Open System Services System Calls Reference Manual (G06.28+)

System Functions (s and S) SPT_WRITEREADX(2)
Use on files opened for nowait I/O
• If the buffer is in an extended data segment, you cannot
deallocate or reduce the size of the extended data seg-
ment before the I/O completes with a call to the Guar-
dian AWAITIOX procedure or is canceled by a call to
the SPT_CANCEL() function or the Guardian CAN-
CELREQ procedure.
• You must not modify the buffer before the I/O completes
with a call to the Guardian AWAITIOX procedure. This
restriction also applies to other processes that might be
sharing the segment. It is the application’s responsibil-
ity to ensure this.
• If the I/O has been initiated with
SPT_WRITEREADX(), the I/O must be completed
with a call to the Guardian AWAITIOX procedure.
• A selectable extended data segment containing the
buffer need not be in use at the time of the call to
AWAITIOX.
• Nowait I/O initiated with SPT_WRITEREADX( ) can
be canceled with a call to SPT_CANCEL() or CAN-
CELREQ. The I/O is canceled if the file is closed
before the I/O completes or if the Guardian AWAITIOX
procedure is called with a positive time limit and
specific file number and the request times out.
Bounds checking
If the extended address of buffer is odd, bounds checking rounds
the address to the next lower word boundary and checks an extra
byte as well. The odd address is used for the transfer.
RETURN VALUES
The SPT_WRITEREADX( ) function returns 0 (zero) upon successful completion. Otherwise,
this function returns a nonzero Guardian file-system error number that indicates the outcome of
the operation.
For information about Guardian file-system error numbers, see the Guardian Procedure Errors
and Messages Manual.
ERRORS
None. This function does not set the errno variable.
RELATED INFORMATION
Functions: SPT_CANCEL(2), SPT_CONTROL(2), SPT_FILE_CLOSE_(2),
SPT_FILE_OPEN_(2), SPT_LOCKFILE(2), SPT_LOCKREC(2), SPT_READLOCKX(2),
SPT_READUPDATELOCKX(2), SPT_READUPDATEX(2), SPT_READX(2),
SPT_SETMODE(2), SPT_UNLOCKFILE(2), SPT_UNLOCKREC(2),
SPT_WRITEUPDATEUNLOCKX(2), SPT_WRITEUPDATEX(2), SPT_WRITEX(2).
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