md/raid1: add documentation to r1_private_data_s data structure.

	mddev_t			*mddev;

	mirror_info_t		*mirrors;

	int			raid_disks;

	/* When choose the best device for a read (read_balance())

	 * we try to keep sequential reads one the same device

	 * using 'last_used' and 'next_seq_sect'

	 */

	int			last_used;

	sector_t		next_seq_sect;

	/* During resync, read_balancing is only allowed on the part

	 * of the array that has been resynced.  'next_resync' tells us

	 * where that is.

	 */

	sector_t		next_resync;

	spinlock_t		device_lock;

	/* list of 'r1bio_t' that need to be processed by raid1d, whether

	 * to retry a read, writeout a resync or recovery block, or

	 * anything else.

	 */

	struct list_head	retry_list;

	/* queue pending writes and submit them on unplug */

	struct bio_list		pending_bio_list;

	/* for use when syncing mirrors: */

	/* queue pending writes to be submitted on unplug */

	struct bio_list		pending_bio_list;

	/* for use when syncing mirrors:

	 * We don't allow both normal IO and resync/recovery IO at

	 * the same time - resync/recovery can only happen when there

	 * is no other IO.  So when either is active, the other has to wait.

	 * See more details description in raid1.c near raise_barrier().

	 */

	wait_queue_head_t	wait_barrier;

	spinlock_t		resync_lock;

	int			nr_pending;

	int			nr_waiting;

	int			nr_queued;

	int			barrier;

	sector_t		next_resync;

	int			fullsync;  /* set to 1 if a full sync is needed,

					    * (fresh device added).

	/* Set to 1 if a full sync is needed, (fresh device added).

	 * Cleared when a sync completes.

	 */

	int			recovery_disabled; /* when the same as

						    * mddev->recovery_disabled

						    * we don't allow recovery

						    * to be attempted as we

						    * expect a read error

	int			fullsync;

	/* When the same as mddev->recovery_disabled we don't allow

	 * recovery to be attempted as we expect a read error.

	 */

	int			recovery_disabled;

	wait_queue_head_t	wait_barrier;

	/* poolinfo contains information about the content of the

	 * mempools - it changes when the array grows or shrinks

	 */

	struct pool_info	*poolinfo;

	mempool_t *r1bio_pool;

	mempool_t *r1buf_pool;

	/* temporary buffer to synchronous IO when attempting to repair

	 * a read error.

	 */

	struct page		*tmppage;

	mempool_t *r1bio_pool;

	mempool_t *r1buf_pool;

	/* When taking over an array from a different personality, we store

	 * the new thread here until we fully activate the array.