[PATCH] swsusp: improve handling of swap partitions

[~andy/linux] / kernel / power / swsusp.c

/*
 * linux/kernel/power/swsusp.c
 *
 * This file provides code to write suspend image to swap and read it back.
 *
 * Copyright (C) 1998-2001 Gabor Kuti <seasons@fornax.hu>
 * Copyright (C) 1998,2001-2005 Pavel Machek <pavel@suse.cz>
 *
 * This file is released under the GPLv2.
 *
 * I'd like to thank the following people for their work:
 *
 * Pavel Machek <pavel@ucw.cz>:
 * Modifications, defectiveness pointing, being with me at the very beginning,
 * suspend to swap space, stop all tasks. Port to 2.4.18-ac and 2.5.17.
 *
 * Steve Doddi <dirk@loth.demon.co.uk>:
 * Support the possibility of hardware state restoring.
 *
 * Raph <grey.havens@earthling.net>:
 * Support for preserving states of network devices and virtual console
 * (including X and svgatextmode)
 *
 * Kurt Garloff <garloff@suse.de>:
 * Straightened the critical function in order to prevent compilers from
 * playing tricks with local variables.
 *
 * Andreas Mohr <a.mohr@mailto.de>
 *
 * Alex Badea <vampire@go.ro>:
 * Fixed runaway init
 *
 * Rafael J. Wysocki <rjw@sisk.pl>
 * Added the swap map data structure and reworked the handling of swap
 *
 * More state savers are welcome. Especially for the scsi layer...
 *
 * For TODOs,FIXMEs also look in Documentation/power/swsusp.txt
 */

#include <linux/module.h>
#include <linux/mm.h>
#include <linux/suspend.h>
#include <linux/smp_lock.h>
#include <linux/file.h>
#include <linux/utsname.h>
#include <linux/version.h>
#include <linux/delay.h>
#include <linux/bitops.h>
#include <linux/spinlock.h>
#include <linux/genhd.h>
#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/swap.h>
#include <linux/pm.h>
#include <linux/device.h>
#include <linux/buffer_head.h>
#include <linux/swapops.h>
#include <linux/bootmem.h>
#include <linux/syscalls.h>
#include <linux/highmem.h>
#include <linux/bio.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"

/*
 * Preferred image size in MB (tunable via /sys/power/image_size).
 * When it is set to N, swsusp will do its best to ensure the image
 * size will not exceed N MB, but if that is impossible, it will
 * try to create the smallest image possible.
 */
unsigned int image_size = 500;

#ifdef CONFIG_HIGHMEM
unsigned int count_highmem_pages(void);
int save_highmem(void);
int restore_highmem(void);
#else
static int save_highmem(void) { return 0; }
static int restore_highmem(void) { return 0; }
static unsigned int count_highmem_pages(void) { return 0; }
#endif

extern char resume_file[];

#define SWSUSP_SIG      "S1SUSPEND"

static struct swsusp_header {
        char reserved[PAGE_SIZE - 20 - sizeof(swp_entry_t)];
        swp_entry_t swsusp_info;
        char    orig_sig[10];
        char    sig[10];
} __attribute__((packed, aligned(PAGE_SIZE))) swsusp_header;

static struct swsusp_info swsusp_info;

/*
 * Saving part...
 */

static unsigned short root_swap = 0xffff;

static int mark_swapfiles(swp_entry_t prev)
{
        int error;

        rw_swap_page_sync(READ,
                          swp_entry(root_swap, 0),
                          virt_to_page((unsigned long)&swsusp_header));
        if (!memcmp("SWAP-SPACE",swsusp_header.sig, 10) ||
            !memcmp("SWAPSPACE2",swsusp_header.sig, 10)) {
                memcpy(swsusp_header.orig_sig,swsusp_header.sig, 10);
                memcpy(swsusp_header.sig,SWSUSP_SIG, 10);
                swsusp_header.swsusp_info = prev;
                error = rw_swap_page_sync(WRITE,
                                          swp_entry(root_swap, 0),
                                          virt_to_page((unsigned long)
                                                       &swsusp_header));
        } else {
                pr_debug("swsusp: Partition is not swap space.\n");
                error = -ENODEV;
        }
        return error;
}

/*
 * Check whether the swap device is the specified resume
 * device, irrespective of whether they are specified by
 * identical names.
 *
 * (Thus, device inode aliasing is allowed.  You can say /dev/hda4
 * instead of /dev/ide/host0/bus0/target0/lun0/part4 [if using devfs]
 * and they'll be considered the same device.  This is *necessary* for
 * devfs, since the resume code can only recognize the form /dev/hda4,
 * but the suspend code would see the long name.)
 */
static inline int is_resume_device(const struct swap_info_struct *swap_info)
{
        struct file *file = swap_info->swap_file;
        struct inode *inode = file->f_dentry->d_inode;

        return S_ISBLK(inode->i_mode) &&
                swsusp_resume_device == MKDEV(imajor(inode), iminor(inode));
}

static int swsusp_swap_check(void) /* This is called before saving image */
{
        int i;

        if (!swsusp_resume_device)
                return -ENODEV;
        spin_lock(&swap_lock);
        for (i = 0; i < MAX_SWAPFILES; i++) {
                if (!(swap_info[i].flags & SWP_WRITEOK))
                        continue;
                if (is_resume_device(swap_info + i)) {
                        spin_unlock(&swap_lock);
                        root_swap = i;
                        return 0;
                }
        }
        spin_unlock(&swap_lock);
        return -ENODEV;
}

/**
 *      write_page - Write one page to a fresh swap location.
 *      @addr:  Address we're writing.
 *      @loc:   Place to store the entry we used.
 *
 *      Allocate a new swap entry and 'sync' it. Note we discard -EIO
 *      errors. That is an artifact left over from swsusp. It did not
 *      check the return of rw_swap_page_sync() at all, since most pages
 *      written back to swap would return -EIO.
 *      This is a partial improvement, since we will at least return other
 *      errors, though we need to eventually fix the damn code.
 */
static int write_page(unsigned long addr, swp_entry_t *loc)
{
        swp_entry_t entry;
        int error = -ENOSPC;

        entry = get_swap_page_of_type(root_swap);
        if (swp_offset(entry)) {
                error = rw_swap_page_sync(WRITE, entry, virt_to_page(addr));
                if (!error || error == -EIO)
                        *loc = entry;
        }
        return error;
}

/**
 *      Swap map-handling functions
 *
 *      The swap map is a data structure used for keeping track of each page
 *      written to the swap.  It consists of many swap_map_page structures
 *      that contain each an array of MAP_PAGE_SIZE swap entries.
 *      These structures are linked together with the help of either the
 *      .next (in memory) or the .next_swap (in swap) member.
 *
 *      The swap map is created during suspend.  At that time we need to keep
 *      it in memory, because we have to free all of the allocated swap
 *      entries if an error occurs.  The memory needed is preallocated
 *      so that we know in advance if there's enough of it.
 *
 *      The first swap_map_page structure is filled with the swap entries that
 *      correspond to the first MAP_PAGE_SIZE data pages written to swap and
 *      so on.  After the all of the data pages have been written, the order
 *      of the swap_map_page structures in the map is reversed so that they
 *      can be read from swap in the original order.  This causes the data
 *      pages to be loaded in exactly the same order in which they have been
 *      saved.
 *
 *      During resume we only need to use one swap_map_page structure
 *      at a time, which means that we only need to use two memory pages for
 *      reading the image - one for reading the swap_map_page structures
 *      and the second for reading the data pages from swap.
 */

#define MAP_PAGE_SIZE   ((PAGE_SIZE - sizeof(swp_entry_t) - sizeof(void *)) \
                        / sizeof(swp_entry_t))

struct swap_map_page {
        swp_entry_t             entries[MAP_PAGE_SIZE];
        swp_entry_t             next_swap;
        struct swap_map_page    *next;
};

static inline void free_swap_map(struct swap_map_page *swap_map)
{
        struct swap_map_page *swp;

        while (swap_map) {
                swp = swap_map->next;
                free_page((unsigned long)swap_map);
                swap_map = swp;
        }
}

static struct swap_map_page *alloc_swap_map(unsigned int nr_pages)
{
        struct swap_map_page *swap_map, *swp;
        unsigned n = 0;

        if (!nr_pages)
                return NULL;

        pr_debug("alloc_swap_map(): nr_pages = %d\n", nr_pages);
        swap_map = (struct swap_map_page *)get_zeroed_page(GFP_ATOMIC);
        swp = swap_map;
        for (n = MAP_PAGE_SIZE; n < nr_pages; n += MAP_PAGE_SIZE) {
                swp->next = (struct swap_map_page *)get_zeroed_page(GFP_ATOMIC);
                swp = swp->next;
                if (!swp) {
                        free_swap_map(swap_map);
                        return NULL;
                }
        }
        return swap_map;
}

/**
 *      reverse_swap_map - reverse the order of pages in the swap map
 *      @swap_map
 */

static inline struct swap_map_page *reverse_swap_map(struct swap_map_page *swap_map)
{
        struct swap_map_page *prev, *next;

        prev = NULL;
        while (swap_map) {
                next = swap_map->next;
                swap_map->next = prev;
                prev = swap_map;
                swap_map = next;
        }
        return prev;
}

/**
 *      free_swap_map_entries - free the swap entries allocated to store
 *      the swap map @swap_map (this is only called in case of an error)
 */
static inline void free_swap_map_entries(struct swap_map_page *swap_map)
{
        while (swap_map) {
                if (swap_map->next_swap.val)
                        swap_free(swap_map->next_swap);
                swap_map = swap_map->next;
        }
}

/**
 *      save_swap_map - save the swap map used for tracing the data pages
 *      stored in the swap
 */

static int save_swap_map(struct swap_map_page *swap_map, swp_entry_t *start)
{
        swp_entry_t entry = (swp_entry_t){0};
        int error;

        while (swap_map) {
                swap_map->next_swap = entry;
                if ((error = write_page((unsigned long)swap_map, &entry)))
                        return error;
                swap_map = swap_map->next;
        }
        *start = entry;
        return 0;
}

/**
 *      free_image_entries - free the swap entries allocated to store
 *      the image data pages (this is only called in case of an error)
 */

static inline void free_image_entries(struct swap_map_page *swp)
{
        unsigned k;

        while (swp) {
                for (k = 0; k < MAP_PAGE_SIZE; k++)
                        if (swp->entries[k].val)
                                swap_free(swp->entries[k]);
                swp = swp->next;
        }
}

/**
 *      The swap_map_handle structure is used for handling the swap map in
 *      a file-alike way
 */

struct swap_map_handle {
        struct swap_map_page *cur;
        unsigned int k;
};

static inline void init_swap_map_handle(struct swap_map_handle *handle,
                                        struct swap_map_page *map)
{
        handle->cur = map;
        handle->k = 0;
}

static inline int swap_map_write_page(struct swap_map_handle *handle,
                                      unsigned long addr)
{
        int error;

        error = write_page(addr, handle->cur->entries + handle->k);
        if (error)
                return error;
        if (++handle->k >= MAP_PAGE_SIZE) {
                handle->cur = handle->cur->next;
                handle->k = 0;
        }
        return 0;
}

/**
 *      save_image_data - save the data pages pointed to by the PBEs
 *      from the list @pblist using the swap map handle @handle
 *      (assume there are @nr_pages data pages to save)
 */

static int save_image_data(struct pbe *pblist,
                           struct swap_map_handle *handle,
                           unsigned int nr_pages)
{
        unsigned int m;
        struct pbe *p;
        int error = 0;

        printk("Saving image data pages (%u pages) ...     ", nr_pages);
        m = nr_pages / 100;
        if (!m)
                m = 1;
        nr_pages = 0;
        for_each_pbe (p, pblist) {
                error = swap_map_write_page(handle, p->address);
                if (error)
                        break;
                if (!(nr_pages % m))
                        printk("\b\b\b\b%3d%%", nr_pages / m);
                nr_pages++;
        }
        if (!error)
                printk("\b\b\b\bdone\n");
        return error;
}

static void dump_info(void)
{
        pr_debug(" swsusp: Version: %u\n",swsusp_info.version_code);
        pr_debug(" swsusp: Num Pages: %ld\n",swsusp_info.num_physpages);
        pr_debug(" swsusp: UTS Sys: %s\n",swsusp_info.uts.sysname);
        pr_debug(" swsusp: UTS Node: %s\n",swsusp_info.uts.nodename);
        pr_debug(" swsusp: UTS Release: %s\n",swsusp_info.uts.release);
        pr_debug(" swsusp: UTS Version: %s\n",swsusp_info.uts.version);
        pr_debug(" swsusp: UTS Machine: %s\n",swsusp_info.uts.machine);
        pr_debug(" swsusp: UTS Domain: %s\n",swsusp_info.uts.domainname);
        pr_debug(" swsusp: CPUs: %d\n",swsusp_info.cpus);
        pr_debug(" swsusp: Image: %ld Pages\n",swsusp_info.image_pages);
        pr_debug(" swsusp: Total: %ld Pages\n", swsusp_info.pages);
}

static void init_header(unsigned int nr_pages)
{
        memset(&swsusp_info, 0, sizeof(swsusp_info));
        swsusp_info.version_code = LINUX_VERSION_CODE;
        swsusp_info.num_physpages = num_physpages;
        memcpy(&swsusp_info.uts, &system_utsname, sizeof(system_utsname));

        swsusp_info.cpus = num_online_cpus();
        swsusp_info.image_pages = nr_pages;
        swsusp_info.pages = nr_pages +
                ((nr_pages * sizeof(long) + PAGE_SIZE - 1) >> PAGE_SHIFT);
}

static int close_swap(void)
{
        swp_entry_t entry;
        int error;

        dump_info();
        error = write_page((unsigned long)&swsusp_info, &entry);
        if (!error) {
                printk( "S" );
                error = mark_swapfiles(entry);
                printk( "|\n" );
        }
        return error;
}

/**
 *      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;
}

/**
 *      save_image_metadata - save the .orig_address fields of the PBEs
 *      from the list @pblist using the swap map handle @handle
 */

static int save_image_metadata(struct pbe *pblist,
                               struct swap_map_handle *handle)
{
        unsigned long *buf;
        unsigned int n = 0;
        struct pbe *p;
        int error = 0;

        printk("Saving image metadata ... ");
        buf = (unsigned long *)get_zeroed_page(GFP_ATOMIC);
        if (!buf)
                return -ENOMEM;
        p = pblist;
        while (p) {
                p = pack_orig_addresses(buf, p);
                error = swap_map_write_page(handle, (unsigned long)buf);
                if (error)
                        break;
                n++;
        }
        free_page((unsigned long)buf);
        if (!error)
                printk("done (%u pages saved)\n", n);
        return error;
}

/**
 *      enough_swap - Make sure we have enough swap to save the image.
 *
 *      Returns TRUE or FALSE after checking the total amount of swap
 *      space avaiable from the resume partition.
 */

static int enough_swap(unsigned int nr_pages)
{
        unsigned int free_swap = swap_info[root_swap].pages -
                swap_info[root_swap].inuse_pages;

        pr_debug("swsusp: free swap pages: %u\n", free_swap);
        return free_swap > (nr_pages + PAGES_FOR_IO +
                (nr_pages + PBES_PER_PAGE - 1) / PBES_PER_PAGE);
}

/**
 *      swsusp_write - Write entire image and metadata.
 *
 *      It is important _NOT_ to umount filesystems at this point. We want
 *      them synced (in case something goes wrong) but we DO not want to mark
 *      filesystem clean: it is not. (And it does not matter, if we resume
 *      correctly, we'll mark system clean, anyway.)
 */

int swsusp_write(struct pbe *pblist, unsigned int nr_pages)
{
        struct swap_map_page *swap_map;
        struct swap_map_handle handle;
        int error;

        if ((error = swsusp_swap_check())) {
                printk(KERN_ERR "swsusp: Cannot find swap device, try swapon -a.\n");
                return error;
        }
        if (!enough_swap(nr_pages)) {
                printk(KERN_ERR "swsusp: Not enough free swap\n");
                return -ENOSPC;
        }

        init_header(nr_pages);
        swap_map = alloc_swap_map(swsusp_info.pages);
        if (!swap_map)
                return -ENOMEM;
        init_swap_map_handle(&handle, swap_map);

        error = save_image_metadata(pblist, &handle);
        if (!error)
                error = save_image_data(pblist, &handle, nr_pages);
        if (error)
                goto Free_image_entries;

        swap_map = reverse_swap_map(swap_map);
        error = save_swap_map(swap_map, &swsusp_info.start);
        if (error)
                goto Free_map_entries;

        error = close_swap();
        if (error)
                goto Free_map_entries;

Free_swap_map:
        free_swap_map(swap_map);
        return error;

Free_map_entries:
        free_swap_map_entries(swap_map);
Free_image_entries:
        free_image_entries(swap_map);
        goto Free_swap_map;
}

/**
 *      swsusp_shrink_memory -  Try to free as much memory as needed
 *
 *      ... but do not OOM-kill anyone
 *
 *      Notice: all userland should be stopped before it is called, or
 *      livelock is possible.
 */

#define SHRINK_BITE     10000

int swsusp_shrink_memory(void)
{
        long size, tmp;
        struct zone *zone;
        unsigned long pages = 0;
        unsigned int i = 0;
        char *p = "-\\|/";

        printk("Shrinking memory...  ");
        do {
                size = 2 * count_highmem_pages();
                size += size / 50 + count_data_pages();
                size += (size + PBES_PER_PAGE - 1) / PBES_PER_PAGE +
                        PAGES_FOR_IO;
                tmp = size;
                for_each_zone (zone)
                        if (!is_highmem(zone))
                                tmp -= zone->free_pages;
                if (tmp > 0) {
                        tmp = shrink_all_memory(SHRINK_BITE);
                        if (!tmp)
                                return -ENOMEM;
                        pages += tmp;
                } else if (size > (image_size * 1024 * 1024) / PAGE_SIZE) {
                        tmp = shrink_all_memory(SHRINK_BITE);
                        pages += tmp;
                }
                printk("\b%c", p[i++%4]);
        } while (tmp > 0);
        printk("\bdone (%lu pages freed)\n", pages);

        return 0;
}

int swsusp_suspend(void)
{
        int error;

        if ((error = arch_prepare_suspend()))
                return error;
        local_irq_disable();
        /* At this point, device_suspend() has been called, but *not*
         * device_power_down(). We *must* device_power_down() now.
         * Otherwise, drivers for some devices (e.g. interrupt controllers)
         * become desynchronized with the actual state of the hardware
         * at resume time, and evil weirdness ensues.
         */
        if ((error = device_power_down(PMSG_FREEZE))) {
                printk(KERN_ERR "Some devices failed to power down, aborting suspend\n");
                goto Enable_irqs;
        }

        if ((error = save_highmem())) {
                printk(KERN_ERR "swsusp: Not enough free pages for highmem\n");
                goto Restore_highmem;
        }

        save_processor_state();
        if ((error = swsusp_arch_suspend()))
                printk(KERN_ERR "Error %d suspending\n", error);
        /* Restore control flow magically appears here */
        restore_processor_state();
Restore_highmem:
        restore_highmem();
        device_power_up();
Enable_irqs:
        local_irq_enable();
        return error;
}

int swsusp_resume(void)
{
        int error;
        local_irq_disable();
        if (device_power_down(PMSG_FREEZE))
                printk(KERN_ERR "Some devices failed to power down, very bad\n");
        /* We'll ignore saved state, but this gets preempt count (etc) right */
        save_processor_state();
        error = swsusp_arch_resume();
        /* Code below is only ever reached in case of failure. Otherwise
         * execution continues at place where swsusp_arch_suspend was called
         */
        BUG_ON(!error);
        /* The only reason why swsusp_arch_resume() can fail is memory being
         * very tight, so we have to free it as soon as we can to avoid
         * subsequent failures
         */
        swsusp_free();
        restore_processor_state();
        restore_highmem();
        touch_softlockup_watchdog();
        device_power_up();
        local_irq_enable();
        return error;
}

/**
 *      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 void mark_unsafe_pages(struct pbe *pblist)
{
        struct zone *zone;
        unsigned long zone_pfn;
        struct pbe *p;

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

        /* 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)
                SetPageNosaveFree(virt_to_page(p->orig_address));

}

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;
        }
}

/*
 *      Using bio to read from swap.
 *      This code requires a bit more work than just using buffer heads
 *      but, it is the recommended way for 2.5/2.6.
 *      The following are to signal the beginning and end of I/O. Bios
 *      finish asynchronously, while we want them to happen synchronously.
 *      A simple atomic_t, and a wait loop take care of this problem.
 */

static atomic_t io_done = ATOMIC_INIT(0);

static int end_io(struct bio *bio, unsigned int num, int err)
{
        if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
                panic("I/O error reading memory image");
        atomic_set(&io_done, 0);
        return 0;
}

static struct block_device *resume_bdev;

/**
 *      submit - submit BIO request.
 *      @rw:    READ or WRITE.
 *      @off    physical offset of page.
 *      @page:  page we're reading or writing.
 *
 *      Straight from the textbook - allocate and initialize the bio.
 *      If we're writing, make sure the page is marked as dirty.
 *      Then submit it and wait.
 */

static int submit(int rw, pgoff_t page_off, void *page)
{
        int error = 0;
        struct bio *bio;

        bio = bio_alloc(GFP_ATOMIC, 1);
        if (!bio)
                return -ENOMEM;
        bio->bi_sector = page_off * (PAGE_SIZE >> 9);
        bio_get(bio);
        bio->bi_bdev = resume_bdev;
        bio->bi_end_io = end_io;

        if (bio_add_page(bio, virt_to_page(page), PAGE_SIZE, 0) < PAGE_SIZE) {
                printk("swsusp: ERROR: adding page to bio at %ld\n",page_off);
                error = -EFAULT;
                goto Done;
        }

        if (rw == WRITE)
                bio_set_pages_dirty(bio);

        atomic_set(&io_done, 1);
        submit_bio(rw | (1 << BIO_RW_SYNC), bio);
        while (atomic_read(&io_done))
                yield();

 Done:
        bio_put(bio);
        return error;
}

static int bio_read_page(pgoff_t page_off, void *page)
{
        return submit(READ, page_off, page);
}

static int bio_write_page(pgoff_t page_off, void *page)
{
        return submit(WRITE, page_off, page);
}

/**
 *      The following functions allow us to read data using a swap map
 *      in a file-alike way
 */

static inline void release_swap_map_reader(struct swap_map_handle *handle)
{
        if (handle->cur)
                free_page((unsigned long)handle->cur);
        handle->cur = NULL;
}

static inline int get_swap_map_reader(struct swap_map_handle *handle,
                                      swp_entry_t start)
{
        int error;

        if (!swp_offset(start))
                return -EINVAL;
        handle->cur = (struct swap_map_page *)get_zeroed_page(GFP_ATOMIC);
        if (!handle->cur)
                return -ENOMEM;
        error = bio_read_page(swp_offset(start), handle->cur);
        if (error) {
                release_swap_map_reader(handle);
                return error;
        }
        handle->k = 0;
        return 0;
}

static inline int swap_map_read_page(struct swap_map_handle *handle, void *buf)
{
        unsigned long offset;
        int error;

        if (!handle->cur)
                return -EINVAL;
        offset = swp_offset(handle->cur->entries[handle->k]);
        if (!offset)
                return -EINVAL;
        error = bio_read_page(offset, buf);
        if (error)
                return error;
        if (++handle->k >= MAP_PAGE_SIZE) {
                handle->k = 0;
                offset = swp_offset(handle->cur->next_swap);
                if (!offset)
                        release_swap_map_reader(handle);
                else
                        error = bio_read_page(offset, handle->cur);
        }
        return error;
}

/*
 * Sanity check if this image makes sense with this kernel/swap context
 * I really don't think that it's foolproof but more than nothing..
 */

static const char *sanity_check(void)
{
        dump_info();
        if (swsusp_info.version_code != LINUX_VERSION_CODE)
                return "kernel version";
        if (swsusp_info.num_physpages != num_physpages)
                return "memory size";
        if (strcmp(swsusp_info.uts.sysname,system_utsname.sysname))
                return "system type";
        if (strcmp(swsusp_info.uts.release,system_utsname.release))
                return "kernel release";
        if (strcmp(swsusp_info.uts.version,system_utsname.version))
                return "version";
        if (strcmp(swsusp_info.uts.machine,system_utsname.machine))
                return "machine";
#if 0
        /* We can't use number of online CPUs when we use hotplug to remove them ;-))) */
        if (swsusp_info.cpus != num_possible_cpus())
                return "number of cpus";
#endif
        return NULL;
}

static int check_header(void)
{
        const char *reason = NULL;
        int error;

        if ((error = bio_read_page(swp_offset(swsusp_header.swsusp_info), &swsusp_info)))
                return error;

        /* Is this same machine? */
        if ((reason = sanity_check())) {
                printk(KERN_ERR "swsusp: Resume mismatch: %s\n",reason);
                return -EPERM;
        }
        return error;
}

static int check_sig(void)
{
        int error;

        memset(&swsusp_header, 0, sizeof(swsusp_header));
        if ((error = bio_read_page(0, &swsusp_header)))
                return error;
        if (!memcmp(SWSUSP_SIG, swsusp_header.sig, 10)) {
                memcpy(swsusp_header.sig, swsusp_header.orig_sig, 10);

                /*
                 * Reset swap signature now.
                 */
                error = bio_write_page(0, &swsusp_header);
        } else {
                return -EINVAL;
        }
        if (!error)
                pr_debug("swsusp: Signature found, resuming\n");
        return error;
}

/**
 *      load_image_data - load the image data using the swap map handle
 *      @handle and store them using the page backup list @pblist
 *      (assume there are @nr_pages pages to load)
 */

static int load_image_data(struct pbe *pblist,
                           struct swap_map_handle *handle,
                           unsigned int nr_pages)
{
        int error;
        unsigned int m;
        struct pbe *p;

        if (!pblist)
                return -EINVAL;
        printk("Loading image data pages (%u pages) ...     ", nr_pages);
        m = nr_pages / 100;
        if (!m)
                m = 1;
        nr_pages = 0;
        p = pblist;
        while (p) {
                error = swap_map_read_page(handle, (void *)p->address);
                if (error)
                        break;
                p = p->next;
                if (!(nr_pages % m))
                        printk("\b\b\b\b%3d%%", nr_pages / m);
                nr_pages++;
        }
        if (!error)
                printk("\b\b\b\bdone\n");
        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;
}

/**
 *      load_image_metadata - load the image metadata using the swap map
 *      handle @handle and put them into the PBEs in the list @pblist
 */

static int load_image_metadata(struct pbe *pblist, struct swap_map_handle *handle)
{
        struct pbe *p;
        unsigned long *buf;
        unsigned int n = 0;
        int error = 0;

        printk("Loading image metadata ... ");
        buf = (unsigned long *)get_zeroed_page(GFP_ATOMIC);
        if (!buf)
                return -ENOMEM;
        p = pblist;
        while (p) {
                error = swap_map_read_page(handle, buf);
                if (error)
                        break;
                p = unpack_orig_addresses(buf, p);
                n++;
        }
        free_page((unsigned long)buf);
        if (!error)
                printk("done (%u pages loaded)\n", n);
        return error;
}

static int check_suspend_image(void)
{
        int error = 0;

        if ((error = check_sig()))
                return error;

        if ((error = check_header()))
                return error;

        return 0;
}

static int read_suspend_image(struct pbe **pblist_ptr)
{
        int error = 0;
        struct pbe *p, *pblist;
        struct swap_map_handle handle;
        unsigned int nr_pages = swsusp_info.image_pages;

        p = alloc_pagedir(nr_pages, GFP_ATOMIC, 0);
        if (!p)
                return -ENOMEM;
        error = get_swap_map_reader(&handle, swsusp_info.start);
        if (error)
                /* The PBE list at p will be released by swsusp_free() */
                return error;
        error = load_image_metadata(p, &handle);
        if (!error) {
                mark_unsafe_pages(p);
                pblist = alloc_pagedir(nr_pages, GFP_ATOMIC, 1);
                if (pblist)
                        copy_page_backup_list(pblist, p);
                free_pagedir(p);
                if (!pblist)
                        error = -ENOMEM;

                /* Allocate memory for the image and read the data from swap */
                if (!error)
                        error = alloc_data_pages(pblist, GFP_ATOMIC, 1);
                if (!error) {
                        release_eaten_pages();
                        error = load_image_data(pblist, &handle, nr_pages);
                }
                if (!error)
                        *pblist_ptr = pblist;
        }
        release_swap_map_reader(&handle);
        return error;
}

/**
 *      swsusp_check - Check for saved image in swap
 */

int swsusp_check(void)
{
        int error;

        resume_bdev = open_by_devnum(swsusp_resume_device, FMODE_READ);
        if (!IS_ERR(resume_bdev)) {
                set_blocksize(resume_bdev, PAGE_SIZE);
                error = check_suspend_image();
                if (error)
                    blkdev_put(resume_bdev);
        } else
                error = PTR_ERR(resume_bdev);

        if (!error)
                pr_debug("swsusp: resume file found\n");
        else
                pr_debug("swsusp: Error %d check for resume file\n", error);
        return error;
}

/**
 *      swsusp_read - Read saved image from swap.
 */

int swsusp_read(struct pbe **pblist_ptr)
{
        int error;

        if (IS_ERR(resume_bdev)) {
                pr_debug("swsusp: block device not initialised\n");
                return PTR_ERR(resume_bdev);
        }

        error = read_suspend_image(pblist_ptr);
        blkdev_put(resume_bdev);

        if (!error)
                pr_debug("swsusp: Reading resume file was successful\n");
        else
                pr_debug("swsusp: Error %d resuming\n", error);
        return error;
}

/**
 *      swsusp_close - close swap device.
 */

void swsusp_close(void)
{
        if (IS_ERR(resume_bdev)) {
                pr_debug("swsusp: block device not initialised\n");
                return;
        }

        blkdev_put(resume_bdev);
}