Drivers

	Linux STREAMS (LiS)

Coding LiS Drivers

This document is concerned with the include files and compilation techniques for STREAMS drivers. It is not intended to be a tutorial on the subject of writing STREAMS drivers. Additional resources are available here for reference material. Please consult the Driver/Kernel Interface section for information about how drivers interact with LiS and the Linux kernel for system services.

Header Files

In your C language source file for a STREAMS driver, you should place the following line of code.

#include <sys/stream.h>

This line will include all of the additional header files and function prototypes needed to code a STREAMS driver.

If your STREAMS driver needs to decode the flush bits in M_FLUSH messages then also include the following.

#include <sys/stropts.h>

If your driver uses some of the portable Driver Kernel Interface (DKI) features of LiS you may need to include some additional header files.

Compilation Options

When you compile your STREAMS driver, put the following compiler option on the gcc (cc) command line for each C language file that contains one or the other of the above include lines.

-I/usr/src/LiS/include -D__KERNEL__ -DLINUX

This directive assumes that you used standard installation procedures for LiS so that the name /usr/src/LiS is a symbolic link to the LiS installation directory. The -D's are necessary to give your driver the kernel's view of the header files and to get the Linux version in those cases where alternatives exist.

Driver Prefix

Choose a short prefix to put on the front of all your identifier names and routine names. For example, "xylo_". Thus, the main streamtab entry for your driver would be:


struct streamtab xylo_info =

    {

      &xylo_rinit,                  /* read queue */
      &xylo_winit,                  /* write queue */
      NULL,                         /* mux read queue  */
      NULL                          /* mux write queue */
    };

The open routine would be called "xylo_open(....)" and so on.

The role of this prefix is to allow the LiS configuration process to build some tables that reference certain symbols within your driver. Just to take one example, the "prefixinfo" structure's name must be known to LiS so that it can build the queue structures that are passed to your driver at open time.

Driver Open Routine

It is important that you get the declaration of your driver open routine correct. There was a different prototype for the open routine in SVR 3 versus SVR 4. The Linux STREAMS package uses the SVR 4 style only. The prototype for your open routine should be as follows:

int xylo_open(queue_t *q, dev_t *dev, 
              int oflag, int sflag, cred_t *cred_p);

These prototypes can be found in the DDI/DKI or consult the LiS include file include/sys/LiS/queue.h. Look for the definition of the structure qinit_t.

Driver Registration

Your driver will be automatically registered with the Linux kernel as a character mode special device driver if it is linked in with LiS. The LiS configuration process builds tables that allow LiS to perform this registration function on behalf of your driver. Thus, your STREAMS drivers should not contain any code to register itself as a Linux driver.