Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1674 insertions, 0 deletions

diff --git a/drivers/block/drbd/drbd_bitmap.c b/drivers/block/drbd/drbd_bitmap.c
new file mode 100644
index 000000000..11a85b740
--- /dev/null
+++ b/drivers/block/drbd/drbd_bitmap.c
@@ -0,0 +1,1674 @@
+/*
+   drbd_bitmap.c
+
+   This file is part of DRBD by Philipp Reisner and Lars Ellenberg.
+
+   Copyright (C) 2004-2008, LINBIT Information Technologies GmbH.
+   Copyright (C) 2004-2008, Philipp Reisner <philipp.reisner@linbit.com>.
+   Copyright (C) 2004-2008, 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.
+ */
+
+#define pr_fmt(fmt)	KBUILD_MODNAME ": " fmt
+
+#include <linux/bitmap.h>
+#include <linux/vmalloc.h>
+#include <linux/string.h>
+#include <linux/drbd.h>
+#include <linux/slab.h>
+#include <linux/highmem.h>
+
+#include "drbd_int.h"
+
+
+/* OPAQUE outside this file!
+ * interface defined in drbd_int.h
+
+ * convention:
+ * function name drbd_bm_... => used elsewhere, "public".
+ * function name      bm_... => internal to implementation, "private".
+ */
+
+
+/*
+ * LIMITATIONS:
+ * We want to support >= peta byte of backend storage, while for now still using
+ * a granularity of one bit per 4KiB of storage.
+ * 1 << 50		bytes backend storage (1 PiB)
+ * 1 << (50 - 12)	bits needed
+ *	38 --> we need u64 to index and count bits
+ * 1 << (38 - 3)	bitmap bytes needed
+ *	35 --> we still need u64 to index and count bytes
+ *			(that's 32 GiB of bitmap for 1 PiB storage)
+ * 1 << (35 - 2)	32bit longs needed
+ *	33 --> we'd even need u64 to index and count 32bit long words.
+ * 1 << (35 - 3)	64bit longs needed
+ *	32 --> we could get away with a 32bit unsigned int to index and count
+ *	64bit long words, but I rather stay with unsigned long for now.
+ *	We probably should neither count nor point to bytes or long words
+ *	directly, but either by bitnumber, or by page index and offset.
+ * 1 << (35 - 12)
+ *	22 --> we need that much 4KiB pages of bitmap.
+ *	1 << (22 + 3) --> on a 64bit arch,
+ *	we need 32 MiB to store the array of page pointers.
+ *
+ * Because I'm lazy, and because the resulting patch was too large, too ugly
+ * and still incomplete, on 32bit we still "only" support 16 TiB (minus some),
+ * (1 << 32) bits * 4k storage.
+ *
+
+ * bitmap storage and IO:
+ *	Bitmap is stored little endian on disk, and is kept little endian in
+ *	core memory. Currently we still hold the full bitmap in core as long
+ *	as we are "attached" to a local disk, which at 32 GiB for 1PiB storage
+ *	seems excessive.
+ *
+ *	We plan to reduce the amount of in-core bitmap pages by paging them in
+ *	and out against their on-disk location as necessary, but need to make
+ *	sure we don't cause too much meta data IO, and must not deadlock in
+ *	tight memory situations. This needs some more work.
+ */
+
+/*
+ * NOTE
+ *  Access to the *bm_pages is protected by bm_lock.
+ *  It is safe to read the other members within the lock.
+ *
+ *  drbd_bm_set_bits is called from bio_endio callbacks,
+ *  We may be called with irq already disabled,
+ *  so we need spin_lock_irqsave().
+ *  And we need the kmap_atomic.
+ */
+struct drbd_bitmap {
+	struct page **bm_pages;
+	spinlock_t bm_lock;
+
+	/* exclusively to be used by __al_write_transaction(),
+	 * drbd_bm_mark_for_writeout() and
+	 * and drbd_bm_write_hinted() -> bm_rw() called from there.
+	 */
+	unsigned int n_bitmap_hints;
+	unsigned int al_bitmap_hints[AL_UPDATES_PER_TRANSACTION];
+
+	/* see LIMITATIONS: above */
+
+	unsigned long bm_set;       /* nr of set bits; THINK maybe atomic_t? */
+	unsigned long bm_bits;
+	size_t   bm_words;
+	size_t   bm_number_of_pages;
+	sector_t bm_dev_capacity;
+	struct mutex bm_change; /* serializes resize operations */
+
+	wait_queue_head_t bm_io_wait; /* used to serialize IO of single pages */
+
+	enum bm_flag bm_flags;
+
+	/* debugging aid, in case we are still racy somewhere */
+	char          *bm_why;
+	struct task_struct *bm_task;
+};
+
+#define bm_print_lock_info(m) __bm_print_lock_info(m, __func__)
+static void __bm_print_lock_info(struct drbd_device *device, const char *func)
+{
+	struct drbd_bitmap *b = device->bitmap;
+	if (!__ratelimit(&drbd_ratelimit_state))
+		return;
+	drbd_err(device, "FIXME %s[%d] in %s, bitmap locked for '%s' by %s[%d]\n",
+		 current->comm, task_pid_nr(current),
+		 func, b->bm_why ?: "?",
+		 b->bm_task->comm, task_pid_nr(b->bm_task));
+}
+
+void drbd_bm_lock(struct drbd_device *device, char *why, enum bm_flag flags)
+{
+	struct drbd_bitmap *b = device->bitmap;
+	int trylock_failed;
+
+	if (!b) {
+		drbd_err(device, "FIXME no bitmap in drbd_bm_lock!?\n");
+		return;
+	}
+
+	trylock_failed = !mutex_trylock(&b->bm_change);
+
+	if (trylock_failed) {
+		drbd_warn(device, "%s[%d] going to '%s' but bitmap already locked for '%s' by %s[%d]\n",
+			  current->comm, task_pid_nr(current),
+			  why, b->bm_why ?: "?",
+			  b->bm_task->comm, task_pid_nr(b->bm_task));
+		mutex_lock(&b->bm_change);
+	}
+	if (BM_LOCKED_MASK & b->bm_flags)
+		drbd_err(device, "FIXME bitmap already locked in bm_lock\n");
+	b->bm_flags |= flags & BM_LOCKED_MASK;
+
+	b->bm_why  = why;
+	b->bm_task = current;
+}
+
+void drbd_bm_unlock(struct drbd_device *device)
+{
+	struct drbd_bitmap *b = device->bitmap;
+	if (!b) {
+		drbd_err(device, "FIXME no bitmap in drbd_bm_unlock!?\n");
+		return;
+	}
+
+	if (!(BM_LOCKED_MASK & device->bitmap->bm_flags))
+		drbd_err(device, "FIXME bitmap not locked in bm_unlock\n");
+
+	b->bm_flags &= ~BM_LOCKED_MASK;
+	b->bm_why  = NULL;
+	b->bm_task = NULL;
+	mutex_unlock(&b->bm_change);
+}
+
+/* we store some "meta" info about our pages in page->private */
+/* at a granularity of 4k storage per bitmap bit:
+ * one peta byte storage: 1<<50 byte, 1<<38 * 4k storage blocks
+ *  1<<38 bits,
+ *  1<<23 4k bitmap pages.
+ * Use 24 bits as page index, covers 2 peta byte storage
+ * at a granularity of 4k per bit.
+ * Used to report the failed page idx on io error from the endio handlers.
+ */
+#define BM_PAGE_IDX_MASK	((1UL<<24)-1)
+/* this page is currently read in, or written back */
+#define BM_PAGE_IO_LOCK		31
+/* if there has been an IO error for this page */
+#define BM_PAGE_IO_ERROR	30
+/* this is to be able to intelligently skip disk IO,
+ * set if bits have been set since last IO. */
+#define BM_PAGE_NEED_WRITEOUT	29
+/* to mark for lazy writeout once syncer cleared all clearable bits,
+ * we if bits have been cleared since last IO. */
+#define BM_PAGE_LAZY_WRITEOUT	28
+/* pages marked with this "HINT" will be considered for writeout
+ * on activity log transactions */
+#define BM_PAGE_HINT_WRITEOUT	27
+
+/* store_page_idx uses non-atomic assignment. It is only used directly after
+ * allocating the page.  All other bm_set_page_* and bm_clear_page_* need to
+ * use atomic bit manipulation, as set_out_of_sync (and therefore bitmap
+ * changes) may happen from various contexts, and wait_on_bit/wake_up_bit
+ * requires it all to be atomic as well. */
+static void bm_store_page_idx(struct page *page, unsigned long idx)
+{
+	BUG_ON(0 != (idx & ~BM_PAGE_IDX_MASK));
+	set_page_private(page, idx);
+}
+
+static unsigned long bm_page_to_idx(struct page *page)
+{
+	return page_private(page) & BM_PAGE_IDX_MASK;
+}
+
+/* As is very unlikely that the same page is under IO from more than one
+ * context, we can get away with a bit per page and one wait queue per bitmap.
+ */
+static void bm_page_lock_io(struct drbd_device *device, int page_nr)
+{
+	struct drbd_bitmap *b = device->bitmap;
+	void *addr = &page_private(b->bm_pages[page_nr]);
+	wait_event(b->bm_io_wait, !test_and_set_bit(BM_PAGE_IO_LOCK, addr));
+}
+
+static void bm_page_unlock_io(struct drbd_device *device, int page_nr)
+{
+	struct drbd_bitmap *b = device->bitmap;
+	void *addr = &page_private(b->bm_pages[page_nr]);
+	clear_bit_unlock(BM_PAGE_IO_LOCK, addr);
+	wake_up(&device->bitmap->bm_io_wait);
+}
+
+/* set _before_ submit_io, so it may be reset due to being changed
+ * while this page is in flight... will get submitted later again */
+static void bm_set_page_unchanged(struct page *page)
+{
+	/* use cmpxchg? */
+	clear_bit(BM_PAGE_NEED_WRITEOUT, &page_private(page));
+	clear_bit(BM_PAGE_LAZY_WRITEOUT, &page_private(page));
+}
+
+static void bm_set_page_need_writeout(struct page *page)
+{
+	set_bit(BM_PAGE_NEED_WRITEOUT, &page_private(page));
+}
+
+void drbd_bm_reset_al_hints(struct drbd_device *device)
+{
+	device->bitmap->n_bitmap_hints = 0;
+}
+
+/**
+ * drbd_bm_mark_for_writeout() - mark a page with a "hint" to be considered for writeout
+ * @device:	DRBD device.
+ * @page_nr:	the bitmap page to mark with the "hint" flag
+ *
+ * From within an activity log transaction, we mark a few pages with these
+ * hints, then call drbd_bm_write_hinted(), which will only write out changed
+ * pages which are flagged with this mark.
+ */
+void drbd_bm_mark_for_writeout(struct drbd_device *device, int page_nr)
+{
+	struct drbd_bitmap *b = device->bitmap;
+	struct page *page;
+	if (page_nr >= device->bitmap->bm_number_of_pages) {
+		drbd_warn(device, "BAD: page_nr: %u, number_of_pages: %u\n",
+			 page_nr, (int)device->bitmap->bm_number_of_pages);
+		return;
+	}
+	page = device->bitmap->bm_pages[page_nr];
+	BUG_ON(b->n_bitmap_hints >= ARRAY_SIZE(b->al_bitmap_hints));
+	if (!test_and_set_bit(BM_PAGE_HINT_WRITEOUT, &page_private(page)))
+		b->al_bitmap_hints[b->n_bitmap_hints++] = page_nr;
+}
+
+static int bm_test_page_unchanged(struct page *page)
+{
+	volatile const unsigned long *addr = &page_private(page);
+	return (*addr & ((1UL<<BM_PAGE_NEED_WRITEOUT)|(1UL<<BM_PAGE_LAZY_WRITEOUT))) == 0;
+}
+
+static void bm_set_page_io_err(struct page *page)
+{
+	set_bit(BM_PAGE_IO_ERROR, &page_private(page));
+}
+
+static void bm_clear_page_io_err(struct page *page)
+{
+	clear_bit(BM_PAGE_IO_ERROR, &page_private(page));
+}
+
+static void bm_set_page_lazy_writeout(struct page *page)
+{
+	set_bit(BM_PAGE_LAZY_WRITEOUT, &page_private(page));
+}
+
+static int bm_test_page_lazy_writeout(struct page *page)
+{
+	return test_bit(BM_PAGE_LAZY_WRITEOUT, &page_private(page));
+}
+
+/* on a 32bit box, this would allow for exactly (2<<38) bits. */
+static unsigned int bm_word_to_page_idx(struct drbd_bitmap *b, unsigned long long_nr)
+{
+	/* page_nr = (word*sizeof(long)) >> PAGE_SHIFT; */
+	unsigned int page_nr = long_nr >> (PAGE_SHIFT - LN2_BPL + 3);
+	BUG_ON(page_nr >= b->bm_number_of_pages);
+	return page_nr;
+}
+
+static unsigned int bm_bit_to_page_idx(struct drbd_bitmap *b, u64 bitnr)
+{
+	/* page_nr = (bitnr/8) >> PAGE_SHIFT; */
+	unsigned int page_nr = bitnr >> (PAGE_SHIFT + 3);
+	BUG_ON(page_nr >= b->bm_number_of_pages);
+	return page_nr;
+}
+
+static unsigned long *__bm_map_pidx(struct drbd_bitmap *b, unsigned int idx)
+{
+	struct page *page = b->bm_pages[idx];
+	return (unsigned long *) kmap_atomic(page);
+}
+
+static unsigned long *bm_map_pidx(struct drbd_bitmap *b, unsigned int idx)
+{
+	return __bm_map_pidx(b, idx);
+}
+
+static void __bm_unmap(unsigned long *p_addr)
+{
+	kunmap_atomic(p_addr);
+};
+
+static void bm_unmap(unsigned long *p_addr)
+{
+	return __bm_unmap(p_addr);
+}
+
+/* long word offset of _bitmap_ sector */
+#define S2W(s)	((s)<<(BM_EXT_SHIFT-BM_BLOCK_SHIFT-LN2_BPL))
+/* word offset from start of bitmap to word number _in_page_
+ * modulo longs per page
+#define MLPP(X) ((X) % (PAGE_SIZE/sizeof(long))
+ hm, well, Philipp thinks gcc might not optimize the % into & (... - 1)
+ so do it explicitly:
+ */
+#define MLPP(X) ((X) & ((PAGE_SIZE/sizeof(long))-1))
+
+/* Long words per page */
+#define LWPP (PAGE_SIZE/sizeof(long))
+
+/*
+ * actually most functions herein should take a struct drbd_bitmap*, not a
+ * struct drbd_device*, but for the debug macros I like to have the device around
+ * to be able to report device specific.
+ */
+
+
+static void bm_free_pages(struct page **pages, unsigned long number)
+{
+	unsigned long i;
+	if (!pages)
+		return;
+
+	for (i = 0; i < number; i++) {
+		if (!pages[i]) {
+			pr_alert("bm_free_pages tried to free a NULL pointer; i=%lu n=%lu\n",
+				 i, number);
+			continue;
+		}
+		__free_page(pages[i]);
+		pages[i] = NULL;
+	}
+}
+
+static inline void bm_vk_free(void *ptr)
+{
+	kvfree(ptr);
+}
+
+/*
+ * "have" and "want" are NUMBER OF PAGES.
+ */
+static struct page **bm_realloc_pages(struct drbd_bitmap *b, unsigned long want)
+{
+	struct page **old_pages = b->bm_pages;
+	struct page **new_pages, *page;
+	unsigned int i, bytes;
+	unsigned long have = b->bm_number_of_pages;
+
+	BUG_ON(have == 0 && old_pages != NULL);
+	BUG_ON(have != 0 && old_pages == NULL);
+
+	if (have == want)
+		return old_pages;
+
+	/* Trying kmalloc first, falling back to vmalloc.
+	 * GFP_NOIO, as this is called while drbd IO is "suspended",
+	 * and during resize or attach on diskless Primary,
+	 * we must not block on IO to ourselves.
+	 * Context is receiver thread or dmsetup. */
+	bytes = sizeof(struct page *)*want;
+	new_pages = kzalloc(bytes, GFP_NOIO | __GFP_NOWARN);
+	if (!new_pages) {
+		new_pages = __vmalloc(bytes,
+				GFP_NOIO | __GFP_ZERO,
+				PAGE_KERNEL);
+		if (!new_pages)
+			return NULL;
+	}
+
+	if (want >= have) {
+		for (i = 0; i < have; i++)
+			new_pages[i] = old_pages[i];
+		for (; i < want; i++) {
+			page = alloc_page(GFP_NOIO | __GFP_HIGHMEM);
+			if (!page) {
+				bm_free_pages(new_pages + have, i - have);
+				bm_vk_free(new_pages);
+				return NULL;
+			}
+			/* we want to know which page it is
+			 * from the endio handlers */
+			bm_store_page_idx(page, i);
+			new_pages[i] = page;
+		}
+	} else {
+		for (i = 0; i < want; i++)
+			new_pages[i] = old_pages[i];
+		/* NOT HERE, we are outside the spinlock!
+		bm_free_pages(old_pages + want, have - want);
+		*/
+	}
+
+	return new_pages;
+}
+
+/*
+ * allocates the drbd_bitmap and stores it in device->bitmap.
+ */
+int drbd_bm_init(struct drbd_device *device)
+{
+	struct drbd_bitmap *b = device->bitmap;
+	WARN_ON(b != NULL);
+	b = kzalloc(sizeof(struct drbd_bitmap), GFP_KERNEL);
+	if (!b)
+		return -ENOMEM;
+	spin_lock_init(&b->bm_lock);
+	mutex_init(&b->bm_change);
+	init_waitqueue_head(&b->bm_io_wait);
+
+	device->bitmap = b;
+
+	return 0;
+}
+
+sector_t drbd_bm_capacity(struct drbd_device *device)
+{
+	if (!expect(device->bitmap))
+		return 0;
+	return device->bitmap->bm_dev_capacity;
+}
+
+/* called on driver unload. TODO: call when a device is destroyed.
+ */
+void drbd_bm_cleanup(struct drbd_device *device)
+{
+	if (!expect(device->bitmap))
+		return;
+	bm_free_pages(device->bitmap->bm_pages, device->bitmap->bm_number_of_pages);
+	bm_vk_free(device->bitmap->bm_pages);
+	kfree(device->bitmap);
+	device->bitmap = NULL;
+}
+
+/*
+ * since (b->bm_bits % BITS_PER_LONG) != 0,
+ * this masks out the remaining bits.
+ * Returns the number of bits cleared.
+ */
+#ifndef BITS_PER_PAGE
+#define BITS_PER_PAGE		(1UL << (PAGE_SHIFT + 3))
+#define BITS_PER_PAGE_MASK	(BITS_PER_PAGE - 1)
+#else
+# if BITS_PER_PAGE != (1UL << (PAGE_SHIFT + 3))
+#  error "ambiguous BITS_PER_PAGE"
+# endif
+#endif
+#define BITS_PER_LONG_MASK	(BITS_PER_LONG - 1)
+static int bm_clear_surplus(struct drbd_bitmap *b)
+{
+	unsigned long mask;
+	unsigned long *p_addr, *bm;
+	int tmp;
+	int cleared = 0;
+
+	/* number of bits modulo bits per page */
+	tmp = (b->bm_bits & BITS_PER_PAGE_MASK);
+	/* mask the used bits of the word containing the last bit */
+	mask = (1UL << (tmp & BITS_PER_LONG_MASK)) -1;
+	/* bitmap is always stored little endian,
+	 * on disk and in core memory alike */
+	mask = cpu_to_lel(mask);
+
+	p_addr = bm_map_pidx(b, b->bm_number_of_pages - 1);
+	bm = p_addr + (tmp/BITS_PER_LONG);
+	if (mask) {
+		/* If mask != 0, we are not exactly aligned, so bm now points
+		 * to the long containing the last bit.
+		 * If mask == 0, bm already points to the word immediately
+		 * after the last (long word aligned) bit. */
+		cleared = hweight_long(*bm & ~mask);
+		*bm &= mask;
+		bm++;
+	}
+
+	if (BITS_PER_LONG == 32 && ((bm - p_addr) & 1) == 1) {
+		/* on a 32bit arch, we may need to zero out
+		 * a padding long to align with a 64bit remote */
+		cleared += hweight_long(*bm);
+		*bm = 0;
+	}
+	bm_unmap(p_addr);
+	return cleared;
+}
+
+static void bm_set_surplus(struct drbd_bitmap *b)
+{
+	unsigned long mask;
+	unsigned long *p_addr, *bm;
+	int tmp;
+
+	/* number of bits modulo bits per page */
+	tmp = (b->bm_bits & BITS_PER_PAGE_MASK);
+	/* mask the used bits of the word containing the last bit */
+	mask = (1UL << (tmp & BITS_PER_LONG_MASK)) -1;
+	/* bitmap is always stored little endian,
+	 * on disk and in core memory alike */
+	mask = cpu_to_lel(mask);
+
+	p_addr = bm_map_pidx(b, b->bm_number_of_pages - 1);
+	bm = p_addr + (tmp/BITS_PER_LONG);
+	if (mask) {
+		/* If mask != 0, we are not exactly aligned, so bm now points
+		 * to the long containing the last bit.
+		 * If mask == 0, bm already points to the word immediately
+		 * after the last (long word aligned) bit. */
+		*bm |= ~mask;
+		bm++;
+	}
+
+	if (BITS_PER_LONG == 32 && ((bm - p_addr) & 1) == 1) {
+		/* on a 32bit arch, we may need to zero out
+		 * a padding long to align with a 64bit remote */
+		*bm = ~0UL;
+	}
+	bm_unmap(p_addr);
+}
+
+/* you better not modify the bitmap while this is running,
+ * or its results will be stale */
+static unsigned long bm_count_bits(struct drbd_bitmap *b)
+{
+	unsigned long *p_addr;
+	unsigned long bits = 0;
+	unsigned long mask = (1UL << (b->bm_bits & BITS_PER_LONG_MASK)) -1;
+	int idx, last_word;
+
+	/* all but last page */
+	for (idx = 0; idx < b->bm_number_of_pages - 1; idx++) {
+		p_addr = __bm_map_pidx(b, idx);
+		bits += bitmap_weight(p_addr, BITS_PER_PAGE);
+		__bm_unmap(p_addr);
+		cond_resched();
+	}
+	/* last (or only) page */
+	last_word = ((b->bm_bits - 1) & BITS_PER_PAGE_MASK) >> LN2_BPL;
+	p_addr = __bm_map_pidx(b, idx);
+	bits += bitmap_weight(p_addr, last_word * BITS_PER_LONG);
+	p_addr[last_word] &= cpu_to_lel(mask);
+	bits += hweight_long(p_addr[last_word]);
+	/* 32bit arch, may have an unused padding long */
+	if (BITS_PER_LONG == 32 && (last_word & 1) == 0)
+		p_addr[last_word+1] = 0;
+	__bm_unmap(p_addr);
+	return bits;
+}
+
+/* offset and len in long words.*/
+static void bm_memset(struct drbd_bitmap *b, size_t offset, int c, size_t len)
+{
+	unsigned long *p_addr, *bm;
+	unsigned int idx;
+	size_t do_now, end;
+
+	end = offset + len;
+
+	if (end > b->bm_words) {
+		pr_alert("bm_memset end > bm_words\n");
+		return;
+	}
+
+	while (offset < end) {
+		do_now = min_t(size_t, ALIGN(offset + 1, LWPP), end) - offset;
+		idx = bm_word_to_page_idx(b, offset);
+		p_addr = bm_map_pidx(b, idx);
+		bm = p_addr + MLPP(offset);
+		if (bm+do_now > p_addr + LWPP) {
+			pr_alert("BUG BUG BUG! p_addr:%p bm:%p do_now:%d\n",
+			       p_addr, bm, (int)do_now);
+		} else
+			memset(bm, c, do_now * sizeof(long));
+		bm_unmap(p_addr);
+		bm_set_page_need_writeout(b->bm_pages[idx]);
+		offset += do_now;
+	}
+}
+
+/* For the layout, see comment above drbd_md_set_sector_offsets(). */
+static u64 drbd_md_on_disk_bits(struct drbd_backing_dev *ldev)
+{
+	u64 bitmap_sectors;
+	if (ldev->md.al_offset == 8)
+		bitmap_sectors = ldev->md.md_size_sect - ldev->md.bm_offset;
+	else
+		bitmap_sectors = ldev->md.al_offset - ldev->md.bm_offset;
+	return bitmap_sectors << (9 + 3);
+}
+
+/*
+ * make sure the bitmap has enough room for the attached storage,
+ * if necessary, resize.
+ * called whenever we may have changed the device size.
+ * returns -ENOMEM if we could not allocate enough memory, 0 on success.
+ * In case this is actually a resize, we copy the old bitmap into the new one.
+ * Otherwise, the bitmap is initialized to all bits set.
+ */
+int drbd_bm_resize(struct drbd_device *device, sector_t capacity, int set_new_bits)
+{
+	struct drbd_bitmap *b = device->bitmap;
+	unsigned long bits, words, owords, obits;
+	unsigned long want, have, onpages; /* number of pages */
+	struct page **npages, **opages = NULL;
+	int err = 0;
+	bool growing;
+
+	if (!expect(b))
+		return -ENOMEM;
+
+	drbd_bm_lock(device, "resize", BM_LOCKED_MASK);
+
+	drbd_info(device, "drbd_bm_resize called with capacity == %llu\n",
+			(unsigned long long)capacity);
+
+	if (capacity == b->bm_dev_capacity)
+		goto out;
+
+	if (capacity == 0) {
+		spin_lock_irq(&b->bm_lock);
+		opages = b->bm_pages;
+		onpages = b->bm_number_of_pages;
+		owords = b->bm_words;
+		b->bm_pages = NULL;
+		b->bm_number_of_pages =
+		b->bm_set   =
+		b->bm_bits  =
+		b->bm_words =
+		b->bm_dev_capacity = 0;
+		spin_unlock_irq(&b->bm_lock);
+		bm_free_pages(opages, onpages);
+		bm_vk_free(opages);
+		goto out;
+	}
+	bits  = BM_SECT_TO_BIT(ALIGN(capacity, BM_SECT_PER_BIT));
+
+	/* if we would use
+	   words = ALIGN(bits,BITS_PER_LONG) >> LN2_BPL;
+	   a 32bit host could present the wrong number of words
+	   to a 64bit host.
+	*/
+	words = ALIGN(bits, 64) >> LN2_BPL;
+
+	if (get_ldev(device)) {
+		u64 bits_on_disk = drbd_md_on_disk_bits(device->ldev);
+		put_ldev(device);
+		if (bits > bits_on_disk) {
+			drbd_info(device, "bits = %lu\n", bits);
+			drbd_info(device, "bits_on_disk = %llu\n", bits_on_disk);
+			err = -ENOSPC;
+			goto out;
+		}
+	}
+
+	want = ALIGN(words*sizeof(long), PAGE_SIZE) >> PAGE_SHIFT;
+	have = b->bm_number_of_pages;
+	if (want == have) {
+		D_ASSERT(device, b->bm_pages != NULL);
+		npages = b->bm_pages;
+	} else {
+		if (drbd_insert_fault(device, DRBD_FAULT_BM_ALLOC))
+			npages = NULL;
+		else
+			npages = bm_realloc_pages(b, want);
+	}
+
+	if (!npages) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	spin_lock_irq(&b->bm_lock);
+	opages = b->bm_pages;
+	owords = b->bm_words;
+	obits  = b->bm_bits;
+
+	growing = bits > obits;
+	if (opages && growing && set_new_bits)
+		bm_set_surplus(b);
+
+	b->bm_pages = npages;
+	b->bm_number_of_pages = want;
+	b->bm_bits  = bits;
+	b->bm_words = words;
+	b->bm_dev_capacity = capacity;
+
+	if (growing) {
+		if (set_new_bits) {
+			bm_memset(b, owords, 0xff, words-owords);
+			b->bm_set += bits - obits;
+		} else
+			bm_memset(b, owords, 0x00, words-owords);
+
+	}
+
+	if (want < have) {
+		/* implicit: (opages != NULL) && (opages != npages) */
+		bm_free_pages(opages + want, have - want);
+	}
+
+	(void)bm_clear_surplus(b);
+
+	spin_unlock_irq(&b->bm_lock);
+	if (opages != npages)
+		bm_vk_free(opages);
+	if (!growing)
+		b->bm_set = bm_count_bits(b);
+	drbd_info(device, "resync bitmap: bits=%lu words=%lu pages=%lu\n", bits, words, want);
+
+ out:
+	drbd_bm_unlock(device);
+	return err;
+}
+
+/* inherently racy:
+ * if not protected by other means, return value may be out of date when
+ * leaving this function...
+ * we still need to lock it, since it is important that this returns
+ * bm_set == 0 precisely.
+ *
+ * maybe bm_set should be atomic_t ?
+ */
+unsigned long _drbd_bm_total_weight(struct drbd_device *device)
+{
+	struct drbd_bitmap *b = device->bitmap;
+	unsigned long s;
+	unsigned long flags;
+
+	if (!expect(b))
+		return 0;
+	if (!expect(b->bm_pages))
+		return 0;
+
+	spin_lock_irqsave(&b->bm_lock, flags);
+	s = b->bm_set;
+	spin_unlock_irqrestore(&b->bm_lock, flags);
+
+	return s;
+}
+
+unsigned long drbd_bm_total_weight(struct drbd_device *device)
+{
+	unsigned long s;
+	/* if I don't have a disk, I don't know about out-of-sync status */
+	if (!get_ldev_if_state(device, D_NEGOTIATING))
+		return 0;
+	s = _drbd_bm_total_weight(device);
+	put_ldev(device);
+	return s;
+}
+
+size_t drbd_bm_words(struct drbd_device *device)
+{
+	struct drbd_bitmap *b = device->bitmap;
+	if (!expect(b))
+		return 0;
+	if (!expect(b->bm_pages))
+		return 0;
+
+	return b->bm_words;
+}
+
+unsigned long drbd_bm_bits(struct drbd_device *device)
+{
+	struct drbd_bitmap *b = device->bitmap;
+	if (!expect(b))
+		return 0;
+
+	return b->bm_bits;
+}
+
+/* merge number words from buffer into the bitmap starting at offset.
+ * buffer[i] is expected to be little endian unsigned long.
+ * bitmap must be locked by drbd_bm_lock.
+ * currently only used from receive_bitmap.
+ */
+void drbd_bm_merge_lel(struct drbd_device *device, size_t offset, size_t number,
+			unsigned long *buffer)
+{
+	struct drbd_bitmap *b = device->bitmap;
+	unsigned long *p_addr, *bm;
+	unsigned long word, bits;
+	unsigned int idx;
+	size_t end, do_now;
+
+	end = offset + number;
+
+	if (!expect(b))
+		return;
+	if (!expect(b->bm_pages))
+		return;
+	if (number == 0)
+		return;
+	WARN_ON(offset >= b->bm_words);
+	WARN_ON(end    >  b->bm_words);
+
+	spin_lock_irq(&b->bm_lock);
+	while (offset < end) {
+		do_now = min_t(size_t, ALIGN(offset+1, LWPP), end) - offset;
+		idx = bm_word_to_page_idx(b, offset);
+		p_addr = bm_map_pidx(b, idx);
+		bm = p_addr + MLPP(offset);
+		offset += do_now;
+		while (do_now--) {
+			bits = hweight_long(*bm);
+			word = *bm | *buffer++;
+			*bm++ = word;
+			b->bm_set += hweight_long(word) - bits;
+		}
+		bm_unmap(p_addr);
+		bm_set_page_need_writeout(b->bm_pages[idx]);
+	}
+	/* with 32bit <-> 64bit cross-platform connect
+	 * this is only correct for current usage,
+	 * where we _know_ that we are 64 bit aligned,
+	 * and know that this function is used in this way, too...
+	 */
+	if (end == b->bm_words)
+		b->bm_set -= bm_clear_surplus(b);
+	spin_unlock_irq(&b->bm_lock);
+}
+
+/* copy number words from the bitmap starting at offset into the buffer.
+ * buffer[i] will be little endian unsigned long.
+ */
+void drbd_bm_get_lel(struct drbd_device *device, size_t offset, size_t number,
+		     unsigned long *buffer)
+{
+	struct drbd_bitmap *b = device->bitmap;
+	unsigned long *p_addr, *bm;
+	size_t end, do_now;
+
+	end = offset + number;
+
+	if (!expect(b))
+		return;
+	if (!expect(b->bm_pages))
+		return;
+
+	spin_lock_irq(&b->bm_lock);
+	if ((offset >= b->bm_words) ||
+	    (end    >  b->bm_words) ||
+	    (number <= 0))
+		drbd_err(device, "offset=%lu number=%lu bm_words=%lu\n",
+			(unsigned long)	offset,
+			(unsigned long)	number,
+			(unsigned long) b->bm_words);
+	else {
+		while (offset < end) {
+			do_now = min_t(size_t, ALIGN(offset+1, LWPP), end) - offset;
+			p_addr = bm_map_pidx(b, bm_word_to_page_idx(b, offset));
+			bm = p_addr + MLPP(offset);
+			offset += do_now;
+			while (do_now--)
+				*buffer++ = *bm++;
+			bm_unmap(p_addr);
+		}
+	}
+	spin_unlock_irq(&b->bm_lock);
+}
+
+/* set all bits in the bitmap */
+void drbd_bm_set_all(struct drbd_device *device)
+{
+	struct drbd_bitmap *b = device->bitmap;
+	if (!expect(b))
+		return;
+	if (!expect(b->bm_pages))
+		return;
+
+	spin_lock_irq(&b->bm_lock);
+	bm_memset(b, 0, 0xff, b->bm_words);
+	(void)bm_clear_surplus(b);
+	b->bm_set = b->bm_bits;
+	spin_unlock_irq(&b->bm_lock);
+}
+
+/* clear all bits in the bitmap */
+void drbd_bm_clear_all(struct drbd_device *device)
+{
+	struct drbd_bitmap *b = device->bitmap;
+	if (!expect(b))
+		return;
+	if (!expect(b->bm_pages))
+		return;
+
+	spin_lock_irq(&b->bm_lock);
+	bm_memset(b, 0, 0, b->bm_words);
+	b->bm_set = 0;
+	spin_unlock_irq(&b->bm_lock);
+}
+
+static void drbd_bm_aio_ctx_destroy(struct kref *kref)
+{
+	struct drbd_bm_aio_ctx *ctx = container_of(kref, struct drbd_bm_aio_ctx, kref);
+	unsigned long flags;
+
+	spin_lock_irqsave(&ctx->device->resource->req_lock, flags);
+	list_del(&ctx->list);
+	spin_unlock_irqrestore(&ctx->device->resource->req_lock, flags);
+	put_ldev(ctx->device);
+	kfree(ctx);
+}
+
+/* bv_page may be a copy, or may be the original */
+static void drbd_bm_endio(struct bio *bio)
+{
+	struct drbd_bm_aio_ctx *ctx = bio->bi_private;
+	struct drbd_device *device = ctx->device;
+	struct drbd_bitmap *b = device->bitmap;
+	unsigned int idx = bm_page_to_idx(bio_first_page_all(bio));
+
+	if ((ctx->flags & BM_AIO_COPY_PAGES) == 0 &&
+	    !bm_test_page_unchanged(b->bm_pages[idx]))
+		drbd_warn(device, "bitmap page idx %u changed during IO!\n", idx);
+
+	if (bio->bi_status) {
+		/* ctx error will hold the completed-last non-zero error code,
+		 * in case error codes differ. */
+		ctx->error = blk_status_to_errno(bio->bi_status);
+		bm_set_page_io_err(b->bm_pages[idx]);
+		/* Not identical to on disk version of it.
+		 * Is BM_PAGE_IO_ERROR enough? */
+		if (__ratelimit(&drbd_ratelimit_state))
+			drbd_err(device, "IO ERROR %d on bitmap page idx %u\n",
+					bio->bi_status, idx);
+	} else {
+		bm_clear_page_io_err(b->bm_pages[idx]);
+		dynamic_drbd_dbg(device, "bitmap page idx %u completed\n", idx);
+	}
+
+	bm_page_unlock_io(device, idx);
+
+	if (ctx->flags & BM_AIO_COPY_PAGES)
+		mempool_free(bio->bi_io_vec[0].bv_page, &drbd_md_io_page_pool);
+
+	bio_put(bio);
+
+	if (atomic_dec_and_test(&ctx->in_flight)) {
+		ctx->done = 1;
+		wake_up(&device->misc_wait);
+		kref_put(&ctx->kref, &drbd_bm_aio_ctx_destroy);
+	}
+}
+
+static void bm_page_io_async(struct drbd_bm_aio_ctx *ctx, int page_nr) __must_hold(local)
+{
+	struct bio *bio = bio_alloc_drbd(GFP_NOIO);
+	struct drbd_device *device = ctx->device;
+	struct drbd_bitmap *b = device->bitmap;
+	struct page *page;
+	unsigned int len;
+	unsigned int op = (ctx->flags & BM_AIO_READ) ? REQ_OP_READ : REQ_OP_WRITE;
+
+	sector_t on_disk_sector =
+		device->ldev->md.md_offset + device->ldev->md.bm_offset;
+	on_disk_sector += ((sector_t)page_nr) << (PAGE_SHIFT-9);
+
+	/* this might happen with very small
+	 * flexible external meta data device,
+	 * or with PAGE_SIZE > 4k */
+	len = min_t(unsigned int, PAGE_SIZE,
+		(drbd_md_last_sector(device->ldev) - on_disk_sector + 1)<<9);
+
+	/* serialize IO on this page */
+	bm_page_lock_io(device, page_nr);
+	/* before memcpy and submit,
+	 * so it can be redirtied any time */
+	bm_set_page_unchanged(b->bm_pages[page_nr]);
+
+	if (ctx->flags & BM_AIO_COPY_PAGES) {
+		page = mempool_alloc(&drbd_md_io_page_pool,
+				GFP_NOIO | __GFP_HIGHMEM);
+		copy_highpage(page, b->bm_pages[page_nr]);
+		bm_store_page_idx(page, page_nr);
+	} else
+		page = b->bm_pages[page_nr];
+	bio_set_dev(bio, device->ldev->md_bdev);
+	bio->bi_iter.bi_sector = on_disk_sector;
+	/* bio_add_page of a single page to an empty bio will always succeed,
+	 * according to api.  Do we want to assert that? */
+	bio_add_page(bio, page, len, 0);
+	bio->bi_private = ctx;
+	bio->bi_end_io = drbd_bm_endio;
+	bio_set_op_attrs(bio, op, 0);
+
+	if (drbd_insert_fault(device, (op == REQ_OP_WRITE) ? DRBD_FAULT_MD_WR : DRBD_FAULT_MD_RD)) {
+		bio_io_error(bio);
+	} else {
+		submit_bio(bio);
+		/* this should not count as user activity and cause the
+		 * resync to throttle -- see drbd_rs_should_slow_down(). */
+		atomic_add(len >> 9, &device->rs_sect_ev);
+	}
+}
+
+/*
+ * bm_rw: read/write the whole bitmap from/to its on disk location.
+ */
+static int bm_rw(struct drbd_device *device, const unsigned int flags, unsigned lazy_writeout_upper_idx) __must_hold(local)
+{
+	struct drbd_bm_aio_ctx *ctx;
+	struct drbd_bitmap *b = device->bitmap;
+	unsigned int num_pages, i, count = 0;
+	unsigned long now;
+	char ppb[10];
+	int err = 0;
+
+	/*
+	 * We are protected against bitmap disappearing/resizing by holding an
+	 * ldev reference (caller must have called get_ldev()).
+	 * For read/write, we are protected against changes to the bitmap by
+	 * the bitmap lock (see drbd_bitmap_io).
+	 * For lazy writeout, we don't care for ongoing changes to the bitmap,
+	 * as we submit copies of pages anyways.
+	 */
+
+	ctx = kmalloc(sizeof(struct drbd_bm_aio_ctx), GFP_NOIO);
+	if (!ctx)
+		return -ENOMEM;
+
+	*ctx = (struct drbd_bm_aio_ctx) {
+		.device = device,
+		.start_jif = jiffies,
+		.in_flight = ATOMIC_INIT(1),
+		.done = 0,
+		.flags = flags,
+		.error = 0,
+		.kref = KREF_INIT(2),
+	};
+
+	if (!get_ldev_if_state(device, D_ATTACHING)) {  /* put is in drbd_bm_aio_ctx_destroy() */
+		drbd_err(device, "ASSERT FAILED: get_ldev_if_state() == 1 in bm_rw()\n");
+		kfree(ctx);
+		return -ENODEV;
+	}
+	/* Here D_ATTACHING is sufficient since drbd_bm_read() is called only from
+	   drbd_adm_attach(), after device->ldev was assigned. */
+
+	if (0 == (ctx->flags & ~BM_AIO_READ))
+		WARN_ON(!(BM_LOCKED_MASK & b->bm_flags));
+
+	spin_lock_irq(&device->resource->req_lock);
+	list_add_tail(&ctx->list, &device->pending_bitmap_io);
+	spin_unlock_irq(&device->resource->req_lock);
+
+	num_pages = b->bm_number_of_pages;
+
+	now = jiffies;
+
+	/* let the layers below us try to merge these bios... */
+
+	if (flags & BM_AIO_READ) {
+		for (i = 0; i < num_pages; i++) {
+			atomic_inc(&ctx->in_flight);
+			bm_page_io_async(ctx, i);
+			++count;
+			cond_resched();
+		}
+	} else if (flags & BM_AIO_WRITE_HINTED) {
+		/* ASSERT: BM_AIO_WRITE_ALL_PAGES is not set. */
+		unsigned int hint;
+		for (hint = 0; hint < b->n_bitmap_hints; hint++) {
+			i = b->al_bitmap_hints[hint];
+			if (i >= num_pages) /* == -1U: no hint here. */
+				continue;
+			/* Several AL-extents may point to the same page. */
+			if (!test_and_clear_bit(BM_PAGE_HINT_WRITEOUT,
+			    &page_private(b->bm_pages[i])))
+				continue;
+			/* Has it even changed? */
+			if (bm_test_page_unchanged(b->bm_pages[i]))
+				continue;
+			atomic_inc(&ctx->in_flight);
+			bm_page_io_async(ctx, i);
+			++count;
+		}
+	} else {
+		for (i = 0; i < num_pages; i++) {
+			/* ignore completely unchanged pages */
+			if (lazy_writeout_upper_idx && i == lazy_writeout_upper_idx)
+				break;
+			if (!(flags & BM_AIO_WRITE_ALL_PAGES) &&
+			    bm_test_page_unchanged(b->bm_pages[i])) {
+				dynamic_drbd_dbg(device, "skipped bm write for idx %u\n", i);
+				continue;
+			}
+			/* during lazy writeout,
+			 * ignore those pages not marked for lazy writeout. */
+			if (lazy_writeout_upper_idx &&
+			    !bm_test_page_lazy_writeout(b->bm_pages[i])) {
+				dynamic_drbd_dbg(device, "skipped bm lazy write for idx %u\n", i);
+				continue;
+			}
+			atomic_inc(&ctx->in_flight);
+			bm_page_io_async(ctx, i);
+			++count;
+			cond_resched();
+		}
+	}
+
+	/*
+	 * We initialize ctx->in_flight to one to make sure drbd_bm_endio
+	 * will not set ctx->done early, and decrement / test it here.  If there
+	 * are still some bios in flight, we need to wait for them here.
+	 * If all IO is done already (or nothing had been submitted), there is
+	 * no need to wait.  Still, we need to put the kref associated with the
+	 * "in_flight reached zero, all done" event.
+	 */
+	if (!atomic_dec_and_test(&ctx->in_flight))
+		wait_until_done_or_force_detached(device, device->ldev, &ctx->done);
+	else
+		kref_put(&ctx->kref, &drbd_bm_aio_ctx_destroy);
+
+	/* summary for global bitmap IO */
+	if (flags == 0) {
+		unsigned int ms = jiffies_to_msecs(jiffies - now);
+		if (ms > 5) {
+			drbd_info(device, "bitmap %s of %u pages took %u ms\n",
+				 (flags & BM_AIO_READ) ? "READ" : "WRITE",
+				 count, ms);
+		}
+	}
+
+	if (ctx->error) {
+		drbd_alert(device, "we had at least one MD IO ERROR during bitmap IO\n");
+		drbd_chk_io_error(device, 1, DRBD_META_IO_ERROR);
+		err = -EIO; /* ctx->error ? */
+	}
+
+	if (atomic_read(&ctx->in_flight))
+		err = -EIO; /* Disk timeout/force-detach during IO... */
+
+	now = jiffies;
+	if (flags & BM_AIO_READ) {
+		b->bm_set = bm_count_bits(b);
+		drbd_info(device, "recounting of set bits took additional %lu jiffies\n",
+		     jiffies - now);
+	}
+	now = b->bm_set;
+
+	if ((flags & ~BM_AIO_READ) == 0)
+		drbd_info(device, "%s (%lu bits) marked out-of-sync by on disk bit-map.\n",
+		     ppsize(ppb, now << (BM_BLOCK_SHIFT-10)), now);
+
+	kref_put(&ctx->kref, &drbd_bm_aio_ctx_destroy);
+	return err;
+}
+
+/**
+ * drbd_bm_read() - Read the whole bitmap from its on disk location.
+ * @device:	DRBD device.
+ */
+int drbd_bm_read(struct drbd_device *device) __must_hold(local)
+{
+	return bm_rw(device, BM_AIO_READ, 0);
+}
+
+/**
+ * drbd_bm_write() - Write the whole bitmap to its on disk location.
+ * @device:	DRBD device.
+ *
+ * Will only write pages that have changed since last IO.
+ */
+int drbd_bm_write(struct drbd_device *device) __must_hold(local)
+{
+	return bm_rw(device, 0, 0);
+}
+
+/**
+ * drbd_bm_write_all() - Write the whole bitmap to its on disk location.
+ * @device:	DRBD device.
+ *
+ * Will write all pages.
+ */
+int drbd_bm_write_all(struct drbd_device *device) __must_hold(local)
+{
+	return bm_rw(device, BM_AIO_WRITE_ALL_PAGES, 0);
+}
+
+/**
+ * drbd_bm_write_lazy() - Write bitmap pages 0 to @upper_idx-1, if they have changed.
+ * @device:	DRBD device.
+ * @upper_idx:	0: write all changed pages; +ve: page index to stop scanning for changed pages
+ */
+int drbd_bm_write_lazy(struct drbd_device *device, unsigned upper_idx) __must_hold(local)
+{
+	return bm_rw(device, BM_AIO_COPY_PAGES, upper_idx);
+}
+
+/**
+ * drbd_bm_write_copy_pages() - Write the whole bitmap to its on disk location.
+ * @device:	DRBD device.
+ *
+ * Will only write pages that have changed since last IO.
+ * In contrast to drbd_bm_write(), this will copy the bitmap pages
+ * to temporary writeout pages. It is intended to trigger a full write-out
+ * while still allowing the bitmap to change, for example if a resync or online
+ * verify is aborted due to a failed peer disk, while local IO continues, or
+ * pending resync acks are still being processed.
+ */
+int drbd_bm_write_copy_pages(struct drbd_device *device) __must_hold(local)
+{
+	return bm_rw(device, BM_AIO_COPY_PAGES, 0);
+}
+
+/**
+ * drbd_bm_write_hinted() - Write bitmap pages with "hint" marks, if they have changed.
+ * @device:	DRBD device.
+ */
+int drbd_bm_write_hinted(struct drbd_device *device) __must_hold(local)
+{
+	return bm_rw(device, BM_AIO_WRITE_HINTED | BM_AIO_COPY_PAGES, 0);
+}
+
+/* NOTE
+ * find_first_bit returns int, we return unsigned long.
+ * For this to work on 32bit arch with bitnumbers > (1<<32),
+ * we'd need to return u64, and get a whole lot of other places
+ * fixed where we still use unsigned long.
+ *
+ * this returns a bit number, NOT a sector!
+ */
+static unsigned long __bm_find_next(struct drbd_device *device, unsigned long bm_fo,
+	const int find_zero_bit)
+{
+	struct drbd_bitmap *b = device->bitmap;
+	unsigned long *p_addr;
+	unsigned long bit_offset;
+	unsigned i;
+
+
+	if (bm_fo > b->bm_bits) {
+		drbd_err(device, "bm_fo=%lu bm_bits=%lu\n", bm_fo, b->bm_bits);
+		bm_fo = DRBD_END_OF_BITMAP;
+	} else {
+		while (bm_fo < b->bm_bits) {
+			/* bit offset of the first bit in the page */
+			bit_offset = bm_fo & ~BITS_PER_PAGE_MASK;
+			p_addr = __bm_map_pidx(b, bm_bit_to_page_idx(b, bm_fo));
+
+			if (find_zero_bit)
+				i = find_next_zero_bit_le(p_addr,
+						PAGE_SIZE*8, bm_fo & BITS_PER_PAGE_MASK);
+			else
+				i = find_next_bit_le(p_addr,
+						PAGE_SIZE*8, bm_fo & BITS_PER_PAGE_MASK);
+
+			__bm_unmap(p_addr);
+			if (i < PAGE_SIZE*8) {
+				bm_fo = bit_offset + i;
+				if (bm_fo >= b->bm_bits)
+					break;
+				goto found;
+			}
+			bm_fo = bit_offset + PAGE_SIZE*8;
+		}
+		bm_fo = DRBD_END_OF_BITMAP;
+	}
+ found:
+	return bm_fo;
+}
+
+static unsigned long bm_find_next(struct drbd_device *device,
+	unsigned long bm_fo, const int find_zero_bit)
+{
+	struct drbd_bitmap *b = device->bitmap;
+	unsigned long i = DRBD_END_OF_BITMAP;
+
+	if (!expect(b))
+		return i;
+	if (!expect(b->bm_pages))
+		return i;
+
+	spin_lock_irq(&b->bm_lock);
+	if (BM_DONT_TEST & b->bm_flags)
+		bm_print_lock_info(device);
+
+	i = __bm_find_next(device, bm_fo, find_zero_bit);
+
+	spin_unlock_irq(&b->bm_lock);
+	return i;
+}
+
+unsigned long drbd_bm_find_next(struct drbd_device *device, unsigned long bm_fo)
+{
+	return bm_find_next(device, bm_fo, 0);
+}
+
+#if 0
+/* not yet needed for anything. */
+unsigned long drbd_bm_find_next_zero(struct drbd_device *device, unsigned long bm_fo)
+{
+	return bm_find_next(device, bm_fo, 1);
+}
+#endif
+
+/* does not spin_lock_irqsave.
+ * you must take drbd_bm_lock() first */
+unsigned long _drbd_bm_find_next(struct drbd_device *device, unsigned long bm_fo)
+{
+	/* WARN_ON(!(BM_DONT_SET & device->b->bm_flags)); */
+	return __bm_find_next(device, bm_fo, 0);
+}
+
+unsigned long _drbd_bm_find_next_zero(struct drbd_device *device, unsigned long bm_fo)
+{
+	/* WARN_ON(!(BM_DONT_SET & device->b->bm_flags)); */
+	return __bm_find_next(device, bm_fo, 1);
+}
+
+/* returns number of bits actually changed.
+ * for val != 0, we change 0 -> 1, return code positive
+ * for val == 0, we change 1 -> 0, return code negative
+ * wants bitnr, not sector.
+ * expected to be called for only a few bits (e - s about BITS_PER_LONG).
+ * Must hold bitmap lock already. */
+static int __bm_change_bits_to(struct drbd_device *device, const unsigned long s,
+	unsigned long e, int val)
+{
+	struct drbd_bitmap *b = device->bitmap;
+	unsigned long *p_addr = NULL;
+	unsigned long bitnr;
+	unsigned int last_page_nr = -1U;
+	int c = 0;
+	int changed_total = 0;
+
+	if (e >= b->bm_bits) {
+		drbd_err(device, "ASSERT FAILED: bit_s=%lu bit_e=%lu bm_bits=%lu\n",
+				s, e, b->bm_bits);
+		e = b->bm_bits ? b->bm_bits -1 : 0;
+	}
+	for (bitnr = s; bitnr <= e; bitnr++) {
+		unsigned int page_nr = bm_bit_to_page_idx(b, bitnr);
+		if (page_nr != last_page_nr) {
+			if (p_addr)
+				__bm_unmap(p_addr);
+			if (c < 0)
+				bm_set_page_lazy_writeout(b->bm_pages[last_page_nr]);
+			else if (c > 0)
+				bm_set_page_need_writeout(b->bm_pages[last_page_nr]);
+			changed_total += c;
+			c = 0;
+			p_addr = __bm_map_pidx(b, page_nr);
+			last_page_nr = page_nr;
+		}
+		if (val)
+			c += (0 == __test_and_set_bit_le(bitnr & BITS_PER_PAGE_MASK, p_addr));
+		else
+			c -= (0 != __test_and_clear_bit_le(bitnr & BITS_PER_PAGE_MASK, p_addr));
+	}
+	if (p_addr)
+		__bm_unmap(p_addr);
+	if (c < 0)
+		bm_set_page_lazy_writeout(b->bm_pages[last_page_nr]);
+	else if (c > 0)
+		bm_set_page_need_writeout(b->bm_pages[last_page_nr]);
+	changed_total += c;
+	b->bm_set += changed_total;
+	return changed_total;
+}
+
+/* returns number of bits actually changed.
+ * for val != 0, we change 0 -> 1, return code positive
+ * for val == 0, we change 1 -> 0, return code negative
+ * wants bitnr, not sector */
+static int bm_change_bits_to(struct drbd_device *device, const unsigned long s,
+	const unsigned long e, int val)
+{
+	unsigned long flags;
+	struct drbd_bitmap *b = device->bitmap;
+	int c = 0;
+
+	if (!expect(b))
+		return 1;
+	if (!expect(b->bm_pages))
+		return 0;
+
+	spin_lock_irqsave(&b->bm_lock, flags);
+	if ((val ? BM_DONT_SET : BM_DONT_CLEAR) & b->bm_flags)
+		bm_print_lock_info(device);
+
+	c = __bm_change_bits_to(device, s, e, val);
+
+	spin_unlock_irqrestore(&b->bm_lock, flags);
+	return c;
+}
+
+/* returns number of bits changed 0 -> 1 */
+int drbd_bm_set_bits(struct drbd_device *device, const unsigned long s, const unsigned long e)
+{
+	return bm_change_bits_to(device, s, e, 1);
+}
+
+/* returns number of bits changed 1 -> 0 */
+int drbd_bm_clear_bits(struct drbd_device *device, const unsigned long s, const unsigned long e)
+{
+	return -bm_change_bits_to(device, s, e, 0);
+}
+
+/* sets all bits in full words,
+ * from first_word up to, but not including, last_word */
+static inline void bm_set_full_words_within_one_page(struct drbd_bitmap *b,
+		int page_nr, int first_word, int last_word)
+{
+	int i;
+	int bits;
+	int changed = 0;
+	unsigned long *paddr = kmap_atomic(b->bm_pages[page_nr]);
+
+	/* I think it is more cache line friendly to hweight_long then set to ~0UL,
+	 * than to first bitmap_weight() all words, then bitmap_fill() all words */
+	for (i = first_word; i < last_word; i++) {
+		bits = hweight_long(paddr[i]);
+		paddr[i] = ~0UL;
+		changed += BITS_PER_LONG - bits;
+	}
+	kunmap_atomic(paddr);
+	if (changed) {
+		/* We only need lazy writeout, the information is still in the
+		 * remote bitmap as well, and is reconstructed during the next
+		 * bitmap exchange, if lost locally due to a crash. */
+		bm_set_page_lazy_writeout(b->bm_pages[page_nr]);
+		b->bm_set += changed;
+	}
+}
+
+/* Same thing as drbd_bm_set_bits,
+ * but more efficient for a large bit range.
+ * You must first drbd_bm_lock().
+ * Can be called to set the whole bitmap in one go.
+ * Sets bits from s to e _inclusive_. */
+void _drbd_bm_set_bits(struct drbd_device *device, const unsigned long s, const unsigned long e)
+{
+	/* First set_bit from the first bit (s)
+	 * up to the next long boundary (sl),
+	 * then assign full words up to the last long boundary (el),
+	 * then set_bit up to and including the last bit (e).
+	 *
+	 * Do not use memset, because we must account for changes,
+	 * so we need to loop over the words with hweight() anyways.
+	 */
+	struct drbd_bitmap *b = device->bitmap;
+	unsigned long sl = ALIGN(s,BITS_PER_LONG);
+	unsigned long el = (e+1) & ~((unsigned long)BITS_PER_LONG-1);
+	int first_page;
+	int last_page;
+	int page_nr;
+	int first_word;
+	int last_word;
+
+	if (e - s <= 3*BITS_PER_LONG) {
+		/* don't bother; el and sl may even be wrong. */
+		spin_lock_irq(&b->bm_lock);
+		__bm_change_bits_to(device, s, e, 1);
+		spin_unlock_irq(&b->bm_lock);
+		return;
+	}
+
+	/* difference is large enough that we can trust sl and el */
+
+	spin_lock_irq(&b->bm_lock);
+
+	/* bits filling the current long */
+	if (sl)
+		__bm_change_bits_to(device, s, sl-1, 1);
+
+	first_page = sl >> (3 + PAGE_SHIFT);
+	last_page = el >> (3 + PAGE_SHIFT);
+
+	/* MLPP: modulo longs per page */
+	/* LWPP: long words per page */
+	first_word = MLPP(sl >> LN2_BPL);
+	last_word = LWPP;
+
+	/* first and full pages, unless first page == last page */
+	for (page_nr = first_page; page_nr < last_page; page_nr++) {
+		bm_set_full_words_within_one_page(device->bitmap, page_nr, first_word, last_word);
+		spin_unlock_irq(&b->bm_lock);
+		cond_resched();
+		first_word = 0;
+		spin_lock_irq(&b->bm_lock);
+	}
+	/* last page (respectively only page, for first page == last page) */
+	last_word = MLPP(el >> LN2_BPL);
+
+	/* consider bitmap->bm_bits = 32768, bitmap->bm_number_of_pages = 1. (or multiples).
+	 * ==> e = 32767, el = 32768, last_page = 2,
+	 * and now last_word = 0.
+	 * We do not want to touch last_page in this case,
+	 * as we did not allocate it, it is not present in bitmap->bm_pages.
+	 */
+	if (last_word)
+		bm_set_full_words_within_one_page(device->bitmap, last_page, first_word, last_word);
+
+	/* possibly trailing bits.
+	 * example: (e & 63) == 63, el will be e+1.
+	 * if that even was the very last bit,
+	 * it would trigger an assert in __bm_change_bits_to()
+	 */
+	if (el <= e)
+		__bm_change_bits_to(device, el, e, 1);
+	spin_unlock_irq(&b->bm_lock);
+}
+
+/* returns bit state
+ * wants bitnr, NOT sector.
+ * inherently racy... area needs to be locked by means of {al,rs}_lru
+ *  1 ... bit set
+ *  0 ... bit not set
+ * -1 ... first out of bounds access, stop testing for bits!
+ */
+int drbd_bm_test_bit(struct drbd_device *device, const unsigned long bitnr)
+{
+	unsigned long flags;
+	struct drbd_bitmap *b = device->bitmap;
+	unsigned long *p_addr;
+	int i;
+
+	if (!expect(b))
+		return 0;
+	if (!expect(b->bm_pages))
+		return 0;
+
+	spin_lock_irqsave(&b->bm_lock, flags);
+	if (BM_DONT_TEST & b->bm_flags)
+		bm_print_lock_info(device);
+	if (bitnr < b->bm_bits) {
+		p_addr = bm_map_pidx(b, bm_bit_to_page_idx(b, bitnr));
+		i = test_bit_le(bitnr & BITS_PER_PAGE_MASK, p_addr) ? 1 : 0;
+		bm_unmap(p_addr);
+	} else if (bitnr == b->bm_bits) {
+		i = -1;
+	} else { /* (bitnr > b->bm_bits) */
+		drbd_err(device, "bitnr=%lu > bm_bits=%lu\n", bitnr, b->bm_bits);
+		i = 0;
+	}
+
+	spin_unlock_irqrestore(&b->bm_lock, flags);
+	return i;
+}
+
+/* returns number of bits set in the range [s, e] */
+int drbd_bm_count_bits(struct drbd_device *device, const unsigned long s, const unsigned long e)
+{
+	unsigned long flags;
+	struct drbd_bitmap *b = device->bitmap;
+	unsigned long *p_addr = NULL;
+	unsigned long bitnr;
+	unsigned int page_nr = -1U;
+	int c = 0;
+
+	/* If this is called without a bitmap, that is a bug.  But just to be
+	 * robust in case we screwed up elsewhere, in that case pretend there
+	 * was one dirty bit in the requested area, so we won't try to do a
+	 * local read there (no bitmap probably implies no disk) */
+	if (!expect(b))
+		return 1;
+	if (!expect(b->bm_pages))
+		return 1;
+
+	spin_lock_irqsave(&b->bm_lock, flags);
+	if (BM_DONT_TEST & b->bm_flags)
+		bm_print_lock_info(device);
+	for (bitnr = s; bitnr <= e; bitnr++) {
+		unsigned int idx = bm_bit_to_page_idx(b, bitnr);
+		if (page_nr != idx) {
+			page_nr = idx;
+			if (p_addr)
+				bm_unmap(p_addr);
+			p_addr = bm_map_pidx(b, idx);
+		}
+		if (expect(bitnr < b->bm_bits))
+			c += (0 != test_bit_le(bitnr - (page_nr << (PAGE_SHIFT+3)), p_addr));
+		else
+			drbd_err(device, "bitnr=%lu bm_bits=%lu\n", bitnr, b->bm_bits);
+	}
+	if (p_addr)
+		bm_unmap(p_addr);
+	spin_unlock_irqrestore(&b->bm_lock, flags);
+	return c;
+}
+
+
+/* inherently racy...
+ * return value may be already out-of-date when this function returns.
+ * but the general usage is that this is only use during a cstate when bits are
+ * only cleared, not set, and typically only care for the case when the return
+ * value is zero, or we already "locked" this "bitmap extent" by other means.
+ *
+ * enr is bm-extent number, since we chose to name one sector (512 bytes)
+ * worth of the bitmap a "bitmap extent".
+ *
+ * TODO
+ * I think since we use it like a reference count, we should use the real
+ * reference count of some bitmap extent element from some lru instead...
+ *
+ */
+int drbd_bm_e_weight(struct drbd_device *device, unsigned long enr)
+{
+	struct drbd_bitmap *b = device->bitmap;
+	int count, s, e;
+	unsigned long flags;
+	unsigned long *p_addr, *bm;
+
+	if (!expect(b))
+		return 0;
+	if (!expect(b->bm_pages))
+		return 0;
+
+	spin_lock_irqsave(&b->bm_lock, flags);
+	if (BM_DONT_TEST & b->bm_flags)
+		bm_print_lock_info(device);
+
+	s = S2W(enr);
+	e = min((size_t)S2W(enr+1), b->bm_words);
+	count = 0;
+	if (s < b->bm_words) {
+		int n = e-s;
+		p_addr = bm_map_pidx(b, bm_word_to_page_idx(b, s));
+		bm = p_addr + MLPP(s);
+		count += bitmap_weight(bm, n * BITS_PER_LONG);
+		bm_unmap(p_addr);
+	} else {
+		drbd_err(device, "start offset (%d) too large in drbd_bm_e_weight\n", s);
+	}
+	spin_unlock_irqrestore(&b->bm_lock, flags);
+	return count;
+}