NAME

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

SYNOPSIS

     #include <sys/kernel.h>

     typedef void (*ich_func_t)(void *arg);

     int
     config_intrhook_establish(struct intr_config_hook *hook);

     void
     config_intrhook_disestablish(struct intr_config_hook *hook);

     void
     config_intrhook_oneshot(ich_func_t func, void *arg);

DESCRIPTION

     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.

     The config_intrhook_oneshot() function schedules a function to be run as described for
     config_intrhook_establish(); the entry is automatically removed from the hook queue after that function
     runs.  This is appropriate when additional device configuration must be done after interrupts are enabled,
     but there is no need to stall the boot process after that.  This function allocates memory using M_WAITOK;
     do not call this while holding any non-sleepable locks.

     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 */
             ich_func_t      ich_func;               /* 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.

RETURN VALUES

     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.

SEE ALSO

     DEVICE_ATTACH(9)

HISTORY

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

AUTHORS

     The functions were written by Justin Gibbs <gibbs@FreeBSD.org>.  This manual page was written by M. Warner
     Losh <imp@FreeBSD.org>.