HP-UX Reference (11i v2 04/09) - 5 Miscellaneous Topics (vol 9)

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ioctl(5) ioctl(5)

of bytes it was able to read;

• If there is no data available, the read fails and errno is set to [EWOULDBLOCK].

For writes, non-blocking I/O prevents all write requests to that device ﬁle from block-

ing, whether the requests succeed or fail. Such a write request completes in one of

three ways:

• If there is enough space available in the system to buffer all the data, the write

completes successfully, having written out all of the data, and returns the number

of bytes written;

• If there is not enough space in the buffer to write out the entire request, the write

completes successfully, having written as much data as possible, and returns the

number of bytes it was able to write;

• If there is no space in the buffer, the write fails and

errno is set to [EWOULD-

BLOCK].

To prohibit non-blocking I/O from interfering with the

O_NDELAY ﬂag (see open (2)

and fcntl (2)), the functionality of

O_NDELAY always supersedes the functionality of

non-blocking I/O. This means that if

O_NDELAY

is set, the driver performs read

requests in accordance with the deﬁnition of O_NDELAY. When O_NDELAY is not

set, the deﬁnition of non-blocking I/O applies.

The default on open of a device ﬁle is that non-blocking I/O is disabled.

FIOGNBIO For those character device ﬁles which support this command, the integer whose

address is arg is set to 1, if non-blocking I/O is enabled. Otherwise, the integer whose

address is arg is set to 0.

WARNINGS

FIOSSAIOSTAT is similar to 4.2 BSD FIOASYNC, with the addition of provisions for security. FIOG-

SAIOSTAT is of HP origin, complements FIOSSAIOSTAT, and allows saving and restoring system asyn-

chronous I/O TTY state for BSD style job control. FIOSSAIOOWN is similar to 4.2 BSD FIOSETOWN

with the addition of provisions for security.

FIOGSAIOOWN is similar to 4.2 BSD FIOGETOWN. Note

also the difference that the 4.2 BSD version of this functionality used process groups, while the HP-UX

version only uses processes. FIOSNBIO is the same as 4.2 BSD FIONBIO, except that it does not inter-

fere with the AT&T O_NDELAY open and fcntl ﬂag. FIOGNBIO is of HP origin, complements

FIOSNBIO, and allows saving and restoring non-blocking I/O TTY state for BSD-style job control.