ioctl.5 (2010 09)

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, nonblocking I/O prevents all write requests to that device ﬁle from

blocking, 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 nonblocking 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

nonblocking 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 nonblocking I/O applies.

The default on open of a device ﬁle is that nonblocking 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 nonblocking 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.

FIOGSAIOSTAT is of HP origin, complements FIOSSAIOSTAT, and allows saving and restoring system

asynchronous 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 interfere with the AT&T

O_NDELAY

open and fcntl ﬂag.

FIOGNBIO is of HP origin, complements FIOSNBIO, and allows saving and restoring nonblocking I/O

TTY state for BSD-style job control.