Open System Services System Calls Reference Manual (G06.29+, H06.08+, J06.03+)

System Functions (n - p) open64(2)
The open fails if any of these conditions is true:
• The file supports enforced record locks, and another process has locked a
portion of the file.
• The file does not allow write access.
• The oflag parameter also specifies the O_RDONLY flag.
If the oflag parameter also specifies the O_SYNC flag, the truncation is a syn-
chronous update.
A program can request some control over when updates should be made per-
manent for a regular file opened for write access.
The file status flags that define the initial state of the open file are:
O_APPEND Open the file only for append access. If set, the file pointer is set to the end of
the file before each write.
This flag is ignored for Telserv terminal devices.
O_NONBLOCK
Open the file for nonblocked access. If set, the call to open64() does not block,
and subsequent read() or write() operations on the file are nonblocking.
When opening a regular disk file or an OSS directory, the O_NONBLOCK flag
is ignored.
Calling the open64() function with the O_NONBLOCK flag for FIFO files and
for character special devices that support nonblocking opens is supported.
Calling the open64() function with the O_NONBLOCK flag is supported for
Telserv terminal devices (tty) as listed:
• For a static window, the open operation is always allowed; it finishes
when the connection is established.
• For a dynamic window, the open operation is allowed only if a connec-
tion is already established.
Calling the open64() function with the O_NONBLOCK flag is supported for
OSSTTY terminal devices (ztty). OSSTTY devices support only three static
windows, one each for #stdin, #stdout, and #stderr.
O_SYNC The O_SYNC flag provides a high level of data integrity for writes to regular
files. For HP NonStop systems, you can use the OSS Monitor to select one of
multiple levels of fault tolerance. For more information, see the discussion of the
FTIOMODE attribute in the Open System Services Management and Operations
Guide.
General Notes on oflag Parameter Flag Values
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