Guardian Procedure Calls Reference Manual

Returned Value
INT
A file-system error code that indicates the outcome of the call.
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• The address of a parameter refers to the selectable segment area but no selectable segment is in use at
the time of the call.
• The address of a parameter references a privileged segment and the caller is not privileged.
• The file system cannot use the user's segment when needed.
The write-buffer and read-buffer memory are overlapping each other partially (however, if both the
buffers point to the same address, it is acceptable).
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Considerations
• EpTAL callers must set toggle
EpTAL callers must set the toggle _64BIT_CALLS before sourcing the FILE_WRITEREAD64_
procedure section from EXTDECS.
• Waited I/O READ
If a waited I/O FILE_WRITEREAD[64]_ is executed, the count-read parameter indicates
the number of bytes actually read.
• Nowait I/O READ
FILE_WRITEREAD_ must complete with a call to the AWAITIOX procedure or the
FILE_COMPLETE_ procedure when used with a file that is opened nowait; FILE_WRITEREAD64_
must complete with a call to the FILE_AWAITIO64_ procedure or the FILE_COMPLETEL_
procedure when used with a file that is opened nowait.
If a nowait I/O FILE_WRITEREAD[64]_ is executed, the count-read parameter has no
meaning and can be omitted. The count of the number of bytes read is obtained when the
FILE_WRITEREAD_ I/O operation completes through the count-transferred parameter
of the AWAITIOX or FILE_COMPLETE_ procedure. The count of the number of bytes read is
obtained when the FILE_WRITEREAD64_ I/O operation completes through the
count-transferred parameter of the FILE_AWAITIO64_ or the FILE_COMPLETEL_
procedure.
You must not change the contents of the data buffers between the initiation and completion
of a nowait FILE_WRITEREAD[64]_ operation. This is because a retry can copy the data again
from the write-buffer and cause the wrong data to be written.
You must avoid sharing a buffer between a FILE_WRITEREAD[64]_ and another I/O operation
because this creates the possibility of changing the contents of the data buffer before the write
operation is completed.
• Buffer considerations
The write-buffer, read-buffer, and count-transferred may be in the user
stack or in an extended data segment. The buffers and count transferred cannot be in the
user code space.
◦
◦ If the write-buffer, read-buffer, or count-transferred is in a selectable
extended data segment, the segment must be in use at the time of the call. Flat segments
allocated by a process are always accessible to the process.
◦ If the file is opened for nowait I/O, and buffer is in an extended data segment, you cannot
deallocate or reduce the size of the extended data segment before the FILE_WRITEREAD_
I/O operation completes with a call to the AWAITIOX or FILE_COMPLETE_ procedure
or the call is canceled by a call to CANCEL or CANCELREQ, or the FILE_WRITEREAD64_
534 Guardian Procedure Calls (F)