STREAMS ioctl Issues

Regular device drivers have user context in the ioctl(9E) call. However, in a STREAMS driver or module, the only guarantee of user context is in the open(9E) and close(9E) routines. Some indication of the calling context where data is used is therefore necessary.

The notion of data models as well as new macros for handling data structure access are discussed in Writing Device Drivers. A STREAMS driver or module writer should use these flags and macros when dealing with structures that change size between data models.

A flag value that represents the data model of the entity invoking the operation has been added to the ioc_flag field of the iocblk(9S) structure, the cq_flag of the copyreq(9S) structure, and the cp_flag of the copyresp(9S) structure.

The data model flag is one of these possibilities:

IOC_ILP32




IOC_LP64

In addition, IOC_NATIVE is conditionally defined to match the data model of the kernel implementation.

By looking at the data model flag field of the relevant iocblk(9S), copyreq(9S), or copyresp(9S) structures, the STREAMS module can determine the best method of handling the data.

The layout of the iocblk, copyreq, and copyresp structures is different between the 32-bit and 64-bit kernels. Be cautious of any data structure overloading in the cp_private, cq_private, or cq_filler fields because alignment has changed.