drbd_bitmap.c

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/*
   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 <[email protected]>.
   Copyright (C) 2004-2008, Lars Ellenberg <[email protected]>.

   drbd is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   drbd is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with drbd; see the file COPYING.  If not, write to
   the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include <linux/bitops.h>
#include <linux/vmalloc.h>
#include <linux/string.h>
#include <linux/drbd.h>
#include <linux/slab.h>
#include <asm/kmap_types.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;

    /* 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_conf *mdev, const char *func)
{
    struct drbd_bitmap *b = mdev->bitmap;
    if (!__ratelimit(&drbd_ratelimit_state))
        return;
    dev_err(DEV, "FIXME %s in %s, bitmap locked for '%s' by %s\n",
        current == mdev->receiver.task ? "receiver" :
        current == mdev->asender.task  ? "asender"  :
        current == mdev->worker.task   ? "worker"   : current->comm,
        func, b->bm_why ?: "?",
        b->bm_task == mdev->receiver.task ? "receiver" :
        b->bm_task == mdev->asender.task  ? "asender"  :
        b->bm_task == mdev->worker.task   ? "worker"   : "?");
}

void drbd_bm_lock(struct drbd_conf *mdev, char *why, enum bm_flag flags)
{
    struct drbd_bitmap *b = mdev->bitmap;
    int trylock_failed;

    if (!b) {
        dev_err(DEV, "FIXME no bitmap in drbd_bm_lock!?\n");
        return;
    }

    trylock_failed = !mutex_trylock(&b->bm_change);

    if (trylock_failed) {
        dev_warn(DEV, "%s going to '%s' but bitmap already locked for '%s' by %s\n",
            current == mdev->receiver.task ? "receiver" :
            current == mdev->asender.task  ? "asender"  :
            current == mdev->worker.task   ? "worker"   : current->comm,
            why, b->bm_why ?: "?",
            b->bm_task == mdev->receiver.task ? "receiver" :
            b->bm_task == mdev->asender.task  ? "asender"  :
            b->bm_task == mdev->worker.task   ? "worker"   : "?");
        mutex_lock(&b->bm_change);
    }
    if (BM_LOCKED_MASK & b->bm_flags)
        dev_err(DEV, "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_conf *mdev)
{
    struct drbd_bitmap *b = mdev->bitmap;
    if (!b) {
        dev_err(DEV, "FIXME no bitmap in drbd_bm_unlock!?\n");
        return;
    }

    if (!(BM_LOCKED_MASK & mdev->bitmap->bm_flags))
        dev_err(DEV, "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

/* 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_conf *mdev, int page_nr)
{
    struct drbd_bitmap *b = mdev->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_conf *mdev, int page_nr)
{
    struct drbd_bitmap *b = mdev->bitmap;
    void *addr = &page_private(b->bm_pages[page_nr]);
    clear_bit(BM_PAGE_IO_LOCK, addr);
    smp_mb__after_clear_bit();
    wake_up(&mdev->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));
}

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_conf*, but for the debug macros I like to have the mdev 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]) {
            printk(KERN_ALERT "drbd: 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 void bm_vk_free(void *ptr, int v)
{
    if (v)
        vfree(ptr);
    else
        kfree(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, vmalloced = 0;
    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_KERNEL is ok, as this is done when a lower level disk is
     * "attached" to the drbd.  Context is receiver thread or cqueue
     * thread.  As we have no disk yet, we are not in the IO path,
     * not even the IO path of the peer. */
    bytes = sizeof(struct page *)*want;
    new_pages = kzalloc(bytes, GFP_KERNEL);
    if (!new_pages) {
        new_pages = vzalloc(bytes);
        if (!new_pages)
            return NULL;
        vmalloced = 1;
    }

    if (want >= have) {
        for (i = 0; i < have; i++)
            new_pages[i] = old_pages[i];
        for (; i < want; i++) {
            page = alloc_page(GFP_HIGHUSER);
            if (!page) {
                bm_free_pages(new_pages + have, i - have);
                bm_vk_free(new_pages, vmalloced);
                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);
        */
    }

    if (vmalloced)
        b->bm_flags |= BM_P_VMALLOCED;
    else
        b->bm_flags &= ~BM_P_VMALLOCED;

    return new_pages;
}

/*
 * called on driver init only. TODO call when a device is created.
 * allocates the drbd_bitmap, and stores it in mdev->bitmap.
 */
int drbd_bm_init(struct drbd_conf *mdev)
{
    struct drbd_bitmap *b = mdev->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);

    mdev->bitmap = b;

    return 0;
}

sector_t drbd_bm_capacity(struct drbd_conf *mdev)
{
    ERR_IF(!mdev->bitmap) return 0;
    return mdev->bitmap->bm_dev_capacity;
}

/* called on driver unload. TODO: call when a device is destroyed.
 */
void drbd_bm_cleanup(struct drbd_conf *mdev)
{
    ERR_IF (!mdev->bitmap) return;
    bm_free_pages(mdev->bitmap->bm_pages, mdev->bitmap->bm_number_of_pages);
    bm_vk_free(mdev->bitmap->bm_pages, (BM_P_VMALLOCED & mdev->bitmap->bm_flags));
    kfree(mdev->bitmap);
    mdev->bitmap = NULL;
}

/*
 * since (b->bm_bits % BITS_PER_LONG) != 0,
 * this masks out the remaining bits.
 * Returns the number of bits cleared.
 */
#define BITS_PER_PAGE       (1UL << (PAGE_SHIFT + 3))
#define BITS_PER_PAGE_MASK  (BITS_PER_PAGE - 1)
#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, i, last_word;

    /* all but last page */
    for (idx = 0; idx < b->bm_number_of_pages - 1; idx++) {
        p_addr = __bm_map_pidx(b, idx);
        for (i = 0; i < LWPP; i++)
            bits += hweight_long(p_addr[i]);
        __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);
    for (i = 0; i < last_word; i++)
        bits += hweight_long(p_addr[i]);
    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) {
        printk(KERN_ALERT "drbd: 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) {
            printk(KERN_ALERT "drbd: 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;
    }
}

/*
 * 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_conf *mdev, sector_t capacity, int set_new_bits)
{
    struct drbd_bitmap *b = mdev->bitmap;
    unsigned long bits, words, owords, obits;
    unsigned long want, have, onpages; /* number of pages */
    struct page **npages, **opages = NULL;
    int err = 0, growing;
    int opages_vmalloced;

    ERR_IF(!b) return -ENOMEM;

    drbd_bm_lock(mdev, "resize", BM_LOCKED_MASK);

    dev_info(DEV, "drbd_bm_resize called with capacity == %llu\n",
            (unsigned long long)capacity);

    if (capacity == b->bm_dev_capacity)
        goto out;

    opages_vmalloced = (BM_P_VMALLOCED & b->bm_flags);

    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, opages_vmalloced);
        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(mdev)) {
        u64 bits_on_disk = ((u64)mdev->ldev->md.md_size_sect-MD_BM_OFFSET) << 12;
        put_ldev(mdev);
        if (bits > bits_on_disk) {
            dev_info(DEV, "bits = %lu\n", bits);
            dev_info(DEV, "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(b->bm_pages != NULL);
        npages = b->bm_pages;
    } else {
        if (drbd_insert_fault(mdev, 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, opages_vmalloced);
    if (!growing)
        b->bm_set = bm_count_bits(b);
    dev_info(DEV, "resync bitmap: bits=%lu words=%lu pages=%lu\n", bits, words, want);

 out:
    drbd_bm_unlock(mdev);
    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_conf *mdev)
{
    struct drbd_bitmap *b = mdev->bitmap;
    unsigned long s;
    unsigned long flags;

    ERR_IF(!b) return 0;
    ERR_IF(!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_conf *mdev)
{
    unsigned long s;
    /* if I don't have a disk, I don't know about out-of-sync status */
    if (!get_ldev_if_state(mdev, D_NEGOTIATING))
        return 0;
    s = _drbd_bm_total_weight(mdev);
    put_ldev(mdev);
    return s;
}

size_t drbd_bm_words(struct drbd_conf *mdev)
{
    struct drbd_bitmap *b = mdev->bitmap;
    ERR_IF(!b) return 0;
    ERR_IF(!b->bm_pages) return 0;

    return b->bm_words;
}

unsigned long drbd_bm_bits(struct drbd_conf *mdev)
{
    struct drbd_bitmap *b = mdev->bitmap;
    ERR_IF(!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_conf *mdev, size_t offset, size_t number,
            unsigned long *buffer)
{
    struct drbd_bitmap *b = mdev->bitmap;
    unsigned long *p_addr, *bm;
    unsigned long word, bits;
    unsigned int idx;
    size_t end, do_now;

    end = offset + number;

    ERR_IF(!b) return;
    ERR_IF(!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_conf *mdev, size_t offset, size_t number,
             unsigned long *buffer)
{
    struct drbd_bitmap *b = mdev->bitmap;
    unsigned long *p_addr, *bm;
    size_t end, do_now;

    end = offset + number;

    ERR_IF(!b) return;
    ERR_IF(!b->bm_pages) return;

    spin_lock_irq(&b->bm_lock);
    if ((offset >= b->bm_words) ||
        (end    >  b->bm_words) ||
        (number <= 0))
        dev_err(DEV, "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_conf *mdev)
{
    struct drbd_bitmap *b = mdev->bitmap;
    ERR_IF(!b) return;
    ERR_IF(!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_conf *mdev)
{
    struct drbd_bitmap *b = mdev->bitmap;
    ERR_IF(!b) return;
    ERR_IF(!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);
}

struct bm_aio_ctx {
    struct drbd_conf *mdev;
    atomic_t in_flight;
    unsigned int done;
    unsigned flags;
#define BM_AIO_COPY_PAGES   1
#define BM_WRITE_ALL_PAGES  2
    int error;
    struct kref kref;
};

static void bm_aio_ctx_destroy(struct kref *kref)
{
    struct bm_aio_ctx *ctx = container_of(kref, struct bm_aio_ctx, kref);

    put_ldev(ctx->mdev);
    kfree(ctx);
}

/* bv_page may be a copy, or may be the original */
static void bm_async_io_complete(struct bio *bio, int error)
{
    struct bm_aio_ctx *ctx = bio->bi_private;
    struct drbd_conf *mdev = ctx->mdev;
    struct drbd_bitmap *b = mdev->bitmap;
    unsigned int idx = bm_page_to_idx(bio->bi_io_vec[0].bv_page);
    int uptodate = bio_flagged(bio, BIO_UPTODATE);


    /* strange behavior of some lower level drivers...
     * fail the request by clearing the uptodate flag,
     * but do not return any error?!
     * do we want to WARN() on this? */
    if (!error && !uptodate)
        error = -EIO;

    if ((ctx->flags & BM_AIO_COPY_PAGES) == 0 &&
        !bm_test_page_unchanged(b->bm_pages[idx]))
        dev_warn(DEV, "bitmap page idx %u changed during IO!\n", idx);

    if (error) {
        /* ctx error will hold the completed-last non-zero error code,
         * in case error codes differ. */
        ctx->error = error;
        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))
            dev_err(DEV, "IO ERROR %d on bitmap page idx %u\n",
                    error, idx);
    } else {
        bm_clear_page_io_err(b->bm_pages[idx]);
        dynamic_dev_dbg(DEV, "bitmap page idx %u completed\n", idx);
    }

    bm_page_unlock_io(mdev, 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(&mdev->misc_wait);
        kref_put(&ctx->kref, &bm_aio_ctx_destroy);
    }
}

static void bm_page_io_async(struct bm_aio_ctx *ctx, int page_nr, int rw) __must_hold(local)
{
    struct bio *bio = bio_alloc_drbd(GFP_NOIO);
    struct drbd_conf *mdev = ctx->mdev;
    struct drbd_bitmap *b = mdev->bitmap;
    struct page *page;
    unsigned int len;

    sector_t on_disk_sector =
        mdev->ldev->md.md_offset + mdev->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(mdev->ldev) - on_disk_sector + 1)<<9);

    /* serialize IO on this page */
    bm_page_lock_io(mdev, 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) {
        void *src, *dest;
        page = mempool_alloc(drbd_md_io_page_pool, __GFP_HIGHMEM|__GFP_WAIT);
        dest = kmap_atomic(page);
        src = kmap_atomic(b->bm_pages[page_nr]);
        memcpy(dest, src, PAGE_SIZE);
        kunmap_atomic(src);
        kunmap_atomic(dest);
        bm_store_page_idx(page, page_nr);
    } else
        page = b->bm_pages[page_nr];

    bio->bi_bdev = mdev->ldev->md_bdev;
    bio->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 = bm_async_io_complete;

    if (drbd_insert_fault(mdev, (rw & WRITE) ? DRBD_FAULT_MD_WR : DRBD_FAULT_MD_RD)) {
        bio->bi_rw |= rw;
        bio_endio(bio, -EIO);
    } else {
        submit_bio(rw, bio);
        /* this should not count as user activity and cause the
         * resync to throttle -- see drbd_rs_should_slow_down(). */
        atomic_add(len >> 9, &mdev->rs_sect_ev);
    }
}

/*
 * bm_rw: read/write the whole bitmap from/to its on disk location.
 */
static int bm_rw(struct drbd_conf *mdev, int rw, unsigned flags, unsigned lazy_writeout_upper_idx) __must_hold(local)
{
    struct bm_aio_ctx *ctx;
    struct drbd_bitmap *b = mdev->bitmap;
    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 bm_aio_ctx), GFP_NOIO);
    if (!ctx)
        return -ENOMEM;

    *ctx = (struct bm_aio_ctx) {
        .mdev = mdev,
        .in_flight = ATOMIC_INIT(1),
        .done = 0,
        .flags = flags,
        .error = 0,
        .kref = { ATOMIC_INIT(2) },
    };

    if (!get_ldev_if_state(mdev, D_ATTACHING)) {  /* put is in bm_aio_ctx_destroy() */
        dev_err(DEV, "ASSERT FAILED: get_ldev_if_state() == 1 in bm_rw()\n");
        kfree(ctx);
        return -ENODEV;
    }

    if (!ctx->flags)
        WARN_ON(!(BM_LOCKED_MASK & b->bm_flags));

    num_pages = b->bm_number_of_pages;

    now = jiffies;

    /* let the layers below us try to merge these bios... */
    for (i = 0; i < num_pages; i++) {
        /* ignore completely unchanged pages */
        if (lazy_writeout_upper_idx && i == lazy_writeout_upper_idx)
            break;
        if (rw & WRITE) {
            if (!(flags & BM_WRITE_ALL_PAGES) &&
                bm_test_page_unchanged(b->bm_pages[i])) {
                dynamic_dev_dbg(DEV, "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_dev_dbg(DEV, "skipped bm lazy write for idx %u\n", i);
                continue;
            }
        }
        atomic_inc(&ctx->in_flight);
        bm_page_io_async(ctx, i, rw);
        ++count;
        cond_resched();
    }

    /*
     * We initialize ctx->in_flight to one to make sure bm_async_io_complete
     * 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_disk_failure(mdev, mdev->ldev, &ctx->done);
    else
        kref_put(&ctx->kref, &bm_aio_ctx_destroy);

    dev_info(DEV, "bitmap %s of %u pages took %lu jiffies\n",
            rw == WRITE ? "WRITE" : "READ",
            count, jiffies - now);

    if (ctx->error) {
        dev_alert(DEV, "we had at least one MD IO ERROR during bitmap IO\n");
        drbd_chk_io_error(mdev, 1, DRBD_META_IO_ERROR);
        err = -EIO; /* ctx->error ? */
    }

    if (atomic_read(&ctx->in_flight))
        err = -EIO; /* Disk failed during IO... */

    now = jiffies;
    if (rw == WRITE) {
        drbd_md_flush(mdev);
    } else /* rw == READ */ {
        b->bm_set = bm_count_bits(b);
        dev_info(DEV, "recounting of set bits took additional %lu jiffies\n",
             jiffies - now);
    }
    now = b->bm_set;

    dev_info(DEV, "%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, &bm_aio_ctx_destroy);
    return err;
}

int drbd_bm_read(struct drbd_conf *mdev) __must_hold(local)
{
    return bm_rw(mdev, READ, 0, 0);
}

int drbd_bm_write(struct drbd_conf *mdev) __must_hold(local)
{
    return bm_rw(mdev, WRITE, 0, 0);
}

int drbd_bm_write_all(struct drbd_conf *mdev) __must_hold(local)
{
    return bm_rw(mdev, WRITE, BM_WRITE_ALL_PAGES, 0);
}

int drbd_bm_write_lazy(struct drbd_conf *mdev, unsigned upper_idx) __must_hold(local)
{
    return bm_rw(mdev, WRITE, BM_AIO_COPY_PAGES, upper_idx);
}

int drbd_bm_write_copy_pages(struct drbd_conf *mdev) __must_hold(local)
{
    return bm_rw(mdev, WRITE, BM_AIO_COPY_PAGES, 0);
}


int drbd_bm_write_page(struct drbd_conf *mdev, unsigned int idx) __must_hold(local)
{
    struct bm_aio_ctx *ctx;
    int err;

    if (bm_test_page_unchanged(mdev->bitmap->bm_pages[idx])) {
        dynamic_dev_dbg(DEV, "skipped bm page write for idx %u\n", idx);
        return 0;
    }

    ctx = kmalloc(sizeof(struct bm_aio_ctx), GFP_NOIO);
    if (!ctx)
        return -ENOMEM;

    *ctx = (struct bm_aio_ctx) {
        .mdev = mdev,
        .in_flight = ATOMIC_INIT(1),
        .done = 0,
        .flags = BM_AIO_COPY_PAGES,
        .error = 0,
        .kref = { ATOMIC_INIT(2) },
    };

    if (!get_ldev_if_state(mdev, D_ATTACHING)) {  /* put is in bm_aio_ctx_destroy() */
        dev_err(DEV, "ASSERT FAILED: get_ldev_if_state() == 1 in drbd_bm_write_page()\n");
        kfree(ctx);
        return -ENODEV;
    }

    bm_page_io_async(ctx, idx, WRITE_SYNC);
    wait_until_done_or_disk_failure(mdev, mdev->ldev, &ctx->done);

    if (ctx->error)
        drbd_chk_io_error(mdev, 1, DRBD_META_IO_ERROR);
        /* that should force detach, so the in memory bitmap will be
         * gone in a moment as well. */

    mdev->bm_writ_cnt++;
    err = atomic_read(&ctx->in_flight) ? -EIO : ctx->error;
    kref_put(&ctx->kref, &bm_aio_ctx_destroy);
    return err;
}

/* 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_conf *mdev, unsigned long bm_fo,
    const int find_zero_bit)
{
    struct drbd_bitmap *b = mdev->bitmap;
    unsigned long *p_addr;
    unsigned long bit_offset;
    unsigned i;


    if (bm_fo > b->bm_bits) {
        dev_err(DEV, "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_conf *mdev,
    unsigned long bm_fo, const int find_zero_bit)
{
    struct drbd_bitmap *b = mdev->bitmap;
    unsigned long i = DRBD_END_OF_BITMAP;

    ERR_IF(!b) return i;
    ERR_IF(!b->bm_pages) return i;

    spin_lock_irq(&b->bm_lock);
    if (BM_DONT_TEST & b->bm_flags)
        bm_print_lock_info(mdev);

    i = __bm_find_next(mdev, bm_fo, find_zero_bit);

    spin_unlock_irq(&b->bm_lock);
    return i;
}

unsigned long drbd_bm_find_next(struct drbd_conf *mdev, unsigned long bm_fo)
{
    return bm_find_next(mdev, bm_fo, 0);
}

#if 0
/* not yet needed for anything. */
unsigned long drbd_bm_find_next_zero(struct drbd_conf *mdev, unsigned long bm_fo)
{
    return bm_find_next(mdev, bm_fo, 1);
}
#endif

/* does not spin_lock_irqsave.
 * you must take drbd_bm_lock() first */
unsigned long _drbd_bm_find_next(struct drbd_conf *mdev, unsigned long bm_fo)
{
    /* WARN_ON(!(BM_DONT_SET & mdev->b->bm_flags)); */
    return __bm_find_next(mdev, bm_fo, 0);
}

unsigned long _drbd_bm_find_next_zero(struct drbd_conf *mdev, unsigned long bm_fo)
{
    /* WARN_ON(!(BM_DONT_SET & mdev->b->bm_flags)); */
    return __bm_find_next(mdev, 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_conf *mdev, const unsigned long s,
    unsigned long e, int val)
{
    struct drbd_bitmap *b = mdev->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) {
        dev_err(DEV, "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_conf *mdev, const unsigned long s,
    const unsigned long e, int val)
{
    unsigned long flags;
    struct drbd_bitmap *b = mdev->bitmap;
    int c = 0;

    ERR_IF(!b) return 1;
    ERR_IF(!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(mdev);

    c = __bm_change_bits_to(mdev, 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_conf *mdev, const unsigned long s, const unsigned long e)
{
    return bm_change_bits_to(mdev, s, e, 1);
}

/* returns number of bits changed 1 -> 0 */
int drbd_bm_clear_bits(struct drbd_conf *mdev, const unsigned long s, const unsigned long e)
{
    return -bm_change_bits_to(mdev, 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;
    unsigned long *paddr = kmap_atomic(b->bm_pages[page_nr]);
    for (i = first_word; i < last_word; i++) {
        bits = hweight_long(paddr[i]);
        paddr[i] = ~0UL;
        b->bm_set += BITS_PER_LONG - bits;
    }
    kunmap_atomic(paddr);
}

/* 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_conf *mdev, 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 = mdev->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(mdev, 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(mdev, 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(mdev->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(mdev->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(mdev, 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_conf *mdev, const unsigned long bitnr)
{
    unsigned long flags;
    struct drbd_bitmap *b = mdev->bitmap;
    unsigned long *p_addr;
    int i;

    ERR_IF(!b) return 0;
    ERR_IF(!b->bm_pages) return 0;

    spin_lock_irqsave(&b->bm_lock, flags);
    if (BM_DONT_TEST & b->bm_flags)
        bm_print_lock_info(mdev);
    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) */
        dev_err(DEV, "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_conf *mdev, const unsigned long s, const unsigned long e)
{
    unsigned long flags;
    struct drbd_bitmap *b = mdev->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) */
    ERR_IF(!b) return 1;
    ERR_IF(!b->bm_pages) return 1;

    spin_lock_irqsave(&b->bm_lock, flags);
    if (BM_DONT_TEST & b->bm_flags)
        bm_print_lock_info(mdev);
    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);
        }
        ERR_IF (bitnr >= b->bm_bits) {
            dev_err(DEV, "bitnr=%lu bm_bits=%lu\n", bitnr, b->bm_bits);
        } else {
            c += (0 != test_bit_le(bitnr - (page_nr << (PAGE_SHIFT+3)), p_addr));
        }
    }
    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_conf *mdev, unsigned long enr)
{
    struct drbd_bitmap *b = mdev->bitmap;
    int count, s, e;
    unsigned long flags;
    unsigned long *p_addr, *bm;

    ERR_IF(!b) return 0;
    ERR_IF(!b->bm_pages) return 0;

    spin_lock_irqsave(&b->bm_lock, flags);
    if (BM_DONT_TEST & b->bm_flags)
        bm_print_lock_info(mdev);

    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);
        while (n--)
            count += hweight_long(*bm++);
        bm_unmap(p_addr);
    } else {
        dev_err(DEV, "start offset (%d) too large in drbd_bm_e_weight\n", s);
    }
    spin_unlock_irqrestore(&b->bm_lock, flags);
    return count;
}

/* Set all bits covered by the AL-extent al_enr.
 * Returns number of bits changed. */
unsigned long drbd_bm_ALe_set_all(struct drbd_conf *mdev, unsigned long al_enr)
{
    struct drbd_bitmap *b = mdev->bitmap;
    unsigned long *p_addr, *bm;
    unsigned long weight;
    unsigned long s, e;
    int count, i, do_now;
    ERR_IF(!b) return 0;
    ERR_IF(!b->bm_pages) return 0;

    spin_lock_irq(&b->bm_lock);
    if (BM_DONT_SET & b->bm_flags)
        bm_print_lock_info(mdev);
    weight = b->bm_set;

    s = al_enr * BM_WORDS_PER_AL_EXT;
    e = min_t(size_t, s + BM_WORDS_PER_AL_EXT, b->bm_words);
    /* assert that s and e are on the same page */
    D_ASSERT((e-1) >> (PAGE_SHIFT - LN2_BPL + 3)
          ==  s    >> (PAGE_SHIFT - LN2_BPL + 3));
    count = 0;
    if (s < b->bm_words) {
        i = do_now = e-s;
        p_addr = bm_map_pidx(b, bm_word_to_page_idx(b, s));
        bm = p_addr + MLPP(s);
        while (i--) {
            count += hweight_long(*bm);
            *bm = -1UL;
            bm++;
        }
        bm_unmap(p_addr);
        b->bm_set += do_now*BITS_PER_LONG - count;
        if (e == b->bm_words)
            b->bm_set -= bm_clear_surplus(b);
    } else {
        dev_err(DEV, "start offset (%lu) too large in drbd_bm_ALe_set_all\n", s);
    }
    weight = b->bm_set - weight;
    spin_unlock_irq(&b->bm_lock);
    return weight;
}