stream.2 (2010 09)

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stream(2) stream(2)

A write to a STREAMS device may fail for one or more of the following STREAMS-speciﬁc conditions:

[EAGAIN] The

O_NONBLOCK ﬂag is set, and the stream cannot accept write() data because

it is ﬂow controlled.

[EINVAL] The

write() function attempts to write to a stream that is linked below a multi-

plexor.

[ENXIO] A hangup occurs on a stream while the

write() function is writing to the stream.

[ERANGE] The nbytes parameter is not within the allowable range.

The

write() system call will also fail if an error message has been received at the stream head of the

stream to which the write() function is attempting to write. In this case, the function returns with

errno set to the value included in the error message.

Ioctl Enhancements

Refer to the streamio (7) man page for a description of STREAMS

ioctl() functionality.

Select Enhancements

The

select() system call checks the status of STREAMS devices.

select() does not provide as

much information for STREAMS devices as

poll(). A program calls

select() so that it can wait for

events on both STREAMS and non-STREAMS devices. If

select() returns an event for a STREAMS

device, the program can call poll() to get more information. Refer to the poll (2) man page for more

information about poll().

select() returns a read event if a poll() POLLIN, POLLERR, POLLNVAL or POLLHUP event exists

on the stream. In other words, select() returns a read event if a normal or priority band message is

waiting to be read, if a read error exists at the stream head, if a write error exists at the stream head, if

the stream is linked under a multiplexor, or if a hang-up has occurred.

select() returns a write event if a poll() POLLOUT, POLLWRNORM, POLLERR,orPOLLNVAL

event

exists on the stream. This means that

select() returns a write event if normal data can be written

without blocking because of ﬂow control, a read error exists at the stream head, a write error exists at the

stream head, or the stream is linked under a multiplexor.

select() returns an exception event if a poll() POLLPRI event exists on the stream. More

speciﬁcally, select() returns an exception event if a high-priority message is waiting to be read.

Signal Enhancements

A new signal,

SIGPOLL, has been added for STREAMS. Processes register to receive a

SIGPOLL signal

for events that occur on a STREAMS device (see the signal (2) man page and

I_SETSIG in the

streamio (7) man page). The default action is to ignore the signal, not to terminate the process.