Merge branch 'for-linus' of git://git.kernel.dk/linux-2.6-block

[deliverable/linux.git] / drivers / block / drbd / drbd_bitmap.c

/*
   drbd_bitmap.c

   This file is part of DRBD by Philipp Reisner and Lars Ellenberg.

   Copyright (C) 2004-2008, LINBIT Information Technologies GmbH.
   Copyright (C) 2004-2008, Philipp Reisner <philipp.reisner@linbit.com>.
   Copyright (C) 2004-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.

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

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

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

#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".

 * Note that since find_first_bit returns int, at the current granularity of
 * the bitmap (4KB per byte), this implementation "only" supports up to
 * 1<<(32+12) == 16 TB...
 */

/*
 * 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;
        /* WARNING unsigned long bm_*:
         * 32bit number of bit offset is just enough for 512 MB bitmap.
         * it will blow up if we make the bitmap bigger...
         * not that it makes much sense to have a bitmap that large,
         * rather change the granularity to 16k or 64k or something.
         * (that implies other problems, however...)
         */
        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 */

        atomic_t bm_async_io;
        wait_queue_head_t bm_io_wait;

        unsigned long  bm_flags;

        /* debugging aid, in case we are still racy somewhere */
        char          *bm_why;
        struct task_struct *bm_task;
};

/* definition of bits in bm_flags */
#define BM_LOCKED       0
#define BM_MD_IO_ERROR  1
#define BM_P_VMALLOCED  2

static int bm_is_locked(struct drbd_bitmap *b)
{
        return test_bit(BM_LOCKED, &b->bm_flags);
}

#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)
{
        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 (__test_and_set_bit(BM_LOCKED, &b->bm_flags))
                dev_err(DEV, "FIXME bitmap already locked in bm_lock\n");

        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 (!__test_and_clear_bit(BM_LOCKED, &mdev->bitmap->bm_flags))
                dev_err(DEV, "FIXME bitmap not locked in bm_unlock\n");

        b->bm_why  = NULL;
        b->bm_task = NULL;
        mutex_unlock(&b->bm_change);
}

/* word offset to long pointer */
static unsigned long *__bm_map_paddr(struct drbd_bitmap *b, unsigned long offset, const enum km_type km)
{
        struct page *page;
        unsigned long page_nr;

        /* page_nr = (word*sizeof(long)) >> PAGE_SHIFT; */
        page_nr = offset >> (PAGE_SHIFT - LN2_BPL + 3);
        BUG_ON(page_nr >= b->bm_number_of_pages);
        page = b->bm_pages[page_nr];

        return (unsigned long *) kmap_atomic(page, km);
}

static unsigned long * bm_map_paddr(struct drbd_bitmap *b, unsigned long offset)
{
        return __bm_map_paddr(b, offset, KM_IRQ1);
}

static void __bm_unmap(unsigned long *p_addr, const enum km_type km)
{
        kunmap_atomic(p_addr, km);
};

static void bm_unmap(unsigned long *p_addr)
{
        return __bm_unmap(p_addr, KM_IRQ1);
}

/* 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 optimze 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 = kmalloc(bytes, GFP_KERNEL);
        if (!new_pages) {
                new_pages = vmalloc(bytes);
                if (!new_pages)
                        return NULL;
                vmalloced = 1;
        }

        memset(new_pages, 0, bytes);
        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;
                        }
                        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)
                set_bit(BM_P_VMALLOCED, &b->bm_flags);
        else
                clear_bit(BM_P_VMALLOCED, &b->bm_flags);

        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, test_bit(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.
 */
static int bm_clear_surplus(struct drbd_bitmap *b)
{
        const unsigned long mask = (1UL << (b->bm_bits & (BITS_PER_LONG-1))) - 1;
        size_t w = b->bm_bits >> LN2_BPL;
        int cleared = 0;
        unsigned long *p_addr, *bm;

        p_addr = bm_map_paddr(b, w);
        bm = p_addr + MLPP(w);
        if (w < b->bm_words) {
                cleared = hweight_long(*bm & ~mask);
                *bm &= mask;
                w++; bm++;
        }

        if (w < b->bm_words) {
                cleared += hweight_long(*bm);
                *bm = 0;
        }
        bm_unmap(p_addr);
        return cleared;
}

static void bm_set_surplus(struct drbd_bitmap *b)
{
        const unsigned long mask = (1UL << (b->bm_bits & (BITS_PER_LONG-1))) - 1;
        size_t w = b->bm_bits >> LN2_BPL;
        unsigned long *p_addr, *bm;

        p_addr = bm_map_paddr(b, w);
        bm = p_addr + MLPP(w);
        if (w < b->bm_words) {
                *bm |= ~mask;
                bm++; w++;
        }

        if (w < b->bm_words) {
                *bm = ~(0UL);
        }
        bm_unmap(p_addr);
}

static unsigned long __bm_count_bits(struct drbd_bitmap *b, const int swap_endian)
{
        unsigned long *p_addr, *bm, offset = 0;
        unsigned long bits = 0;
        unsigned long i, do_now;

        while (offset < b->bm_words) {
                i = do_now = min_t(size_t, b->bm_words-offset, LWPP);
                p_addr = __bm_map_paddr(b, offset, KM_USER0);
                bm = p_addr + MLPP(offset);
                while (i--) {
#ifndef __LITTLE_ENDIAN
                        if (swap_endian)
                                *bm = lel_to_cpu(*bm);
#endif
                        bits += hweight_long(*bm++);
                }
                __bm_unmap(p_addr, KM_USER0);
                offset += do_now;
                cond_resched();
        }

        return bits;
}

static unsigned long bm_count_bits(struct drbd_bitmap *b)
{
        return __bm_count_bits(b, 0);
}

static unsigned long bm_count_bits_swap_endian(struct drbd_bitmap *b)
{
        return __bm_count_bits(b, 1);
}

/* 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;
        size_t do_now, end;

#define BM_SECTORS_PER_BIT (BM_BLOCK_SIZE/512)

        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;
                p_addr = bm_map_paddr(b, offset);
                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);
                        break; /* breaks to after catch_oob_access_end() only! */
                }
                memset(bm, c, do_now * sizeof(long));
                bm_unmap(p_addr);
                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)
{
        struct drbd_bitmap *b = mdev->bitmap;
        unsigned long bits, words, owords, obits, *p_addr, *bm;
        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");

        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 = test_bit(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)) {
                D_ASSERT((u64)bits <= (((u64)mdev->ldev->md.md_size_sect-MD_BM_OFFSET) << 12));
                put_ldev(mdev);
        }

        /* one extra long to catch off by one errors */
        want = ALIGN((words+1)*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 (FAULT_ACTIVE(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)
                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) {
                bm_memset(b, owords, 0xff, words-owords);
                b->bm_set += bits - obits;
        }

        if (want < have) {
                /* implicit: (opages != NULL) && (opages != npages) */
                bm_free_pages(opages + want, have - want);
        }

        p_addr = bm_map_paddr(b, words);
        bm = p_addr + MLPP(words);
        *bm = DRBD_MAGIC;
        bm_unmap(p_addr);

        (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\n", bits, words);

 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 ?
 */
static 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;
        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;
                p_addr = bm_map_paddr(b, offset);
                bm = p_addr + MLPP(offset);
                offset += do_now;
                while (do_now--) {
                        bits = hweight_long(*bm);
                        word = *bm | lel_to_cpu(*buffer++);
                        *bm++ = word;
                        b->bm_set += hweight_long(word) - bits;
                }
                bm_unmap(p_addr);
        }
        /* 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_paddr(b, offset);
                        bm = p_addr + MLPP(offset);
                        offset += do_now;
                        while (do_now--)
                                *buffer++ = cpu_to_lel(*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);
}

static void bm_async_io_complete(struct bio *bio, int error)
{
        struct drbd_bitmap *b = bio->bi_private;
        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 (error) {
                /* doh. what now?
                 * for now, set all bits, and flag MD_IO_ERROR */
                __set_bit(BM_MD_IO_ERROR, &b->bm_flags);
        }
        if (atomic_dec_and_test(&b->bm_async_io))
                wake_up(&b->bm_io_wait);

        bio_put(bio);
}

static void bm_page_io_async(struct drbd_conf *mdev, struct drbd_bitmap *b, int page_nr, int rw) __must_hold(local)
{
        /* we are process context. we always get a bio */
        struct bio *bio = bio_alloc(GFP_KERNEL, 1);
        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 */
        len = min_t(unsigned int, PAGE_SIZE,
                (drbd_md_last_sector(mdev->ldev) - on_disk_sector + 1)<<9);

        bio->bi_bdev = mdev->ldev->md_bdev;
        bio->bi_sector = on_disk_sector;
        bio_add_page(bio, b->bm_pages[page_nr], len, 0);
        bio->bi_private = b;
        bio->bi_end_io = bm_async_io_complete;

        if (FAULT_ACTIVE(mdev, (rw & WRITE) ? DRBD_FAULT_MD_WR : DRBD_FAULT_MD_RD)) {
                bio->bi_rw |= rw;
                bio_endio(bio, -EIO);
        } else {
                submit_bio(rw, bio);
        }
}

# if defined(__LITTLE_ENDIAN)
        /* nothing to do, on disk == in memory */
# define bm_cpu_to_lel(x) ((void)0)
# else
void bm_cpu_to_lel(struct drbd_bitmap *b)
{
        /* need to cpu_to_lel all the pages ...
         * this may be optimized by using
         * cpu_to_lel(-1) == -1 and cpu_to_lel(0) == 0;
         * the following is still not optimal, but better than nothing */
        unsigned int i;
        unsigned long *p_addr, *bm;
        if (b->bm_set == 0) {
                /* no page at all; avoid swap if all is 0 */
                i = b->bm_number_of_pages;
        } else if (b->bm_set == b->bm_bits) {
                /* only the last page */
                i = b->bm_number_of_pages - 1;
        } else {
                /* all pages */
                i = 0;
        }
        for (; i < b->bm_number_of_pages; i++) {
                p_addr = kmap_atomic(b->bm_pages[i], KM_USER0);
                for (bm = p_addr; bm < p_addr + PAGE_SIZE/sizeof(long); bm++)
                        *bm = cpu_to_lel(*bm);
                kunmap_atomic(p_addr, KM_USER0);
        }
}
# endif
/* lel_to_cpu == cpu_to_lel */
# define bm_lel_to_cpu(x) bm_cpu_to_lel(x)

/*
 * bm_rw: read/write the whole bitmap from/to its on disk location.
 */
static int bm_rw(struct drbd_conf *mdev, int rw) __must_hold(local)
{
        struct drbd_bitmap *b = mdev->bitmap;
        /* sector_t sector; */
        int bm_words, num_pages, i;
        unsigned long now;
        char ppb[10];
        int err = 0;

        WARN_ON(!bm_is_locked(b));

        /* no spinlock here, the drbd_bm_lock should be enough! */

        bm_words  = drbd_bm_words(mdev);
        num_pages = (bm_words*sizeof(long) + PAGE_SIZE-1) >> PAGE_SHIFT;

        /* on disk bitmap is little endian */
        if (rw == WRITE)
                bm_cpu_to_lel(b);

        now = jiffies;
        atomic_set(&b->bm_async_io, num_pages);
        __clear_bit(BM_MD_IO_ERROR, &b->bm_flags);

        /* let the layers below us try to merge these bios... */
        for (i = 0; i < num_pages; i++)
                bm_page_io_async(mdev, b, i, rw);

        drbd_blk_run_queue(bdev_get_queue(mdev->ldev->md_bdev));
        wait_event(b->bm_io_wait, atomic_read(&b->bm_async_io) == 0);

        if (test_bit(BM_MD_IO_ERROR, &b->bm_flags)) {
                dev_alert(DEV, "we had at least one MD IO ERROR during bitmap IO\n");
                drbd_chk_io_error(mdev, 1, TRUE);
                err = -EIO;
        }

        now = jiffies;
        if (rw == WRITE) {
                /* swap back endianness */
                bm_lel_to_cpu(b);
                /* flush bitmap to stable storage */
                drbd_md_flush(mdev);
        } else /* rw == READ */ {
                /* just read, if necessary adjust endianness */
                b->bm_set = bm_count_bits_swap_endian(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);

        return err;
}

/**
 * drbd_bm_read() - Read the whole bitmap from its on disk location.
 * @mdev:       DRBD device.
 */
int drbd_bm_read(struct drbd_conf *mdev) __must_hold(local)
{
        return bm_rw(mdev, READ);
}

/**
 * drbd_bm_write() - Write the whole bitmap to its on disk location.
 * @mdev:       DRBD device.
 */
int drbd_bm_write(struct drbd_conf *mdev) __must_hold(local)
{
        return bm_rw(mdev, WRITE);
}

/**
 * drbd_bm_write_sect: Writes a 512 (MD_SECTOR_SIZE) byte piece of the bitmap
 * @mdev:       DRBD device.
 * @enr:        Extent number in the resync lru (happens to be sector offset)
 *
 * The BM_EXT_SIZE is on purpose exactly the amount of the bitmap covered
 * by a single sector write. Therefore enr == sector offset from the
 * start of the bitmap.
 */
int drbd_bm_write_sect(struct drbd_conf *mdev, unsigned long enr) __must_hold(local)
{
        sector_t on_disk_sector = enr + mdev->ldev->md.md_offset
                                      + mdev->ldev->md.bm_offset;
        int bm_words, num_words, offset;
        int err = 0;

        mutex_lock(&mdev->md_io_mutex);
        bm_words  = drbd_bm_words(mdev);
        offset    = S2W(enr);   /* word offset into bitmap */
        num_words = min(S2W(1), bm_words - offset);
        if (num_words < S2W(1))
                memset(page_address(mdev->md_io_page), 0, MD_SECTOR_SIZE);
        drbd_bm_get_lel(mdev, offset, num_words,
                        page_address(mdev->md_io_page));
        if (!drbd_md_sync_page_io(mdev, mdev->ldev, on_disk_sector, WRITE)) {
                int i;
                err = -EIO;
                dev_err(DEV, "IO ERROR writing bitmap sector %lu "
                    "(meta-disk sector %llus)\n",
                    enr, (unsigned long long)on_disk_sector);
                drbd_chk_io_error(mdev, 1, TRUE);
                for (i = 0; i < AL_EXT_PER_BM_SECT; i++)
                        drbd_bm_ALe_set_all(mdev, enr*AL_EXT_PER_BM_SECT+i);
        }
        mdev->bm_writ_cnt++;
        mutex_unlock(&mdev->md_io_mutex);
        return err;
}

/* NOTE
 * find_first_bit returns int, we return unsigned long.
 * should not make much difference anyways, but ...
 *
 * this returns a bit number, NOT a sector!
 */
#define BPP_MASK ((1UL << (PAGE_SHIFT+3)) - 1)
static unsigned long __bm_find_next(struct drbd_conf *mdev, unsigned long bm_fo,
        const int find_zero_bit, const enum km_type km)
{
        struct drbd_bitmap *b = mdev->bitmap;
        unsigned long i = -1UL;
        unsigned long *p_addr;
        unsigned long bit_offset; /* bit offset of the mapped page. */

        if (bm_fo > b->bm_bits) {
                dev_err(DEV, "bm_fo=%lu bm_bits=%lu\n", bm_fo, b->bm_bits);
        } else {
                while (bm_fo < b->bm_bits) {
                        unsigned long offset;
                        bit_offset = bm_fo & ~BPP_MASK; /* bit offset of the page */
                        offset = bit_offset >> LN2_BPL;    /* word offset of the page */
                        p_addr = __bm_map_paddr(b, offset, km);

                        if (find_zero_bit)
                                i = find_next_zero_bit(p_addr, PAGE_SIZE*8, bm_fo & BPP_MASK);
                        else
                                i = find_next_bit(p_addr, PAGE_SIZE*8, bm_fo & BPP_MASK);

                        __bm_unmap(p_addr, km);
                        if (i < PAGE_SIZE*8) {
                                i = bit_offset + i;
                                if (i >= b->bm_bits)
                                        break;
                                goto found;
                        }
                        bm_fo = bit_offset + PAGE_SIZE*8;
                }
                i = -1UL;
        }
 found:
        return i;
}

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 = -1UL;

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

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

        i = __bm_find_next(mdev, bm_fo, find_zero_bit, KM_IRQ1);

        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_is_locked(mdev)); */
        return __bm_find_next(mdev, bm_fo, 0, KM_USER1);
}

unsigned long _drbd_bm_find_next_zero(struct drbd_conf *mdev, unsigned long bm_fo)
{
        /* WARN_ON(!bm_is_locked(mdev)); */
        return __bm_find_next(mdev, bm_fo, 1, KM_USER1);
}

/* 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. */
int __bm_change_bits_to(struct drbd_conf *mdev, const unsigned long s,
        unsigned long e, int val, const enum km_type km)
{
        struct drbd_bitmap *b = mdev->bitmap;
        unsigned long *p_addr = NULL;
        unsigned long bitnr;
        unsigned long last_page_nr = -1UL;
        int c = 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 long offset = bitnr>>LN2_BPL;
                unsigned long page_nr = offset >> (PAGE_SHIFT - LN2_BPL + 3);
                if (page_nr != last_page_nr) {
                        if (p_addr)
                                __bm_unmap(p_addr, km);
                        p_addr = __bm_map_paddr(b, offset, km);
                        last_page_nr = page_nr;
                }
                if (val)
                        c += (0 == __test_and_set_bit(bitnr & BPP_MASK, p_addr));
                else
                        c -= (0 != __test_and_clear_bit(bitnr & BPP_MASK, p_addr));
        }
        if (p_addr)
                __bm_unmap(p_addr, km);
        b->bm_set += c;
        return c;
}

/* 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 */
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 (bm_is_locked(b))
                bm_print_lock_info(mdev);

        c = __bm_change_bits_to(mdev, s, e, val, KM_IRQ1);

        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], KM_USER0);
        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, KM_USER0);
}

/* Same thing as drbd_bm_set_bits, but without taking the spin_lock_irqsave.
 * 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.
         */
        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. */
                __bm_change_bits_to(mdev, s, e, 1, KM_USER0);
                return;
        }

        /* difference is large enough that we can trust sl and el */

        /* bits filling the current long */
        if (sl)
                __bm_change_bits_to(mdev, s, sl-1, 1, KM_USER0);

        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);
                cond_resched();
                first_word = 0;
        }

        /* last page (respectively only page, for first page == last page) */
        last_word = MLPP(el >> LN2_BPL);
        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, KM_USER0);
}

/* 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_is_locked(b))
                bm_print_lock_info(mdev);
        if (bitnr < b->bm_bits) {
                unsigned long offset = bitnr>>LN2_BPL;
                p_addr = bm_map_paddr(b, offset);
                i = test_bit(bitnr & BPP_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, page_nr = -1;
        unsigned long bitnr;
        int c = 0;
        size_t w;

        /* 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_is_locked(b))
                bm_print_lock_info(mdev);
        for (bitnr = s; bitnr <= e; bitnr++) {
                w = bitnr >> LN2_BPL;
                if (page_nr != w >> (PAGE_SHIFT - LN2_BPL + 3)) {
                        page_nr = w >> (PAGE_SHIFT - LN2_BPL + 3);
                        if (p_addr)
                                bm_unmap(p_addr);
                        p_addr = bm_map_paddr(b, w);
                }
                ERR_IF (bitnr >= b->bm_bits) {
                        dev_err(DEV, "bitnr=%lu bm_bits=%lu\n", bitnr, b->bm_bits);
                } else {
                        c += (0 != test_bit(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_is_locked(b))
                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_paddr(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 */
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;
        int count, s, e, i, do_now;
        ERR_IF(!b) return 0;
        ERR_IF(!b->bm_pages) return 0;

        spin_lock_irq(&b->bm_lock);
        if (bm_is_locked(b))
                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_paddr(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 (%d) too large in drbd_bm_ALe_set_all\n", s);
        }
        weight = b->bm_set - weight;
        spin_unlock_irq(&b->bm_lock);
        return weight;
}