Open System Services System Calls Reference Manual (G06.28+, H06.05+)

SPT_WRITEX(2) OSS System Calls Reference Manual
Nowait I/O and SPT_WRITEX() calls
If a nowait SPT_WRITE () call is executed, count_written has
no meaning and can be omitted. The count of the number of
bytes written is obtained when the I/O operation completes
through the count-transferred parameter of the Guardian
AWAITIOX procedure.
The SPT_WRITEX() function must complete with a
corresponding call to the Guardian AWAITIOX procedure when
used with a file that is opened for nowait I/O.
Do not change the contents of the data buffer between the initia-
tion and completion of a nowait write operation. A retry can
copy the data again from the user buffer and cause the wrong
data to be written. Avoid sharing a buffer between a write and
another I/O operation because the contents of the write buffer
might change before the write is completed.
Disk File Considerations
Large data transfers for unstructured files using default mode
Default mode allows I/O sizes for unstructured files to be as
large as 56KB (57,344), excepting writes to audited files, if the
unstructured buffer size (or block size) is 4KB (4096). Default
mode refers to the mode of the file if SPT_SETMODE() func-
tion 141 is not invoked.
For an unstructured file with an unstructured buffer size other
than 4KB, DP2 automatically adjusts the unstructured buffer
size to 4KB, if possible, when an I/O larger than 4KB is
attempted. However, this adjustment is not possible for files that
have extents with an odd number of pages; in such cases, an I/O
over 4KB is not possible. The switch to a different unstructured
buffer size will have a transient performance impact, so HP
recommends that the size be initially set to 4KB, which is the
default. Transfer sizes over 4KB are not supported in default
mode for unstructured access to structured files.
Large data transfers using SPT_SETMODE(141)
You can use SPT_SETMODE() function 141 to enable large
data transfers (more than 4096 bytes) for files opened with
unstructured access, regardless of unstructured buffer size.
When you use SPT_SETMODE(141) to enable large data
transfers, you can to specify up to 56K (57344) bytes for the
write_count parameter. See the description of SETMODE func-
tions in the Guardian Procedure Calls Reference Manual.
File is locked
If you call SPT_WRITEX() is made and the file is locked
through a file number other than that supplied in the call, the call
is rejected with Guardian file-system error 73 (file is
locked).
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