Initial file dump from open source releaseHEADmaster

1 files changed, 1943 insertions, 0 deletions

diff --git a/drivers/block/drbd/drbd_worker.c b/drivers/block/drbd/drbd_worker.c
new file mode 100644
index 00000000..891c0eca
--- /dev/null
+++ b/drivers/block/drbd/drbd_worker.c
@@ -0,0 +1,1943 @@
+/*
+   drbd_worker.c
+
+   This file is part of DRBD by Philipp Reisner and Lars Ellenberg.
+
+   Copyright (C) 2001-2008, LINBIT Information Technologies GmbH.
+   Copyright (C) 1999-2008, Philipp Reisner <philipp.reisner@linbit.com>.
+   Copyright (C) 2002-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.
+
+   drbd is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2, or (at your option)
+   any later version.
+
+   drbd is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with drbd; see the file COPYING.  If not, write to
+   the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
+
+ */
+
+#include <linux/module.h>
+#include <linux/drbd.h>
+#include <linux/sched.h>
+#include <linux/wait.h>
+#include <linux/mm.h>
+#include <linux/memcontrol.h>
+#include <linux/mm_inline.h>
+#include <linux/slab.h>
+#include <linux/random.h>
+#include <linux/string.h>
+#include <linux/scatterlist.h>
+
+#include "drbd_int.h"
+#include "drbd_req.h"
+
+static int w_make_ov_request(struct drbd_work *w, int cancel);
+
+
+/* endio handlers:
+ *   drbd_md_io_complete (defined here)
+ *   drbd_request_endio (defined here)
+ *   drbd_peer_request_endio (defined here)
+ *   bm_async_io_complete (defined in drbd_bitmap.c)
+ *
+ * For all these callbacks, note the following:
+ * The callbacks will be called in irq context by the IDE drivers,
+ * and in Softirqs/Tasklets/BH context by the SCSI drivers.
+ * Try to get the locking right :)
+ *
+ */
+
+
+/* About the global_state_lock
+   Each state transition on an device holds a read lock. In case we have
+   to evaluate the resync after dependencies, we grab a write lock, because
+   we need stable states on all devices for that.  */
+rwlock_t global_state_lock;
+
+/* used for synchronous meta data and bitmap IO
+ * submitted by drbd_md_sync_page_io()
+ */
+void drbd_md_io_complete(struct bio *bio, int error)
+{
+	struct drbd_md_io *md_io;
+	struct drbd_conf *mdev;
+
+	md_io = (struct drbd_md_io *)bio->bi_private;
+	mdev = container_of(md_io, struct drbd_conf, md_io);
+
+	md_io->error = error;
+
+	/* We grabbed an extra reference in _drbd_md_sync_page_io() to be able
+	 * to timeout on the lower level device, and eventually detach from it.
+	 * If this io completion runs after that timeout expired, this
+	 * drbd_md_put_buffer() may allow us to finally try and re-attach.
+	 * During normal operation, this only puts that extra reference
+	 * down to 1 again.
+	 * Make sure we first drop the reference, and only then signal
+	 * completion, or we may (in drbd_al_read_log()) cycle so fast into the
+	 * next drbd_md_sync_page_io(), that we trigger the
+	 * ASSERT(atomic_read(&mdev->md_io_in_use) == 1) there.
+	 */
+	drbd_md_put_buffer(mdev);
+	md_io->done = 1;
+	wake_up(&mdev->misc_wait);
+	bio_put(bio);
+	if (mdev->ldev) /* special case: drbd_md_read() during drbd_adm_attach() */
+		put_ldev(mdev);
+}
+
+/* reads on behalf of the partner,
+ * "submitted" by the receiver
+ */
+void drbd_endio_read_sec_final(struct drbd_peer_request *peer_req) __releases(local)
+{
+	unsigned long flags = 0;
+	struct drbd_conf *mdev = peer_req->w.mdev;
+
+	spin_lock_irqsave(&mdev->tconn->req_lock, flags);
+	mdev->read_cnt += peer_req->i.size >> 9;
+	list_del(&peer_req->w.list);
+	if (list_empty(&mdev->read_ee))
+		wake_up(&mdev->ee_wait);
+	if (test_bit(__EE_WAS_ERROR, &peer_req->flags))
+		__drbd_chk_io_error(mdev, DRBD_READ_ERROR);
+	spin_unlock_irqrestore(&mdev->tconn->req_lock, flags);
+
+	drbd_queue_work(&mdev->tconn->sender_work, &peer_req->w);
+	put_ldev(mdev);
+}
+
+/* writes on behalf of the partner, or resync writes,
+ * "submitted" by the receiver, final stage.  */
+static void drbd_endio_write_sec_final(struct drbd_peer_request *peer_req) __releases(local)
+{
+	unsigned long flags = 0;
+	struct drbd_conf *mdev = peer_req->w.mdev;
+	struct drbd_interval i;
+	int do_wake;
+	u64 block_id;
+	int do_al_complete_io;
+
+	/* after we moved peer_req to done_ee,
+	 * we may no longer access it,
+	 * it may be freed/reused already!
+	 * (as soon as we release the req_lock) */
+	i = peer_req->i;
+	do_al_complete_io = peer_req->flags & EE_CALL_AL_COMPLETE_IO;
+	block_id = peer_req->block_id;
+
+	spin_lock_irqsave(&mdev->tconn->req_lock, flags);
+	mdev->writ_cnt += peer_req->i.size >> 9;
+	list_move_tail(&peer_req->w.list, &mdev->done_ee);
+
+	/*
+	 * Do not remove from the write_requests tree here: we did not send the
+	 * Ack yet and did not wake possibly waiting conflicting requests.
+	 * Removed from the tree from "drbd_process_done_ee" within the
+	 * appropriate w.cb (e_end_block/e_end_resync_block) or from
+	 * _drbd_clear_done_ee.
+	 */
+
+	do_wake = list_empty(block_id == ID_SYNCER ? &mdev->sync_ee : &mdev->active_ee);
+
+	if (test_bit(__EE_WAS_ERROR, &peer_req->flags))
+		__drbd_chk_io_error(mdev, DRBD_WRITE_ERROR);
+	spin_unlock_irqrestore(&mdev->tconn->req_lock, flags);
+
+	if (block_id == ID_SYNCER)
+		drbd_rs_complete_io(mdev, i.sector);
+
+	if (do_wake)
+		wake_up(&mdev->ee_wait);
+
+	if (do_al_complete_io)
+		drbd_al_complete_io(mdev, &i);
+
+	wake_asender(mdev->tconn);
+	put_ldev(mdev);
+}
+
+/* writes on behalf of the partner, or resync writes,
+ * "submitted" by the receiver.
+ */
+void drbd_peer_request_endio(struct bio *bio, int error)
+{
+	struct drbd_peer_request *peer_req = bio->bi_private;
+	struct drbd_conf *mdev = peer_req->w.mdev;
+	int uptodate = bio_flagged(bio, BIO_UPTODATE);
+	int is_write = bio_data_dir(bio) == WRITE;
+
+	if (error && __ratelimit(&drbd_ratelimit_state))
+		dev_warn(DEV, "%s: error=%d s=%llus\n",
+				is_write ? "write" : "read", error,
+				(unsigned long long)peer_req->i.sector);
+	if (!error && !uptodate) {
+		if (__ratelimit(&drbd_ratelimit_state))
+			dev_warn(DEV, "%s: setting error to -EIO s=%llus\n",
+					is_write ? "write" : "read",
+					(unsigned long long)peer_req->i.sector);
+		/* strange behavior of some lower level drivers...
+		 * fail the request by clearing the uptodate flag,
+		 * but do not return any error?! */
+		error = -EIO;
+	}
+
+	if (error)
+		set_bit(__EE_WAS_ERROR, &peer_req->flags);
+
+	bio_put(bio); /* no need for the bio anymore */
+	if (atomic_dec_and_test(&peer_req->pending_bios)) {
+		if (is_write)
+			drbd_endio_write_sec_final(peer_req);
+		else
+			drbd_endio_read_sec_final(peer_req);
+	}
+}
+
+/* read, readA or write requests on R_PRIMARY coming from drbd_make_request
+ */
+void drbd_request_endio(struct bio *bio, int error)
+{
+	unsigned long flags;
+	struct drbd_request *req = bio->bi_private;
+	struct drbd_conf *mdev = req->w.mdev;
+	struct bio_and_error m;
+	enum drbd_req_event what;
+	int uptodate = bio_flagged(bio, BIO_UPTODATE);
+
+	if (!error && !uptodate) {
+		dev_warn(DEV, "p %s: setting error to -EIO\n",
+			 bio_data_dir(bio) == WRITE ? "write" : "read");
+		/* strange behavior of some lower level drivers...
+		 * fail the request by clearing the uptodate flag,
+		 * but do not return any error?! */
+		error = -EIO;
+	}
+
+
+	/* If this request was aborted locally before,
+	 * but now was completed "successfully",
+	 * chances are that this caused arbitrary data corruption.
+	 *
+	 * "aborting" requests, or force-detaching the disk, is intended for
+	 * completely blocked/hung local backing devices which do no longer
+	 * complete requests at all, not even do error completions.  In this
+	 * situation, usually a hard-reset and failover is the only way out.
+	 *
+	 * By "aborting", basically faking a local error-completion,
+	 * we allow for a more graceful swichover by cleanly migrating services.
+	 * Still the affected node has to be rebooted "soon".
+	 *
+	 * By completing these requests, we allow the upper layers to re-use
+	 * the associated data pages.
+	 *
+	 * If later the local backing device "recovers", and now DMAs some data
+	 * from disk into the original request pages, in the best case it will
+	 * just put random data into unused pages; but typically it will corrupt
+	 * meanwhile completely unrelated data, causing all sorts of damage.
+	 *
+	 * Which means delayed successful completion,
+	 * especially for READ requests,
+	 * is a reason to panic().
+	 *
+	 * We assume that a delayed *error* completion is OK,
+	 * though we still will complain noisily about it.
+	 */
+	if (unlikely(req->rq_state & RQ_LOCAL_ABORTED)) {
+		if (__ratelimit(&drbd_ratelimit_state))
+			dev_emerg(DEV, "delayed completion of aborted local request; disk-timeout may be too aggressive\n");
+
+		if (!error)
+			panic("possible random memory corruption caused by delayed completion of aborted local request\n");
+	}
+
+	/* to avoid recursion in __req_mod */
+	if (unlikely(error)) {
+		what = (bio_data_dir(bio) == WRITE)
+			? WRITE_COMPLETED_WITH_ERROR
+			: (bio_rw(bio) == READ)
+			  ? READ_COMPLETED_WITH_ERROR
+			  : READ_AHEAD_COMPLETED_WITH_ERROR;
+	} else
+		what = COMPLETED_OK;
+
+	bio_put(req->private_bio);
+	req->private_bio = ERR_PTR(error);
+
+	/* not req_mod(), we need irqsave here! */
+	spin_lock_irqsave(&mdev->tconn->req_lock, flags);
+	__req_mod(req, what, &m);
+	spin_unlock_irqrestore(&mdev->tconn->req_lock, flags);
+	put_ldev(mdev);
+
+	if (m.bio)
+		complete_master_bio(mdev, &m);
+}
+
+void drbd_csum_ee(struct drbd_conf *mdev, struct crypto_hash *tfm,
+		  struct drbd_peer_request *peer_req, void *digest)
+{
+	struct hash_desc desc;
+	struct scatterlist sg;
+	struct page *page = peer_req->pages;
+	struct page *tmp;
+	unsigned len;
+
+	desc.tfm = tfm;
+	desc.flags = 0;
+
+	sg_init_table(&sg, 1);
+	crypto_hash_init(&desc);
+
+	while ((tmp = page_chain_next(page))) {
+		/* all but the last page will be fully used */
+		sg_set_page(&sg, page, PAGE_SIZE, 0);
+		crypto_hash_update(&desc, &sg, sg.length);
+		page = tmp;
+	}
+	/* and now the last, possibly only partially used page */
+	len = peer_req->i.size & (PAGE_SIZE - 1);
+	sg_set_page(&sg, page, len ?: PAGE_SIZE, 0);
+	crypto_hash_update(&desc, &sg, sg.length);
+	crypto_hash_final(&desc, digest);
+}
+
+void drbd_csum_bio(struct drbd_conf *mdev, struct crypto_hash *tfm, struct bio *bio, void *digest)
+{
+	struct hash_desc desc;
+	struct scatterlist sg;
+	struct bio_vec *bvec;
+	int i;
+
+	desc.tfm = tfm;
+	desc.flags = 0;
+
+	sg_init_table(&sg, 1);
+	crypto_hash_init(&desc);
+
+	bio_for_each_segment(bvec, bio, i) {
+		sg_set_page(&sg, bvec->bv_page, bvec->bv_len, bvec->bv_offset);
+		crypto_hash_update(&desc, &sg, sg.length);
+	}
+	crypto_hash_final(&desc, digest);
+}
+
+/* MAYBE merge common code with w_e_end_ov_req */
+static int w_e_send_csum(struct drbd_work *w, int cancel)
+{
+	struct drbd_peer_request *peer_req = container_of(w, struct drbd_peer_request, w);
+	struct drbd_conf *mdev = w->mdev;
+	int digest_size;
+	void *digest;
+	int err = 0;
+
+	if (unlikely(cancel))
+		goto out;
+
+	if (unlikely((peer_req->flags & EE_WAS_ERROR) != 0))
+		goto out;
+
+	digest_size = crypto_hash_digestsize(mdev->tconn->csums_tfm);
+	digest = kmalloc(digest_size, GFP_NOIO);
+	if (digest) {
+		sector_t sector = peer_req->i.sector;
+		unsigned int size = peer_req->i.size;
+		drbd_csum_ee(mdev, mdev->tconn->csums_tfm, peer_req, digest);
+		/* Free peer_req and pages before send.
+		 * In case we block on congestion, we could otherwise run into
+		 * some distributed deadlock, if the other side blocks on
+		 * congestion as well, because our receiver blocks in
+		 * drbd_alloc_pages due to pp_in_use > max_buffers. */
+		drbd_free_peer_req(mdev, peer_req);
+		peer_req = NULL;
+		inc_rs_pending(mdev);
+		err = drbd_send_drequest_csum(mdev, sector, size,
+					      digest, digest_size,
+					      P_CSUM_RS_REQUEST);
+		kfree(digest);
+	} else {
+		dev_err(DEV, "kmalloc() of digest failed.\n");
+		err = -ENOMEM;
+	}
+
+out:
+	if (peer_req)
+		drbd_free_peer_req(mdev, peer_req);
+
+	if (unlikely(err))
+		dev_err(DEV, "drbd_send_drequest(..., csum) failed\n");
+	return err;
+}
+
+#define GFP_TRY	(__GFP_HIGHMEM | __GFP_NOWARN)
+
+static int read_for_csum(struct drbd_conf *mdev, sector_t sector, int size)
+{
+	struct drbd_peer_request *peer_req;
+
+	if (!get_ldev(mdev))
+		return -EIO;
+
+	if (drbd_rs_should_slow_down(mdev, sector))
+		goto defer;
+
+	/* GFP_TRY, because if there is no memory available right now, this may
+	 * be rescheduled for later. It is "only" background resync, after all. */
+	peer_req = drbd_alloc_peer_req(mdev, ID_SYNCER /* unused */, sector,
+				       size, GFP_TRY);
+	if (!peer_req)
+		goto defer;
+
+	peer_req->w.cb = w_e_send_csum;
+	spin_lock_irq(&mdev->tconn->req_lock);
+	list_add(&peer_req->w.list, &mdev->read_ee);
+	spin_unlock_irq(&mdev->tconn->req_lock);
+
+	atomic_add(size >> 9, &mdev->rs_sect_ev);
+	if (drbd_submit_peer_request(mdev, peer_req, READ, DRBD_FAULT_RS_RD) == 0)
+		return 0;
+
+	/* If it failed because of ENOMEM, retry should help.  If it failed
+	 * because bio_add_page failed (probably broken lower level driver),
+	 * retry may or may not help.
+	 * If it does not, you may need to force disconnect. */
+	spin_lock_irq(&mdev->tconn->req_lock);
+	list_del(&peer_req->w.list);
+	spin_unlock_irq(&mdev->tconn->req_lock);
+
+	drbd_free_peer_req(mdev, peer_req);
+defer:
+	put_ldev(mdev);
+	return -EAGAIN;
+}
+
+int w_resync_timer(struct drbd_work *w, int cancel)
+{
+	struct drbd_conf *mdev = w->mdev;
+	switch (mdev->state.conn) {
+	case C_VERIFY_S:
+		w_make_ov_request(w, cancel);
+		break;
+	case C_SYNC_TARGET:
+		w_make_resync_request(w, cancel);
+		break;
+	}
+
+	return 0;
+}
+
+void resync_timer_fn(unsigned long data)
+{
+	struct drbd_conf *mdev = (struct drbd_conf *) data;
+
+	if (list_empty(&mdev->resync_work.list))
+		drbd_queue_work(&mdev->tconn->sender_work, &mdev->resync_work);
+}
+
+static void fifo_set(struct fifo_buffer *fb, int value)
+{
+	int i;
+
+	for (i = 0; i < fb->size; i++)
+		fb->values[i] = value;
+}
+
+static int fifo_push(struct fifo_buffer *fb, int value)
+{
+	int ov;
+
+	ov = fb->values[fb->head_index];
+	fb->values[fb->head_index++] = value;
+
+	if (fb->head_index >= fb->size)
+		fb->head_index = 0;
+
+	return ov;
+}
+
+static void fifo_add_val(struct fifo_buffer *fb, int value)
+{
+	int i;
+
+	for (i = 0; i < fb->size; i++)
+		fb->values[i] += value;
+}
+
+struct fifo_buffer *fifo_alloc(int fifo_size)
+{
+	struct fifo_buffer *fb;
+
+	fb = kzalloc(sizeof(struct fifo_buffer) + sizeof(int) * fifo_size, GFP_NOIO);
+	if (!fb)
+		return NULL;
+
+	fb->head_index = 0;
+	fb->size = fifo_size;
+	fb->total = 0;
+
+	return fb;
+}
+
+static int drbd_rs_controller(struct drbd_conf *mdev)
+{
+	struct disk_conf *dc;
+	unsigned int sect_in;  /* Number of sectors that came in since the last turn */
+	unsigned int want;     /* The number of sectors we want in the proxy */
+	int req_sect; /* Number of sectors to request in this turn */
+	int correction; /* Number of sectors more we need in the proxy*/
+	int cps; /* correction per invocation of drbd_rs_controller() */
+	int steps; /* Number of time steps to plan ahead */
+	int curr_corr;
+	int max_sect;
+	struct fifo_buffer *plan;
+
+	sect_in = atomic_xchg(&mdev->rs_sect_in, 0); /* Number of sectors that came in */
+	mdev->rs_in_flight -= sect_in;
+
+	dc = rcu_dereference(mdev->ldev->disk_conf);
+	plan = rcu_dereference(mdev->rs_plan_s);
+
+	steps = plan->size; /* (dc->c_plan_ahead * 10 * SLEEP_TIME) / HZ; */
+
+	if (mdev->rs_in_flight + sect_in == 0) { /* At start of resync */
+		want = ((dc->resync_rate * 2 * SLEEP_TIME) / HZ) * steps;
+	} else { /* normal path */
+		want = dc->c_fill_target ? dc->c_fill_target :
+			sect_in * dc->c_delay_target * HZ / (SLEEP_TIME * 10);
+	}
+
+	correction = want - mdev->rs_in_flight - plan->total;
+
+	/* Plan ahead */
+	cps = correction / steps;
+	fifo_add_val(plan, cps);
+	plan->total += cps * steps;
+
+	/* What we do in this step */
+	curr_corr = fifo_push(plan, 0);
+	plan->total -= curr_corr;
+
+	req_sect = sect_in + curr_corr;
+	if (req_sect < 0)
+		req_sect = 0;
+
+	max_sect = (dc->c_max_rate * 2 * SLEEP_TIME) / HZ;
+	if (req_sect > max_sect)
+		req_sect = max_sect;
+
+	/*
+	dev_warn(DEV, "si=%u if=%d wa=%u co=%d st=%d cps=%d pl=%d cc=%d rs=%d\n",
+		 sect_in, mdev->rs_in_flight, want, correction,
+		 steps, cps, mdev->rs_planed, curr_corr, req_sect);
+	*/
+
+	return req_sect;
+}
+
+static int drbd_rs_number_requests(struct drbd_conf *mdev)
+{
+	int number;
+
+	rcu_read_lock();
+	if (rcu_dereference(mdev->rs_plan_s)->size) {
+		number = drbd_rs_controller(mdev) >> (BM_BLOCK_SHIFT - 9);
+		mdev->c_sync_rate = number * HZ * (BM_BLOCK_SIZE / 1024) / SLEEP_TIME;
+	} else {
+		mdev->c_sync_rate = rcu_dereference(mdev->ldev->disk_conf)->resync_rate;
+		number = SLEEP_TIME * mdev->c_sync_rate  / ((BM_BLOCK_SIZE / 1024) * HZ);
+	}
+	rcu_read_unlock();
+
+	/* ignore the amount of pending requests, the resync controller should
+	 * throttle down to incoming reply rate soon enough anyways. */
+	return number;
+}
+
+int w_make_resync_request(struct drbd_work *w, int cancel)
+{
+	struct drbd_conf *mdev = w->mdev;
+	unsigned long bit;
+	sector_t sector;
+	const sector_t capacity = drbd_get_capacity(mdev->this_bdev);
+	int max_bio_size;
+	int number, rollback_i, size;
+	int align, queued, sndbuf;
+	int i = 0;
+
+	if (unlikely(cancel))
+		return 0;
+
+	if (mdev->rs_total == 0) {
+		/* empty resync? */
+		drbd_resync_finished(mdev);
+		return 0;
+	}
+
+	if (!get_ldev(mdev)) {
+		/* Since we only need to access mdev->rsync a
+		   get_ldev_if_state(mdev,D_FAILED) would be sufficient, but
+		   to continue resync with a broken disk makes no sense at
+		   all */
+		dev_err(DEV, "Disk broke down during resync!\n");
+		return 0;
+	}
+
+	max_bio_size = queue_max_hw_sectors(mdev->rq_queue) << 9;
+	number = drbd_rs_number_requests(mdev);
+	if (number == 0)
+		goto requeue;
+
+	for (i = 0; i < number; i++) {
+		/* Stop generating RS requests, when half of the send buffer is filled */
+		mutex_lock(&mdev->tconn->data.mutex);
+		if (mdev->tconn->data.socket) {
+			queued = mdev->tconn->data.socket->sk->sk_wmem_queued;
+			sndbuf = mdev->tconn->data.socket->sk->sk_sndbuf;
+		} else {
+			queued = 1;
+			sndbuf = 0;
+		}
+		mutex_unlock(&mdev->tconn->data.mutex);
+		if (queued > sndbuf / 2)
+			goto requeue;
+
+next_sector:
+		size = BM_BLOCK_SIZE;
+		bit  = drbd_bm_find_next(mdev, mdev->bm_resync_fo);
+
+		if (bit == DRBD_END_OF_BITMAP) {
+			mdev->bm_resync_fo = drbd_bm_bits(mdev);
+			put_ldev(mdev);
+			return 0;
+		}
+
+		sector = BM_BIT_TO_SECT(bit);
+
+		if (drbd_rs_should_slow_down(mdev, sector) ||
+		    drbd_try_rs_begin_io(mdev, sector)) {
+			mdev->bm_resync_fo = bit;
+			goto requeue;
+		}
+		mdev->bm_resync_fo = bit + 1;
+
+		if (unlikely(drbd_bm_test_bit(mdev, bit) == 0)) {
+			drbd_rs_complete_io(mdev, sector);
+			goto next_sector;
+		}
+
+#if DRBD_MAX_BIO_SIZE > BM_BLOCK_SIZE
+		/* try to find some adjacent bits.
+		 * we stop if we have already the maximum req size.
+		 *
+		 * Additionally always align bigger requests, in order to
+		 * be prepared for all stripe sizes of software RAIDs.
+		 */
+		align = 1;
+		rollback_i = i;
+		for (;;) {
+			if (size + BM_BLOCK_SIZE > max_bio_size)
+				break;
+
+			/* Be always aligned */
+			if (sector & ((1<<(align+3))-1))
+				break;
+
+			/* do not cross extent boundaries */
+			if (((bit+1) & BM_BLOCKS_PER_BM_EXT_MASK) == 0)
+				break;
+			/* now, is it actually dirty, after all?
+			 * caution, drbd_bm_test_bit is tri-state for some
+			 * obscure reason; ( b == 0 ) would get the out-of-band
+			 * only accidentally right because of the "oddly sized"
+			 * adjustment below */
+			if (drbd_bm_test_bit(mdev, bit+1) != 1)
+				break;
+			bit++;
+			size += BM_BLOCK_SIZE;
+			if ((BM_BLOCK_SIZE << align) <= size)
+				align++;
+			i++;
+		}
+		/* if we merged some,
+		 * reset the offset to start the next drbd_bm_find_next from */
+		if (size > BM_BLOCK_SIZE)
+			mdev->bm_resync_fo = bit + 1;
+#endif
+
+		/* adjust very last sectors, in case we are oddly sized */
+		if (sector + (size>>9) > capacity)
+			size = (capacity-sector)<<9;
+		if (mdev->tconn->agreed_pro_version >= 89 && mdev->tconn->csums_tfm) {
+			switch (read_for_csum(mdev, sector, size)) {
+			case -EIO: /* Disk failure */
+				put_ldev(mdev);
+				return -EIO;
+			case -EAGAIN: /* allocation failed, or ldev busy */
+				drbd_rs_complete_io(mdev, sector);
+				mdev->bm_resync_fo = BM_SECT_TO_BIT(sector);
+				i = rollback_i;
+				goto requeue;
+			case 0:
+				/* everything ok */
+				break;
+			default:
+				BUG();
+			}
+		} else {
+			int err;
+
+			inc_rs_pending(mdev);
+			err = drbd_send_drequest(mdev, P_RS_DATA_REQUEST,
+						 sector, size, ID_SYNCER);
+			if (err) {
+				dev_err(DEV, "drbd_send_drequest() failed, aborting...\n");
+				dec_rs_pending(mdev);
+				put_ldev(mdev);
+				return err;
+			}
+		}
+	}
+
+	if (mdev->bm_resync_fo >= drbd_bm_bits(mdev)) {
+		/* last syncer _request_ was sent,
+		 * but the P_RS_DATA_REPLY not yet received.  sync will end (and
+		 * next sync group will resume), as soon as we receive the last
+		 * resync data block, and the last bit is cleared.
+		 * until then resync "work" is "inactive" ...
+		 */
+		put_ldev(mdev);
+		return 0;
+	}
+
+ requeue:
+	mdev->rs_in_flight += (i << (BM_BLOCK_SHIFT - 9));
+	mod_timer(&mdev->resync_timer, jiffies + SLEEP_TIME);
+	put_ldev(mdev);
+	return 0;
+}
+
+static int w_make_ov_request(struct drbd_work *w, int cancel)
+{
+	struct drbd_conf *mdev = w->mdev;
+	int number, i, size;
+	sector_t sector;
+	const sector_t capacity = drbd_get_capacity(mdev->this_bdev);
+	bool stop_sector_reached = false;
+
+	if (unlikely(cancel))
+		return 1;
+
+	number = drbd_rs_number_requests(mdev);
+
+	sector = mdev->ov_position;
+	for (i = 0; i < number; i++) {
+		if (sector >= capacity)
+			return 1;
+
+		/* We check for "finished" only in the reply path:
+		 * w_e_end_ov_reply().
+		 * We need to send at least one request out. */
+		stop_sector_reached = i > 0
+			&& verify_can_do_stop_sector(mdev)
+			&& sector >= mdev->ov_stop_sector;
+		if (stop_sector_reached)
+			break;
+
+		size = BM_BLOCK_SIZE;
+
+		if (drbd_rs_should_slow_down(mdev, sector) ||
+		    drbd_try_rs_begin_io(mdev, sector)) {
+			mdev->ov_position = sector;
+			goto requeue;
+		}
+
+		if (sector + (size>>9) > capacity)
+			size = (capacity-sector)<<9;
+
+		inc_rs_pending(mdev);
+		if (drbd_send_ov_request(mdev, sector, size)) {
+			dec_rs_pending(mdev);
+			return 0;
+		}
+		sector += BM_SECT_PER_BIT;
+	}
+	mdev->ov_position = sector;
+
+ requeue:
+	mdev->rs_in_flight += (i << (BM_BLOCK_SHIFT - 9));
+	if (i == 0 || !stop_sector_reached)
+		mod_timer(&mdev->resync_timer, jiffies + SLEEP_TIME);
+	return 1;
+}
+
+int w_ov_finished(struct drbd_work *w, int cancel)
+{
+	struct drbd_conf *mdev = w->mdev;
+	kfree(w);
+	ov_out_of_sync_print(mdev);
+	drbd_resync_finished(mdev);
+
+	return 0;
+}
+
+static int w_resync_finished(struct drbd_work *w, int cancel)
+{
+	struct drbd_conf *mdev = w->mdev;
+	kfree(w);
+
+	drbd_resync_finished(mdev);
+
+	return 0;
+}
+
+static void ping_peer(struct drbd_conf *mdev)
+{
+	struct drbd_tconn *tconn = mdev->tconn;
+
+	clear_bit(GOT_PING_ACK, &tconn->flags);
+	request_ping(tconn);
+	wait_event(tconn->ping_wait,
+		   test_bit(GOT_PING_ACK, &tconn->flags) || mdev->state.conn < C_CONNECTED);
+}
+
+int drbd_resync_finished(struct drbd_conf *mdev)
+{
+	unsigned long db, dt, dbdt;
+	unsigned long n_oos;
+	union drbd_state os, ns;
+	struct drbd_work *w;
+	char *khelper_cmd = NULL;
+	int verify_done = 0;
+
+	/* Remove all elements from the resync LRU. Since future actions
+	 * might set bits in the (main) bitmap, then the entries in the
+	 * resync LRU would be wrong. */
+	if (drbd_rs_del_all(mdev)) {
+		/* In case this is not possible now, most probably because
+		 * there are P_RS_DATA_REPLY Packets lingering on the worker's
+		 * queue (or even the read operations for those packets
+		 * is not finished by now).   Retry in 100ms. */
+
+		schedule_timeout_interruptible(HZ / 10);
+		w = kmalloc(sizeof(struct drbd_work), GFP_ATOMIC);
+		if (w) {
+			w->cb = w_resync_finished;
+			w->mdev = mdev;
+			drbd_queue_work(&mdev->tconn->sender_work, w);
+			return 1;
+		}
+		dev_err(DEV, "Warn failed to drbd_rs_del_all() and to kmalloc(w).\n");
+	}
+
+	dt = (jiffies - mdev->rs_start - mdev->rs_paused) / HZ;
+	if (dt <= 0)
+		dt = 1;
+	
+	db = mdev->rs_total;
+	/* adjust for verify start and stop sectors, respective reached position */
+	if (mdev->state.conn == C_VERIFY_S || mdev->state.conn == C_VERIFY_T)
+		db -= mdev->ov_left;
+
+	dbdt = Bit2KB(db/dt);
+	mdev->rs_paused /= HZ;
+
+	if (!get_ldev(mdev))
+		goto out;
+
+	ping_peer(mdev);
+
+	spin_lock_irq(&mdev->tconn->req_lock);
+	os = drbd_read_state(mdev);
+
+	verify_done = (os.conn == C_VERIFY_S || os.conn == C_VERIFY_T);
+
+	/* This protects us against multiple calls (that can happen in the presence
+	   of application IO), and against connectivity loss just before we arrive here. */
+	if (os.conn <= C_CONNECTED)
+		goto out_unlock;
+
+	ns = os;
+	ns.conn = C_CONNECTED;
+
+	dev_info(DEV, "%s done (total %lu sec; paused %lu sec; %lu K/sec)\n",
+	     verify_done ? "Online verify" : "Resync",
+	     dt + mdev->rs_paused, mdev->rs_paused, dbdt);
+
+	n_oos = drbd_bm_total_weight(mdev);
+
+	if (os.conn == C_VERIFY_S || os.conn == C_VERIFY_T) {
+		if (n_oos) {
+			dev_alert(DEV, "Online verify found %lu %dk block out of sync!\n",
+			      n_oos, Bit2KB(1));
+			khelper_cmd = "out-of-sync";
+		}
+	} else {
+		D_ASSERT((n_oos - mdev->rs_failed) == 0);
+
+		if (os.conn == C_SYNC_TARGET || os.conn == C_PAUSED_SYNC_T)
+			khelper_cmd = "after-resync-target";
+
+		if (mdev->tconn->csums_tfm && mdev->rs_total) {
+			const unsigned long s = mdev->rs_same_csum;
+			const unsigned long t = mdev->rs_total;
+			const int ratio =
+				(t == 0)     ? 0 :
+			(t < 100000) ? ((s*100)/t) : (s/(t/100));
+			dev_info(DEV, "%u %% had equal checksums, eliminated: %luK; "
+			     "transferred %luK total %luK\n",
+			     ratio,
+			     Bit2KB(mdev->rs_same_csum),
+			     Bit2KB(mdev->rs_total - mdev->rs_same_csum),
+			     Bit2KB(mdev->rs_total));
+		}
+	}
+
+	if (mdev->rs_failed) {
+		dev_info(DEV, "            %lu failed blocks\n", mdev->rs_failed);
+
+		if (os.conn == C_SYNC_TARGET || os.conn == C_PAUSED_SYNC_T) {
+			ns.disk = D_INCONSISTENT;
+			ns.pdsk = D_UP_TO_DATE;
+		} else {
+			ns.disk = D_UP_TO_DATE;
+			ns.pdsk = D_INCONSISTENT;
+		}
+	} else {
+		ns.disk = D_UP_TO_DATE;
+		ns.pdsk = D_UP_TO_DATE;
+
+		if (os.conn == C_SYNC_TARGET || os.conn == C_PAUSED_SYNC_T) {
+			if (mdev->p_uuid) {
+				int i;
+				for (i = UI_BITMAP ; i <= UI_HISTORY_END ; i++)
+					_drbd_uuid_set(mdev, i, mdev->p_uuid[i]);
+				drbd_uuid_set(mdev, UI_BITMAP, mdev->ldev->md.uuid[UI_CURRENT]);
+				_drbd_uuid_set(mdev, UI_CURRENT, mdev->p_uuid[UI_CURRENT]);
+			} else {
+				dev_err(DEV, "mdev->p_uuid is NULL! BUG\n");
+			}
+		}
+
+		if (!(os.conn == C_VERIFY_S || os.conn == C_VERIFY_T)) {
+			/* for verify runs, we don't update uuids here,
+			 * so there would be nothing to report. */
+			drbd_uuid_set_bm(mdev, 0UL);
+			drbd_print_uuids(mdev, "updated UUIDs");
+			if (mdev->p_uuid) {
+				/* Now the two UUID sets are equal, update what we
+				 * know of the peer. */
+				int i;
+				for (i = UI_CURRENT ; i <= UI_HISTORY_END ; i++)
+					mdev->p_uuid[i] = mdev->ldev->md.uuid[i];
+			}
+		}
+	}
+
+	_drbd_set_state(mdev, ns, CS_VERBOSE, NULL);
+out_unlock:
+	spin_unlock_irq(&mdev->tconn->req_lock);
+	put_ldev(mdev);
+out:
+	mdev->rs_total  = 0;
+	mdev->rs_failed = 0;
+	mdev->rs_paused = 0;
+
+	/* reset start sector, if we reached end of device */
+	if (verify_done && mdev->ov_left == 0)
+		mdev->ov_start_sector = 0;
+
+	drbd_md_sync(mdev);
+
+	if (khelper_cmd)
+		drbd_khelper(mdev, khelper_cmd);
+
+	return 1;
+}
+
+/* helper */
+static void move_to_net_ee_or_free(struct drbd_conf *mdev, struct drbd_peer_request *peer_req)
+{
+	if (drbd_peer_req_has_active_page(peer_req)) {
+		/* This might happen if sendpage() has not finished */
+		int i = (peer_req->i.size + PAGE_SIZE -1) >> PAGE_SHIFT;
+		atomic_add(i, &mdev->pp_in_use_by_net);
+		atomic_sub(i, &mdev->pp_in_use);
+		spin_lock_irq(&mdev->tconn->req_lock);
+		list_add_tail(&peer_req->w.list, &mdev->net_ee);
+		spin_unlock_irq(&mdev->tconn->req_lock);
+		wake_up(&drbd_pp_wait);
+	} else
+		drbd_free_peer_req(mdev, peer_req);
+}
+
+/**
+ * w_e_end_data_req() - Worker callback, to send a P_DATA_REPLY packet in response to a P_DATA_REQUEST
+ * @mdev:	DRBD device.
+ * @w:		work object.
+ * @cancel:	The connection will be closed anyways
+ */
+int w_e_end_data_req(struct drbd_work *w, int cancel)
+{
+	struct drbd_peer_request *peer_req = container_of(w, struct drbd_peer_request, w);
+	struct drbd_conf *mdev = w->mdev;
+	int err;
+
+	if (unlikely(cancel)) {
+		drbd_free_peer_req(mdev, peer_req);
+		dec_unacked(mdev);
+		return 0;
+	}
+
+	if (likely((peer_req->flags & EE_WAS_ERROR) == 0)) {
+		err = drbd_send_block(mdev, P_DATA_REPLY, peer_req);
+	} else {
+		if (__ratelimit(&drbd_ratelimit_state))
+			dev_err(DEV, "Sending NegDReply. sector=%llus.\n",
+			    (unsigned long long)peer_req->i.sector);
+
+		err = drbd_send_ack(mdev, P_NEG_DREPLY, peer_req);
+	}
+
+	dec_unacked(mdev);
+
+	move_to_net_ee_or_free(mdev, peer_req);
+
+	if (unlikely(err))
+		dev_err(DEV, "drbd_send_block() failed\n");
+	return err;
+}
+
+/**
+ * w_e_end_rsdata_req() - Worker callback to send a P_RS_DATA_REPLY packet in response to a P_RS_DATA_REQUEST
+ * @mdev:	DRBD device.
+ * @w:		work object.
+ * @cancel:	The connection will be closed anyways
+ */
+int w_e_end_rsdata_req(struct drbd_work *w, int cancel)
+{
+	struct drbd_peer_request *peer_req = container_of(w, struct drbd_peer_request, w);
+	struct drbd_conf *mdev = w->mdev;
+	int err;
+
+	if (unlikely(cancel)) {
+		drbd_free_peer_req(mdev, peer_req);
+		dec_unacked(mdev);
+		return 0;
+	}
+
+	if (get_ldev_if_state(mdev, D_FAILED)) {
+		drbd_rs_complete_io(mdev, peer_req->i.sector);
+		put_ldev(mdev);
+	}
+
+	if (mdev->state.conn == C_AHEAD) {
+		err = drbd_send_ack(mdev, P_RS_CANCEL, peer_req);
+	} else if (likely((peer_req->flags & EE_WAS_ERROR) == 0)) {
+		if (likely(mdev->state.pdsk >= D_INCONSISTENT)) {
+			inc_rs_pending(mdev);
+			err = drbd_send_block(mdev, P_RS_DATA_REPLY, peer_req);
+		} else {
+			if (__ratelimit(&drbd_ratelimit_state))
+				dev_err(DEV, "Not sending RSDataReply, "
+				    "partner DISKLESS!\n");
+			err = 0;
+		}
+	} else {
+		if (__ratelimit(&drbd_ratelimit_state))
+			dev_err(DEV, "Sending NegRSDReply. sector %llus.\n",
+			    (unsigned long long)peer_req->i.sector);
+
+		err = drbd_send_ack(mdev, P_NEG_RS_DREPLY, peer_req);
+
+		/* update resync data with failure */
+		drbd_rs_failed_io(mdev, peer_req->i.sector, peer_req->i.size);
+	}
+
+	dec_unacked(mdev);
+
+	move_to_net_ee_or_free(mdev, peer_req);
+
+	if (unlikely(err))
+		dev_err(DEV, "drbd_send_block() failed\n");
+	return err;
+}
+
+int w_e_end_csum_rs_req(struct drbd_work *w, int cancel)
+{
+	struct drbd_peer_request *peer_req = container_of(w, struct drbd_peer_request, w);
+	struct drbd_conf *mdev = w->mdev;
+	struct digest_info *di;
+	int digest_size;
+	void *digest = NULL;
+	int err, eq = 0;
+
+	if (unlikely(cancel)) {
+		drbd_free_peer_req(mdev, peer_req);
+		dec_unacked(mdev);
+		return 0;
+	}
+
+	if (get_ldev(mdev)) {
+		drbd_rs_complete_io(mdev, peer_req->i.sector);
+		put_ldev(mdev);
+	}
+
+	di = peer_req->digest;
+
+	if (likely((peer_req->flags & EE_WAS_ERROR) == 0)) {
+		/* quick hack to try to avoid a race against reconfiguration.
+		 * a real fix would be much more involved,
+		 * introducing more locking mechanisms */
+		if (mdev->tconn->csums_tfm) {
+			digest_size = crypto_hash_digestsize(mdev->tconn->csums_tfm);
+			D_ASSERT(digest_size == di->digest_size);
+			digest = kmalloc(digest_size, GFP_NOIO);
+		}
+		if (digest) {
+			drbd_csum_ee(mdev, mdev->tconn->csums_tfm, peer_req, digest);
+			eq = !memcmp(digest, di->digest, digest_size);
+			kfree(digest);
+		}
+
+		if (eq) {
+			drbd_set_in_sync(mdev, peer_req->i.sector, peer_req->i.size);
+			/* rs_same_csums unit is BM_BLOCK_SIZE */
+			mdev->rs_same_csum += peer_req->i.size >> BM_BLOCK_SHIFT;
+			err = drbd_send_ack(mdev, P_RS_IS_IN_SYNC, peer_req);
+		} else {
+			inc_rs_pending(mdev);
+			peer_req->block_id = ID_SYNCER; /* By setting block_id, digest pointer becomes invalid! */
+			peer_req->flags &= ~EE_HAS_DIGEST; /* This peer request no longer has a digest pointer */
+			kfree(di);
+			err = drbd_send_block(mdev, P_RS_DATA_REPLY, peer_req);
+		}
+	} else {
+		err = drbd_send_ack(mdev, P_NEG_RS_DREPLY, peer_req);
+		if (__ratelimit(&drbd_ratelimit_state))
+			dev_err(DEV, "Sending NegDReply. I guess it gets messy.\n");
+	}
+
+	dec_unacked(mdev);
+	move_to_net_ee_or_free(mdev, peer_req);
+
+	if (unlikely(err))
+		dev_err(DEV, "drbd_send_block/ack() failed\n");
+	return err;
+}
+
+int w_e_end_ov_req(struct drbd_work *w, int cancel)
+{
+	struct drbd_peer_request *peer_req = container_of(w, struct drbd_peer_request, w);
+	struct drbd_conf *mdev = w->mdev;
+	sector_t sector = peer_req->i.sector;
+	unsigned int size = peer_req->i.size;
+	int digest_size;
+	void *digest;
+	int err = 0;
+
+	if (unlikely(cancel))
+		goto out;
+
+	digest_size = crypto_hash_digestsize(mdev->tconn->verify_tfm);
+	digest = kmalloc(digest_size, GFP_NOIO);
+	if (!digest) {
+		err = 1;	/* terminate the connection in case the allocation failed */
+		goto out;
+	}
+
+	if (likely(!(peer_req->flags & EE_WAS_ERROR)))
+		drbd_csum_ee(mdev, mdev->tconn->verify_tfm, peer_req, digest);
+	else
+		memset(digest, 0, digest_size);
+
+	/* Free e and pages before send.
+	 * In case we block on congestion, we could otherwise run into
+	 * some distributed deadlock, if the other side blocks on
+	 * congestion as well, because our receiver blocks in
+	 * drbd_alloc_pages due to pp_in_use > max_buffers. */
+	drbd_free_peer_req(mdev, peer_req);
+	peer_req = NULL;
+	inc_rs_pending(mdev);
+	err = drbd_send_drequest_csum(mdev, sector, size, digest, digest_size, P_OV_REPLY);
+	if (err)
+		dec_rs_pending(mdev);
+	kfree(digest);
+
+out:
+	if (peer_req)
+		drbd_free_peer_req(mdev, peer_req);
+	dec_unacked(mdev);
+	return err;
+}
+
+void drbd_ov_out_of_sync_found(struct drbd_conf *mdev, sector_t sector, int size)
+{
+	if (mdev->ov_last_oos_start + mdev->ov_last_oos_size == sector) {
+		mdev->ov_last_oos_size += size>>9;
+	} else {
+		mdev->ov_last_oos_start = sector;
+		mdev->ov_last_oos_size = size>>9;
+	}
+	drbd_set_out_of_sync(mdev, sector, size);
+}
+
+int w_e_end_ov_reply(struct drbd_work *w, int cancel)
+{
+	struct drbd_peer_request *peer_req = container_of(w, struct drbd_peer_request, w);
+	struct drbd_conf *mdev = w->mdev;
+	struct digest_info *di;
+	void *digest;
+	sector_t sector = peer_req->i.sector;
+	unsigned int size = peer_req->i.size;
+	int digest_size;
+	int err, eq = 0;
+	bool stop_sector_reached = false;
+
+	if (unlikely(cancel)) {
+		drbd_free_peer_req(mdev, peer_req);
+		dec_unacked(mdev);
+		return 0;
+	}
+
+	/* after "cancel", because after drbd_disconnect/drbd_rs_cancel_all
+	 * the resync lru has been cleaned up already */
+	if (get_ldev(mdev)) {
+		drbd_rs_complete_io(mdev, peer_req->i.sector);
+		put_ldev(mdev);
+	}
+
+	di = peer_req->digest;
+
+	if (likely((peer_req->flags & EE_WAS_ERROR) == 0)) {
+		digest_size = crypto_hash_digestsize(mdev->tconn->verify_tfm);
+		digest = kmalloc(digest_size, GFP_NOIO);
+		if (digest) {
+			drbd_csum_ee(mdev, mdev->tconn->verify_tfm, peer_req, digest);
+
+			D_ASSERT(digest_size == di->digest_size);
+			eq = !memcmp(digest, di->digest, digest_size);
+			kfree(digest);
+		}
+	}
+
+	/* Free peer_req and pages before send.
+	 * In case we block on congestion, we could otherwise run into
+	 * some distributed deadlock, if the other side blocks on
+	 * congestion as well, because our receiver blocks in
+	 * drbd_alloc_pages due to pp_in_use > max_buffers. */
+	drbd_free_peer_req(mdev, peer_req);
+	if (!eq)
+		drbd_ov_out_of_sync_found(mdev, sector, size);
+	else
+		ov_out_of_sync_print(mdev);
+
+	err = drbd_send_ack_ex(mdev, P_OV_RESULT, sector, size,
+			       eq ? ID_IN_SYNC : ID_OUT_OF_SYNC);
+
+	dec_unacked(mdev);
+
+	--mdev->ov_left;
+
+	/* let's advance progress step marks only for every other megabyte */
+	if ((mdev->ov_left & 0x200) == 0x200)
+		drbd_advance_rs_marks(mdev, mdev->ov_left);
+
+	stop_sector_reached = verify_can_do_stop_sector(mdev) &&
+		(sector + (size>>9)) >= mdev->ov_stop_sector;
+
+	if (mdev->ov_left == 0 || stop_sector_reached) {
+		ov_out_of_sync_print(mdev);
+		drbd_resync_finished(mdev);
+	}
+
+	return err;
+}
+
+int w_prev_work_done(struct drbd_work *w, int cancel)
+{
+	struct drbd_wq_barrier *b = container_of(w, struct drbd_wq_barrier, w);
+
+	complete(&b->done);
+	return 0;
+}
+
+/* FIXME
+ * We need to track the number of pending barrier acks,
+ * and to be able to wait for them.
+ * See also comment in drbd_adm_attach before drbd_suspend_io.
+ */
+int drbd_send_barrier(struct drbd_tconn *tconn)
+{
+	struct p_barrier *p;
+	struct drbd_socket *sock;
+
+	sock = &tconn->data;
+	p = conn_prepare_command(tconn, sock);
+	if (!p)
+		return -EIO;
+	p->barrier = tconn->send.current_epoch_nr;
+	p->pad = 0;
+	tconn->send.current_epoch_writes = 0;
+
+	return conn_send_command(tconn, sock, P_BARRIER, sizeof(*p), NULL, 0);
+}
+
+int w_send_write_hint(struct drbd_work *w, int cancel)
+{
+	struct drbd_conf *mdev = w->mdev;
+	struct drbd_socket *sock;
+
+	if (cancel)
+		return 0;
+	sock = &mdev->tconn->data;
+	if (!drbd_prepare_command(mdev, sock))
+		return -EIO;
+	return drbd_send_command(mdev, sock, P_UNPLUG_REMOTE, 0, NULL, 0);
+}
+
+static void re_init_if_first_write(struct drbd_tconn *tconn, unsigned int epoch)
+{
+	if (!tconn->send.seen_any_write_yet) {
+		tconn->send.seen_any_write_yet = true;
+		tconn->send.current_epoch_nr = epoch;
+		tconn->send.current_epoch_writes = 0;
+	}
+}
+
+static void maybe_send_barrier(struct drbd_tconn *tconn, unsigned int epoch)
+{
+	/* re-init if first write on this connection */
+	if (!tconn->send.seen_any_write_yet)
+		return;
+	if (tconn->send.current_epoch_nr != epoch) {
+		if (tconn->send.current_epoch_writes)
+			drbd_send_barrier(tconn);
+		tconn->send.current_epoch_nr = epoch;
+	}
+}
+
+int w_send_out_of_sync(struct drbd_work *w, int cancel)
+{
+	struct drbd_request *req = container_of(w, struct drbd_request, w);
+	struct drbd_conf *mdev = w->mdev;
+	struct drbd_tconn *tconn = mdev->tconn;
+	int err;
+
+	if (unlikely(cancel)) {
+		req_mod(req, SEND_CANCELED);
+		return 0;
+	}
+
+	/* this time, no tconn->send.current_epoch_writes++;
+	 * If it was sent, it was the closing barrier for the last
+	 * replicated epoch, before we went into AHEAD mode.
+	 * No more barriers will be sent, until we leave AHEAD mode again. */
+	maybe_send_barrier(tconn, req->epoch);
+
+	err = drbd_send_out_of_sync(mdev, req);
+	req_mod(req, OOS_HANDED_TO_NETWORK);
+
+	return err;
+}
+
+/**
+ * w_send_dblock() - Worker callback to send a P_DATA packet in order to mirror a write request
+ * @mdev:	DRBD device.
+ * @w:		work object.
+ * @cancel:	The connection will be closed anyways
+ */
+int w_send_dblock(struct drbd_work *w, int cancel)
+{
+	struct drbd_request *req = container_of(w, struct drbd_request, w);
+	struct drbd_conf *mdev = w->mdev;
+	struct drbd_tconn *tconn = mdev->tconn;
+	int err;
+
+	if (unlikely(cancel)) {
+		req_mod(req, SEND_CANCELED);
+		return 0;
+	}
+
+	re_init_if_first_write(tconn, req->epoch);
+	maybe_send_barrier(tconn, req->epoch);
+	tconn->send.current_epoch_writes++;
+
+	err = drbd_send_dblock(mdev, req);
+	req_mod(req, err ? SEND_FAILED : HANDED_OVER_TO_NETWORK);
+
+	return err;
+}
+
+/**
+ * w_send_read_req() - Worker callback to send a read request (P_DATA_REQUEST) packet
+ * @mdev:	DRBD device.
+ * @w:		work object.
+ * @cancel:	The connection will be closed anyways
+ */
+int w_send_read_req(struct drbd_work *w, int cancel)
+{
+	struct drbd_request *req = container_of(w, struct drbd_request, w);
+	struct drbd_conf *mdev = w->mdev;
+	struct drbd_tconn *tconn = mdev->tconn;
+	int err;
+
+	if (unlikely(cancel)) {
+		req_mod(req, SEND_CANCELED);
+		return 0;
+	}
+
+	/* Even read requests may close a write epoch,
+	 * if there was any yet. */
+	maybe_send_barrier(tconn, req->epoch);
+
+	err = drbd_send_drequest(mdev, P_DATA_REQUEST, req->i.sector, req->i.size,
+				 (unsigned long)req);
+
+	req_mod(req, err ? SEND_FAILED : HANDED_OVER_TO_NETWORK);
+
+	return err;
+}
+
+int w_restart_disk_io(struct drbd_work *w, int cancel)
+{
+	struct drbd_request *req = container_of(w, struct drbd_request, w);
+	struct drbd_conf *mdev = w->mdev;
+
+	if (bio_data_dir(req->master_bio) == WRITE && req->rq_state & RQ_IN_ACT_LOG)
+		drbd_al_begin_io(mdev, &req->i, false);
+
+	drbd_req_make_private_bio(req, req->master_bio);
+	req->private_bio->bi_bdev = mdev->ldev->backing_bdev;
+	generic_make_request(req->private_bio);
+
+	return 0;
+}
+
+static int _drbd_may_sync_now(struct drbd_conf *mdev)
+{
+	struct drbd_conf *odev = mdev;
+	int resync_after;
+
+	while (1) {
+		if (!odev->ldev || odev->state.disk == D_DISKLESS)
+			return 1;
+		rcu_read_lock();
+		resync_after = rcu_dereference(odev->ldev->disk_conf)->resync_after;
+		rcu_read_unlock();
+		if (resync_after == -1)
+			return 1;
+		odev = minor_to_mdev(resync_after);
+		if (!odev)
+			return 1;
+		if ((odev->state.conn >= C_SYNC_SOURCE &&
+		     odev->state.conn <= C_PAUSED_SYNC_T) ||
+		    odev->state.aftr_isp || odev->state.peer_isp ||
+		    odev->state.user_isp)
+			return 0;
+	}
+}
+
+/**
+ * _drbd_pause_after() - Pause resync on all devices that may not resync now
+ * @mdev:	DRBD device.
+ *
+ * Called from process context only (admin command and after_state_ch).
+ */
+static int _drbd_pause_after(struct drbd_conf *mdev)
+{
+	struct drbd_conf *odev;
+	int i, rv = 0;
+
+	rcu_read_lock();
+	idr_for_each_entry(&minors, odev, i) {
+		if (odev->state.conn == C_STANDALONE && odev->state.disk == D_DISKLESS)
+			continue;
+		if (!_drbd_may_sync_now(odev))
+			rv |= (__drbd_set_state(_NS(odev, aftr_isp, 1), CS_HARD, NULL)
+			       != SS_NOTHING_TO_DO);
+	}
+	rcu_read_unlock();
+
+	return rv;
+}
+
+/**
+ * _drbd_resume_next() - Resume resync on all devices that may resync now
+ * @mdev:	DRBD device.
+ *
+ * Called from process context only (admin command and worker).
+ */
+static int _drbd_resume_next(struct drbd_conf *mdev)
+{
+	struct drbd_conf *odev;
+	int i, rv = 0;
+
+	rcu_read_lock();
+	idr_for_each_entry(&minors, odev, i) {
+		if (odev->state.conn == C_STANDALONE && odev->state.disk == D_DISKLESS)
+			continue;
+		if (odev->state.aftr_isp) {
+			if (_drbd_may_sync_now(odev))
+				rv |= (__drbd_set_state(_NS(odev, aftr_isp, 0),
+							CS_HARD, NULL)
+				       != SS_NOTHING_TO_DO) ;
+		}
+	}
+	rcu_read_unlock();
+	return rv;
+}
+
+void resume_next_sg(struct drbd_conf *mdev)
+{
+	write_lock_irq(&global_state_lock);
+	_drbd_resume_next(mdev);
+	write_unlock_irq(&global_state_lock);
+}
+
+void suspend_other_sg(struct drbd_conf *mdev)
+{
+	write_lock_irq(&global_state_lock);
+	_drbd_pause_after(mdev);
+	write_unlock_irq(&global_state_lock);
+}
+
+/* caller must hold global_state_lock */
+enum drbd_ret_code drbd_resync_after_valid(struct drbd_conf *mdev, int o_minor)
+{
+	struct drbd_conf *odev;
+	int resync_after;
+
+	if (o_minor == -1)
+		return NO_ERROR;
+	if (o_minor < -1 || o_minor > MINORMASK)
+		return ERR_RESYNC_AFTER;
+
+	/* check for loops */
+	odev = minor_to_mdev(o_minor);
+	while (1) {
+		if (odev == mdev)
+			return ERR_RESYNC_AFTER_CYCLE;
+
+		/* You are free to depend on diskless, non-existing,
+		 * or not yet/no longer existing minors.
+		 * We only reject dependency loops.
+		 * We cannot follow the dependency chain beyond a detached or
+		 * missing minor.
+		 */
+		if (!odev || !odev->ldev || odev->state.disk == D_DISKLESS)
+			return NO_ERROR;
+
+		rcu_read_lock();
+		resync_after = rcu_dereference(odev->ldev->disk_conf)->resync_after;
+		rcu_read_unlock();
+		/* dependency chain ends here, no cycles. */
+		if (resync_after == -1)
+			return NO_ERROR;
+
+		/* follow the dependency chain */
+		odev = minor_to_mdev(resync_after);
+	}
+}
+
+/* caller must hold global_state_lock */
+void drbd_resync_after_changed(struct drbd_conf *mdev)
+{
+	int changes;
+
+	do {
+		changes  = _drbd_pause_after(mdev);
+		changes |= _drbd_resume_next(mdev);
+	} while (changes);
+}
+
+void drbd_rs_controller_reset(struct drbd_conf *mdev)
+{
+	struct fifo_buffer *plan;
+
+	atomic_set(&mdev->rs_sect_in, 0);
+	atomic_set(&mdev->rs_sect_ev, 0);
+	mdev->rs_in_flight = 0;
+
+	/* Updating the RCU protected object in place is necessary since
+	   this function gets called from atomic context.
+	   It is valid since all other updates also lead to an completely
+	   empty fifo */
+	rcu_read_lock();
+	plan = rcu_dereference(mdev->rs_plan_s);
+	plan->total = 0;
+	fifo_set(plan, 0);
+	rcu_read_unlock();
+}
+
+void start_resync_timer_fn(unsigned long data)
+{
+	struct drbd_conf *mdev = (struct drbd_conf *) data;
+
+	drbd_queue_work(&mdev->tconn->sender_work, &mdev->start_resync_work);
+}
+
+int w_start_resync(struct drbd_work *w, int cancel)
+{
+	struct drbd_conf *mdev = w->mdev;
+
+	if (atomic_read(&mdev->unacked_cnt) || atomic_read(&mdev->rs_pending_cnt)) {
+		dev_warn(DEV, "w_start_resync later...\n");
+		mdev->start_resync_timer.expires = jiffies + HZ/10;
+		add_timer(&mdev->start_resync_timer);
+		return 0;
+	}
+
+	drbd_start_resync(mdev, C_SYNC_SOURCE);
+	clear_bit(AHEAD_TO_SYNC_SOURCE, &mdev->flags);
+	return 0;
+}
+
+/**
+ * drbd_start_resync() - Start the resync process
+ * @mdev:	DRBD device.
+ * @side:	Either C_SYNC_SOURCE or C_SYNC_TARGET
+ *
+ * This function might bring you directly into one of the
+ * C_PAUSED_SYNC_* states.
+ */
+void drbd_start_resync(struct drbd_conf *mdev, enum drbd_conns side)
+{
+	union drbd_state ns;
+	int r;
+
+	if (mdev->state.conn >= C_SYNC_SOURCE && mdev->state.conn < C_AHEAD) {
+		dev_err(DEV, "Resync already running!\n");
+		return;
+	}
+
+	if (!test_bit(B_RS_H_DONE, &mdev->flags)) {
+		if (side == C_SYNC_TARGET) {
+			/* Since application IO was locked out during C_WF_BITMAP_T and
+			   C_WF_SYNC_UUID we are still unmodified. Before going to C_SYNC_TARGET
+			   we check that we might make the data inconsistent. */
+			r = drbd_khelper(mdev, "before-resync-target");
+			r = (r >> 8) & 0xff;
+			if (r > 0) {
+				dev_info(DEV, "before-resync-target handler returned %d, "
+					 "dropping connection.\n", r);
+				conn_request_state(mdev->tconn, NS(conn, C_DISCONNECTING), CS_HARD);
+				return;
+			}
+		} else /* C_SYNC_SOURCE */ {
+			r = drbd_khelper(mdev, "before-resync-source");
+			r = (r >> 8) & 0xff;
+			if (r > 0) {
+				if (r == 3) {
+					dev_info(DEV, "before-resync-source handler returned %d, "
+						 "ignoring. Old userland tools?", r);
+				} else {
+					dev_info(DEV, "before-resync-source handler returned %d, "
+						 "dropping connection.\n", r);
+					conn_request_state(mdev->tconn, NS(conn, C_DISCONNECTING), CS_HARD);
+					return;
+				}
+			}
+		}
+	}
+
+	if (current == mdev->tconn->worker.task) {
+		/* The worker should not sleep waiting for state_mutex,
+		   that can take long */
+		if (!mutex_trylock(mdev->state_mutex)) {
+			set_bit(B_RS_H_DONE, &mdev->flags);
+			mdev->start_resync_timer.expires = jiffies + HZ/5;
+			add_timer(&mdev->start_resync_timer);
+			return;
+		}
+	} else {
+		mutex_lock(mdev->state_mutex);
+	}
+	clear_bit(B_RS_H_DONE, &mdev->flags);
+
+	write_lock_irq(&global_state_lock);
+	/* Did some connection breakage or IO error race with us? */
+	if (mdev->state.conn < C_CONNECTED
+	|| !get_ldev_if_state(mdev, D_NEGOTIATING)) {
+		write_unlock_irq(&global_state_lock);
+		mutex_unlock(mdev->state_mutex);
+		return;
+	}
+
+	ns = drbd_read_state(mdev);
+
+	ns.aftr_isp = !_drbd_may_sync_now(mdev);
+
+	ns.conn = side;
+
+	if (side == C_SYNC_TARGET)
+		ns.disk = D_INCONSISTENT;
+	else /* side == C_SYNC_SOURCE */
+		ns.pdsk = D_INCONSISTENT;
+
+	r = __drbd_set_state(mdev, ns, CS_VERBOSE, NULL);
+	ns = drbd_read_state(mdev);
+
+	if (ns.conn < C_CONNECTED)
+		r = SS_UNKNOWN_ERROR;
+
+	if (r == SS_SUCCESS) {
+		unsigned long tw = drbd_bm_total_weight(mdev);
+		unsigned long now = jiffies;
+		int i;
+
+		mdev->rs_failed    = 0;
+		mdev->rs_paused    = 0;
+		mdev->rs_same_csum = 0;
+		mdev->rs_last_events = 0;
+		mdev->rs_last_sect_ev = 0;
+		mdev->rs_total     = tw;
+		mdev->rs_start     = now;
+		for (i = 0; i < DRBD_SYNC_MARKS; i++) {
+			mdev->rs_mark_left[i] = tw;
+			mdev->rs_mark_time[i] = now;
+		}
+		_drbd_pause_after(mdev);
+	}
+	write_unlock_irq(&global_state_lock);
+
+	if (r == SS_SUCCESS) {
+		/* reset rs_last_bcast when a resync or verify is started,
+		 * to deal with potential jiffies wrap. */
+		mdev->rs_last_bcast = jiffies - HZ;
+
+		dev_info(DEV, "Began resync as %s (will sync %lu KB [%lu bits set]).\n",
+		     drbd_conn_str(ns.conn),
+		     (unsigned long) mdev->rs_total << (BM_BLOCK_SHIFT-10),
+		     (unsigned long) mdev->rs_total);
+		if (side == C_SYNC_TARGET)
+			mdev->bm_resync_fo = 0;
+
+		/* Since protocol 96, we must serialize drbd_gen_and_send_sync_uuid
+		 * with w_send_oos, or the sync target will get confused as to
+		 * how much bits to resync.  We cannot do that always, because for an
+		 * empty resync and protocol < 95, we need to do it here, as we call
+		 * drbd_resync_finished from here in that case.
+		 * We drbd_gen_and_send_sync_uuid here for protocol < 96,
+		 * and from after_state_ch otherwise. */
+		if (side == C_SYNC_SOURCE && mdev->tconn->agreed_pro_version < 96)
+			drbd_gen_and_send_sync_uuid(mdev);
+
+		if (mdev->tconn->agreed_pro_version < 95 && mdev->rs_total == 0) {
+			/* This still has a race (about when exactly the peers
+			 * detect connection loss) that can lead to a full sync
+			 * on next handshake. In 8.3.9 we fixed this with explicit
+			 * resync-finished notifications, but the fix
+			 * introduces a protocol change.  Sleeping for some
+			 * time longer than the ping interval + timeout on the
+			 * SyncSource, to give the SyncTarget the chance to
+			 * detect connection loss, then waiting for a ping
+			 * response (implicit in drbd_resync_finished) reduces
+			 * the race considerably, but does not solve it. */
+			if (side == C_SYNC_SOURCE) {
+				struct net_conf *nc;
+				int timeo;
+
+				rcu_read_lock();
+				nc = rcu_dereference(mdev->tconn->net_conf);
+				timeo = nc->ping_int * HZ + nc->ping_timeo * HZ / 9;
+				rcu_read_unlock();
+				schedule_timeout_interruptible(timeo);
+			}
+			drbd_resync_finished(mdev);
+		}
+
+		drbd_rs_controller_reset(mdev);
+		/* ns.conn may already be != mdev->state.conn,
+		 * we may have been paused in between, or become paused until
+		 * the timer triggers.
+		 * No matter, that is handled in resync_timer_fn() */
+		if (ns.conn == C_SYNC_TARGET)
+			mod_timer(&mdev->resync_timer, jiffies);
+
+		drbd_md_sync(mdev);
+	}
+	put_ldev(mdev);
+	mutex_unlock(mdev->state_mutex);
+}
+
+/* If the resource already closed the current epoch, but we did not
+ * (because we have not yet seen new requests), we should send the
+ * corresponding barrier now.  Must be checked within the same spinlock
+ * that is used to check for new requests. */
+bool need_to_send_barrier(struct drbd_tconn *connection)
+{
+	if (!connection->send.seen_any_write_yet)
+		return false;
+
+	/* Skip barriers that do not contain any writes.
+	 * This may happen during AHEAD mode. */
+	if (!connection->send.current_epoch_writes)
+		return false;
+
+	/* ->req_lock is held when requests are queued on
+	 * connection->sender_work, and put into ->transfer_log.
+	 * It is also held when ->current_tle_nr is increased.
+	 * So either there are already new requests queued,
+	 * and corresponding barriers will be send there.
+	 * Or nothing new is queued yet, so the difference will be 1.
+	 */
+	if (atomic_read(&connection->current_tle_nr) !=
+	    connection->send.current_epoch_nr + 1)
+		return false;
+
+	return true;
+}
+
+bool dequeue_work_batch(struct drbd_work_queue *queue, struct list_head *work_list)
+{
+	spin_lock_irq(&queue->q_lock);
+	list_splice_init(&queue->q, work_list);
+	spin_unlock_irq(&queue->q_lock);
+	return !list_empty(work_list);
+}
+
+bool dequeue_work_item(struct drbd_work_queue *queue, struct list_head *work_list)
+{
+	spin_lock_irq(&queue->q_lock);
+	if (!list_empty(&queue->q))
+		list_move(queue->q.next, work_list);
+	spin_unlock_irq(&queue->q_lock);
+	return !list_empty(work_list);
+}
+
+void wait_for_work(struct drbd_tconn *connection, struct list_head *work_list)
+{
+	DEFINE_WAIT(wait);
+	struct net_conf *nc;
+	int uncork, cork;
+
+	dequeue_work_item(&connection->sender_work, work_list);
+	if (!list_empty(work_list))
+		return;
+
+	/* Still nothing to do?
+	 * Maybe we still need to close the current epoch,
+	 * even if no new requests are queued yet.
+	 *
+	 * Also, poke TCP, just in case.
+	 * Then wait for new work (or signal). */
+	rcu_read_lock();
+	nc = rcu_dereference(connection->net_conf);
+	uncork = nc ? nc->tcp_cork : 0;
+	rcu_read_unlock();
+	if (uncork) {
+		mutex_lock(&connection->data.mutex);
+		if (connection->data.socket)
+			drbd_tcp_uncork(connection->data.socket);
+		mutex_unlock(&connection->data.mutex);
+	}
+
+	for (;;) {
+		int send_barrier;
+		prepare_to_wait(&connection->sender_work.q_wait, &wait, TASK_INTERRUPTIBLE);
+		spin_lock_irq(&connection->req_lock);
+		spin_lock(&connection->sender_work.q_lock);	/* FIXME get rid of this one? */
+		/* dequeue single item only,
+		 * we still use drbd_queue_work_front() in some places */
+		if (!list_empty(&connection->sender_work.q))
+			list_move(connection->sender_work.q.next, work_list);
+		spin_unlock(&connection->sender_work.q_lock);	/* FIXME get rid of this one? */
+		if (!list_empty(work_list) || signal_pending(current)) {
+			spin_unlock_irq(&connection->req_lock);
+			break;
+		}
+		send_barrier = need_to_send_barrier(connection);
+		spin_unlock_irq(&connection->req_lock);
+		if (send_barrier) {
+			drbd_send_barrier(connection);
+			connection->send.current_epoch_nr++;
+		}
+		schedule();
+		/* may be woken up for other things but new work, too,
+		 * e.g. if the current epoch got closed.
+		 * In which case we send the barrier above. */
+	}
+	finish_wait(&connection->sender_work.q_wait, &wait);
+
+	/* someone may have changed the config while we have been waiting above. */
+	rcu_read_lock();
+	nc = rcu_dereference(connection->net_conf);
+	cork = nc ? nc->tcp_cork : 0;
+	rcu_read_unlock();
+	mutex_lock(&connection->data.mutex);
+	if (connection->data.socket) {
+		if (cork)
+			drbd_tcp_cork(connection->data.socket);
+		else if (!uncork)
+			drbd_tcp_uncork(connection->data.socket);
+	}
+	mutex_unlock(&connection->data.mutex);
+}
+
+int drbd_worker(struct drbd_thread *thi)
+{
+	struct drbd_tconn *tconn = thi->tconn;
+	struct drbd_work *w = NULL;
+	struct drbd_conf *mdev;
+	LIST_HEAD(work_list);
+	int vnr;
+
+	while (get_t_state(thi) == RUNNING) {
+		drbd_thread_current_set_cpu(thi);
+
+		/* as long as we use drbd_queue_work_front(),
+		 * we may only dequeue single work items here, not batches. */
+		if (list_empty(&work_list))
+			wait_for_work(tconn, &work_list);
+
+		if (signal_pending(current)) {
+			flush_signals(current);
+			if (get_t_state(thi) == RUNNING) {
+				conn_warn(tconn, "Worker got an unexpected signal\n");
+				continue;
+			}
+			break;
+		}
+
+		if (get_t_state(thi) != RUNNING)
+			break;
+
+		while (!list_empty(&work_list)) {
+			w = list_first_entry(&work_list, struct drbd_work, list);
+			list_del_init(&w->list);
+			if (w->cb(w, tconn->cstate < C_WF_REPORT_PARAMS) == 0)
+				continue;
+			if (tconn->cstate >= C_WF_REPORT_PARAMS)
+				conn_request_state(tconn, NS(conn, C_NETWORK_FAILURE), CS_HARD);
+		}
+	}
+
+	do {
+		while (!list_empty(&work_list)) {
+			w = list_first_entry(&work_list, struct drbd_work, list);
+			list_del_init(&w->list);
+			w->cb(w, 1);
+		}
+		dequeue_work_batch(&tconn->sender_work, &work_list);
+	} while (!list_empty(&work_list));
+
+	rcu_read_lock();
+	idr_for_each_entry(&tconn->volumes, mdev, vnr) {
+		D_ASSERT(mdev->state.disk == D_DISKLESS && mdev->state.conn == C_STANDALONE);
+		kref_get(&mdev->kref);
+		rcu_read_unlock();
+		drbd_mdev_cleanup(mdev);
+		kref_put(&mdev->kref, &drbd_minor_destroy);
+		rcu_read_lock();
+	}
+	rcu_read_unlock();
+
+	return 0;
+}