FreeBSD Device Drivers

Implementing Mutexes

Example 4-3 is a revision of Example 4-1 that uses a mutex to serialize access to race_list.

Note

To save space, the functions race_ioctl, race_new, race_find, and race_destroy aren’t listed here, as they haven’t been changed.

Example 4-3. race_mtx.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 <sys/lock.h>
  #include <sys/mutex.h>
  #include "race_ioctl.h"

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

  struct race_softc {
          LIST_ENTRY(race_softc) list;
          int unit;
  };

  static LIST_HEAD(, race_softc) race_list = LIST_HEAD_INITIALIZER(&race_list);
 static struct mtx race_mtx; ...