// SPDX-License-Identifier: GPL-2.0-or-later
/*
   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>.

 */

#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;
}