Specifications

Operating System Routines
COM$SETATTNAST
Description
A driver FDT routine calls COM$SETATTNAST to service a $QIO request that
specifies a set-attention-AST function.
If the p1 argument of the request contains a zero, COM$SETATTNAST transfers
control to COM$FLUSHATTNS, which disables all ASTs indicated by the PID
and I/O channel number (IRP$W_CHAN). COM$FLUSHATTNS searches through
the AST control block (ACB) list, extracts each identified ACB, deallocates, and
returns to the caller of COM$SETATTNAST.
If the p1 argument of the request contains the address of an AST routine,
COM$SETATTNAST decrements PCB$W_ASTCNT and allocates an expanded
AST control block (ACB) that contains the following information:
• Spinlock index SPL$C_QUEUEAST
• Address of the AST routine (as specified in p1)
• AST parameter (as specified in p2)
• Access mode (as specified in p3 and maximized against the current process’s
access mode and bit ACB$V_QUOTA set to indicate a process-requested AST)
• Number of the assigned I/O channel
• PID of the requesting process
COM$SETATTNAST links the ACB to the start of the specified linked list
of ACBs located in a UCB extension area. (See Section 1.19 for information
on defining an extension to a UCB.) COM$DELATTNAST can later use the
expanded ACB to fork to IPL$_QUEUEAST, at which IPL it reformats the block
into a standard ACB.
If the process exceeds buffered I/O or AST quotas, or if there is no memory
available to allocate the expanded ACB, COM$SETATTNAST restores PCB$W_
ASTCNT to its original value and transfers control to EXE$ABORTIO with error
status.
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