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     dev_clone, drain_dev_clone_events — eventhandler for name-based device
     cloning in devfs


     #include <sys/param.h>
     #include <sys/conf.h>

     clone_handler(void *arg, struct ucred *cr, char *name, int namelen,
         struct cdev **dev);

     EVENTHANDLER_REGISTER(dev_clone, clone_handler, arg, priority);



     A device driver may register a listener that will be notified each time a
     name lookup on the devfs(5) mount point fails to find the vnode.  A
     listener shall be registered for the dev_clone event.  When called, it is
     supplied with the first argument arg that was specified at handler
     registration time, appropriate credentials cr, and a name name of length
     namelen that we look for.  If the handler decides that the name is
     appropriate and wants to create the device that will be associated with
     the name, it should return it to devfs in the dev argument.

     The drain_dev_clone_events() function is a barrier.  It is guaranteed
     that all calls to eventhandlers for dev_clone that were started before
     drain_dev_clone_events() call, are finished before it returns control.


     devfs(5), namei(9)