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     config_intrhook — schedule a function to be run after interrupts have been enabled, but
     before root is mounted


     #include <sys/kernel.h>

     config_intrhook_establish(struct intr_config_hook *hook);

     config_intrhook_disestablish(struct intr_config_hook *hook);


     The config_intrhook_establish() function schedules a function to be run after interrupts
     have been enabled, but before root is mounted.  If the system has already passed this point
     in its initialization, the function is called immediately.

     The config_intrhook_disestablish() function removes the entry from the hook queue.

     Before root is mounted, all the previously established hooks are run.  The boot process is
     then stalled until all handlers remove their hook from the hook queue with
     config_intrhook_disestablish().  The boot process then proceeds to attempt to mount the root
     file system.  Any driver that can potentially provide devices they wish to be mounted as
     root must use either this hook, or probe all these devices in the initial probe.  Since
     interrupts are disabled during the probe process, many drivers need a method to probe for
     devices with interrupts enabled.

     The requests are made with the intr_config_hook structure.  This structure is defined as

     struct intr_config_hook {
             TAILQ_ENTRY(intr_config_hook) ich_links;/* Private */
             void    (*ich_func)(void *arg);         /* function to call */
             void    *ich_arg;                       /* Argument to call */

     Storage for the intr_config_hook structure must be provided by the driver.  It must be
     stable from just before the hook is established until after the hook is disestablished.

     Specifically, hooks are run at SI_SUB_INT_CONFIG_HOOKS(), which is immediately after the
     scheduler is started, and just before the root file system device is discovered.


     A zero return value means the hook was successfully added to the queue (with either deferred
     or immediate execution).  A non-zero return value means the hook could not be added to the
     queue because it was already on the queue.




     These functions were introduced in FreeBSD 3.0 with the CAM subsystem, but are available for
     any driver to use.


     The functions were written by Justin Gibbs <>.  This manual page was
     written by M. Warner Losh <>.