its own pool of buffers uses a buffer return exit routine that assumes control of the buffers after they are freed by a user.

Buffer return exit routines can receive control after buffers are released by a FREE_BUFFER request. See Buffer return exit routine for more information.