BUFLIST Keyword

The BUFLIST parameter specifies the address of a storage area that contains the addresses of up to 16 buffers. These buffers do not have to be contiguous. The system transfers data to and from the set of buffers in the list in order of ascending buffer number. Figure 1 illustrates a buffer list used with a cache structure.

Either 31-bit addressable (below 2GB) or 64-bit addressable (above 2GB) real or virtual storage areas are supported for the BUFLIST keyword, depending on the specifications for the BUFADDRTYPE and BUFADDRSIZE keywords. However, pageable high virtual storage areas (above 2GB) may not be used.

Storage for the buffer list must have the following characteristics:

The buffer list consists of a maximum 128-byte storage area that can contain a list of 0 to 16 buffer addresses.
Each entry in the buffer list consists of an 8-byte field. For 31-bit addresses, the high-order (left-most) 4 bytes are reserved and the low-order (right-most) 4 bytes contain the real or virtual address of a buffer. For 64-bit addresses, the entire 8 bytes contain the real address of a buffer.

To specify the ALET of each buffer in the buffer list, use the following parameter:

BUFALET

The BUFALET parameter specifies an access list entry token (ALET) to be used in referencing all of the BUFLIST entries. All the buffers must be in the same address or data space.

To specify the number of buffer entries in the list, use the following parameter:

BUFNUM

Note: The system ignores any other buffer entries in the list greater than the number of buffers specified on BUFNUM.

Each buffer specified by BUFLIST must have the following characteristics:

The buffer size must be 256, 512, 1024, 2048, or 4096 bytes.
All of the buffers must be the same size.
The buffer must start on a 256-byte boundary.
The buffer must not cross a 4096-byte boundary.
The buffer must not reside below storage address 512.

For the following IXLCACHE requests, each buffer in the list must be 4096 bytes long and must start on a 4096-byte boundary:

WRITE_DATALIST
UNLOCK_CASTOUT
PROCESS_REFLIST
READ_COCLASS
READ_DIRINFO
READ_COSTATS

To specify the number of 256-byte increments in each BUFLIST buffer for all requests except those that must start on a 4096-byte boundary, use the following parameter:

BUFINCRNUM

Valid values are 1, 2, 4, 8, and 16. For example, if you specify BUFINCRNUM=4, each buffer in the buffer list is 4 x 256 bytes, or 1024 bytes.

To specify whether the buffer addresses are real or virtual addresses, use one of the following parameters:

BUFADDRTYPE=REAL
BUFADDRTYPE=VIRTUAL

To specify whether the BUFLIST entry address in real storage is a 31-bit or a 64-bit address, use one of the following parameters:

BUFADDRSIZE=31
BUFADDRSIZE=64

Figure 1 and Figure 2 show examples of a buffer list:

Figure 1. Format of Buffer List Specified by the BUFLIST Parameter

Figure 2. Format of Buffer List (BUFLIST) - 64-bit Addresses