Buffer List Header

The buffer list header indicates whether the buffer list describes buffers for DSCBs. The DSCB bit must be set to 1 and the VIR bit to zero for CVAF to process a request to read or write a DSCB. Provide buffer lists and buffers in your program's protect key. CVAF uses the protect key and subpool fields in the buffer list header only if you code ACCESS=RLSE.

Each buffer list header contains a count of the number of entries in the buffer list that directly follows the header.

The forward chain address chains buffer lists together. The format of the buffer list header is shown in Table 1.

Table 1. Format of a Buffer List Header
Offset	Length or Bit Pattern	Name	Description
0 (X'00')	8	BFLHDR	Buffer list header.
0 (X'00')	1	BFLHNOE	Number of entries.
1 (X'01')	1	BFLHFL	Key and flag byte.
	xxxx . . . .	BFLHKEY	Protect key of buffer list and buffers.
	. . . . 1 . . .	BFLHVIR	Reserved.
	. . . . . 1 . .	BFLHDSCB	Buffer list entries describe DSCBs.
	. . . . . . 1 .	BFLHWREV	Write multiple DSCBs in reverse order.
	. . . . . . .x		Reserved.
2 (X'02')	1	BFLHNOEN	Number of entries needed to read all DSCBs describing the DSN. Set by CVAFDIR READ when processing a READ of a format-1 or format-8 DSCB. Applicable to all volume types and set regardless of the value provided in BFLHNOE.
3 (X'03')	1	BFLHSP	Identifies the subpool of buffer list and buffers.
4 (X'04')	4	BFLHFCHN	Forward chain address of next buffer list.