Specifications

Operating System Routines

EXE$SETCHAR, EXE$SETMODE

Description

A driver uses EXE$SETCHAR or EXE$SETMODE as an FDT routine to process

the set-device-mode (IO$_SETMODE) and set-device-characteristics (IO$_

SETCHAR) functions. If setting device characteristics requires device activity

or synchronization with fork processing, the driver’s FDT entry must specify

EXE$SETMODE. Otherwise, it can specify EXE$SETCHAR.

EXE$SETCHAR and EXE$SETMODE examine the current value of UCB$B_

DEVCLASS to determine whether the device permits the speciﬁed function. If

the device class is disk (DC$_DISK), the routines place SS$_ILLIOFUNC status

in R0 and transfer control to EXE$ABORTIO to terminate the request.

EXE$SETCHAR and EXE$SETMODE then ensure that the process has read

access to the quadword containing the new device characteristics. If it does

not, the routines place SS$_ACCVIO status in R0 and transfer control to

EXE$ABORTIO to terminate the request.

If the request passes these checks, EXE$SETCHAR and EXE$SETMODE proceed

as follows:

• EXE$SETCHAR stores the speciﬁed characteristics in the UCB. For an IO$_

SETCHAR function, the device type and class ﬁelds (UCB$B_DEVCLASS

and UCB$B_DEVTYPE, respectively) receive the ﬁrst word of data. For both

IO$_SETCHAR and IO$_SETMODE functions, EXE$SETCHAR writes the

second word into the default-buffer-size ﬁeld (UCB$W_DEVBUFSIZ) and

the third and fourth words into the device-dependent-characteristics ﬁeld

(UCB$Q_DEVDEPEND).

Finally, EXE$SETCHAR stores normal completion status (SS$_NORMAL)

in R0 and transfers control to EXE$FINISHIO to insert the IRP in the

systemwide I/O postprocessing queue.

• EXE$SETMODE stores the speciﬁed quadword of characteristics in IRP$L_

MEDIA, places normal completion status (SS$_NORMAL) in R0, and

transfers control to EXE$QIODRVPKT to deliver the IRP to the driver’s

start-I/O routine.

The driver’s start-I/O routine copies data from IRP$L_MEDIA and the following

longword into UCB$W_DEVBUFSIZ, UCB$Q_DEVDEPEND, and, if the I/O

function is IO$_SETCHAR, UCB$B_DEVCLASS and UCB$B_DEVTYPE as well.

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