/*
 *  linux/mm/swapfile.c
 *
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *  Swap reorganised 29.12.95, Stephen Tweedie
 */

#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/kernel_stat.h>
#include <linux/swap.h>
#include <linux/vmalloc.h>
#include <linux/pagemap.h>
#include <linux/namei.h>
#include <linux/shm.h>
#include <linux/blkdev.h>
#include <linux/buffer_head.h>

#include <asm/pgtable.h>
#include <linux/swapops.h>

spinlock_t swaplock = SPIN_LOCK_UNLOCKED;
unsigned int nr_swapfiles;
int total_swap_pages;
static int swap_overflow;

static const char Bad_file[] = "Bad swap file entry ";
static const char Unused_file[] = "Unused swap file entry ";
static const char Bad_offset[] = "Bad swap offset entry ";
static const char Unused_offset[] = "Unused swap offset entry ";

struct swap_list_t swap_list = {-1, -1};

struct swap_info_struct swap_info[MAX_SWAPFILES];

#define SWAPFILE_CLUSTER 256

static inline int scan_swap_map(struct swap_info_struct *si)
{
        unsigned long offset;
        /* 
         * We try to cluster swap pages by allocating them
         * sequentially in swap.  Once we've allocated
         * SWAPFILE_CLUSTER pages this way, however, we resort to
         * first-free allocation, starting a new cluster.  This
         * prevents us from scattering swap pages all over the entire
         * swap partition, so that we reduce overall disk seek times
         * between swap pages.  -- sct */
        if (si->cluster_nr) {
                while (si->cluster_next <= si->highest_bit) {
                        offset = si->cluster_next++;
                        if (si->swap_map[offset])
                                continue;
                        si->cluster_nr--;
                        goto got_page;
                }
        }
        si->cluster_nr = SWAPFILE_CLUSTER;

        /* try to find an empty (even not aligned) cluster. */
        offset = si->lowest_bit;
 check_next_cluster:
        if (offset+SWAPFILE_CLUSTER-1 <= si->highest_bit)
        {
                int nr;
                for (nr = offset; nr < offset+SWAPFILE_CLUSTER; nr++)
                        if (si->swap_map[nr])
                        {
                                offset = nr+1;
                                goto check_next_cluster;
                        }
                /* We found a completly empty cluster, so start
                 * using it.
                 */
                goto got_page;
        }
        /* No luck, so now go finegrined as usual. -Andrea */
        for (offset = si->lowest_bit; offset <= si->highest_bit ; offset++) {
                if (si->swap_map[offset])
                        continue;
                si->lowest_bit = offset+1;
        got_page:
                if (offset == si->lowest_bit)
                        si->lowest_bit++;
                if (offset == si->highest_bit)
                        si->highest_bit--;
                if (si->lowest_bit > si->highest_bit) {
                        si->lowest_bit = si->max;
                        si->highest_bit = 0;
                }
                si->swap_map[offset] = 1;
                nr_swap_pages--;
                si->cluster_next = offset+1;
                return offset;
        }
        si->lowest_bit = si->max;
        si->highest_bit = 0;
        return 0;
}

swp_entry_t get_swap_page(void)
{
        struct swap_info_struct * p;
        unsigned long offset;
        swp_entry_t entry;
        int type, wrapped = 0;

        entry.val = 0;  /* Out of memory */
        swap_list_lock();
        type = swap_list.next;
        if (type < 0)
                goto out;
        if (nr_swap_pages <= 0)
                goto out;

        while (1) {
                p = &swap_info[type];
                if ((p->flags & SWP_ACTIVE) == SWP_ACTIVE) {
                        swap_device_lock(p);
                        offset = scan_swap_map(p);
                        swap_device_unlock(p);
                        if (offset) {
                                entry = swp_entry(type,offset);
                                type = swap_info[type].next;
                                if (type < 0 ||
                                        p->prio != swap_info[type].prio) {
                                                swap_list.next = swap_list.head;
                                } else {
                                        swap_list.next = type;
                                }
                                goto out;
                        }
                }
                type = p->next;
                if (!wrapped) {
                        if (type < 0 || p->prio != swap_info[type].prio) {
                                type = swap_list.head;
                                wrapped = 1;
                        }
                } else
                        if (type < 0)
                                goto out;       /* out of swap space */
        }
out:
        swap_list_unlock();
        return entry;
}

static struct swap_info_struct * swap_info_get(swp_entry_t entry)
{
        struct swap_info_struct * p;
        unsigned long offset, type;

        if (!entry.val)
                goto out;
        type = swp_type(entry);
        if (type >= nr_swapfiles)
                goto bad_nofile;
        p = & swap_info[type];
        if (!(p->flags & SWP_USED))
                goto bad_device;
        offset = swp_offset(entry);
        if (offset >= p->max)
                goto bad_offset;
        if (!p->swap_map[offset])
                goto bad_free;
        swap_list_lock();
        if (p->prio > swap_info[swap_list.next].prio)
                swap_list.next = type;
        swap_device_lock(p);
        return p;

bad_free:
        printk(KERN_ERR "swap_free: %s%08lx\n", Unused_offset, entry.val);
        goto out;
bad_offset:
        printk(KERN_ERR "swap_free: %s%08lx\n", Bad_offset, entry.val);
        goto out;
bad_device:
        printk(KERN_ERR "swap_free: %s%08lx\n", Unused_file, entry.val);
        goto out;
bad_nofile:
        printk(KERN_ERR "swap_free: %s%08lx\n", Bad_file, entry.val);
out:
        return NULL;
}       

static void swap_info_put(struct swap_info_struct * p)
{
        swap_device_unlock(p);
        swap_list_unlock();
}

static int swap_entry_free(struct swap_info_struct *p, unsigned long offset)
{
        int count = p->swap_map[offset];

        if (count < SWAP_MAP_MAX) {
                count--;
                p->swap_map[offset] = count;
                if (!count) {
                        if (offset < p->lowest_bit)
                                p->lowest_bit = offset;
                        if (offset > p->highest_bit)
                                p->highest_bit = offset;
                        nr_swap_pages++;
                }
        }
        return count;
}

/*
 * Caller has made sure that the swapdevice corresponding to entry
 * is still around or has not been recycled.
 */
void swap_free(swp_entry_t entry)
{
        struct swap_info_struct * p;

        p = swap_info_get(entry);
        if (p) {
                swap_entry_free(p, swp_offset(entry));
                swap_info_put(p);
        }
}

/*
 * Check if we're the only user of a swap page,
 * when the page is locked.
 */
static int exclusive_swap_page(struct page *page)
{
        int retval = 0;
        struct swap_info_struct * p;
        swp_entry_t entry;

        entry.val = page->index;
        p = swap_info_get(entry);
        if (p) {
                /* Is the only swap cache user the cache itself? */
                if (p->swap_map[swp_offset(entry)] == 1) {
                        /* Recheck the page count with the pagecache lock held.. */
                        read_lock(&swapper_space.page_lock);
                        if (page_count(page) - !!PagePrivate(page) == 2)
                                retval = 1;
                        read_unlock(&swapper_space.page_lock);
                }
                swap_info_put(p);
        }
        return retval;
}

/*
 * We can use this swap cache entry directly
 * if there are no other references to it.
 *
 * Here "exclusive_swap_page()" does the real
 * work, but we opportunistically check whether
 * we need to get all the locks first..
 */
int can_share_swap_page(struct page *page)
{
        int retval = 0;

        if (!PageLocked(page))
                BUG();
        switch (page_count(page)) {
        case 3:
                if (!PagePrivate(page))
                        break;
                /* Fallthrough */
        case 2:
                if (!PageSwapCache(page))
                        break;
                retval = exclusive_swap_page(page);
                break;
        case 1:
                if (PageReserved(page))
                        break;
                retval = 1;
        }
        return retval;
}

/*
 * Work out if there are any other processes sharing this
 * swap cache page. Free it if you can. Return success.
 */
int remove_exclusive_swap_page(struct page *page)
{
        int retval;
        struct swap_info_struct * p;
        swp_entry_t entry;

        BUG_ON(page_has_buffers(page));
        BUG_ON(!PageLocked(page));

        if (!PageSwapCache(page))
                return 0;
        if (PageWriteback(page))
                return 0;
        if (page_count(page) != 2) /* 2: us + cache */
                return 0;

        entry.val = page->index;
        p = swap_info_get(entry);
        if (!p)
                return 0;

        /* Is the only swap cache user the cache itself? */
        retval = 0;
        if (p->swap_map[swp_offset(entry)] == 1) {
                /* Recheck the page count with the pagecache lock held.. */
                write_lock(&swapper_space.page_lock);
                if ((page_count(page) == 2) && !PageWriteback(page)) {
                        __delete_from_swap_cache(page);
                        SetPageDirty(page);
                        retval = 1;
                }
                write_unlock(&swapper_space.page_lock);
        }
        swap_info_put(p);

        if (retval) {
                swap_free(entry);
                page_cache_release(page);
        }

        return retval;
}

/*
 * Free the swap entry like above, but also try to
 * free the page cache entry if it is the last user.
 */
void free_swap_and_cache(swp_entry_t entry)
{
        struct swap_info_struct * p;
        struct page *page = NULL;

        p = swap_info_get(entry);
        if (p) {
                if (swap_entry_free(p, swp_offset(entry)) == 1)
                        page = find_trylock_page(&swapper_space, entry.val);
                swap_info_put(p);
        }
        if (page) {
                int one_user;

                BUG_ON(page_has_buffers(page));
                page_cache_get(page);
                one_user = (page_count(page) == 2);
                /* Only cache user (+us), or swap space full? Free it! */
                if (!PageWriteback(page) && (one_user || vm_swap_full())) {
                        delete_from_swap_cache(page);
                        SetPageDirty(page);
                }
                unlock_page(page);
                page_cache_release(page);
        }
}

/*
 * The swap entry has been read in advance, and we return 1 to indicate
 * that the page has been used or is no longer needed.
 *
 * Always set the resulting pte to be nowrite (the same as COW pages
 * after one process has exited).  We don't know just how many PTEs will
 * share this swap entry, so be cautious and let do_wp_page work out
 * what to do if a write is requested later.
 */
/* mmlist_lock and vma->vm_mm->page_table_lock are held */
static inline void unuse_pte(struct vm_area_struct * vma, unsigned long address,
        pte_t *dir, swp_entry_t entry, struct page* page)
{
        pte_t pte = *dir;

        if (likely(pte_to_swp_entry(pte).val != entry.val))
                return;
        if (unlikely(pte_none(pte) || pte_present(pte)))
                return;
        get_page(page);
        set_pte(dir, pte_mkold(mk_pte(page, vma->vm_page_prot)));
        page_add_rmap(page, dir);
        swap_free(entry);
        ++vma->vm_mm->rss;
}

/* mmlist_lock and vma->vm_mm->page_table_lock are held */
static inline void unuse_pmd(struct vm_area_struct * vma, pmd_t *dir,
        unsigned long address, unsigned long size, unsigned long offset,
        swp_entry_t entry, struct page* page)
{
        pte_t * pte;
        unsigned long end;

        if (pmd_none(*dir))
                return;
        if (pmd_bad(*dir)) {
                pmd_ERROR(*dir);
                pmd_clear(dir);
                return;
        }
        pte = pte_offset_map(dir, address);
        offset += address & PMD_MASK;
        address &= ~PMD_MASK;
        end = address + size;
        if (end > PMD_SIZE)
                end = PMD_SIZE;
        do {
                unuse_pte(vma, offset+address-vma->vm_start, pte, entry, page);
                address += PAGE_SIZE;
                pte++;
        } while (address && (address < end));
        pte_unmap(pte - 1);
}

/* mmlist_lock and vma->vm_mm->page_table_lock are held */
static inline void unuse_pgd(struct vm_area_struct * vma, pgd_t *dir,
        unsigned long address, unsigned long size,
        swp_entry_t entry, struct page* page)
{
        pmd_t * pmd;
        unsigned long offset, end;

        if (pgd_none(*dir))
                return;
        if (pgd_bad(*dir)) {
                pgd_ERROR(*dir);
                pgd_clear(dir);
                return;
        }
        pmd = pmd_offset(dir, address);
        offset = address & PGDIR_MASK;
        address &= ~PGDIR_MASK;
        end = address + size;
        if (end > PGDIR_SIZE)
                end = PGDIR_SIZE;
        if (address >= end)
                BUG();
        do {
                unuse_pmd(vma, pmd, address, end - address, offset, entry,
                          page);
                address = (address + PMD_SIZE) & PMD_MASK;
                pmd++;
        } while (address && (address < end));
}

/* mmlist_lock and vma->vm_mm->page_table_lock are held */
static void unuse_vma(struct vm_area_struct * vma, pgd_t *pgdir,
                        swp_entry_t entry, struct page* page)
{
        unsigned long start = vma->vm_start, end = vma->vm_end;

        if (start >= end)
                BUG();
        do {
                unuse_pgd(vma, pgdir, start, end - start, entry, page);
                start = (start + PGDIR_SIZE) & PGDIR_MASK;
                pgdir++;
        } while (start && (start < end));
}

static void unuse_process(struct mm_struct * mm,
                        swp_entry_t entry, struct page* page)
{
        struct vm_area_struct* vma;

        /*
         * Go through process' page directory.
         */
        spin_lock(&mm->page_table_lock);
        for (vma = mm->mmap; vma; vma = vma->vm_next) {
                pgd_t * pgd = pgd_offset(mm, vma->vm_start);
                unuse_vma(vma, pgd, entry, page);
        }
        spin_unlock(&mm->page_table_lock);
        return;
}

/*
 * Scan swap_map from current position to next entry still in use.
 * Recycle to start on reaching the end, returning 0 when empty.
 */
static int find_next_to_unuse(struct swap_info_struct *si, int prev)
{
        int max = si->max;
        int i = prev;
        int count;

        /*
         * No need for swap_device_lock(si) here: we're just looking
         * for whether an entry is in use, not modifying it; false
         * hits are okay, and sys_swapoff() has already prevented new
         * allocations from this area (while holding swap_list_lock()).
         */
        for (;;) {
                if (++i >= max) {
                        if (!prev) {
                                i = 0;
                                break;
                        }
                        /*
                         * No entries in use at top of swap_map,
                         * loop back to start and recheck there.
                         */
                        max = prev + 1;
                        prev = 0;
                        i = 1;
                }
                count = si->swap_map[i];
                if (count && count != SWAP_MAP_BAD)
                        break;
        }
        return i;
}

/*
 * We completely avoid races by reading each swap page in advance,
 * and then search for the process using it.  All the necessary
 * page table adjustments can then be made atomically.
 */
static int try_to_unuse(unsigned int type)
{
        struct swap_info_struct * si = &swap_info[type];
        struct mm_struct *start_mm;
        unsigned short *swap_map;
        unsigned short swcount;
        struct page *page;
        swp_entry_t entry;
        int i = 0;
        int retval = 0;
        int reset_overflow = 0;

        /*
         * When searching mms for an entry, a good strategy is to
         * start at the first mm we freed the previous entry from
         * (though actually we don't notice whether we or coincidence
         * freed the entry).  Initialize this start_mm with a hold.
         *
         * A simpler strategy would be to start at the last mm we
         * freed the previous entry from; but that would take less
         * advantage of mmlist ordering (now preserved by swap_out()),
         * which clusters forked address spaces together, most recent
         * child immediately after parent.  If we race with dup_mmap(),
         * we very much want to resolve parent before child, otherwise
         * we may miss some entries: using last mm would invert that.
         */
        start_mm = &init_mm;
        atomic_inc(&init_mm.mm_users);

        /*
         * Keep on scanning until all entries have gone.  Usually,
         * one pass through swap_map is enough, but not necessarily:
         * mmput() removes mm from mmlist before exit_mmap() and its
         * zap_page_range().  That's not too bad, those entries are
         * on their way out, and handled faster there than here.
         * do_munmap() behaves similarly, taking the range out of mm's
         * vma list before zap_page_range().  But unfortunately, when
         * unmapping a part of a vma, it takes the whole out first,
         * then reinserts what's left after (might even reschedule if
         * open() method called) - so swap entries may be invisible
         * to swapoff for a while, then reappear - but that is rare.
         */
        while ((i = find_next_to_unuse(si, i))) {
                /* 
                 * Get a page for the entry, using the existing swap
                 * cache page if there is one.  Otherwise, get a clean
                 * page and read the swap into it. 
                 */
                swap_map = &si->swap_map[i];
                entry = swp_entry(type, i);
                page = read_swap_cache_async(entry);
                if (!page) {
                        /*
                         * Either swap_duplicate() failed because entry
                         * has been freed independently, and will not be
                         * reused since sys_swapoff() already disabled
                         * allocation from here, or alloc_page() failed.
                         */
                        if (!*swap_map)
                                continue;
                        retval = -ENOMEM;
                        break;
                }

                /*
                 * Don't hold on to start_mm if it looks like exiting.
                 */
                if (atomic_read(&start_mm->mm_users) == 1) {
                        mmput(start_mm);
                        start_mm = &init_mm;
                        atomic_inc(&init_mm.mm_users);
                }

                /*
                 * Wait for and lock page.  When do_swap_page races with
                 * try_to_unuse, do_swap_page can handle the fault much
                 * faster than try_to_unuse can locate the entry.  This
                 * apparently redundant "wait_on_page_locked" lets try_to_unuse
                 * defer to do_swap_page in such a case - in some tests,
                 * do_swap_page and try_to_unuse repeatedly compete.
                 */
                wait_on_page_locked(page);
                wait_on_page_writeback(page);
                lock_page(page);
                wait_on_page_writeback(page);

                /*
                 * Remove all references to entry, without blocking.
                 * Whenever we reach init_mm, there's no address space
                 * to search, but use it as a reminder to search shmem.
                 */
                swcount = *swap_map;
                if (swcount > 1) {
                        flush_page_to_ram(page);
                        if (start_mm == &init_mm)
                                shmem_unuse(entry, page);
                        else
                                unuse_process(start_mm, entry, page);
                }
                if (*swap_map > 1) {
                        int set_start_mm = (*swap_map >= swcount);
                        struct list_head *p = &start_mm->mmlist;
                        struct mm_struct *new_start_mm = start_mm;
                        struct mm_struct *mm;

                        spin_lock(&mmlist_lock);
                        while (*swap_map > 1 &&
                                        (p = p->next) != &start_mm->mmlist) {
                                mm = list_entry(p, struct mm_struct, mmlist);
                                swcount = *swap_map;
                                if (mm == &init_mm) {
                                        set_start_mm = 1;
                                        shmem_unuse(entry, page);
                                } else
                                        unuse_process(mm, entry, page);
                                if (set_start_mm && *swap_map < swcount) {
                                        new_start_mm = mm;
                                        set_start_mm = 0;
                                }
                        }
                        atomic_inc(&new_start_mm->mm_users);
                        spin_unlock(&mmlist_lock);
                        mmput(start_mm);
                        start_mm = new_start_mm;
                }

                /*
                 * How could swap count reach 0x7fff when the maximum
                 * pid is 0x7fff, and there's no way to repeat a swap
                 * page within an mm (except in shmem, where it's the
                 * shared object which takes the reference count)?
                 * We believe SWAP_MAP_MAX cannot occur in Linux 2.4.
                 *
                 * If that's wrong, then we should worry more about
                 * exit_mmap() and do_munmap() cases described above:
                 * we might be resetting SWAP_MAP_MAX too early here.
                 * We know "Undead"s can happen, they're okay, so don't
                 * report them; but do report if we reset SWAP_MAP_MAX.
                 */
                if (*swap_map == SWAP_MAP_MAX) {
                        swap_list_lock();
                        swap_device_lock(si);
                        nr_swap_pages++;
                        *swap_map = 1;
                        swap_device_unlock(si);
                        swap_list_unlock();
                        reset_overflow = 1;
                }

                /*
                 * If a reference remains (rare), we would like to leave
                 * the page in the swap cache; but try_to_swap_out could
                 * then re-duplicate the entry once we drop page lock,
                 * so we might loop indefinitely; also, that page could
                 * not be swapped out to other storage meanwhile.  So:
                 * delete from cache even if there's another reference,
                 * after ensuring that the data has been saved to disk -
                 * since if the reference remains (rarer), it will be
                 * read from disk into another page.  Splitting into two
                 * pages would be incorrect if swap supported "shared
                 * private" pages, but they are handled by tmpfs files.
                 * Note shmem_unuse already deleted its from swap cache.
                 */
                if ((*swap_map > 1) && PageDirty(page) && PageSwapCache(page)) {
                        swap_writepage(page);
                        lock_page(page);
                        wait_on_page_writeback(page);
                }
                if (PageSwapCache(page))
                        delete_from_swap_cache(page);

                /*
                 * So we could skip searching mms once swap count went
                 * to 1, we did not mark any present ptes as dirty: must
                 * mark page dirty so try_to_swap_out will preserve it.
                 */
                SetPageDirty(page);
                unlock_page(page);
                page_cache_release(page);

                /*
                 * Make sure that we aren't completely killing
                 * interactive performance.  Interruptible check on
                 * signal_pending() would be nice, but changes the spec?
                 */
                if (need_resched())
                        schedule();
        }

        mmput(start_mm);
        if (reset_overflow) {
                printk(KERN_WARNING "swapoff: cleared swap entry overflow\n");
                swap_overflow = 0;
        }
        return retval;
}

/*
 * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
 * corresponds to page offset `offset'.
 */
sector_t map_swap_page(struct swap_info_struct *sis, pgoff_t offset)
{
        struct swap_extent *se = sis->curr_swap_extent;
        struct swap_extent *start_se = se;

        for ( ; ; ) {
                struct list_head *lh;

                if (se->start_page <= offset &&
                                offset < (se->start_page + se->nr_pages)) {
                        return se->start_block + (offset - se->start_page);
                }
                lh = se->list.prev;
                if (lh == &sis->extent_list)
                        lh = lh->prev;
                se = list_entry(lh, struct swap_extent, list);
                sis->curr_swap_extent = se;
                BUG_ON(se == start_se);         /* It *must* be present */
        }
}

/*
 * Free all of a swapdev's extent information
 */
static void destroy_swap_extents(struct swap_info_struct *sis)
{
        while (!list_empty(&sis->extent_list)) {
                struct swap_extent *se;

                se = list_entry(sis->extent_list.next,
                                struct swap_extent, list);
                list_del(&se->list);
                kfree(se);
        }
        sis->nr_extents = 0;
}

/*
 * Add a block range (and the corresponding page range) into this swapdev's
 * extent list.  The extent list is kept sorted in block order.
 *
 * This function rather assumes that it is called in ascending sector_t order.
 * It doesn't look for extent coalescing opportunities.
 */
static int
add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
                unsigned long nr_pages, sector_t start_block)
{
        struct swap_extent *se;
        struct swap_extent *new_se;
        struct list_head *lh;

        lh = sis->extent_list.next;     /* The highest-addressed block */
        while (lh != &sis->extent_list) {
                se = list_entry(lh, struct swap_extent, list);
                if (se->start_block + se->nr_pages == start_block) {
                        /* Merge it */
                        se->nr_pages += nr_pages;
                        return 0;
                }
                lh = lh->next;
        }

        /*
         * No merge.  Insert a new extent, preserving ordering.
         */
        new_se = kmalloc(sizeof(*se), GFP_KERNEL);
        if (new_se == NULL)
                return -ENOMEM;
        new_se->start_page = start_page;
        new_se->nr_pages = nr_pages;
        new_se->start_block = start_block;

        lh = sis->extent_list.prev;     /* The lowest block */
        while (lh != &sis->extent_list) {
                se = list_entry(lh, struct swap_extent, list);
                if (se->start_block > start_block)
                        break;
                lh = lh->prev;
        }
        list_add_tail(&new_se->list, lh);
        sis->nr_extents++;
        return 0;
}

/*
 * A `swap extent' is a simple thing which maps a contiguous range of pages
 * onto a contiguous range of disk blocks.  An ordered list of swap extents
 * is built at swapon time and is then used at swap_writepage/swap_readpage
 * time for locating where on disk a page belongs.
 *
 * If the swapfile is an S_ISBLK block device, a single extent is installed.
 * This is done so that the main operating code can treat S_ISBLK and S_ISREG
 * swap files identically.
 *
 * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
 * extent list operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
 * swapfiles are handled *identically* after swapon time.
 *
 * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
 * and will parse them into an ordered extent list, in PAGE_SIZE chunks.  If
 * some stray blocks are found which do not fall within the PAGE_SIZE alignment
 * requirements, they are simply tossed out - we will never use those blocks
 * for swapping.
 *
 * The amount of disk space which a single swap extent represents varies.
 * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
 * extents in the list.  To avoid much list walking, we cache the previous
 * search location in `curr_swap_extent', and start new searches from there.
 * This is extremely effective.  The average number of iterations in
 * map_swap_page() has been measured at about 0.3 per page.  - akpm.
 */
static int setup_swap_extents(struct swap_info_struct *sis)
{
        struct inode *inode;
        unsigned blocks_per_page;
        unsigned long page_no;
        unsigned blkbits;
        sector_t probe_block;
        sector_t last_block;
        int ret;

        inode = sis->swap_file->f_dentry->d_inode;
        if (S_ISBLK(inode->i_mode)) {
                ret = add_swap_extent(sis, 0, sis->max, 0);
                goto done;
        }

        blkbits = inode->i_blkbits;
        blocks_per_page = PAGE_SIZE >> blkbits;

        /*
         * Map all the blocks into the extent list.  This code doesn't try
         * to be very smart.
         */
        probe_block = 0;
        page_no = 0;
        last_block = inode->i_size >> blkbits;
        while ((probe_block + blocks_per_page) <= last_block &&
                        page_no < sis->max) {
                unsigned block_in_page;
                sector_t first_block;

                first_block = bmap(inode, probe_block);
                if (first_block == 0)
                        goto bad_bmap;

                /*
                 * It must be PAGE_SIZE aligned on-disk
                 */
                if (first_block & (blocks_per_page - 1)) {
                        probe_block++;
                        goto reprobe;
                }

                for (block_in_page = 1; block_in_page < blocks_per_page;
                                        block_in_page++) {
                        sector_t block;

                        block = bmap(inode, probe_block + block_in_page);
                        if (block == 0)
                                goto bad_bmap;
                        if (block != first_block + block_in_page) {
                                /* Discontiguity */
                                probe_block++;
                                goto reprobe;
                        }
                }

                /*
                 * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
                 */
                ret = add_swap_extent(sis, page_no, 1,
                                first_block >> (PAGE_SHIFT - blkbits));
                if (ret)
                        goto out;
                page_no++;
                probe_block += blocks_per_page;
reprobe:
                continue;
        }
        ret = 0;
        if (page_no == 0)
                ret = -EINVAL;
        sis->max = page_no;
        sis->highest_bit = page_no - 1;
done:
        sis->curr_swap_extent = list_entry(sis->extent_list.prev,
                                        struct swap_extent, list);
        goto out;
bad_bmap:
        printk(KERN_ERR "swapon: swapfile has holes\n");
        ret = -EINVAL;
out:
        return ret;
}

asmlinkage long sys_swapoff(const char * specialfile)
{
        struct swap_info_struct * p = NULL;
        unsigned short *swap_map;
        struct file *swap_file;
        struct nameidata nd;
        int i, type, prev;
        int err;
        
        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;

        err = user_path_walk(specialfile, &nd);
        if (err)
                goto out;

        prev = -1;
        swap_list_lock();
        for (type = swap_list.head; type >= 0; type = swap_info[type].next) {
                p = swap_info + type;
                if ((p->flags & SWP_ACTIVE) == SWP_ACTIVE) {
                        if (p->swap_file->f_dentry == nd.dentry)
                                break;
                }
                prev = type;
        }
        err = -EINVAL;
        if (type < 0) {
                swap_list_unlock();
                goto out_dput;
        }

        if (prev < 0) {
                swap_list.head = p->next;
        } else {
                swap_info[prev].next = p->next;
        }
        if (type == swap_list.next) {
                /* just pick something that's safe... */
                swap_list.next = swap_list.head;
        }
        nr_swap_pages -= p->pages;
        total_swap_pages -= p->pages;
        p->flags &= ~SWP_WRITEOK;
        swap_list_unlock();
        err = try_to_unuse(type);
        if (err) {
                /* re-insert swap space back into swap_list */
                swap_list_lock();
                for (prev = -1, i = swap_list.head; i >= 0; prev = i, i = swap_info[i].next)
                        if (p->prio >= swap_info[i].prio)
                                break;
                p->next = i;
                if (prev < 0)
                        swap_list.head = swap_list.next = p - swap_info;
                else
                        swap_info[prev].next = p - swap_info;
                nr_swap_pages += p->pages;
                total_swap_pages += p->pages;
                p->flags |= SWP_WRITEOK;
                swap_list_unlock();
                goto out_dput;
        }
        swap_list_lock();
        swap_device_lock(p);
        swap_file = p->swap_file;
        p->swap_file = NULL;
        p->max = 0;
        swap_map = p->swap_map;
        p->swap_map = NULL;
        p->flags = 0;
        destroy_swap_extents(p);
        swap_device_unlock(p);
        swap_list_unlock();
        vfree(swap_map);
        if (S_ISBLK(swap_file->f_dentry->d_inode->i_mode)) {
                struct block_device *bdev;
                bdev = swap_file->f_dentry->d_inode->i_bdev;
                set_blocksize(bdev, p->old_block_size);
                bd_release(bdev);

        }
        filp_close(swap_file, NULL);
        err = 0;

out_dput:
        path_release(&nd);
out:
        return err;
}

int get_swaparea_info(char *buf)
{
        char * page = (char *) __get_free_page(GFP_KERNEL);
        struct swap_info_struct *ptr = swap_info;
        int i, len;

        if (!page)
                return -ENOMEM;

        len = sprintf(buf, "Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
        for (i = 0 ; i < nr_swapfiles ; i++, ptr++) {
                int j, usedswap;
                struct file *file;
                char *path;

                if (!(ptr->flags & SWP_USED) || !ptr->swap_map)
                        continue;

                file = ptr->swap_file;
                path = d_path(file->f_dentry, file->f_vfsmnt, page, PAGE_SIZE);
                for (j = 0,usedswap = 0; j < ptr->max; ++j)
                        switch (ptr->swap_map[j]) {
                                case SWAP_MAP_BAD:
                                case 0:
                                        continue;
                                default:
                                        usedswap++;
                        }
                len += sprintf(buf + len, "%-39s %s\t%d\t%d\t%d\n",
                               path,
                               S_ISBLK(file->f_dentry->d_inode->i_mode) ?
                                        "partition" : "file\t",
                               ptr->pages << (PAGE_SHIFT - 10),
                               usedswap << (PAGE_SHIFT - 10),
                               ptr->prio);
        }
        free_page((unsigned long) page);
        return len;
}

/*
 * Written 01/25/92 by Simmule Turner, heavily changed by Linus.
 *
 * The swapon system call
 */
asmlinkage long sys_swapon(const char * specialfile, int swap_flags)
{
        struct swap_info_struct * p;
        char *name = NULL;
        struct block_device *bdev = NULL;
        struct file *swap_file = NULL;
        struct address_space *mapping;
        unsigned int type;
        int i, prev;
        int error;
        static int least_priority = 0;
        union swap_header *swap_header = 0;
        int swap_header_version;
        int nr_good_pages = 0;
        unsigned long maxpages = 1;
        int swapfilesize;
        unsigned short *swap_map;
        struct page *page = NULL;

        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;
        swap_list_lock();
        p = swap_info;
        for (type = 0 ; type < nr_swapfiles ; type++,p++)
                if (!(p->flags & SWP_USED))
                        break;
        error = -EPERM;
        if (type >= MAX_SWAPFILES) {
                swap_list_unlock();
                goto out;
        }
        if (type >= nr_swapfiles)
                nr_swapfiles = type+1;
        INIT_LIST_HEAD(&p->extent_list);
        p->flags = SWP_USED;
        p->nr_extents = 0;
        p->swap_file = NULL;
        p->old_block_size = 0;
        p->swap_map = NULL;
        p->lowest_bit = 0;
        p->highest_bit = 0;
        p->cluster_nr = 0;
        p->sdev_lock = SPIN_LOCK_UNLOCKED;
        p->next = -1;
        if (swap_flags & SWAP_FLAG_PREFER) {
                p->prio =
                  (swap_flags & SWAP_FLAG_PRIO_MASK)>>SWAP_FLAG_PRIO_SHIFT;
        } else {
                p->prio = --least_priority;
        }
        swap_list_unlock();
        name = getname(specialfile);
        error = PTR_ERR(name);
        if (IS_ERR(name))
                goto bad_swap_2;
        swap_file = filp_open(name, O_RDWR, 0);
        error = PTR_ERR(swap_file);
        if (IS_ERR(swap_file)) {
                swap_file = NULL;
                goto bad_swap_2;
        }

        p->swap_file = swap_file;

        error = -EINVAL;
        if (S_ISBLK(swap_file->f_dentry->d_inode->i_mode)) {
                bdev = swap_file->f_dentry->d_inode->i_bdev;
                error = bd_claim(bdev, sys_swapon);
                if (error < 0) {
                        bdev = NULL;
                        goto bad_swap;
                }
                p->old_block_size = block_size(bdev);
                error = set_blocksize(swap_file->f_dentry->d_inode->i_bdev,
                                      PAGE_SIZE);
                if (error < 0)
                        goto bad_swap;
                p->bdev = bdev;
        } else if (S_ISREG(swap_file->f_dentry->d_inode->i_mode)) {
                p->bdev = swap_file->f_dentry->d_inode->i_sb->s_bdev;
        } else {
                goto bad_swap;
        }

        mapping = swap_file->f_dentry->d_inode->i_mapping;
        swapfilesize = mapping->host->i_size >> PAGE_SHIFT;

        error = -EBUSY;
        for (i = 0 ; i < nr_swapfiles ; i++) {
                struct swap_info_struct *q = &swap_info[i];
                if (i == type || !q->swap_file)
                        continue;
                if (mapping == q->swap_file->f_dentry->d_inode->i_mapping)
                        goto bad_swap;
        }

        /*
         * Read the swap header.
         */
        page = read_cache_page(mapping, 0,
                        (filler_t *)mapping->a_ops->readpage, swap_file);
        if (IS_ERR(page)) {
                error = PTR_ERR(page);
                goto bad_swap;
        }
        wait_on_page_locked(page);
        if (!PageUptodate(page))
                goto bad_swap;
        kmap(page);
        swap_header = page_address(page);

        if (!memcmp("SWAP-SPACE",swap_header->magic.magic,10))
                swap_header_version = 1;
        else if (!memcmp("SWAPSPACE2",swap_header->magic.magic,10))
                swap_header_version = 2;
        else {
                printk("Unable to find swap-space signature\n");
                error = -EINVAL;
                goto bad_swap;
        }
        
        switch (swap_header_version) {
        case 1:
                printk(KERN_ERR "version 0 swap is no longer supported. "
                        "Use mkswap -v1 %s\n", name);
                error = -EINVAL;
                goto bad_swap;
        case 2:
                /* Check the swap header's sub-version and the size of
                   the swap file and bad block lists */
                if (swap_header->info.version != 1) {
                        printk(KERN_WARNING
                               "Unable to handle swap header version %d\n",
                               swap_header->info.version);
                        error = -EINVAL;
                        goto bad_swap;
                }

                p->lowest_bit  = 1;
                maxpages = swp_offset(swp_entry(0,~0UL)) - 1;
                if (maxpages > swap_header->info.last_page)
                        maxpages = swap_header->info.last_page;
                p->highest_bit = maxpages - 1;

                error = -EINVAL;
                if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
                        goto bad_swap;
                
                /* OK, set up the swap map and apply the bad block list */
                if (!(p->swap_map = vmalloc(maxpages * sizeof(short)))) {
                        error = -ENOMEM;
                        goto bad_swap;
                }

                error = 0;
                memset(p->swap_map, 0, maxpages * sizeof(short));
                for (i=0; i<swap_header->info.nr_badpages; i++) {
                        int page = swap_header->info.badpages[i];
                        if (page <= 0 || page >= swap_header->info.last_page)
                                error = -EINVAL;
                        else
                                p->swap_map[page] = SWAP_MAP_BAD;
                }
                nr_good_pages = swap_header->info.last_page -
                                swap_header->info.nr_badpages -
                                1 /* header page */;
                if (error) 
                        goto bad_swap;
        }
        
        if (swapfilesize && maxpages > swapfilesize) {
                printk(KERN_WARNING
                       "Swap area shorter than signature indicates\n");
                error = -EINVAL;
                goto bad_swap;
        }
        if (!nr_good_pages) {
                printk(KERN_WARNING "Empty swap-file\n");
                error = -EINVAL;
                goto bad_swap;
        }
        p->swap_map[0] = SWAP_MAP_BAD;
        p->max = maxpages;
        p->pages = nr_good_pages;

        if (setup_swap_extents(p))
                goto bad_swap;

        swap_list_lock();
        swap_device_lock(p);
        p->flags = SWP_ACTIVE;
        nr_swap_pages += nr_good_pages;
        total_swap_pages += nr_good_pages;
        printk(KERN_INFO "Adding %dk swap on %s.  Priority:%d extents:%d\n",
                nr_good_pages<<(PAGE_SHIFT-10), name,
                p->prio, p->nr_extents);

        /* insert swap space into swap_list: */
        prev = -1;
        for (i = swap_list.head; i >= 0; i = swap_info[i].next) {
                if (p->prio >= swap_info[i].prio) {
                        break;
                }
                prev = i;
        }
        p->next = i;
        if (prev < 0) {
                swap_list.head = swap_list.next = p - swap_info;
        } else {
                swap_info[prev].next = p - swap_info;
        }
        swap_device_unlock(p);
        swap_list_unlock();
        error = 0;
        goto out;
bad_swap:
        if (bdev) {
                set_blocksize(bdev, p->old_block_size);
                bd_release(bdev);
        }
bad_swap_2:
        swap_list_lock();
        swap_map = p->swap_map;
        p->swap_file = NULL;
        p->swap_map = NULL;
        p->flags = 0;
        if (!(swap_flags & SWAP_FLAG_PREFER))
                ++least_priority;
        swap_list_unlock();
        destroy_swap_extents(p);
        if (swap_map)
                vfree(swap_map);
        if (swap_file && !IS_ERR(swap_file))
                filp_close(swap_file, NULL);
out:
        if (page && !IS_ERR(page)) {
                kunmap(page);
                page_cache_release(page);
        }
        if (name)
                putname(name);
        return error;
}

void si_swapinfo(struct sysinfo *val)
{
        unsigned int i;
        unsigned long nr_to_be_unused = 0;

        swap_list_lock();
        for (i = 0; i < nr_swapfiles; i++) {
                unsigned int j;
                if (!(swap_info[i].flags & SWP_USED) ||
                     (swap_info[i].flags & SWP_WRITEOK))
                        continue;
                for (j = 0; j < swap_info[i].max; ++j) {
                        switch (swap_info[i].swap_map[j]) {
                                case 0:
                                case SWAP_MAP_BAD:
                                        continue;
                                default:
                                        nr_to_be_unused++;
                        }
                }
        }
        val->freeswap = nr_swap_pages + nr_to_be_unused;
        val->totalswap = total_swap_pages + nr_to_be_unused;
        swap_list_unlock();
}

/*
 * Verify that a swap entry is valid and increment its swap map count.
 *
 * Note: if swap_map[] reaches SWAP_MAP_MAX the entries are treated as
 * "permanent", but will be reclaimed by the next swapoff.
 */
int swap_duplicate(swp_entry_t entry)
{
        struct swap_info_struct * p;
        unsigned long offset, type;
        int result = 0;

        type = swp_type(entry);
        if (type >= nr_swapfiles)
                goto bad_file;
        p = type + swap_info;
        offset = swp_offset(entry);

        swap_device_lock(p);
        if (offset < p->max && p->swap_map[offset]) {
                if (p->swap_map[offset] < SWAP_MAP_MAX - 1) {
                        p->swap_map[offset]++;
                        result = 1;
                } else if (p->swap_map[offset] <= SWAP_MAP_MAX) {
                        if (swap_overflow++ < 5)
                                printk(KERN_WARNING "swap_dup: swap entry overflow\n");
                        p->swap_map[offset] = SWAP_MAP_MAX;
                        result = 1;
                }
        }
        swap_device_unlock(p);
out:
        return result;

bad_file:
        printk(KERN_ERR "swap_dup: %s%08lx\n", Bad_file, entry.val);
        goto out;
}

struct swap_info_struct *
get_swap_info_struct(unsigned type)
{
        return &swap_info[type];
}

/*
 * swap_device_lock prevents swap_map being freed. Don't grab an extra
 * reference on the swaphandle, it doesn't matter if it becomes unused.
 */
int valid_swaphandles(swp_entry_t entry, unsigned long *offset)
{
        int ret = 0, i = 1 << page_cluster;
        unsigned long toff;
        struct swap_info_struct *swapdev = swp_type(entry) + swap_info;

        if (!page_cluster)      /* no readahead */
                return 0;
        toff = (swp_offset(entry) >> page_cluster) << page_cluster;
        if (!toff)              /* first page is swap header */
                toff++, i--;
        *offset = toff;

        swap_device_lock(swapdev);
        do {
                /* Don't read-ahead past the end of the swap area */
                if (toff >= swapdev->max)
                        break;
                /* Don't read in free or bad pages */
                if (!swapdev->swap_map[toff])
                        break;
                if (swapdev->swap_map[toff] == SWAP_MAP_BAD)
                        break;
                toff++;
                ret++;
        } while (--i);
        swap_device_unlock(swapdev);
        return ret;
}