HP-UX Reference (11i v1 05/09) - 5 Miscellaneous Topics (vol 9)

ioctl(5) ioctl(5)

• If there is not enough data available to satisfy the entire request, the read completes suc-

cessfully, having read as much data as possible, and returns the number 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 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

EWOULDBLOCK.

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. FIOGSAIOSTAT is

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 provi-

sions 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 non-blocking

I/O TTY state for BSD-style job control.