update block_device_operations documentation

--------------------------- block_device_operations -----------------------

prototypes:

	int (*open) (struct inode *, struct file *);

	int (*release) (struct inode *, struct file *);

	int (*ioctl) (struct inode *, struct file *, unsigned, unsigned long);

	int (*open) (struct block_device *, fmode_t);

	int (*release) (struct gendisk *, fmode_t);

	int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);

	int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);

	int (*direct_access) (struct block_device *, sector_t, void **, unsigned long *);

	int (*media_changed) (struct gendisk *);

	void (*unlock_native_capacity) (struct gendisk *);

	int (*revalidate_disk) (struct gendisk *);

	int (*getgeo)(struct block_device *, struct hd_geometry *);

	void (*swap_slot_free_notify) (struct block_device *, unsigned long);

locking rules:

			BKL	bd_sem

open:			yes	yes

release:		yes	yes

ioctl:			yes	no

			BKL	bd_mutex

open:			no	yes

release:		no	yes

ioctl:			no	no

compat_ioctl:		no	no

direct_access:		no	no

media_changed:		no	no

unlock_native_capacity:	no	no

revalidate_disk:	no	no

getgeo:			no	no

swap_slot_free_notify:	no	no	(see below)

media_changed, unlock_native_capacity and revalidate_disk are called only from

check_disk_change().

swap_slot_free_notify is called with swap_lock and sometimes the page lock

held.

The last two are called only from check_disk_change().

--------------------------- file_operations -------------------------------

prototypes: