FreeBSD Device Drivers

A More Complex Synchronization Problem

Example 4-1 is a complete character driver that lets you manipulate a doubly linked list through its d_ioctl function. You can add or remove an item from the list, determine whether an item is on the list, or print every item on the list. Example 4-1 also contains some synchronization problems.

Note

Take a quick look at this code and try to identify the synchronization problems.

Example 4-1. race.c

#include <sys/param.h>
  #include <sys/module.h>
  #include <sys/kernel.h>
  #include <sys/systm.h>

  #include <sys/conf.h>
  #include <sys/uio.h>
  #include <sys/malloc.h>
  #include <sys/ioccom.h>
  #include <sys/queue.h>
  #include "race_ioctl.h"

  MALLOC_DEFINE(M_RACE, "race", "race object");

  struct race_softc {
         LIST_ENTRY(race_softc) ...