In 2.5 (the bug's been there since 2.5.42), rmmod:ing a
modular IDE subdriver like ide-cd or ide-scsi and then
rebooting causes an oops in device_shutdown(). This is because
the IDE layer doesn't reset the drive->gendev.driver pointer
that it previously set up to point to data structures in the
subdriver module. device_shutdown() sees a non-NULL ->driver,
dereferences it, and oopses.

The patch below for 2.5.54 fixes two generic bugs related to
unloading of modular IDE subdrivers, and one specific to ide-scsi:

1. ata_attach() needs to set drive->gendev.driver = NULL
   when no specific driver claims the drive. This prevents a
   drive previously owned by a subdriver module from keeping
   its ->gendev.driver pointing into that module.

2. ide_unregister_driver() needs to unregister &driver->gen_driver;
   this is to balance the corresponding register call in
   ide_register_driver(). [This part of the patch is originally
   by Patrick Mochel.]

3. ide-scsi.c abuses ide_driver_t's busy field as a counter
   while the field in fact is a single-bit boolean. This causes
   the busyness of the driver to be incorrect while the driver
   is active. (From my recent patch for 2.4.20-ac2/2.4.21-pre2.)