drbd: Replaced some casts by an union. Improved comments

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

drivers/block/drbd/drbd_int.h

@@ -759,15 +759,18 @@ struct digest_info {
 struct drbd_epoch_entry {
 	struct drbd_work w;
 	struct hlist_node colision;
-	struct drbd_epoch *epoch;
+	struct drbd_epoch *epoch; /* for writes */
 	struct drbd_conf *mdev;
 	struct page *pages;
 	atomic_t pending_bios;
 	unsigned int size;
 	/* see comments on ee flag bits below */
 	unsigned long flags;
 	sector_t sector;
-	u64 block_id;
+	union {
+		u64 block_id;
+		struct digest_info *digest;
+	};
 };
 
 /* ee flag bits.
@@ -1032,10 +1035,10 @@ struct drbd_conf {
 	spinlock_t epoch_lock;
 	unsigned int epochs;
 	enum write_ordering_e write_ordering;
-	struct list_head active_ee; /* IO in progress */
-	struct list_head sync_ee;   /* IO in progress */
+	struct list_head active_ee; /* IO in progress (P_DATA gets written to disk) */
+	struct list_head sync_ee;   /* IO in progress (P_RS_DATA_REPLY gets written to disk) */
 	struct list_head done_ee;   /* send ack */
-	struct list_head read_ee;   /* IO in progress */
+	struct list_head read_ee;   /* IO in progress (any read) */
 	struct list_head net_ee;    /* zero-copy network send in progress */
 	struct hlist_head *ee_hash; /* is proteced by req_lock! */
 	unsigned int ee_hash_s;

drivers/block/drbd/drbd_receiver.c

@@ -2097,7 +2097,7 @@ static int receive_DataRequest(struct drbd_conf *mdev, struct p_header *h)
 		if (drbd_recv(mdev, di->digest, digest_size) != digest_size)
 			goto out_free_e;
 
-		e->block_id = (u64)(unsigned long)di;
+		e->digest = di;
 		if (h->command == P_CSUM_RS_REQUEST) {
 			D_ASSERT(mdev->agreed_pro_version >= 89);
 			e->w.cb = w_e_end_csum_rs_req;
@@ -3769,6 +3769,7 @@ static void drbd_disconnect(struct drbd_conf *mdev)
 	drbd_thread_stop(&mdev->asender);
 	drbd_free_sock(mdev);
 
+	/* wait for current activity to cease. */
 	spin_lock_irq(&mdev->req_lock);
 	_drbd_wait_ee_list_empty(mdev, &mdev->active_ee);
 	_drbd_wait_ee_list_empty(mdev, &mdev->sync_ee);

drivers/block/drbd/drbd_worker.c

@@ -1018,7 +1018,7 @@ int w_e_end_csum_rs_req(struct drbd_conf *mdev, struct drbd_work *w, int cancel)
 
 	drbd_rs_complete_io(mdev, e->sector);
 
-	di = (struct digest_info *)(unsigned long)e->block_id;
+	di = e->digest;
 
 	if (likely((e->flags & EE_WAS_ERROR) == 0)) {
 		/* quick hack to try to avoid a race against reconfiguration.
@@ -1126,7 +1126,7 @@ int w_e_end_ov_reply(struct drbd_conf *mdev, struct drbd_work *w, int cancel)
 	 * the resync lru has been cleaned up already */
 	drbd_rs_complete_io(mdev, e->sector);
 
-	di = (struct digest_info *)(unsigned long)e->block_id;
+	di = e->digest;
 
 	if (likely((e->flags & EE_WAS_ERROR) == 0)) {
 		digest_size = crypto_hash_digestsize(mdev->verify_tfm);