Specifications

Operating System Routines
EXE$READCHK, EXE$READCHKR
EXE$READCHK, EXE$READCHKR
Verify that a process has write access to the pages in the buffer specified in a
$QIO request.
Module
SYSQIOFDT
Input
Location Contents
R0 Virtual address of buffer
R1 Size of transfer in bytes
R3 Address of IRP
Output
Location Contents
R0 Virtual address of buffer (EXE$READCHK), SS$_
NORMAL (EXE$READCHKR), or error status
R1 Size of transfer in bytes
R2 1, indicating a read function
R3 Address of IRP
IRP$W_STS IRP$V_FUNC set, indicating a read function
IRP$L_BCNT Size of transfer in bytes
Synchronization
EXE$READCHK and EXE$READCHKR are called by a driver FDT routine at
IPL$_ASTDEL.
Description
A driver uses either of these routines to check the write accessibility of a
user-specified buffer. A driver typically calls EXE$READCHKR instead of
EXE$READCHK when it must regain control before the request is aborted in the
event the buffer is inaccessible.
EXE$READCHK calls EXE$READCHKR.
EXE$READCHKR performs the following tasks:
• Moves the transfer byte count into IRP$L_BCNT. If the byte count is negative,
it returns SS$_BADPARAM status to its caller.
3–50