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swapfile.c

/*
 *  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/hugetlb.h>
#include <linux/mman.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/writeback.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/rmap.h>
#include <linux/security.h>
#include <linux/backing-dev.h>
#include <linux/mutex.h>
#include <linux/capability.h>
#include <linux/syscalls.h>

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

DEFINE_SPINLOCK(swap_lock);
unsigned int nr_swapfiles;
long 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};

static struct swap_info_struct swap_info[MAX_SWAPFILES];

static DEFINE_MUTEX(swapon_mutex);

/*
 * We need this because the bdev->unplug_fn can sleep and we cannot
 * hold swap_lock while calling the unplug_fn. And swap_lock
 * cannot be turned into a mutex.
 */
static DECLARE_RWSEM(swap_unplug_sem);

void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page)
{
      swp_entry_t entry;

      down_read(&swap_unplug_sem);
      entry.val = page_private(page);
      if (PageSwapCache(page)) {
            struct block_device *bdev = swap_info[swp_type(entry)].bdev;
            struct backing_dev_info *bdi;

            /*
             * If the page is removed from swapcache from under us (with a
             * racy try_to_unuse/swapoff) we need an additional reference
             * count to avoid reading garbage from page_private(page) above.
             * If the WARN_ON triggers during a swapoff it maybe the race
             * condition and it's harmless. However if it triggers without
             * swapoff it signals a problem.
             */
            WARN_ON(page_count(page) <= 1);

            bdi = bdev->bd_inode->i_mapping->backing_dev_info;
            blk_run_backing_dev(bdi, page);
      }
      up_read(&swap_unplug_sem);
}

#define SWAPFILE_CLUSTER      256
#define LATENCY_LIMIT         256

static inline unsigned long scan_swap_map(struct swap_info_struct *si)
{
      unsigned long offset, last_in_cluster;
      int latency_ration = LATENCY_LIMIT;

      /* 
       * 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
       * But we do now try to find an empty cluster.  -Andrea
       */

      si->flags += SWP_SCANNING;
      if (unlikely(!si->cluster_nr)) {
            si->cluster_nr = SWAPFILE_CLUSTER - 1;
            if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER)
                  goto lowest;
            spin_unlock(&swap_lock);

            offset = si->lowest_bit;
            last_in_cluster = offset + SWAPFILE_CLUSTER - 1;

            /* Locate the first empty (unaligned) cluster */
            for (; last_in_cluster <= si->highest_bit; offset++) {
                  if (si->swap_map[offset])
                        last_in_cluster = offset + SWAPFILE_CLUSTER;
                  else if (offset == last_in_cluster) {
                        spin_lock(&swap_lock);
                        si->cluster_next = offset-SWAPFILE_CLUSTER+1;
                        goto cluster;
                  }
                  if (unlikely(--latency_ration < 0)) {
                        cond_resched();
                        latency_ration = LATENCY_LIMIT;
                  }
            }
            spin_lock(&swap_lock);
            goto lowest;
      }

      si->cluster_nr--;
cluster:
      offset = si->cluster_next;
      if (offset > si->highest_bit)
lowest:           offset = si->lowest_bit;
checks:     if (!(si->flags & SWP_WRITEOK))
            goto no_page;
      if (!si->highest_bit)
            goto no_page;
      if (!si->swap_map[offset]) {
            if (offset == si->lowest_bit)
                  si->lowest_bit++;
            if (offset == si->highest_bit)
                  si->highest_bit--;
            si->inuse_pages++;
            if (si->inuse_pages == si->pages) {
                  si->lowest_bit = si->max;
                  si->highest_bit = 0;
            }
            si->swap_map[offset] = 1;
            si->cluster_next = offset + 1;
            si->flags -= SWP_SCANNING;
            return offset;
      }

      spin_unlock(&swap_lock);
      while (++offset <= si->highest_bit) {
            if (!si->swap_map[offset]) {
                  spin_lock(&swap_lock);
                  goto checks;
            }
            if (unlikely(--latency_ration < 0)) {
                  cond_resched();
                  latency_ration = LATENCY_LIMIT;
            }
      }
      spin_lock(&swap_lock);
      goto lowest;

no_page:
      si->flags -= SWP_SCANNING;
      return 0;
}

swp_entry_t get_swap_page(void)
{
      struct swap_info_struct *si;
      pgoff_t offset;
      int type, next;
      int wrapped = 0;

      spin_lock(&swap_lock);
      if (nr_swap_pages <= 0)
            goto noswap;
      nr_swap_pages--;

      for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) {
            si = swap_info + type;
            next = si->next;
            if (next < 0 ||
                (!wrapped && si->prio != swap_info[next].prio)) {
                  next = swap_list.head;
                  wrapped++;
            }

            if (!si->highest_bit)
                  continue;
            if (!(si->flags & SWP_WRITEOK))
                  continue;

            swap_list.next = next;
            offset = scan_swap_map(si);
            if (offset) {
                  spin_unlock(&swap_lock);
                  return swp_entry(type, offset);
            }
            next = swap_list.next;
      }

      nr_swap_pages++;
noswap:
      spin_unlock(&swap_lock);
      return (swp_entry_t) {0};
}

swp_entry_t get_swap_page_of_type(int type)
{
      struct swap_info_struct *si;
      pgoff_t offset;

      spin_lock(&swap_lock);
      si = swap_info + type;
      if (si->flags & SWP_WRITEOK) {
            nr_swap_pages--;
            offset = scan_swap_map(si);
            if (offset) {
                  spin_unlock(&swap_lock);
                  return swp_entry(type, offset);
            }
            nr_swap_pages++;
      }
      spin_unlock(&swap_lock);
      return (swp_entry_t) {0};
}

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;
      spin_lock(&swap_lock);
      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 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;
                  if (p->prio > swap_info[swap_list.next].prio)
                        swap_list.next = p - swap_info;
                  nr_swap_pages++;
                  p->inuse_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));
            spin_unlock(&swap_lock);
      }
}

/*
 * How many references to page are currently swapped out?
 */
static inline int page_swapcount(struct page *page)
{
      int count = 0;
      struct swap_info_struct *p;
      swp_entry_t entry;

      entry.val = page_private(page);
      p = swap_info_get(entry);
      if (p) {
            /* Subtract the 1 for the swap cache itself */
            count = p->swap_map[swp_offset(entry)] - 1;
            spin_unlock(&swap_lock);
      }
      return count;
}

/*
 * We can use this swap cache entry directly
 * if there are no other references to it.
 */
int can_share_swap_page(struct page *page)
{
      int count;

      BUG_ON(!PageLocked(page));
      count = page_mapcount(page);
      if (count <= 1 && PageSwapCache(page))
            count += page_swapcount(page);
      return count == 1;
}

/*
 * 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(PagePrivate(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_private(page);
      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 swapcache lock held.. */
            write_lock_irq(&swapper_space.tree_lock);
            if ((page_count(page) == 2) && !PageWriteback(page)) {
                  __delete_from_swap_cache(page);
                  SetPageDirty(page);
                  retval = 1;
            }
            write_unlock_irq(&swapper_space.tree_lock);
      }
      spin_unlock(&swap_lock);

      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;

      if (is_migration_entry(entry))
            return;

      p = swap_info_get(entry);
      if (p) {
            if (swap_entry_free(p, swp_offset(entry)) == 1) {
                  page = find_get_page(&swapper_space, entry.val);
                  if (page && unlikely(TestSetPageLocked(page))) {
                        page_cache_release(page);
                        page = NULL;
                  }
            }
            spin_unlock(&swap_lock);
      }
      if (page) {
            int one_user;

            BUG_ON(PagePrivate(page));
            one_user = (page_count(page) == 2);
            /* Only cache user (+us), or swap space full? Free it! */
            /* Also recheck PageSwapCache after page is locked (above) */
            if (PageSwapCache(page) && !PageWriteback(page) &&
                              (one_user || vm_swap_full())) {
                  delete_from_swap_cache(page);
                  SetPageDirty(page);
            }
            unlock_page(page);
            page_cache_release(page);
      }
}

#ifdef CONFIG_HIBERNATION
/*
 * Find the swap type that corresponds to given device (if any).
 *
 * @offset - number of the PAGE_SIZE-sized block of the device, starting
 * from 0, in which the swap header is expected to be located.
 *
 * This is needed for the suspend to disk (aka swsusp).
 */
int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
{
      struct block_device *bdev = NULL;
      int i;

      if (device)
            bdev = bdget(device);

      spin_lock(&swap_lock);
      for (i = 0; i < nr_swapfiles; i++) {
            struct swap_info_struct *sis = swap_info + i;

            if (!(sis->flags & SWP_WRITEOK))
                  continue;

            if (!bdev) {
                  if (bdev_p)
                        *bdev_p = sis->bdev;

                  spin_unlock(&swap_lock);
                  return i;
            }
            if (bdev == sis->bdev) {
                  struct swap_extent *se;

                  se = list_entry(sis->extent_list.next,
                              struct swap_extent, list);
                  if (se->start_block == offset) {
                        if (bdev_p)
                              *bdev_p = sis->bdev;

                        spin_unlock(&swap_lock);
                        bdput(bdev);
                        return i;
                  }
            }
      }
      spin_unlock(&swap_lock);
      if (bdev)
            bdput(bdev);

      return -ENODEV;
}

/*
 * Return either the total number of swap pages of given type, or the number
 * of free pages of that type (depending on @free)
 *
 * This is needed for software suspend
 */
unsigned int count_swap_pages(int type, int free)
{
      unsigned int n = 0;

      if (type < nr_swapfiles) {
            spin_lock(&swap_lock);
            if (swap_info[type].flags & SWP_WRITEOK) {
                  n = swap_info[type].pages;
                  if (free)
                        n -= swap_info[type].inuse_pages;
            }
            spin_unlock(&swap_lock);
      }
      return n;
}
#endif

/*
 * No need to decide whether this PTE shares the swap entry with others,
 * just let do_wp_page work it out if a write is requested later - to
 * force COW, vm_page_prot omits write permission from any private vma.
 */
static void unuse_pte(struct vm_area_struct *vma, pte_t *pte,
            unsigned long addr, swp_entry_t entry, struct page *page)
{
      inc_mm_counter(vma->vm_mm, anon_rss);
      get_page(page);
      set_pte_at(vma->vm_mm, addr, pte,
               pte_mkold(mk_pte(page, vma->vm_page_prot)));
      page_add_anon_rmap(page, vma, addr);
      swap_free(entry);
      /*
       * Move the page to the active list so it is not
       * immediately swapped out again after swapon.
       */
      activate_page(page);
}

static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
                        unsigned long addr, unsigned long end,
                        swp_entry_t entry, struct page *page)
{
      pte_t swp_pte = swp_entry_to_pte(entry);
      pte_t *pte;
      spinlock_t *ptl;
      int found = 0;

      pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
      do {
            /*
             * swapoff spends a _lot_ of time in this loop!
             * Test inline before going to call unuse_pte.
             */
            if (unlikely(pte_same(*pte, swp_pte))) {
                  unuse_pte(vma, pte++, addr, entry, page);
                  found = 1;
                  break;
            }
      } while (pte++, addr += PAGE_SIZE, addr != end);
      pte_unmap_unlock(pte - 1, ptl);
      return found;
}

static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
                        unsigned long addr, unsigned long end,
                        swp_entry_t entry, struct page *page)
{
      pmd_t *pmd;
      unsigned long next;

      pmd = pmd_offset(pud, addr);
      do {
            next = pmd_addr_end(addr, end);
            if (pmd_none_or_clear_bad(pmd))
                  continue;
            if (unuse_pte_range(vma, pmd, addr, next, entry, page))
                  return 1;
      } while (pmd++, addr = next, addr != end);
      return 0;
}

static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
                        unsigned long addr, unsigned long end,
                        swp_entry_t entry, struct page *page)
{
      pud_t *pud;
      unsigned long next;

      pud = pud_offset(pgd, addr);
      do {
            next = pud_addr_end(addr, end);
            if (pud_none_or_clear_bad(pud))
                  continue;
            if (unuse_pmd_range(vma, pud, addr, next, entry, page))
                  return 1;
      } while (pud++, addr = next, addr != end);
      return 0;
}

static int unuse_vma(struct vm_area_struct *vma,
                        swp_entry_t entry, struct page *page)
{
      pgd_t *pgd;
      unsigned long addr, end, next;

      if (page->mapping) {
            addr = page_address_in_vma(page, vma);
            if (addr == -EFAULT)
                  return 0;
            else
                  end = addr + PAGE_SIZE;
      } else {
            addr = vma->vm_start;
            end = vma->vm_end;
      }

      pgd = pgd_offset(vma->vm_mm, addr);
      do {
            next = pgd_addr_end(addr, end);
            if (pgd_none_or_clear_bad(pgd))
                  continue;
            if (unuse_pud_range(vma, pgd, addr, next, entry, page))
                  return 1;
      } while (pgd++, addr = next, addr != end);
      return 0;
}

static int unuse_mm(struct mm_struct *mm,
                        swp_entry_t entry, struct page *page)
{
      struct vm_area_struct *vma;

      if (!down_read_trylock(&mm->mmap_sem)) {
            /*
             * Activate page so shrink_cache is unlikely to unmap its
             * ptes while lock is dropped, so swapoff can make progress.
             */
            activate_page(page);
            unlock_page(page);
            down_read(&mm->mmap_sem);
            lock_page(page);
      }
      for (vma = mm->mmap; vma; vma = vma->vm_next) {
            if (vma->anon_vma && unuse_vma(vma, entry, page))
                  break;
      }
      up_read(&mm->mmap_sem);
      /*
       * Currently unuse_mm cannot fail, but leave error handling
       * at call sites for now, since we change it from time to time.
       */
      return 0;
}

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

      /*
       * No need for swap_lock 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_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;
      unsigned int i = 0;
      int retval = 0;
      int reset_overflow = 0;
      int shmem;

      /*
       * 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, which clusters forked mms
       * together, child after parent.  If we race with dup_mmap(), we
       * prefer to resolve parent before child, lest we miss entries
       * duplicated after we scanned child: using last mm would invert
       * that.  Though it's only a serious concern when an overflowed
       * swap count is reset from SWAP_MAP_MAX, preventing a rescan.
       */
      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:
       * there are races when an instance of an entry might be missed.
       */
      while ((i = find_next_to_unuse(si, i)) != 0) {
            if (signal_pending(current)) {
                  retval = -EINTR;
                  break;
            }

            /* 
             * 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, NULL, 0);
            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.
             * Whenever we reach init_mm, there's no address space
             * to search, but use it as a reminder to search shmem.
             */
            shmem = 0;
            swcount = *swap_map;
            if (swcount > 1) {
                  if (start_mm == &init_mm)
                        shmem = shmem_unuse(entry, page);
                  else
                        retval = unuse_mm(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 *prev_mm = start_mm;
                  struct mm_struct *mm;

                  atomic_inc(&new_start_mm->mm_users);
                  atomic_inc(&prev_mm->mm_users);
                  spin_lock(&mmlist_lock);
                  while (*swap_map > 1 && !retval &&
                              (p = p->next) != &start_mm->mmlist) {
                        mm = list_entry(p, struct mm_struct, mmlist);
                        if (!atomic_inc_not_zero(&mm->mm_users))
                              continue;
                        spin_unlock(&mmlist_lock);
                        mmput(prev_mm);
                        prev_mm = mm;

                        cond_resched();

                        swcount = *swap_map;
                        if (swcount <= 1)
                              ;
                        else if (mm == &init_mm) {
                              set_start_mm = 1;
                              shmem = shmem_unuse(entry, page);
                        } else
                              retval = unuse_mm(mm, entry, page);
                        if (set_start_mm && *swap_map < swcount) {
                              mmput(new_start_mm);
                              atomic_inc(&mm->mm_users);
                              new_start_mm = mm;
                              set_start_mm = 0;
                        }
                        spin_lock(&mmlist_lock);
                  }
                  spin_unlock(&mmlist_lock);
                  mmput(prev_mm);
                  mmput(start_mm);
                  start_mm = new_start_mm;
            }
            if (retval) {
                  unlock_page(page);
                  page_cache_release(page);
                  break;
            }

            /*
             * 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) {
                  spin_lock(&swap_lock);
                  *swap_map = 1;
                  spin_unlock(&swap_lock);
                  reset_overflow = 1;
            }

            /*
             * If a reference remains (rare), we would like to leave
             * the page in the swap cache; but try_to_unmap 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 a swappage from
             * the swap cache, unless the move to filepage failed:
             * in which case it left swappage in cache, lowered its
             * swap count to pass quickly through the loops above,
             * and now we must reincrement count to try again later.
             */
            if ((*swap_map > 1) && PageDirty(page) && PageSwapCache(page)) {
                  struct writeback_control wbc = {
                        .sync_mode = WB_SYNC_NONE,
                  };

                  swap_writepage(page, &wbc);
                  lock_page(page);
                  wait_on_page_writeback(page);
            }
            if (PageSwapCache(page)) {
                  if (shmem)
                        swap_duplicate(entry);
                  else
                        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 shrink_page_list will preserve it.
             */
            SetPageDirty(page);
            unlock_page(page);
            page_cache_release(page);

            /*
             * Make sure that we aren't completely killing
             * interactive performance.
             */
            cond_resched();
      }

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

/*
 * After a successful try_to_unuse, if no swap is now in use, we know
 * we can empty the mmlist.  swap_lock must be held on entry and exit.
 * Note that mmlist_lock nests inside swap_lock, and an mm must be
 * added to the mmlist just after page_duplicate - before would be racy.
 */
static void drain_mmlist(void)
{
      struct list_head *p, *next;
      unsigned int i;

      for (i = 0; i < nr_swapfiles; i++)
            if (swap_info[i].inuse_pages)
                  return;
      spin_lock(&mmlist_lock);
      list_for_each_safe(p, next, &init_mm.mmlist)
            list_del_init(p);
      spin_unlock(&mmlist_lock);
}

/*
 * 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.next;
            if (lh == &sis->extent_list)
                  lh = lh->next;
            se = list_entry(lh, struct swap_extent, list);
            sis->curr_swap_extent = se;
            BUG_ON(se == start_se);       /* It *must* be present */
      }
}

#ifdef CONFIG_HIBERNATION
/*
 * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
 * corresponding to given index in swap_info (swap type).
 */
sector_t swapdev_block(int swap_type, pgoff_t offset)
{
      struct swap_info_struct *sis;

      if (swap_type >= nr_swapfiles)
            return 0;

      sis = swap_info + swap_type;
      return (sis->flags & SWP_WRITEOK) ? map_swap_page(sis, offset) : 0;
}
#endif /* CONFIG_HIBERNATION */

/*
 * 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);
      }
}

/*
 * Add a block range (and the corresponding page range) into this swapdev's
 * extent list.  The extent list is kept sorted in page order.
 *
 * This function rather assumes that it is called in ascending page order.
 */
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.prev;   /* The highest page extent */
      if (lh != &sis->extent_list) {
            se = list_entry(lh, struct swap_extent, list);
            BUG_ON(se->start_page + se->nr_pages != start_page);
            if (se->start_block + se->nr_pages == start_block) {
                  /* Merge it */
                  se->nr_pages += nr_pages;
                  return 0;
            }
      }

      /*
       * 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;

      list_add_tail(&new_se->list, &sis->extent_list);
      return 1;
}

/*
 * 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.
 *
 * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon.  This
 * prevents root from shooting her foot off by ftruncating an in-use swapfile,
 * which will scribble on the fs.
 *
 * 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, sector_t *span)
{
      struct inode *inode;
      unsigned blocks_per_page;
      unsigned long page_no;
      unsigned blkbits;
      sector_t probe_block;
      sector_t last_block;
      sector_t lowest_block = -1;
      sector_t highest_block = 0;
      int nr_extents = 0;
      int ret;

      inode = sis->swap_file->f_mapping->host;
      if (S_ISBLK(inode->i_mode)) {
            ret = add_swap_extent(sis, 0, sis->max, 0);
            *span = sis->pages;
            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 = i_size_read(inode) >> 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;
                  }
            }

            first_block >>= (PAGE_SHIFT - blkbits);
            if (page_no) {    /* exclude the header page */
                  if (first_block < lowest_block)
                        lowest_block = first_block;
                  if (first_block > highest_block)
                        highest_block = first_block;
            }

            /*
             * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
             */
            ret = add_swap_extent(sis, page_no, 1, first_block);
            if (ret < 0)
                  goto out;
            nr_extents += ret;
            page_no++;
            probe_block += blocks_per_page;
reprobe:
            continue;
      }
      ret = nr_extents;
      *span = 1 + highest_block - lowest_block;
      if (page_no == 0)
            page_no = 1;      /* force Empty message */
      sis->max = page_no;
      sis->pages = page_no - 1;
      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;
}

#if 0 /* We don't need this yet */
#include <linux/backing-dev.h>
int page_queue_congested(struct page *page)
{
      struct backing_dev_info *bdi;

      BUG_ON(!PageLocked(page));    /* It pins the swap_info_struct */

      if (PageSwapCache(page)) {
            swp_entry_t entry = { .val = page_private(page) };
            struct swap_info_struct *sis;

            sis = get_swap_info_struct(swp_type(entry));
            bdi = sis->bdev->bd_inode->i_mapping->backing_dev_info;
      } else
            bdi = page->mapping->backing_dev_info;
      return bdi_write_congested(bdi);
}
#endif

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

      pathname = getname(specialfile);
      err = PTR_ERR(pathname);
      if (IS_ERR(pathname))
            goto out;

      victim = filp_open(pathname, O_RDWR|O_LARGEFILE, 0);
      putname(pathname);
      err = PTR_ERR(victim);
      if (IS_ERR(victim))
            goto out;

      mapping = victim->f_mapping;
      prev = -1;
      spin_lock(&swap_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_mapping == mapping)
                        break;
            }
            prev = type;
      }
      if (type < 0) {
            err = -EINVAL;
            spin_unlock(&swap_lock);
            goto out_dput;
      }
      if (!security_vm_enough_memory(p->pages))
            vm_unacct_memory(p->pages);
      else {
            err = -ENOMEM;
            spin_unlock(&swap_lock);
            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;
      spin_unlock(&swap_lock);

      current->flags |= PF_SWAPOFF;
      err = try_to_unuse(type);
      current->flags &= ~PF_SWAPOFF;

      if (err) {
            /* re-insert swap space back into swap_list */
            spin_lock(&swap_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;
            spin_unlock(&swap_lock);
            goto out_dput;
      }

      /* wait for any unplug function to finish */
      down_write(&swap_unplug_sem);
      up_write(&swap_unplug_sem);

      destroy_swap_extents(p);
      mutex_lock(&swapon_mutex);
      spin_lock(&swap_lock);
      drain_mmlist();

      /* wait for anyone still in scan_swap_map */
      p->highest_bit = 0;           /* cuts scans short */
      while (p->flags >= SWP_SCANNING) {
            spin_unlock(&swap_lock);
            schedule_timeout_uninterruptible(1);
            spin_lock(&swap_lock);
      }

      swap_file = p->swap_file;
      p->swap_file = NULL;
      p->max = 0;
      swap_map = p->swap_map;
      p->swap_map = NULL;
      p->flags = 0;
      spin_unlock(&swap_lock);
      mutex_unlock(&swapon_mutex);
      vfree(swap_map);
      inode = mapping->host;
      if (S_ISBLK(inode->i_mode)) {
            struct block_device *bdev = I_BDEV(inode);
            set_blocksize(bdev, p->old_block_size);
            bd_release(bdev);
      } else {
            mutex_lock(&inode->i_mutex);
            inode->i_flags &= ~S_SWAPFILE;
            mutex_unlock(&inode->i_mutex);
      }
      filp_close(swap_file, NULL);
      err = 0;

out_dput:
      filp_close(victim, NULL);
out:
      return err;
}

#ifdef CONFIG_PROC_FS
/* iterator */
static void *swap_start(struct seq_file *swap, loff_t *pos)
{
      struct swap_info_struct *ptr = swap_info;
      int i;
      loff_t l = *pos;

      mutex_lock(&swapon_mutex);

      if (!l)
            return SEQ_START_TOKEN;

      for (i = 0; i < nr_swapfiles; i++, ptr++) {
            if (!(ptr->flags & SWP_USED) || !ptr->swap_map)
                  continue;
            if (!--l)
                  return ptr;
      }

      return NULL;
}

static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
{
      struct swap_info_struct *ptr;
      struct swap_info_struct *endptr = swap_info + nr_swapfiles;

      if (v == SEQ_START_TOKEN)
            ptr = swap_info;
      else {
            ptr = v;
            ptr++;
      }

      for (; ptr < endptr; ptr++) {
            if (!(ptr->flags & SWP_USED) || !ptr->swap_map)
                  continue;
            ++*pos;
            return ptr;
      }

      return NULL;
}

static void swap_stop(struct seq_file *swap, void *v)
{
      mutex_unlock(&swapon_mutex);
}

static int swap_show(struct seq_file *swap, void *v)
{
      struct swap_info_struct *ptr = v;
      struct file *file;
      int len;

      if (ptr == SEQ_START_TOKEN) {
            seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
            return 0;
      }

      file = ptr->swap_file;
      len = seq_path(swap, file->f_path.mnt, file->f_path.dentry, " \t\n\\");
      seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
                   len < 40 ? 40 - len : 1, " ",
                   S_ISBLK(file->f_path.dentry->d_inode->i_mode) ?
                        "partition" : "file\t",
                   ptr->pages << (PAGE_SHIFT - 10),
                   ptr->inuse_pages << (PAGE_SHIFT - 10),
                   ptr->prio);
      return 0;
}

static const struct seq_operations swaps_op = {
      .start =    swap_start,
      .next =           swap_next,
      .stop =           swap_stop,
      .show =           swap_show
};

static int swaps_open(struct inode *inode, struct file *file)
{
      return seq_open(file, &swaps_op);
}

static const struct file_operations proc_swaps_operations = {
      .open       = swaps_open,
      .read       = seq_read,
      .llseek           = seq_lseek,
      .release    = seq_release,
};

static int __init procswaps_init(void)
{
      struct proc_dir_entry *entry;

      entry = create_proc_entry("swaps", 0, NULL);
      if (entry)
            entry->proc_fops = &proc_swaps_operations;
      return 0;
}
__initcall(procswaps_init);
#endif /* CONFIG_PROC_FS */

/*
 * Written 01/25/92 by Simmule Turner, heavily changed by Linus.
 *
 * The swapon system call
 */
asmlinkage long sys_swapon(const char __user * 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;
      union swap_header *swap_header = NULL;
      int swap_header_version;
      unsigned int nr_good_pages = 0;
      int nr_extents = 0;
      sector_t span;
      unsigned long maxpages = 1;
      int swapfilesize;
      unsigned short *swap_map;
      struct page *page = NULL;
      struct inode *inode = NULL;
      int did_down = 0;

      if (!capable(CAP_SYS_ADMIN))
            return -EPERM;
      spin_lock(&swap_lock);
      p = swap_info;
      for (type = 0 ; type < nr_swapfiles ; type++,p++)
            if (!(p->flags & SWP_USED))
                  break;
      error = -EPERM;
      if (type >= MAX_SWAPFILES) {
            spin_unlock(&swap_lock);
            goto out;
      }
      if (type >= nr_swapfiles)
            nr_swapfiles = type+1;
      INIT_LIST_HEAD(&p->extent_list);
      p->flags = SWP_USED;
      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->inuse_pages = 0;
      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;
      }
      spin_unlock(&swap_lock);
      name = getname(specialfile);
      error = PTR_ERR(name);
      if (IS_ERR(name)) {
            name = NULL;
            goto bad_swap_2;
      }
      swap_file = filp_open(name, O_RDWR|O_LARGEFILE, 0);
      error = PTR_ERR(swap_file);
      if (IS_ERR(swap_file)) {
            swap_file = NULL;
            goto bad_swap_2;
      }

      p->swap_file = swap_file;
      mapping = swap_file->f_mapping;
      inode = mapping->host;

      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_mapping)
                  goto bad_swap;
      }

      error = -EINVAL;
      if (S_ISBLK(inode->i_mode)) {
            bdev = I_BDEV(inode);
            error = bd_claim(bdev, sys_swapon);
            if (error < 0) {
                  bdev = NULL;
                  error = -EINVAL;
                  goto bad_swap;
            }
            p->old_block_size = block_size(bdev);
            error = set_blocksize(bdev, PAGE_SIZE);
            if (error < 0)
                  goto bad_swap;
            p->bdev = bdev;
      } else if (S_ISREG(inode->i_mode)) {
            p->bdev = inode->i_sb->s_bdev;
            mutex_lock(&inode->i_mutex);
            did_down = 1;
            if (IS_SWAPFILE(inode)) {
                  error = -EBUSY;
                  goto bad_swap;
            }
      } else {
            goto bad_swap;
      }

      swapfilesize = i_size_read(inode) >> PAGE_SHIFT;

      /*
       * Read the swap header.
       */
      if (!mapping->a_ops->readpage) {
            error = -EINVAL;
            goto bad_swap;
      }
      page = read_mapping_page(mapping, 0, swap_file);
      if (IS_ERR(page)) {
            error = PTR_ERR(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(KERN_ERR "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;
            p->cluster_next = 1;

            /*
             * Find out how many pages are allowed for a single swap
             * device. There are two limiting factors: 1) the number of
             * bits for the swap offset in the swp_entry_t type and
             * 2) the number of bits in the a swap pte as defined by
             * the different architectures. In order to find the
             * largest possible bit mask a swap entry with swap type 0
             * and swap offset ~0UL is created, encoded to a swap pte,
             * decoded to a swp_entry_t again and finally the swap
             * offset is extracted. This will mask all the bits from
             * the initial ~0UL mask that can't be encoded in either
             * the swp_entry_t or the architecture definition of a
             * swap pte.
             */
            maxpages = swp_offset(pte_to_swp_entry(swp_entry_to_pte(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 (!maxpages)
                  goto bad_swap;
            if (swapfilesize && maxpages > swapfilesize) {
                  printk(KERN_WARNING
                         "Swap area shorter than signature indicates\n");
                  goto bad_swap;
            }
            if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
                  goto bad_swap;
            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_nr = swap_header->info.badpages[i];
                  if (page_nr <= 0 || page_nr >= swap_header->info.last_page)
                        error = -EINVAL;
                  else
                        p->swap_map[page_nr] = 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 (nr_good_pages) {
            p->swap_map[0] = SWAP_MAP_BAD;
            p->max = maxpages;
            p->pages = nr_good_pages;
            nr_extents = setup_swap_extents(p, &span);
            if (nr_extents < 0) {
                  error = nr_extents;
                  goto bad_swap;
            }
            nr_good_pages = p->pages;
      }
      if (!nr_good_pages) {
            printk(KERN_WARNING "Empty swap-file\n");
            error = -EINVAL;
            goto bad_swap;
      }

      mutex_lock(&swapon_mutex);
      spin_lock(&swap_lock);
      p->flags = SWP_ACTIVE;
      nr_swap_pages += nr_good_pages;
      total_swap_pages += nr_good_pages;

      printk(KERN_INFO "Adding %uk swap on %s.  "
                  "Priority:%d extents:%d across:%lluk\n",
            nr_good_pages<<(PAGE_SHIFT-10), name, p->prio,
            nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10));

      /* 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;
      }
      spin_unlock(&swap_lock);
      mutex_unlock(&swapon_mutex);
      error = 0;
      goto out;
bad_swap:
      if (bdev) {
            set_blocksize(bdev, p->old_block_size);
            bd_release(bdev);
      }
      destroy_swap_extents(p);
bad_swap_2:
      spin_lock(&swap_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;
      spin_unlock(&swap_lock);
      vfree(swap_map);
      if (swap_file)
            filp_close(swap_file, NULL);
out:
      if (page && !IS_ERR(page)) {
            kunmap(page);
            page_cache_release(page);
      }
      if (name)
            putname(name);
      if (did_down) {
            if (!error)
                  inode->i_flags |= S_SWAPFILE;
            mutex_unlock(&inode->i_mutex);
      }
      return error;
}

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

      spin_lock(&swap_lock);
      for (i = 0; i < nr_swapfiles; i++) {
            if (!(swap_info[i].flags & SWP_USED) ||
                 (swap_info[i].flags & SWP_WRITEOK))
                  continue;
            nr_to_be_unused += swap_info[i].inuse_pages;
      }
      val->freeswap = nr_swap_pages + nr_to_be_unused;
      val->totalswap = total_swap_pages + nr_to_be_unused;
      spin_unlock(&swap_lock);
}

/*
 * 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;

      if (is_migration_entry(entry))
            return 1;

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

      spin_lock(&swap_lock);
      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;
            }
      }
      spin_unlock(&swap_lock);
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_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 our_page_cluster = page_cluster;
      int ret = 0, i = 1 << our_page_cluster;
      unsigned long toff;
      struct swap_info_struct *swapdev = swp_type(entry) + swap_info;

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

      spin_lock(&swap_lock);
      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);
      spin_unlock(&swap_lock);
      return ret;
}

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