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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 follows:

     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 ⟨⟩.