Specifications

Data Structures

1.8 Device Data Block (DDB)

The device data block (DDB) is a block that identiﬁes the generic device-controller

name and driver name for a set of devices attached to a single controller. System

routines and device drivers refer to the DDB. The driver-loading procedure

creates a DDB for each controller during autoconﬁguration at system startup and

dynamically creates additional DDBs for new controllers as they are added to the

system using the SYSGEN command CONNECT. The procedure initializes all

ﬁelds in the DDB. All the DDBs in the I/O database are linked in a singly linked

list. The contents of IOC$GL_DEVLIST point to the ﬁrst entry in the list.

The device data block is illustrated in Figure 1–11 and described in Table 1–10.

Figure 1–11 Device Data Block (DDB)

DDB$L_LINK* 0

DDB$L_UCB* 4

DDB$W_SIZE*DDB$B_TYPE*Unused 8

DDB$L_DDT 12

DDB$L_ACPD 16

DDB$T_NAME* (16 bytes) 20

DDB$T_DRVNAME* (16 bytes) 36

DDB$L_SB* 52

DDB$L_CONLINK* 56

DDB$L_ALLOCLS* 60

DDB$L_2P_UCB* 64

*A read-only ﬁeld

1–34