Common ioctl Interfaces

Many ioctl operations are common to a class of STREAMS drivers or STREAMS modules. Modules that deal with terminals usually implement a subset of the termio(7I) ioctls. Similarly, drivers that deal with audio devices usually implement a subset of the audio(7I) interfaces.

Because no data structures have changed size as a result of the LP64 data model for either termio(7I) or audio(7I), you do no need to use any of the structure macros to decode any of these ioctls.

FIORDCHK

The FIORDCHK ioctl returns a count (in bytes) of the number of bytes to be read as the return value. Although FIORDCHK should be able to return more than MAXINT bytes, it is constrained to returning an int by the type of the ioctl(2) function.

FIONREAD

The FIONREAD ioctl returns the number of data bytes (in all data messages queued) in the location pointed to by the arg parameter. The ioctl returns a 32-bit quantity for both 32-bit and 64-bit application., Therefore, code that passes the address of a long variable needs to be changed to pass an int variable for 64-bit applications.

I_NREAD

The I_NREAD ioctl (streamio(7I)) is an informational ioctl that counts the data bytes as well as the number of messages in the stream head read queue. The number of data bytes is returned in the location pointed to by the arg parameter of the ioctl. The number of messages in the stream head read queue is returned as the return value of the ioctl.

Like FIONREAD, the arg parameter to the I_NREAD ioctl should be a pointer to an int, not a long. And, like FIORDCHK, the return value is constrained to be less than or equal to MAXINT bytes, even if more data is available.

signal Message

STREAMS modules and drivers send signals to application processes through a special signal message. If the signal specified by the module or driver is not SIGPOLL (see signal(3C)), the signal is delivered to the process group associated with the stream. If the signal is SIGPOLL, the signal is only sent to processes that have registered for the signal by using the I_SETSIG ioctl(2).

Modules or drivers use an M_SIG message to insert an explicit in-band signal into a message stream. For example, a message can be sent to the application process immediately before a particular service interface message. When the M_SIG message reaches the head of the stream read queue, a signal is generated and the M_SIG message is removed. The service interface message is the next message to be processed by the user. (The M_SIG message is usually defined as part of the service interface of the driver or module.)