[PATCH] dm: fix mapped device ref counting

[linux-2.6/verdex.git] / kernel / power / snapshot.c

/*
 * linux/kernel/power/snapshot.c
 *
 * This file provide system snapshot/restore functionality.
 *
 * Copyright (C) 1998-2005 Pavel Machek <pavel@suse.cz>
 *
 * This file is released under the GPLv2, and is based on swsusp.c.
 *
 */


#include <linux/version.h>
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/suspend.h>
#include <linux/smp_lock.h>
#include <linux/delay.h>
#include <linux/bitops.h>
#include <linux/spinlock.h>
#include <linux/kernel.h>
#include <linux/pm.h>
#include <linux/device.h>
#include <linux/bootmem.h>
#include <linux/syscalls.h>
#include <linux/console.h>
#include <linux/highmem.h>

#include <asm/uaccess.h>
#include <asm/mmu_context.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>
#include <asm/io.h>

#include "power.h"

struct pbe *pagedir_nosave;
static unsigned int nr_copy_pages;
static unsigned int nr_meta_pages;
static unsigned long *buffer;

#ifdef CONFIG_HIGHMEM
unsigned int count_highmem_pages(void)
{
        struct zone *zone;
        unsigned long zone_pfn;
        unsigned int n = 0;

        for_each_zone (zone)
                if (is_highmem(zone)) {
                        mark_free_pages(zone);
                        for (zone_pfn = 0; zone_pfn < zone->spanned_pages; zone_pfn++) {
                                struct page *page;
                                unsigned long pfn = zone_pfn + zone->zone_start_pfn;
                                if (!pfn_valid(pfn))
                                        continue;
                                page = pfn_to_page(pfn);
                                if (PageReserved(page))
                                        continue;
                                if (PageNosaveFree(page))
                                        continue;
                                n++;
                        }
                }
        return n;
}

struct highmem_page {
        char *data;
        struct page *page;
        struct highmem_page *next;
};

static struct highmem_page *highmem_copy;

static int save_highmem_zone(struct zone *zone)
{
        unsigned long zone_pfn;
        mark_free_pages(zone);
        for (zone_pfn = 0; zone_pfn < zone->spanned_pages; ++zone_pfn) {
                struct page *page;
                struct highmem_page *save;
                void *kaddr;
                unsigned long pfn = zone_pfn + zone->zone_start_pfn;

                if (!(pfn%10000))
                        printk(".");
                if (!pfn_valid(pfn))
                        continue;
                page = pfn_to_page(pfn);
                /*
                 * This condition results from rvmalloc() sans vmalloc_32()
                 * and architectural memory reservations. This should be
                 * corrected eventually when the cases giving rise to this
                 * are better understood.
                 */
                if (PageReserved(page))
                        continue;
                BUG_ON(PageNosave(page));
                if (PageNosaveFree(page))
                        continue;
                save = kmalloc(sizeof(struct highmem_page), GFP_ATOMIC);
                if (!save)
                        return -ENOMEM;
                save->next = highmem_copy;
                save->page = page;
                save->data = (void *) get_zeroed_page(GFP_ATOMIC);
                if (!save->data) {
                        kfree(save);
                        return -ENOMEM;
                }
                kaddr = kmap_atomic(page, KM_USER0);
                memcpy(save->data, kaddr, PAGE_SIZE);
                kunmap_atomic(kaddr, KM_USER0);
                highmem_copy = save;
        }
        return 0;
}

int save_highmem(void)
{
        struct zone *zone;
        int res = 0;

        pr_debug("swsusp: Saving Highmem");
        drain_local_pages();
        for_each_zone (zone) {
                if (is_highmem(zone))
                        res = save_highmem_zone(zone);
                if (res)
                        return res;
        }
        printk("\n");
        return 0;
}

int restore_highmem(void)
{
        printk("swsusp: Restoring Highmem\n");
        while (highmem_copy) {
                struct highmem_page *save = highmem_copy;
                void *kaddr;
                highmem_copy = save->next;

                kaddr = kmap_atomic(save->page, KM_USER0);
                memcpy(kaddr, save->data, PAGE_SIZE);
                kunmap_atomic(kaddr, KM_USER0);
                free_page((long) save->data);
                kfree(save);
        }
        return 0;
}
#else
static inline unsigned int count_highmem_pages(void) {return 0;}
static inline int save_highmem(void) {return 0;}
static inline int restore_highmem(void) {return 0;}
#endif

static int pfn_is_nosave(unsigned long pfn)
{
        unsigned long nosave_begin_pfn = __pa(&__nosave_begin) >> PAGE_SHIFT;
        unsigned long nosave_end_pfn = PAGE_ALIGN(__pa(&__nosave_end)) >> PAGE_SHIFT;
        return (pfn >= nosave_begin_pfn) && (pfn < nosave_end_pfn);
}

/**
 *      saveable - Determine whether a page should be cloned or not.
 *      @pfn:   The page
 *
 *      We save a page if it's Reserved, and not in the range of pages
 *      statically defined as 'unsaveable', or if it isn't reserved, and
 *      isn't part of a free chunk of pages.
 */

static int saveable(struct zone *zone, unsigned long *zone_pfn)
{
        unsigned long pfn = *zone_pfn + zone->zone_start_pfn;
        struct page *page;

        if (!pfn_valid(pfn))
                return 0;

        page = pfn_to_page(pfn);
        BUG_ON(PageReserved(page) && PageNosave(page));
        if (PageNosave(page))
                return 0;
        if (PageReserved(page) && pfn_is_nosave(pfn))
                return 0;
        if (PageNosaveFree(page))
                return 0;

        return 1;
}

unsigned int count_data_pages(void)
{
        struct zone *zone;
        unsigned long zone_pfn;
        unsigned int n = 0;

        for_each_zone (zone) {
                if (is_highmem(zone))
                        continue;
                mark_free_pages(zone);
                for (zone_pfn = 0; zone_pfn < zone->spanned_pages; ++zone_pfn)
                        n += saveable(zone, &zone_pfn);
        }
        return n;
}

static void copy_data_pages(struct pbe *pblist)
{
        struct zone *zone;
        unsigned long zone_pfn;
        struct pbe *pbe, *p;

        pbe = pblist;
        for_each_zone (zone) {
                if (is_highmem(zone))
                        continue;
                mark_free_pages(zone);
                /* This is necessary for swsusp_free() */
                for_each_pb_page (p, pblist)
                        SetPageNosaveFree(virt_to_page(p));
                for_each_pbe (p, pblist)
                        SetPageNosaveFree(virt_to_page(p->address));
                for (zone_pfn = 0; zone_pfn < zone->spanned_pages; ++zone_pfn) {
                        if (saveable(zone, &zone_pfn)) {
                                struct page *page;
                                page = pfn_to_page(zone_pfn + zone->zone_start_pfn);
                                BUG_ON(!pbe);
                                pbe->orig_address = (unsigned long)page_address(page);
                                /* copy_page is not usable for copying task structs. */
                                memcpy((void *)pbe->address, (void *)pbe->orig_address, PAGE_SIZE);
                                pbe = pbe->next;
                        }
                }
        }
        BUG_ON(pbe);
}


/**
 *      free_pagedir - free pages allocated with alloc_pagedir()
 */

static void free_pagedir(struct pbe *pblist, int clear_nosave_free)
{
        struct pbe *pbe;

        while (pblist) {
                pbe = (pblist + PB_PAGE_SKIP)->next;
                ClearPageNosave(virt_to_page(pblist));
                if (clear_nosave_free)
                        ClearPageNosaveFree(virt_to_page(pblist));
                free_page((unsigned long)pblist);
                pblist = pbe;
        }
}

/**
 *      fill_pb_page - Create a list of PBEs on a given memory page
 */

static inline void fill_pb_page(struct pbe *pbpage)
{
        struct pbe *p;

        p = pbpage;
        pbpage += PB_PAGE_SKIP;
        do
                p->next = p + 1;
        while (++p < pbpage);
}

/**
 *      create_pbe_list - Create a list of PBEs on top of a given chain
 *      of memory pages allocated with alloc_pagedir()
 */

static inline void create_pbe_list(struct pbe *pblist, unsigned int nr_pages)
{
        struct pbe *pbpage, *p;
        unsigned int num = PBES_PER_PAGE;

        for_each_pb_page (pbpage, pblist) {
                if (num >= nr_pages)
                        break;

                fill_pb_page(pbpage);
                num += PBES_PER_PAGE;
        }
        if (pbpage) {
                for (num -= PBES_PER_PAGE - 1, p = pbpage; num < nr_pages; p++, num++)
                        p->next = p + 1;
                p->next = NULL;
        }
}

static unsigned int unsafe_pages;

/**
 *      @safe_needed - on resume, for storing the PBE list and the image,
 *      we can only use memory pages that do not conflict with the pages
 *      used before suspend.
 *
 *      The unsafe pages are marked with the PG_nosave_free flag
 *      and we count them using unsafe_pages
 */

static inline void *alloc_image_page(gfp_t gfp_mask, int safe_needed)
{
        void *res;

        res = (void *)get_zeroed_page(gfp_mask);
        if (safe_needed)
                while (res && PageNosaveFree(virt_to_page(res))) {
                        /* The page is unsafe, mark it for swsusp_free() */
                        SetPageNosave(virt_to_page(res));
                        unsafe_pages++;
                        res = (void *)get_zeroed_page(gfp_mask);
                }
        if (res) {
                SetPageNosave(virt_to_page(res));
                SetPageNosaveFree(virt_to_page(res));
        }
        return res;
}

unsigned long get_safe_page(gfp_t gfp_mask)
{
        return (unsigned long)alloc_image_page(gfp_mask, 1);
}

/**
 *      alloc_pagedir - Allocate the page directory.
 *
 *      First, determine exactly how many pages we need and
 *      allocate them.
 *
 *      We arrange the pages in a chain: each page is an array of PBES_PER_PAGE
 *      struct pbe elements (pbes) and the last element in the page points
 *      to the next page.
 *
 *      On each page we set up a list of struct_pbe elements.
 */

static struct pbe *alloc_pagedir(unsigned int nr_pages, gfp_t gfp_mask,
                                 int safe_needed)
{
        unsigned int num;
        struct pbe *pblist, *pbe;

        if (!nr_pages)
                return NULL;

        pblist = alloc_image_page(gfp_mask, safe_needed);
        /* FIXME: rewrite this ugly loop */
        for (pbe = pblist, num = PBES_PER_PAGE; pbe && num < nr_pages;
                        pbe = pbe->next, num += PBES_PER_PAGE) {
                pbe += PB_PAGE_SKIP;
                pbe->next = alloc_image_page(gfp_mask, safe_needed);
        }
        if (!pbe) { /* get_zeroed_page() failed */
                free_pagedir(pblist, 1);
                pblist = NULL;
        } else
                create_pbe_list(pblist, nr_pages);
        return pblist;
}

/**
 * Free pages we allocated for suspend. Suspend pages are alocated
 * before atomic copy, so we need to free them after resume.
 */

void swsusp_free(void)
{
        struct zone *zone;
        unsigned long zone_pfn;

        for_each_zone(zone) {
                for (zone_pfn = 0; zone_pfn < zone->spanned_pages; ++zone_pfn)
                        if (pfn_valid(zone_pfn + zone->zone_start_pfn)) {
                                struct page *page;
                                page = pfn_to_page(zone_pfn + zone->zone_start_pfn);
                                if (PageNosave(page) && PageNosaveFree(page)) {
                                        ClearPageNosave(page);
                                        ClearPageNosaveFree(page);
                                        free_page((long) page_address(page));
                                }
                        }
        }
        nr_copy_pages = 0;
        nr_meta_pages = 0;
        pagedir_nosave = NULL;
        buffer = NULL;
}


/**
 *      enough_free_mem - Make sure we enough free memory to snapshot.
 *
 *      Returns TRUE or FALSE after checking the number of available
 *      free pages.
 */

static int enough_free_mem(unsigned int nr_pages)
{
        struct zone *zone;
        unsigned int n = 0;

        for_each_zone (zone)
                if (!is_highmem(zone))
                        n += zone->free_pages;
        pr_debug("swsusp: available memory: %u pages\n", n);
        return n > (nr_pages + PAGES_FOR_IO +
                (nr_pages + PBES_PER_PAGE - 1) / PBES_PER_PAGE);
}

static int alloc_data_pages(struct pbe *pblist, gfp_t gfp_mask, int safe_needed)
{
        struct pbe *p;

        for_each_pbe (p, pblist) {
                p->address = (unsigned long)alloc_image_page(gfp_mask, safe_needed);
                if (!p->address)
                        return -ENOMEM;
        }
        return 0;
}

static struct pbe *swsusp_alloc(unsigned int nr_pages)
{
        struct pbe *pblist;

        if (!(pblist = alloc_pagedir(nr_pages, GFP_ATOMIC | __GFP_COLD, 0))) {
                printk(KERN_ERR "suspend: Allocating pagedir failed.\n");
                return NULL;
        }

        if (alloc_data_pages(pblist, GFP_ATOMIC | __GFP_COLD, 0)) {
                printk(KERN_ERR "suspend: Allocating image pages failed.\n");
                swsusp_free();
                return NULL;
        }

        return pblist;
}

asmlinkage int swsusp_save(void)
{
        unsigned int nr_pages;

        pr_debug("swsusp: critical section: \n");

        drain_local_pages();
        nr_pages = count_data_pages();
        printk("swsusp: Need to copy %u pages\n", nr_pages);

        pr_debug("swsusp: pages needed: %u + %lu + %u, free: %u\n",
                 nr_pages,
                 (nr_pages + PBES_PER_PAGE - 1) / PBES_PER_PAGE,
                 PAGES_FOR_IO, nr_free_pages());

        if (!enough_free_mem(nr_pages)) {
                printk(KERN_ERR "swsusp: Not enough free memory\n");
                return -ENOMEM;
        }

        pagedir_nosave = swsusp_alloc(nr_pages);
        if (!pagedir_nosave)
                return -ENOMEM;

        /* During allocating of suspend pagedir, new cold pages may appear.
         * Kill them.
         */
        drain_local_pages();
        copy_data_pages(pagedir_nosave);

        /*
         * End of critical section. From now on, we can write to memory,
         * but we should not touch disk. This specially means we must _not_
         * touch swap space! Except we must write out our image of course.
         */

        nr_copy_pages = nr_pages;
        nr_meta_pages = (nr_pages * sizeof(long) + PAGE_SIZE - 1) >> PAGE_SHIFT;

        printk("swsusp: critical section/: done (%d pages copied)\n", nr_pages);
        return 0;
}

static void init_header(struct swsusp_info *info)
{
        memset(info, 0, sizeof(struct swsusp_info));
        info->version_code = LINUX_VERSION_CODE;
        info->num_physpages = num_physpages;
        memcpy(&info->uts, &system_utsname, sizeof(system_utsname));
        info->cpus = num_online_cpus();
        info->image_pages = nr_copy_pages;
        info->pages = nr_copy_pages + nr_meta_pages + 1;
        info->size = info->pages;
        info->size <<= PAGE_SHIFT;
}

/**
 *      pack_orig_addresses - the .orig_address fields of the PBEs from the
 *      list starting at @pbe are stored in the array @buf[] (1 page)
 */

static inline struct pbe *pack_orig_addresses(unsigned long *buf, struct pbe *pbe)
{
        int j;

        for (j = 0; j < PAGE_SIZE / sizeof(long) && pbe; j++) {
                buf[j] = pbe->orig_address;
                pbe = pbe->next;
        }
        if (!pbe)
                for (; j < PAGE_SIZE / sizeof(long); j++)
                        buf[j] = 0;
        return pbe;
}

/**
 *      snapshot_read_next - used for reading the system memory snapshot.
 *
 *      On the first call to it @handle should point to a zeroed
 *      snapshot_handle structure.  The structure gets updated and a pointer
 *      to it should be passed to this function every next time.
 *
 *      The @count parameter should contain the number of bytes the caller
 *      wants to read from the snapshot.  It must not be zero.
 *
 *      On success the function returns a positive number.  Then, the caller
 *      is allowed to read up to the returned number of bytes from the memory
 *      location computed by the data_of() macro.  The number returned
 *      may be smaller than @count, but this only happens if the read would
 *      cross a page boundary otherwise.
 *
 *      The function returns 0 to indicate the end of data stream condition,
 *      and a negative number is returned on error.  In such cases the
 *      structure pointed to by @handle is not updated and should not be used
 *      any more.
 */

int snapshot_read_next(struct snapshot_handle *handle, size_t count)
{
        if (handle->page > nr_meta_pages + nr_copy_pages)
                return 0;
        if (!buffer) {
                /* This makes the buffer be freed by swsusp_free() */
                buffer = alloc_image_page(GFP_ATOMIC, 0);
                if (!buffer)
                        return -ENOMEM;
        }
        if (!handle->offset) {
                init_header((struct swsusp_info *)buffer);
                handle->buffer = buffer;
                handle->pbe = pagedir_nosave;
        }
        if (handle->prev < handle->page) {
                if (handle->page <= nr_meta_pages) {
                        handle->pbe = pack_orig_addresses(buffer, handle->pbe);
                        if (!handle->pbe)
                                handle->pbe = pagedir_nosave;
                } else {
                        handle->buffer = (void *)handle->pbe->address;
                        handle->pbe = handle->pbe->next;
                }
                handle->prev = handle->page;
        }
        handle->buf_offset = handle->page_offset;
        if (handle->page_offset + count >= PAGE_SIZE) {
                count = PAGE_SIZE - handle->page_offset;
                handle->page_offset = 0;
                handle->page++;
        } else {
                handle->page_offset += count;
        }
        handle->offset += count;
        return count;
}

/**
 *      mark_unsafe_pages - mark the pages that cannot be used for storing
 *      the image during resume, because they conflict with the pages that
 *      had been used before suspend
 */

static int mark_unsafe_pages(struct pbe *pblist)
{
        struct zone *zone;
        unsigned long zone_pfn;
        struct pbe *p;

        if (!pblist) /* a sanity check */
                return -EINVAL;

        /* Clear page flags */
        for_each_zone (zone) {
                for (zone_pfn = 0; zone_pfn < zone->spanned_pages; ++zone_pfn)
                        if (pfn_valid(zone_pfn + zone->zone_start_pfn))
                                ClearPageNosaveFree(pfn_to_page(zone_pfn +
                                        zone->zone_start_pfn));
        }

        /* Mark orig addresses */
        for_each_pbe (p, pblist) {
                if (virt_addr_valid(p->orig_address))
                        SetPageNosaveFree(virt_to_page(p->orig_address));
                else
                        return -EFAULT;
        }

        unsafe_pages = 0;

        return 0;
}

static void copy_page_backup_list(struct pbe *dst, struct pbe *src)
{
        /* We assume both lists contain the same number of elements */
        while (src) {
                dst->orig_address = src->orig_address;
                dst = dst->next;
                src = src->next;
        }
}

static int check_header(struct swsusp_info *info)
{
        char *reason = NULL;

        if (info->version_code != LINUX_VERSION_CODE)
                reason = "kernel version";
        if (info->num_physpages != num_physpages)
                reason = "memory size";
        if (strcmp(info->uts.sysname,system_utsname.sysname))
                reason = "system type";
        if (strcmp(info->uts.release,system_utsname.release))
                reason = "kernel release";
        if (strcmp(info->uts.version,system_utsname.version))
                reason = "version";
        if (strcmp(info->uts.machine,system_utsname.machine))
                reason = "machine";
        if (reason) {
                printk(KERN_ERR "swsusp: Resume mismatch: %s\n", reason);
                return -EPERM;
        }
        return 0;
}

/**
 *      load header - check the image header and copy data from it
 */

static int load_header(struct snapshot_handle *handle,
                              struct swsusp_info *info)
{
        int error;
        struct pbe *pblist;

        error = check_header(info);
        if (!error) {
                pblist = alloc_pagedir(info->image_pages, GFP_ATOMIC, 0);
                if (!pblist)
                        return -ENOMEM;
                pagedir_nosave = pblist;
                handle->pbe = pblist;
                nr_copy_pages = info->image_pages;
                nr_meta_pages = info->pages - info->image_pages - 1;
        }
        return error;
}

/**
 *      unpack_orig_addresses - copy the elements of @buf[] (1 page) to
 *      the PBEs in the list starting at @pbe
 */

static inline struct pbe *unpack_orig_addresses(unsigned long *buf,
                                                struct pbe *pbe)
{
        int j;

        for (j = 0; j < PAGE_SIZE / sizeof(long) && pbe; j++) {
                pbe->orig_address = buf[j];
                pbe = pbe->next;
        }
        return pbe;
}

/**
 *      prepare_image - use metadata contained in the PBE list
 *      pointed to by pagedir_nosave to mark the pages that will
 *      be overwritten in the process of restoring the system
 *      memory state from the image ("unsafe" pages) and allocate
 *      memory for the image
 *
 *      The idea is to allocate the PBE list first and then
 *      allocate as many pages as it's needed for the image data,
 *      but not to assign these pages to the PBEs initially.
 *      Instead, we just mark them as allocated and create a list
 *      of "safe" which will be used later
 */

struct safe_page {
        struct safe_page *next;
        char padding[PAGE_SIZE - sizeof(void *)];
};

static struct safe_page *safe_pages;

static int prepare_image(struct snapshot_handle *handle)
{
        int error = 0;
        unsigned int nr_pages = nr_copy_pages;
        struct pbe *p, *pblist = NULL;

        p = pagedir_nosave;
        error = mark_unsafe_pages(p);
        if (!error) {
                pblist = alloc_pagedir(nr_pages, GFP_ATOMIC, 1);
                if (pblist)
                        copy_page_backup_list(pblist, p);
                free_pagedir(p, 0);
                if (!pblist)
                        error = -ENOMEM;
        }
        safe_pages = NULL;
        if (!error && nr_pages > unsafe_pages) {
                nr_pages -= unsafe_pages;
                while (nr_pages--) {
                        struct safe_page *ptr;

                        ptr = (struct safe_page *)get_zeroed_page(GFP_ATOMIC);
                        if (!ptr) {
                                error = -ENOMEM;
                                break;
                        }
                        if (!PageNosaveFree(virt_to_page(ptr))) {
                                /* The page is "safe", add it to the list */
                                ptr->next = safe_pages;
                                safe_pages = ptr;
                        }
                        /* Mark the page as allocated */
                        SetPageNosave(virt_to_page(ptr));
                        SetPageNosaveFree(virt_to_page(ptr));
                }
        }
        if (!error) {
                pagedir_nosave = pblist;
        } else {
                handle->pbe = NULL;
                swsusp_free();
        }
        return error;
}

static void *get_buffer(struct snapshot_handle *handle)
{
        struct pbe *pbe = handle->pbe, *last = handle->last_pbe;
        struct page *page = virt_to_page(pbe->orig_address);

        if (PageNosave(page) && PageNosaveFree(page)) {
                /*
                 * We have allocated the "original" page frame and we can
                 * use it directly to store the read page
                 */
                pbe->address = 0;
                if (last && last->next)
                        last->next = NULL;
                return (void *)pbe->orig_address;
        }
        /*
         * The "original" page frame has not been allocated and we have to
         * use a "safe" page frame to store the read page
         */
        pbe->address = (unsigned long)safe_pages;
        safe_pages = safe_pages->next;
        if (last)
                last->next = pbe;
        handle->last_pbe = pbe;
        return (void *)pbe->address;
}

/**
 *      snapshot_write_next - used for writing the system memory snapshot.
 *
 *      On the first call to it @handle should point to a zeroed
 *      snapshot_handle structure.  The structure gets updated and a pointer
 *      to it should be passed to this function every next time.
 *
 *      The @count parameter should contain the number of bytes the caller
 *      wants to write to the image.  It must not be zero.
 *
 *      On success the function returns a positive number.  Then, the caller
 *      is allowed to write up to the returned number of bytes to the memory
 *      location computed by the data_of() macro.  The number returned
 *      may be smaller than @count, but this only happens if the write would
 *      cross a page boundary otherwise.
 *
 *      The function returns 0 to indicate the "end of file" condition,
 *      and a negative number is returned on error.  In such cases the
 *      structure pointed to by @handle is not updated and should not be used
 *      any more.
 */

int snapshot_write_next(struct snapshot_handle *handle, size_t count)
{
        int error = 0;

        if (handle->prev && handle->page > nr_meta_pages + nr_copy_pages)
                return 0;
        if (!buffer) {
                /* This makes the buffer be freed by swsusp_free() */
                buffer = alloc_image_page(GFP_ATOMIC, 0);
                if (!buffer)
                        return -ENOMEM;
        }
        if (!handle->offset)
                handle->buffer = buffer;
        if (handle->prev < handle->page) {
                if (!handle->prev) {
                        error = load_header(handle, (struct swsusp_info *)buffer);
                        if (error)
                                return error;
                } else if (handle->prev <= nr_meta_pages) {
                        handle->pbe = unpack_orig_addresses(buffer, handle->pbe);
                        if (!handle->pbe) {
                                error = prepare_image(handle);
                                if (error)
                                        return error;
                                handle->pbe = pagedir_nosave;
                                handle->last_pbe = NULL;
                                handle->buffer = get_buffer(handle);
                        }
                } else {
                        handle->pbe = handle->pbe->next;
                        handle->buffer = get_buffer(handle);
                }
                handle->prev = handle->page;
        }
        handle->buf_offset = handle->page_offset;
        if (handle->page_offset + count >= PAGE_SIZE) {
                count = PAGE_SIZE - handle->page_offset;
                handle->page_offset = 0;
                handle->page++;
        } else {
                handle->page_offset += count;
        }
        handle->offset += count;
        return count;
}

int snapshot_image_loaded(struct snapshot_handle *handle)
{
        return !(!handle->pbe || handle->pbe->next || !nr_copy_pages ||
                handle->page <= nr_meta_pages + nr_copy_pages);
}