diff --git a/Documentation/DocBook/tracepoint.tmpl b/Documentation/DocBook/tracepoint.tmpl
index 8bca1d5..e8473ea 100644
--- a/Documentation/DocBook/tracepoint.tmpl
+++ b/Documentation/DocBook/tracepoint.tmpl
@@ -16,6 +16,15 @@
      </address>
     </affiliation>
    </author>
+   <author>
+    <firstname>William</firstname>
+    <surname>Cohen</surname>
+    <affiliation>
+     <address>
+      <email>wcohen@redhat.com</email>
+     </address>
+    </affiliation>
+   </author>
   </authorgroup>
 
   <legalnotice>
@@ -91,4 +100,8 @@
 !Iinclude/trace/events/signal.h
   </chapter>
 
+  <chapter id="block">
+   <title>Block IO</title>
+!Iinclude/trace/events/block.h
+  </chapter>
 </book>
diff --git a/Documentation/block/biodoc.txt b/Documentation/block/biodoc.txt
index 6fab97e..508b5b2 100644
--- a/Documentation/block/biodoc.txt
+++ b/Documentation/block/biodoc.txt
@@ -1162,8 +1162,8 @@
 
 As mentioned, there is no virtual mapping of a bio. For DMA, this is
 not a problem as the driver probably never will need a virtual mapping.
-Instead it needs a bus mapping (pci_map_page for a single segment or
-use blk_rq_map_sg for scatter gather) to be able to ship it to the driver. For
+Instead it needs a bus mapping (dma_map_page for a single segment or
+use dma_map_sg for scatter gather) to be able to ship it to the driver. For
 PIO drivers (or drivers that need to revert to PIO transfer once in a
 while (IDE for example)), where the CPU is doing the actual data
 transfer a virtual mapping is needed. If the driver supports highmem I/O,
diff --git a/block/Kconfig b/block/Kconfig
index 62a5921..f9e89f4 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -78,8 +78,9 @@
 	Protection.  If in doubt, say N.
 
 config BLK_CGROUP
-	tristate
+	tristate "Block cgroup support"
 	depends on CGROUPS
+	depends on CFQ_GROUP_IOSCHED
 	default n
 	---help---
 	Generic block IO controller cgroup interface. This is the common
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 31e7a93..4c4700d 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -8,6 +8,7 @@
 #include <linux/blkdev.h>
 #include <linux/bootmem.h>	/* for max_pfn/max_low_pfn */
 #include <linux/gcd.h>
+#include <linux/lcm.h>
 #include <linux/jiffies.h>
 
 #include "blk.h"
@@ -461,16 +462,6 @@
 }
 EXPORT_SYMBOL(blk_queue_stack_limits);
 
-static unsigned int lcm(unsigned int a, unsigned int b)
-{
-	if (a && b)
-		return (a * b) / gcd(a, b);
-	else if (b)
-		return b;
-
-	return a;
-}
-
 /**
  * blk_stack_limits - adjust queue_limits for stacked devices
  * @t:	the stacking driver limits (top device)
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 2ae2cb3..4426739 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -106,6 +106,19 @@
 	return queue_var_show(max_sectors_kb, (page));
 }
 
+static ssize_t queue_max_segments_show(struct request_queue *q, char *page)
+{
+	return queue_var_show(queue_max_segments(q), (page));
+}
+
+static ssize_t queue_max_segment_size_show(struct request_queue *q, char *page)
+{
+	if (test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags))
+		return queue_var_show(queue_max_segment_size(q), (page));
+
+	return queue_var_show(PAGE_CACHE_SIZE, (page));
+}
+
 static ssize_t queue_logical_block_size_show(struct request_queue *q, char *page)
 {
 	return queue_var_show(queue_logical_block_size(q), page);
@@ -280,6 +293,16 @@
 	.show = queue_max_hw_sectors_show,
 };
 
+static struct queue_sysfs_entry queue_max_segments_entry = {
+	.attr = {.name = "max_segments", .mode = S_IRUGO },
+	.show = queue_max_segments_show,
+};
+
+static struct queue_sysfs_entry queue_max_segment_size_entry = {
+	.attr = {.name = "max_segment_size", .mode = S_IRUGO },
+	.show = queue_max_segment_size_show,
+};
+
 static struct queue_sysfs_entry queue_iosched_entry = {
 	.attr = {.name = "scheduler", .mode = S_IRUGO | S_IWUSR },
 	.show = elv_iosched_show,
@@ -355,6 +378,8 @@
 	&queue_ra_entry.attr,
 	&queue_max_hw_sectors_entry.attr,
 	&queue_max_sectors_entry.attr,
+	&queue_max_segments_entry.attr,
+	&queue_max_segment_size_entry.attr,
 	&queue_iosched_entry.attr,
 	&queue_hw_sector_size_entry.attr,
 	&queue_logical_block_size_entry.attr,
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index dee9d93..8d5a2f2 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -47,6 +47,7 @@
 #define CFQ_SERVICE_SHIFT       12
 
 #define CFQQ_SEEK_THR		(sector_t)(8 * 100)
+#define CFQQ_CLOSE_THR		(sector_t)(8 * 1024)
 #define CFQQ_SECT_THR_NONROT	(sector_t)(2 * 32)
 #define CFQQ_SEEKY(cfqq)	(hweight32(cfqq->seek_history) > 32/8)
 
@@ -1660,9 +1661,9 @@
 }
 
 static inline int cfq_rq_close(struct cfq_data *cfqd, struct cfq_queue *cfqq,
-			       struct request *rq, bool for_preempt)
+			       struct request *rq)
 {
-	return cfq_dist_from_last(cfqd, rq) <= CFQQ_SEEK_THR;
+	return cfq_dist_from_last(cfqd, rq) <= CFQQ_CLOSE_THR;
 }
 
 static struct cfq_queue *cfqq_close(struct cfq_data *cfqd,
@@ -1689,7 +1690,7 @@
 	 * will contain the closest sector.
 	 */
 	__cfqq = rb_entry(parent, struct cfq_queue, p_node);
-	if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq, false))
+	if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq))
 		return __cfqq;
 
 	if (blk_rq_pos(__cfqq->next_rq) < sector)
@@ -1700,7 +1701,7 @@
 		return NULL;
 
 	__cfqq = rb_entry(node, struct cfq_queue, p_node);
-	if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq, false))
+	if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq))
 		return __cfqq;
 
 	return NULL;
@@ -3103,7 +3104,7 @@
 	 * if this request is as-good as one we would expect from the
 	 * current cfqq, let it preempt
 	 */
-	if (cfq_rq_close(cfqd, cfqq, rq, true))
+	if (cfq_rq_close(cfqd, cfqq, rq))
 		return true;
 
 	return false;
diff --git a/drivers/block/DAC960.c b/drivers/block/DAC960.c
index 459f1bc..c5f22bb 100644
--- a/drivers/block/DAC960.c
+++ b/drivers/block/DAC960.c
@@ -2533,7 +2533,6 @@
   	Controller->RequestQueue[n] = RequestQueue;
   	blk_queue_bounce_limit(RequestQueue, Controller->BounceBufferLimit);
   	RequestQueue->queuedata = Controller;
-  	blk_queue_max_hw_segments(RequestQueue, Controller->DriverScatterGatherLimit);
 	blk_queue_max_segments(RequestQueue, Controller->DriverScatterGatherLimit);
 	blk_queue_max_hw_sectors(RequestQueue, Controller->MaxBlocksPerCommand);
 	disk->queue = RequestQueue;
diff --git a/drivers/block/drbd/drbd_actlog.c b/drivers/block/drbd/drbd_actlog.c
index 17956ff..43e57f39 100644
--- a/drivers/block/drbd/drbd_actlog.c
+++ b/drivers/block/drbd/drbd_actlog.c
@@ -536,7 +536,9 @@
 	put_ldev(mdev);
 }
 
+/* sector to word */
 #define S2W(s)	((s)<<(BM_EXT_SHIFT-BM_BLOCK_SHIFT-LN2_BPL))
+
 /* activity log to on disk bitmap -- prepare bio unless that sector
  * is already covered by previously prepared bios */
 static int atodb_prepare_unless_covered(struct drbd_conf *mdev,
@@ -546,13 +548,20 @@
 {
 	struct bio *bio;
 	struct page *page;
-	sector_t on_disk_sector = enr + mdev->ldev->md.md_offset
-				      + mdev->ldev->md.bm_offset;
+	sector_t on_disk_sector;
 	unsigned int page_offset = PAGE_SIZE;
 	int offset;
 	int i = 0;
 	int err = -ENOMEM;
 
+	/* We always write aligned, full 4k blocks,
+	 * so we can ignore the logical_block_size (for now) */
+	enr &= ~7U;
+	on_disk_sector = enr + mdev->ldev->md.md_offset
+			     + mdev->ldev->md.bm_offset;
+
+	D_ASSERT(!(on_disk_sector & 7U));
+
 	/* Check if that enr is already covered by an already created bio.
 	 * Caution, bios[] is not NULL terminated,
 	 * but only initialized to all NULL.
@@ -588,7 +597,7 @@
 
 	offset = S2W(enr);
 	drbd_bm_get_lel(mdev, offset,
-			min_t(size_t, S2W(1), drbd_bm_words(mdev) - offset),
+			min_t(size_t, S2W(8), drbd_bm_words(mdev) - offset),
 			kmap(page) + page_offset);
 	kunmap(page);
 
@@ -597,7 +606,7 @@
 	bio->bi_bdev = mdev->ldev->md_bdev;
 	bio->bi_sector = on_disk_sector;
 
-	if (bio_add_page(bio, page, MD_SECTOR_SIZE, page_offset) != MD_SECTOR_SIZE)
+	if (bio_add_page(bio, page, 4096, page_offset) != 4096)
 		goto out_put_page;
 
 	atomic_inc(&wc->count);
diff --git a/drivers/block/drbd/drbd_bitmap.c b/drivers/block/drbd/drbd_bitmap.c
index b61057e..f58e765 100644
--- a/drivers/block/drbd/drbd_bitmap.c
+++ b/drivers/block/drbd/drbd_bitmap.c
@@ -66,7 +66,7 @@
 	size_t   bm_words;
 	size_t   bm_number_of_pages;
 	sector_t bm_dev_capacity;
-	struct semaphore bm_change; /* serializes resize operations */
+	struct mutex bm_change; /* serializes resize operations */
 
 	atomic_t bm_async_io;
 	wait_queue_head_t bm_io_wait;
@@ -114,7 +114,7 @@
 		return;
 	}
 
-	trylock_failed = down_trylock(&b->bm_change);
+	trylock_failed = !mutex_trylock(&b->bm_change);
 
 	if (trylock_failed) {
 		dev_warn(DEV, "%s going to '%s' but bitmap already locked for '%s' by %s\n",
@@ -125,7 +125,7 @@
 		    b->bm_task == mdev->receiver.task ? "receiver" :
 		    b->bm_task == mdev->asender.task  ? "asender"  :
 		    b->bm_task == mdev->worker.task   ? "worker"   : "?");
-		down(&b->bm_change);
+		mutex_lock(&b->bm_change);
 	}
 	if (__test_and_set_bit(BM_LOCKED, &b->bm_flags))
 		dev_err(DEV, "FIXME bitmap already locked in bm_lock\n");
@@ -147,7 +147,7 @@
 
 	b->bm_why  = NULL;
 	b->bm_task = NULL;
-	up(&b->bm_change);
+	mutex_unlock(&b->bm_change);
 }
 
 /* word offset to long pointer */
@@ -295,7 +295,7 @@
 	if (!b)
 		return -ENOMEM;
 	spin_lock_init(&b->bm_lock);
-	init_MUTEX(&b->bm_change);
+	mutex_init(&b->bm_change);
 	init_waitqueue_head(&b->bm_io_wait);
 
 	mdev->bitmap = b;
diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index d9301e8..e5e86a7 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -261,6 +261,9 @@
 		[P_OV_REQUEST]          = "OVRequest",
 		[P_OV_REPLY]            = "OVReply",
 		[P_OV_RESULT]           = "OVResult",
+		[P_CSUM_RS_REQUEST]     = "CsumRSRequest",
+		[P_RS_IS_IN_SYNC]	= "CsumRSIsInSync",
+		[P_COMPRESSED_BITMAP]   = "CBitmap",
 		[P_MAX_CMD]	        = NULL,
 	};
 
@@ -443,13 +446,18 @@
 	char csums_alg[SHARED_SECRET_MAX];
 } __packed;
 
+enum drbd_conn_flags {
+	CF_WANT_LOSE = 1,
+	CF_DRY_RUN = 2,
+};
+
 struct p_protocol {
 	struct p_header head;
 	u32 protocol;
 	u32 after_sb_0p;
 	u32 after_sb_1p;
 	u32 after_sb_2p;
-	u32 want_lose;
+	u32 conn_flags;
 	u32 two_primaries;
 
               /* Since protocol version 87 and higher. */
@@ -791,6 +799,8 @@
 				 * while this is set. */
 	RESIZE_PENDING,		/* Size change detected locally, waiting for the response from
 				 * the peer, if it changed there as well. */
+	CONN_DRY_RUN,		/* Expect disconnect after resync handshake. */
+	GOT_PING_ACK,		/* set when we receive a ping_ack packet, misc wait gets woken */
 };
 
 struct drbd_bitmap; /* opaque for drbd_conf */
diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index ab871e0..67e0fc5 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -1668,7 +1668,7 @@
 int drbd_send_protocol(struct drbd_conf *mdev)
 {
 	struct p_protocol *p;
-	int size, rv;
+	int size, cf, rv;
 
 	size = sizeof(struct p_protocol);
 
@@ -1685,9 +1685,21 @@
 	p->after_sb_0p   = cpu_to_be32(mdev->net_conf->after_sb_0p);
 	p->after_sb_1p   = cpu_to_be32(mdev->net_conf->after_sb_1p);
 	p->after_sb_2p   = cpu_to_be32(mdev->net_conf->after_sb_2p);
-	p->want_lose     = cpu_to_be32(mdev->net_conf->want_lose);
 	p->two_primaries = cpu_to_be32(mdev->net_conf->two_primaries);
 
+	cf = 0;
+	if (mdev->net_conf->want_lose)
+		cf |= CF_WANT_LOSE;
+	if (mdev->net_conf->dry_run) {
+		if (mdev->agreed_pro_version >= 92)
+			cf |= CF_DRY_RUN;
+		else {
+			dev_err(DEV, "--dry-run is not supported by peer");
+			return 0;
+		}
+	}
+	p->conn_flags    = cpu_to_be32(cf);
+
 	if (mdev->agreed_pro_version >= 87)
 		strcpy(p->integrity_alg, mdev->net_conf->integrity_alg);
 
@@ -3161,14 +3173,18 @@
 void drbd_free_sock(struct drbd_conf *mdev)
 {
 	if (mdev->data.socket) {
+		mutex_lock(&mdev->data.mutex);
 		kernel_sock_shutdown(mdev->data.socket, SHUT_RDWR);
 		sock_release(mdev->data.socket);
 		mdev->data.socket = NULL;
+		mutex_unlock(&mdev->data.mutex);
 	}
 	if (mdev->meta.socket) {
+		mutex_lock(&mdev->meta.mutex);
 		kernel_sock_shutdown(mdev->meta.socket, SHUT_RDWR);
 		sock_release(mdev->meta.socket);
 		mdev->meta.socket = NULL;
+		mutex_unlock(&mdev->meta.mutex);
 	}
 }
 
diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index 4df3b40..6429d2b 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -285,8 +285,8 @@
 		}
 
 		if (r == SS_NO_UP_TO_DATE_DISK && force &&
-		    (mdev->state.disk == D_INCONSISTENT ||
-		     mdev->state.disk == D_OUTDATED)) {
+		    (mdev->state.disk < D_UP_TO_DATE &&
+		     mdev->state.disk >= D_INCONSISTENT)) {
 			mask.disk = D_MASK;
 			val.disk  = D_UP_TO_DATE;
 			forced = 1;
@@ -407,7 +407,7 @@
 	}
 
 	reply->ret_code =
-		drbd_set_role(mdev, R_PRIMARY, primary_args.overwrite_peer);
+		drbd_set_role(mdev, R_PRIMARY, primary_args.primary_force);
 
 	return 0;
 }
@@ -941,6 +941,25 @@
 
 	drbd_md_set_sector_offsets(mdev, nbc);
 
+	/* allocate a second IO page if logical_block_size != 512 */
+	logical_block_size = bdev_logical_block_size(nbc->md_bdev);
+	if (logical_block_size == 0)
+		logical_block_size = MD_SECTOR_SIZE;
+
+	if (logical_block_size != MD_SECTOR_SIZE) {
+		if (!mdev->md_io_tmpp) {
+			struct page *page = alloc_page(GFP_NOIO);
+			if (!page)
+				goto force_diskless_dec;
+
+			dev_warn(DEV, "Meta data's bdev logical_block_size = %d != %d\n",
+			     logical_block_size, MD_SECTOR_SIZE);
+			dev_warn(DEV, "Workaround engaged (has performance impact).\n");
+
+			mdev->md_io_tmpp = page;
+		}
+	}
+
 	if (!mdev->bitmap) {
 		if (drbd_bm_init(mdev)) {
 			retcode = ERR_NOMEM;
@@ -980,25 +999,6 @@
 		goto force_diskless_dec;
 	}
 
-	/* allocate a second IO page if logical_block_size != 512 */
-	logical_block_size = bdev_logical_block_size(nbc->md_bdev);
-	if (logical_block_size == 0)
-		logical_block_size = MD_SECTOR_SIZE;
-
-	if (logical_block_size != MD_SECTOR_SIZE) {
-		if (!mdev->md_io_tmpp) {
-			struct page *page = alloc_page(GFP_NOIO);
-			if (!page)
-				goto force_diskless_dec;
-
-			dev_warn(DEV, "Meta data's bdev logical_block_size = %d != %d\n",
-			     logical_block_size, MD_SECTOR_SIZE);
-			dev_warn(DEV, "Workaround engaged (has performance impact).\n");
-
-			mdev->md_io_tmpp = page;
-		}
-	}
-
 	/* Reset the "barriers don't work" bits here, then force meta data to
 	 * be written, to ensure we determine if barriers are supported. */
 	if (nbc->dc.no_md_flush)
diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index d065c64..ed9f1de 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -2513,6 +2513,10 @@
 	}
 
 	if (hg == -100) {
+		/* FIXME this log message is not correct if we end up here
+		 * after an attempted attach on a diskless node.
+		 * We just refuse to attach -- well, we drop the "connection"
+		 * to that disk, in a way... */
 		dev_alert(DEV, "Split-Brain detected, dropping connection!\n");
 		drbd_khelper(mdev, "split-brain");
 		return C_MASK;
@@ -2538,6 +2542,16 @@
 		}
 	}
 
+	if (mdev->net_conf->dry_run || test_bit(CONN_DRY_RUN, &mdev->flags)) {
+		if (hg == 0)
+			dev_info(DEV, "dry-run connect: No resync, would become Connected immediately.\n");
+		else
+			dev_info(DEV, "dry-run connect: Would become %s, doing a %s resync.",
+				 drbd_conn_str(hg > 0 ? C_SYNC_SOURCE : C_SYNC_TARGET),
+				 abs(hg) >= 2 ? "full" : "bit-map based");
+		return C_MASK;
+	}
+
 	if (abs(hg) >= 2) {
 		dev_info(DEV, "Writing the whole bitmap, full sync required after drbd_sync_handshake.\n");
 		if (drbd_bitmap_io(mdev, &drbd_bmio_set_n_write, "set_n_write from sync_handshake"))
@@ -2585,7 +2599,7 @@
 	struct p_protocol *p = (struct p_protocol *)h;
 	int header_size, data_size;
 	int p_proto, p_after_sb_0p, p_after_sb_1p, p_after_sb_2p;
-	int p_want_lose, p_two_primaries;
+	int p_want_lose, p_two_primaries, cf;
 	char p_integrity_alg[SHARED_SECRET_MAX] = "";
 
 	header_size = sizeof(*p) - sizeof(*h);
@@ -2598,8 +2612,14 @@
 	p_after_sb_0p	= be32_to_cpu(p->after_sb_0p);
 	p_after_sb_1p	= be32_to_cpu(p->after_sb_1p);
 	p_after_sb_2p	= be32_to_cpu(p->after_sb_2p);
-	p_want_lose	= be32_to_cpu(p->want_lose);
 	p_two_primaries = be32_to_cpu(p->two_primaries);
+	cf		= be32_to_cpu(p->conn_flags);
+	p_want_lose = cf & CF_WANT_LOSE;
+
+	clear_bit(CONN_DRY_RUN, &mdev->flags);
+
+	if (cf & CF_DRY_RUN)
+		set_bit(CONN_DRY_RUN, &mdev->flags);
 
 	if (p_proto != mdev->net_conf->wire_protocol) {
 		dev_err(DEV, "incompatible communication protocols\n");
@@ -3118,13 +3138,16 @@
 
 		put_ldev(mdev);
 		if (nconn == C_MASK) {
+			nconn = C_CONNECTED;
 			if (mdev->state.disk == D_NEGOTIATING) {
 				drbd_force_state(mdev, NS(disk, D_DISKLESS));
-				nconn = C_CONNECTED;
 			} else if (peer_state.disk == D_NEGOTIATING) {
 				dev_err(DEV, "Disk attach process on the peer node was aborted.\n");
 				peer_state.disk = D_DISKLESS;
+				real_peer_disk = D_DISKLESS;
 			} else {
+				if (test_and_clear_bit(CONN_DRY_RUN, &mdev->flags))
+					return FALSE;
 				D_ASSERT(oconn == C_WF_REPORT_PARAMS);
 				drbd_force_state(mdev, NS(conn, C_DISCONNECTING));
 				return FALSE;
@@ -3594,10 +3617,7 @@
 
 	/* asender does not clean up anything. it must not interfere, either */
 	drbd_thread_stop(&mdev->asender);
-
-	mutex_lock(&mdev->data.mutex);
 	drbd_free_sock(mdev);
-	mutex_unlock(&mdev->data.mutex);
 
 	spin_lock_irq(&mdev->req_lock);
 	_drbd_wait_ee_list_empty(mdev, &mdev->active_ee);
@@ -4054,6 +4074,8 @@
 {
 	/* restore idle timeout */
 	mdev->meta.socket->sk->sk_rcvtimeo = mdev->net_conf->ping_int*HZ;
+	if (!test_and_set_bit(GOT_PING_ACK, &mdev->flags))
+		wake_up(&mdev->misc_wait);
 
 	return TRUE;
 }
diff --git a/drivers/block/drbd/drbd_worker.c b/drivers/block/drbd/drbd_worker.c
index b453c2b..44bf6d1 100644
--- a/drivers/block/drbd/drbd_worker.c
+++ b/drivers/block/drbd/drbd_worker.c
@@ -938,7 +938,8 @@
 
 		if (eq) {
 			drbd_set_in_sync(mdev, e->sector, e->size);
-			mdev->rs_same_csum++;
+			/* rs_same_csums unit is BM_BLOCK_SIZE */
+			mdev->rs_same_csum += e->size >> BM_BLOCK_SHIFT;
 			ok = drbd_send_ack(mdev, P_RS_IS_IN_SYNC, e);
 		} else {
 			inc_rs_pending(mdev);
@@ -1288,6 +1289,14 @@
 	return retcode;
 }
 
+static void ping_peer(struct drbd_conf *mdev)
+{
+	clear_bit(GOT_PING_ACK, &mdev->flags);
+	request_ping(mdev);
+	wait_event(mdev->misc_wait,
+		   test_bit(GOT_PING_ACK, &mdev->flags) || mdev->state.conn < C_CONNECTED);
+}
+
 /**
  * drbd_start_resync() - Start the resync process
  * @mdev:	DRBD device.
@@ -1371,7 +1380,6 @@
 		_drbd_pause_after(mdev);
 	}
 	write_unlock_irq(&global_state_lock);
-	drbd_state_unlock(mdev);
 	put_ldev(mdev);
 
 	if (r == SS_SUCCESS) {
@@ -1382,11 +1390,8 @@
 
 		if (mdev->rs_total == 0) {
 			/* Peer still reachable? Beware of failing before-resync-target handlers! */
-			request_ping(mdev);
-			__set_current_state(TASK_INTERRUPTIBLE);
-			schedule_timeout(mdev->net_conf->ping_timeo*HZ/9); /* 9 instead 10 */
+			ping_peer(mdev);
 			drbd_resync_finished(mdev);
-			return;
 		}
 
 		/* ns.conn may already be != mdev->state.conn,
@@ -1398,6 +1403,7 @@
 
 		drbd_md_sync(mdev);
 	}
+	drbd_state_unlock(mdev);
 }
 
 int drbd_worker(struct drbd_thread *thi)
diff --git a/drivers/block/paride/pcd.c b/drivers/block/paride/pcd.c
index 8866ca3..71acf4e 100644
--- a/drivers/block/paride/pcd.c
+++ b/drivers/block/paride/pcd.c
@@ -341,11 +341,11 @@
 	       && (j++ < PCD_SPIN))
 		udelay(PCD_DELAY);
 
-	if ((r & (IDE_ERR & stop)) || (j >= PCD_SPIN)) {
+	if ((r & (IDE_ERR & stop)) || (j > PCD_SPIN)) {
 		s = read_reg(cd, 7);
 		e = read_reg(cd, 1);
 		p = read_reg(cd, 2);
-		if (j >= PCD_SPIN)
+		if (j > PCD_SPIN)
 			e |= 0x100;
 		if (fun)
 			printk("%s: %s %s: alt=0x%x stat=0x%x err=0x%x"
diff --git a/drivers/block/paride/pf.c b/drivers/block/paride/pf.c
index ddb4f9a..c059aab 100644
--- a/drivers/block/paride/pf.c
+++ b/drivers/block/paride/pf.c
@@ -391,11 +391,11 @@
 	       && (j++ < PF_SPIN))
 		udelay(PF_SPIN_DEL);
 
-	if ((r & (STAT_ERR & stop)) || (j >= PF_SPIN)) {
+	if ((r & (STAT_ERR & stop)) || (j > PF_SPIN)) {
 		s = read_reg(pf, 7);
 		e = read_reg(pf, 1);
 		p = read_reg(pf, 2);
-		if (j >= PF_SPIN)
+		if (j > PF_SPIN)
 			e |= 0x100;
 		if (fun)
 			printk("%s: %s %s: alt=0x%x stat=0x%x err=0x%x"
diff --git a/drivers/block/paride/pt.c b/drivers/block/paride/pt.c
index 1e4006e..bc5825f 100644
--- a/drivers/block/paride/pt.c
+++ b/drivers/block/paride/pt.c
@@ -274,11 +274,11 @@
 	       && (j++ < PT_SPIN))
 		udelay(PT_SPIN_DEL);
 
-	if ((r & (STAT_ERR & stop)) || (j >= PT_SPIN)) {
+	if ((r & (STAT_ERR & stop)) || (j > PT_SPIN)) {
 		s = read_reg(pi, 7);
 		e = read_reg(pi, 1);
 		p = read_reg(pi, 2);
-		if (j >= PT_SPIN)
+		if (j > PT_SPIN)
 			e |= 0x100;
 		if (fun)
 			printk("%s: %s %s: alt=0x%x stat=0x%x err=0x%x"
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 3c64af0..653817c 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -347,14 +347,13 @@
 	set_capacity(vblk->disk, cap);
 
 	/* We can handle whatever the host told us to handle. */
-	blk_queue_max_phys_segments(q, vblk->sg_elems-2);
-	blk_queue_max_hw_segments(q, vblk->sg_elems-2);
+	blk_queue_max_segments(q, vblk->sg_elems-2);
 
 	/* No need to bounce any requests */
 	blk_queue_bounce_limit(q, BLK_BOUNCE_ANY);
 
 	/* No real sector limit. */
-	blk_queue_max_sectors(q, -1U);
+	blk_queue_max_hw_sectors(q, -1U);
 
 	/* Host can optionally specify maximum segment size and number of
 	 * segments. */
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 83881df..a82ab3e 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -2185,7 +2185,7 @@
 	blk_queue_prep_rq(sdp->request_queue, sd_prep_fn);
 
 	gd->driverfs_dev = &sdp->sdev_gendev;
-	gd->flags = GENHD_FL_EXT_DEVT | GENHD_FL_DRIVERFS;
+	gd->flags = GENHD_FL_EXT_DEVT;
 	if (sdp->removable)
 		gd->flags |= GENHD_FL_REMOVABLE;
 
diff --git a/fs/bio.c b/fs/bio.c
index e1f9221..e7bf6ca 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -554,7 +554,7 @@
 					.bi_rw = bio->bi_rw,
 				};
 
-				if (q->merge_bvec_fn(q, &bvm, prev) < len) {
+				if (q->merge_bvec_fn(q, &bvm, prev) < prev->bv_len) {
 					prev->bv_len -= len;
 					return 0;
 				}
@@ -607,7 +607,7 @@
 		 * merge_bvec_fn() returns number of bytes it can accept
 		 * at this offset
 		 */
-		if (q->merge_bvec_fn(q, &bvm, bvec) < len) {
+		if (q->merge_bvec_fn(q, &bvm, bvec) < bvec->bv_len) {
 			bvec->bv_page = NULL;
 			bvec->bv_len = 0;
 			bvec->bv_offset = 0;
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 76fc4d5..6841effa 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -553,108 +553,85 @@
 	return ret;
 }
 
-static void unpin_sb_for_writeback(struct super_block **psb)
+static void unpin_sb_for_writeback(struct super_block *sb)
 {
-	struct super_block *sb = *psb;
-
-	if (sb) {
-		up_read(&sb->s_umount);
-		put_super(sb);
-		*psb = NULL;
-	}
+	up_read(&sb->s_umount);
+	put_super(sb);
 }
 
+enum sb_pin_state {
+	SB_PINNED,
+	SB_NOT_PINNED,
+	SB_PIN_FAILED
+};
+
 /*
  * For WB_SYNC_NONE writeback, the caller does not have the sb pinned
  * before calling writeback. So make sure that we do pin it, so it doesn't
  * go away while we are writing inodes from it.
- *
- * Returns 0 if the super was successfully pinned (or pinning wasn't needed),
- * 1 if we failed.
  */
-static int pin_sb_for_writeback(struct writeback_control *wbc,
-				struct inode *inode, struct super_block **psb)
+static enum sb_pin_state pin_sb_for_writeback(struct writeback_control *wbc,
+					      struct super_block *sb)
 {
-	struct super_block *sb = inode->i_sb;
-
-	/*
-	 * If this sb is already pinned, nothing more to do. If not and
-	 * *psb is non-NULL, unpin the old one first
-	 */
-	if (sb == *psb)
-		return 0;
-	else if (*psb)
-		unpin_sb_for_writeback(psb);
-
 	/*
 	 * Caller must already hold the ref for this
 	 */
 	if (wbc->sync_mode == WB_SYNC_ALL) {
 		WARN_ON(!rwsem_is_locked(&sb->s_umount));
-		return 0;
+		return SB_NOT_PINNED;
 	}
-
 	spin_lock(&sb_lock);
 	sb->s_count++;
 	if (down_read_trylock(&sb->s_umount)) {
 		if (sb->s_root) {
 			spin_unlock(&sb_lock);
-			goto pinned;
+			return SB_PINNED;
 		}
 		/*
 		 * umounted, drop rwsem again and fall through to failure
 		 */
 		up_read(&sb->s_umount);
 	}
-
 	sb->s_count--;
 	spin_unlock(&sb_lock);
-	return 1;
-pinned:
-	*psb = sb;
-	return 0;
+	return SB_PIN_FAILED;
 }
 
-static void writeback_inodes_wb(struct bdi_writeback *wb,
-				struct writeback_control *wbc)
+/*
+ * Write a portion of b_io inodes which belong to @sb.
+ * If @wbc->sb != NULL, then find and write all such
+ * inodes. Otherwise write only ones which go sequentially
+ * in reverse order.
+ * Return 1, if the caller writeback routine should be
+ * interrupted. Otherwise return 0.
+ */
+static int writeback_sb_inodes(struct super_block *sb,
+			       struct bdi_writeback *wb,
+			       struct writeback_control *wbc)
 {
-	struct super_block *sb = wbc->sb, *pin_sb = NULL;
-	const unsigned long start = jiffies;	/* livelock avoidance */
-
-	spin_lock(&inode_lock);
-
-	if (!wbc->for_kupdate || list_empty(&wb->b_io))
-		queue_io(wb, wbc->older_than_this);
-
 	while (!list_empty(&wb->b_io)) {
-		struct inode *inode = list_entry(wb->b_io.prev,
-						struct inode, i_list);
 		long pages_skipped;
-
-		/*
-		 * super block given and doesn't match, skip this inode
-		 */
-		if (sb && sb != inode->i_sb) {
+		struct inode *inode = list_entry(wb->b_io.prev,
+						 struct inode, i_list);
+		if (wbc->sb && sb != inode->i_sb) {
+			/* super block given and doesn't
+			   match, skip this inode */
 			redirty_tail(inode);
 			continue;
 		}
-
+		if (sb != inode->i_sb)
+			/* finish with this superblock */
+			return 0;
 		if (inode->i_state & (I_NEW | I_WILL_FREE)) {
 			requeue_io(inode);
 			continue;
 		}
-
 		/*
 		 * Was this inode dirtied after sync_sb_inodes was called?
 		 * This keeps sync from extra jobs and livelock.
 		 */
-		if (inode_dirtied_after(inode, start))
-			break;
-
-		if (pin_sb_for_writeback(wbc, inode, &pin_sb)) {
-			requeue_io(inode);
-			continue;
-		}
+		if (inode_dirtied_after(inode, wbc->wb_start))
+			return 1;
 
 		BUG_ON(inode->i_state & (I_FREEING | I_CLEAR));
 		__iget(inode);
@@ -673,14 +650,50 @@
 		spin_lock(&inode_lock);
 		if (wbc->nr_to_write <= 0) {
 			wbc->more_io = 1;
-			break;
+			return 1;
 		}
 		if (!list_empty(&wb->b_more_io))
 			wbc->more_io = 1;
 	}
+	/* b_io is empty */
+	return 1;
+}
 
-	unpin_sb_for_writeback(&pin_sb);
+static void writeback_inodes_wb(struct bdi_writeback *wb,
+				struct writeback_control *wbc)
+{
+	int ret = 0;
 
+	wbc->wb_start = jiffies; /* livelock avoidance */
+	spin_lock(&inode_lock);
+	if (!wbc->for_kupdate || list_empty(&wb->b_io))
+		queue_io(wb, wbc->older_than_this);
+
+	while (!list_empty(&wb->b_io)) {
+		struct inode *inode = list_entry(wb->b_io.prev,
+						 struct inode, i_list);
+		struct super_block *sb = inode->i_sb;
+		enum sb_pin_state state;
+
+		if (wbc->sb && sb != wbc->sb) {
+			/* super block given and doesn't
+			   match, skip this inode */
+			redirty_tail(inode);
+			continue;
+		}
+		state = pin_sb_for_writeback(wbc, sb);
+
+		if (state == SB_PIN_FAILED) {
+			requeue_io(inode);
+			continue;
+		}
+		ret = writeback_sb_inodes(sb, wb, wbc);
+
+		if (state == SB_PINNED)
+			unpin_sb_for_writeback(sb);
+		if (ret)
+			break;
+	}
 	spin_unlock(&inode_lock);
 	/* Leave any unwritten inodes on b_io */
 }
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index ebd22db..41551c9 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -921,26 +921,7 @@
 extern void blk_queue_make_request(struct request_queue *, make_request_fn *);
 extern void blk_queue_bounce_limit(struct request_queue *, u64);
 extern void blk_queue_max_hw_sectors(struct request_queue *, unsigned int);
-
-/* Temporary compatibility wrapper */
-static inline void blk_queue_max_sectors(struct request_queue *q, unsigned int max)
-{
-	blk_queue_max_hw_sectors(q, max);
-}
-
 extern void blk_queue_max_segments(struct request_queue *, unsigned short);
-
-static inline void blk_queue_max_phys_segments(struct request_queue *q, unsigned short max)
-{
-	blk_queue_max_segments(q, max);
-}
-
-static inline void blk_queue_max_hw_segments(struct request_queue *q, unsigned short max)
-{
-	blk_queue_max_segments(q, max);
-}
-
-
 extern void blk_queue_max_segment_size(struct request_queue *, unsigned int);
 extern void blk_queue_max_discard_sectors(struct request_queue *q,
 		unsigned int max_discard_sectors);
@@ -1030,11 +1011,6 @@
 
 extern int blk_verify_command(unsigned char *cmd, fmode_t has_write_perm);
 
-#define MAX_PHYS_SEGMENTS 128
-#define MAX_HW_SEGMENTS 128
-#define SAFE_MAX_SECTORS 255
-#define MAX_SEGMENT_SIZE	65536
-
 enum blk_default_limits {
 	BLK_MAX_SEGMENTS	= 128,
 	BLK_SAFE_MAX_SECTORS	= 255,
diff --git a/include/linux/drbd.h b/include/linux/drbd.h
index 7896227..4341b1a 100644
--- a/include/linux/drbd.h
+++ b/include/linux/drbd.h
@@ -56,7 +56,7 @@
 #define REL_VERSION "8.3.7"
 #define API_VERSION 88
 #define PRO_VERSION_MIN 86
-#define PRO_VERSION_MAX 91
+#define PRO_VERSION_MAX 92
 
 
 enum drbd_io_error_p {
diff --git a/include/linux/drbd_nl.h b/include/linux/drbd_nl.h
index a4d82f8..f7431a4 100644
--- a/include/linux/drbd_nl.h
+++ b/include/linux/drbd_nl.h
@@ -12,7 +12,7 @@
 #endif
 
 NL_PACKET(primary, 1,
-       NL_BIT(		1,	T_MAY_IGNORE,	overwrite_peer)
+       NL_BIT(		1,	T_MAY_IGNORE,	primary_force)
 )
 
 NL_PACKET(secondary, 2, )
@@ -63,6 +63,7 @@
 	NL_BIT(		41,	T_MAY_IGNORE,	always_asbp)
 	NL_BIT(		61,	T_MAY_IGNORE,	no_cork)
 	NL_BIT(		62,	T_MANDATORY,	auto_sndbuf_size)
+	NL_BIT(		70,	T_MANDATORY,	dry_run)
 )
 
 NL_PACKET(disconnect, 6, )
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 56b5051..5f2f4c4 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -109,7 +109,7 @@
 };
 
 #define GENHD_FL_REMOVABLE			1
-#define GENHD_FL_DRIVERFS			2
+/* 2 is unused */
 #define GENHD_FL_MEDIA_CHANGE_NOTIFY		4
 #define GENHD_FL_CD				8
 #define GENHD_FL_UP				16
diff --git a/include/linux/lcm.h b/include/linux/lcm.h
new file mode 100644
index 0000000..7bf01d7
--- /dev/null
+++ b/include/linux/lcm.h
@@ -0,0 +1,8 @@
+#ifndef _LCM_H
+#define _LCM_H
+
+#include <linux/compiler.h>
+
+unsigned long lcm(unsigned long a, unsigned long b) __attribute_const__;
+
+#endif /* _LCM_H */
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 76e8903..36520de 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -34,6 +34,9 @@
 	enum writeback_sync_modes sync_mode;
 	unsigned long *older_than_this;	/* If !NULL, only write back inodes
 					   older than this */
+	unsigned long wb_start;         /* Time writeback_inodes_wb was
+					   called. This is needed to avoid
+					   extra jobs and livelock */
 	long nr_to_write;		/* Write this many pages, and decrement
 					   this for each page written */
 	long pages_skipped;		/* Pages which were not written */
diff --git a/include/trace/events/block.h b/include/trace/events/block.h
index 5fb7273..d870a918 100644
--- a/include/trace/events/block.h
+++ b/include/trace/events/block.h
@@ -40,6 +40,16 @@
 		  __entry->nr_sector, __entry->errors)
 );
 
+/**
+ * block_rq_abort - abort block operation request
+ * @q: queue containing the block operation request
+ * @rq: block IO operation request
+ *
+ * Called immediately after pending block IO operation request @rq in
+ * queue @q is aborted. The fields in the operation request @rq
+ * can be examined to determine which device and sectors the pending
+ * operation would access.
+ */
 DEFINE_EVENT(block_rq_with_error, block_rq_abort,
 
 	TP_PROTO(struct request_queue *q, struct request *rq),
@@ -47,6 +57,15 @@
 	TP_ARGS(q, rq)
 );
 
+/**
+ * block_rq_requeue - place block IO request back on a queue
+ * @q: queue holding operation
+ * @rq: block IO operation request
+ *
+ * The block operation request @rq is being placed back into queue
+ * @q.  For some reason the request was not completed and needs to be
+ * put back in the queue.
+ */
 DEFINE_EVENT(block_rq_with_error, block_rq_requeue,
 
 	TP_PROTO(struct request_queue *q, struct request *rq),
@@ -54,6 +73,17 @@
 	TP_ARGS(q, rq)
 );
 
+/**
+ * block_rq_complete - block IO operation completed by device driver
+ * @q: queue containing the block operation request
+ * @rq: block operations request
+ *
+ * The block_rq_complete tracepoint event indicates that some portion
+ * of operation request has been completed by the device driver.  If
+ * the @rq->bio is %NULL, then there is absolutely no additional work to
+ * do for the request. If @rq->bio is non-NULL then there is
+ * additional work required to complete the request.
+ */
 DEFINE_EVENT(block_rq_with_error, block_rq_complete,
 
 	TP_PROTO(struct request_queue *q, struct request *rq),
@@ -95,6 +125,16 @@
 		  __entry->nr_sector, __entry->comm)
 );
 
+/**
+ * block_rq_insert - insert block operation request into queue
+ * @q: target queue
+ * @rq: block IO operation request
+ *
+ * Called immediately before block operation request @rq is inserted
+ * into queue @q.  The fields in the operation request @rq struct can
+ * be examined to determine which device and sectors the pending
+ * operation would access.
+ */
 DEFINE_EVENT(block_rq, block_rq_insert,
 
 	TP_PROTO(struct request_queue *q, struct request *rq),
@@ -102,6 +142,14 @@
 	TP_ARGS(q, rq)
 );
 
+/**
+ * block_rq_issue - issue pending block IO request operation to device driver
+ * @q: queue holding operation
+ * @rq: block IO operation operation request
+ *
+ * Called when block operation request @rq from queue @q is sent to a
+ * device driver for processing.
+ */
 DEFINE_EVENT(block_rq, block_rq_issue,
 
 	TP_PROTO(struct request_queue *q, struct request *rq),
@@ -109,6 +157,17 @@
 	TP_ARGS(q, rq)
 );
 
+/**
+ * block_bio_bounce - used bounce buffer when processing block operation
+ * @q: queue holding the block operation
+ * @bio: block operation
+ *
+ * A bounce buffer was used to handle the block operation @bio in @q.
+ * This occurs when hardware limitations prevent a direct transfer of
+ * data between the @bio data memory area and the IO device.  Use of a
+ * bounce buffer requires extra copying of data and decreases
+ * performance.
+ */
 TRACE_EVENT(block_bio_bounce,
 
 	TP_PROTO(struct request_queue *q, struct bio *bio),
@@ -138,6 +197,14 @@
 		  __entry->nr_sector, __entry->comm)
 );
 
+/**
+ * block_bio_complete - completed all work on the block operation
+ * @q: queue holding the block operation
+ * @bio: block operation completed
+ *
+ * This tracepoint indicates there is no further work to do on this
+ * block IO operation @bio.
+ */
 TRACE_EVENT(block_bio_complete,
 
 	TP_PROTO(struct request_queue *q, struct bio *bio),
@@ -193,6 +260,14 @@
 		  __entry->nr_sector, __entry->comm)
 );
 
+/**
+ * block_bio_backmerge - merging block operation to the end of an existing operation
+ * @q: queue holding operation
+ * @bio: new block operation to merge
+ *
+ * Merging block request @bio to the end of an existing block request
+ * in queue @q.
+ */
 DEFINE_EVENT(block_bio, block_bio_backmerge,
 
 	TP_PROTO(struct request_queue *q, struct bio *bio),
@@ -200,6 +275,14 @@
 	TP_ARGS(q, bio)
 );
 
+/**
+ * block_bio_frontmerge - merging block operation to the beginning of an existing operation
+ * @q: queue holding operation
+ * @bio: new block operation to merge
+ *
+ * Merging block IO operation @bio to the beginning of an existing block
+ * operation in queue @q.
+ */
 DEFINE_EVENT(block_bio, block_bio_frontmerge,
 
 	TP_PROTO(struct request_queue *q, struct bio *bio),
@@ -207,6 +290,13 @@
 	TP_ARGS(q, bio)
 );
 
+/**
+ * block_bio_queue - putting new block IO operation in queue
+ * @q: queue holding operation
+ * @bio: new block operation
+ *
+ * About to place the block IO operation @bio into queue @q.
+ */
 DEFINE_EVENT(block_bio, block_bio_queue,
 
 	TP_PROTO(struct request_queue *q, struct bio *bio),
@@ -243,6 +333,15 @@
 		  __entry->nr_sector, __entry->comm)
 );
 
+/**
+ * block_getrq - get a free request entry in queue for block IO operations
+ * @q: queue for operations
+ * @bio: pending block IO operation
+ * @rw: low bit indicates a read (%0) or a write (%1)
+ *
+ * A request struct for queue @q has been allocated to handle the
+ * block IO operation @bio.
+ */
 DEFINE_EVENT(block_get_rq, block_getrq,
 
 	TP_PROTO(struct request_queue *q, struct bio *bio, int rw),
@@ -250,6 +349,17 @@
 	TP_ARGS(q, bio, rw)
 );
 
+/**
+ * block_sleeprq - waiting to get a free request entry in queue for block IO operation
+ * @q: queue for operation
+ * @bio: pending block IO operation
+ * @rw: low bit indicates a read (%0) or a write (%1)
+ *
+ * In the case where a request struct cannot be provided for queue @q
+ * the process needs to wait for an request struct to become
+ * available.  This tracepoint event is generated each time the
+ * process goes to sleep waiting for request struct become available.
+ */
 DEFINE_EVENT(block_get_rq, block_sleeprq,
 
 	TP_PROTO(struct request_queue *q, struct bio *bio, int rw),
@@ -257,6 +367,14 @@
 	TP_ARGS(q, bio, rw)
 );
 
+/**
+ * block_plug - keep operations requests in request queue
+ * @q: request queue to plug
+ *
+ * Plug the request queue @q.  Do not allow block operation requests
+ * to be sent to the device driver. Instead, accumulate requests in
+ * the queue to improve throughput performance of the block device.
+ */
 TRACE_EVENT(block_plug,
 
 	TP_PROTO(struct request_queue *q),
@@ -293,6 +411,13 @@
 	TP_printk("[%s] %d", __entry->comm, __entry->nr_rq)
 );
 
+/**
+ * block_unplug_timer - timed release of operations requests in queue to device driver
+ * @q: request queue to unplug
+ *
+ * Unplug the request queue @q because a timer expired and allow block
+ * operation requests to be sent to the device driver.
+ */
 DEFINE_EVENT(block_unplug, block_unplug_timer,
 
 	TP_PROTO(struct request_queue *q),
@@ -300,6 +425,13 @@
 	TP_ARGS(q)
 );
 
+/**
+ * block_unplug_io - release of operations requests in request queue
+ * @q: request queue to unplug
+ *
+ * Unplug request queue @q because device driver is scheduled to work
+ * on elements in the request queue.
+ */
 DEFINE_EVENT(block_unplug, block_unplug_io,
 
 	TP_PROTO(struct request_queue *q),
@@ -307,6 +439,17 @@
 	TP_ARGS(q)
 );
 
+/**
+ * block_split - split a single bio struct into two bio structs
+ * @q: queue containing the bio
+ * @bio: block operation being split
+ * @new_sector: The starting sector for the new bio
+ *
+ * The bio request @bio in request queue @q needs to be split into two
+ * bio requests. The newly created @bio request starts at
+ * @new_sector. This split may be required due to hardware limitation
+ * such as operation crossing device boundaries in a RAID system.
+ */
 TRACE_EVENT(block_split,
 
 	TP_PROTO(struct request_queue *q, struct bio *bio,
@@ -337,6 +480,16 @@
 		  __entry->comm)
 );
 
+/**
+ * block_remap - map request for a partition to the raw device
+ * @q: queue holding the operation
+ * @bio: revised operation
+ * @dev: device for the operation
+ * @from: original sector for the operation
+ *
+ * An operation for a partition on a block device has been mapped to the
+ * raw block device.
+ */
 TRACE_EVENT(block_remap,
 
 	TP_PROTO(struct request_queue *q, struct bio *bio, dev_t dev,
@@ -370,6 +523,17 @@
 		  (unsigned long long)__entry->old_sector)
 );
 
+/**
+ * block_rq_remap - map request for a block operation request
+ * @q: queue holding the operation
+ * @rq: block IO operation request
+ * @dev: device for the operation
+ * @from: original sector for the operation
+ *
+ * The block operation request @rq in @q has been remapped.  The block
+ * operation request @rq holds the current information and @from hold
+ * the original sector.
+ */
 TRACE_EVENT(block_rq_remap,
 
 	TP_PROTO(struct request_queue *q, struct request *rq, dev_t dev,
diff --git a/lib/Makefile b/lib/Makefile
index 2e152ae..0d40152 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -21,7 +21,7 @@
 
 obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \
 	 bust_spinlocks.o hexdump.o kasprintf.o bitmap.o scatterlist.o \
-	 string_helpers.o gcd.o list_sort.o
+	 string_helpers.o gcd.o lcm.o list_sort.o
 
 ifeq ($(CONFIG_DEBUG_KOBJECT),y)
 CFLAGS_kobject.o += -DDEBUG
diff --git a/lib/lcm.c b/lib/lcm.c
new file mode 100644
index 0000000..157cd88
--- /dev/null
+++ b/lib/lcm.c
@@ -0,0 +1,15 @@
+#include <linux/kernel.h>
+#include <linux/gcd.h>
+#include <linux/module.h>
+
+/* Lowest common multiple */
+unsigned long lcm(unsigned long a, unsigned long b)
+{
+	if (a && b)
+		return (a * b) / gcd(a, b);
+	else if (b)
+		return b;
+
+	return a;
+}
+EXPORT_SYMBOL_GPL(lcm);