Specifications

Operating System Routines

IOC$CANCELIO

Conditionally marks a UCB so that its current I/O request will be canceled.

Module

IOSUBNPAG

Input

Location Contents

R2 Channel index number

R3 Address of IRP

R4 Address of current PCB

R5 Address of UCB

IRP$L_PID Process identiﬁcation of the process that queued the

I/O request

IRP$W_CHAN I/O request channel index number

PCB$L_PID Process identiﬁcation of the process that requested

cancellation

UCB$L_STS UCB$V_BSY set if device is busy, clear if device is

idle

Output

Location Contents

UCB$L_STS UCB$V_CANCEL set if the I/O request should be

canceled

Synchronization

IOC$CANCELIO executes at its caller’s IPL, obtains no spinlocks, and returns

control to its caller at the caller’s IPL. It is usually called by EXE$CANCEL (if

speciﬁed in the DDT as the driver’s cancel-I/O routine) at fork IPL, holding the

corresponding fork lock in a multiprocessing environment.

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