Considerations for the successful completion of a receive

If the application requires that the CSM storage be pagefixed, the application must check the BLXEN_TYPE flag in the buffer list entry, ISTBLXEN. If the buffer is pageable, the application can use the IVTCSM REQUEST=FIX_BUFFER macroinstruction to ensure that the storage is pagefixed.

If the CSM storage received is from a data space, the application can gain addressability to the storage by using the ALET that is returned in the buffer list. The application can use the IVTCSM REQUEST=COPY_DATA macroinstruction if it needs to copy the data.

If the application wishes to perform I/O directly from the data space storage, it must build the I/O structures in accordance with the ESAME mode of the machine. When the machine is in ESAME mode, 64-bit I/O structures must be used. When the machine is not in ESAME mode, 31-bit I/O structures must be used.

After processing the data, the application has the following options:

Return the storage to CSM using the IVTCSM REQUEST=FREE_BUFFER macroinstruction.
Note: If a logical image of a buffer has been created on an ASSIGN_BUFFER request, the buffer may not be immediately returned to the pool. CSM determines when all users sharing a CSM buffer have called CSM to return the storage. CSM maintains a use count and when all users, including the original requester, have returned the storage, the buffer is actually returned to the pool. CSM performs this function without explicit application involvement.
Use the received data area as the storage area for a subsequent APPCCMD send operation.
In this case, CSM storage return responsibilities are transferred to a different process. The data must not be altered because the received data area is considered a read-only copy. The original requester of the CSM storage may have a CSM free routine outstanding and is entitled to the return of the storage with the data unaltered.