/*
   * Resizable virtual memory filesystem for Linux.
   *
   * Copyright (C) 2000 Linus Torvalds.
   *		 2000 Transmeta Corp.
   *		 2000-2001 Christoph Rohland
   *		 2000-2001 SAP AG
   *		 2002 Red Hat Inc.

   * Copyright (C) 2002-2005 Hugh Dickins.
   * Copyright (C) 2002-2005 VERITAS Software Corporation.

   * Copyright (C) 2004 Andi Kleen, SuSE Labs
   *
   * Extended attribute support for tmpfs:
   * Copyright (c) 2004, Luke Kenneth Casson Leighton <lkcl@lkcl.net>
   * Copyright (c) 2004 Red Hat, Inc., James Morris <jmorris@redhat.com>
   *

   * tiny-shmem:
   * Copyright (c) 2004, 2008 Matt Mackall <mpm@selenic.com>
   *

   * This file is released under the GPL.
   */

  #include <linux/fs.h>
  #include <linux/init.h>
  #include <linux/vfs.h>
  #include <linux/mount.h>

  #include <linux/pagemap.h>

  #include <linux/file.h>
  #include <linux/mm.h>
  #include <linux/module.h>

  #include <linux/percpu_counter.h>

  #include <linux/swap.h>
  
  static struct vfsmount *shm_mnt;
  
  #ifdef CONFIG_SHMEM

  /*
   * This virtual memory filesystem is heavily based on the ramfs. It
   * extends ramfs by the ability to use swap and honor resource limits
   * which makes it a completely usable filesystem.
   */

  #include <linux/xattr.h>

  #include <linux/exportfs.h>

  #include <linux/posix_acl.h>

  #include <linux/generic_acl.h>

  #include <linux/mman.h>

  #include <linux/string.h>
  #include <linux/slab.h>
  #include <linux/backing-dev.h>
  #include <linux/shmem_fs.h>

  #include <linux/writeback.h>

  #include <linux/blkdev.h>
  #include <linux/security.h>
  #include <linux/swapops.h>
  #include <linux/mempolicy.h>
  #include <linux/namei.h>

  #include <linux/ctype.h>

  #include <linux/migrate.h>

  #include <linux/highmem.h>

  #include <linux/seq_file.h>

  #include <linux/magic.h>

  #include <asm/uaccess.h>
  #include <asm/div64.h>
  #include <asm/pgtable.h>

  /*
   * The maximum size of a shmem/tmpfs file is limited by the maximum size of
   * its triple-indirect swap vector - see illustration at shmem_swp_entry().
   *
   * With 4kB page size, maximum file size is just over 2TB on a 32-bit kernel,
   * but one eighth of that on a 64-bit kernel.  With 8kB page size, maximum
   * file size is just over 4TB on a 64-bit kernel, but 16TB on a 32-bit kernel,
   * MAX_LFS_FILESIZE being then more restrictive than swap vector layout.
   *
   * We use / and * instead of shifts in the definitions below, so that the swap
   * vector can be tested with small even values (e.g. 20) for ENTRIES_PER_PAGE.
   */

  #define ENTRIES_PER_PAGE (PAGE_CACHE_SIZE/sizeof(unsigned long))

  #define ENTRIES_PER_PAGEPAGE ((unsigned long long)ENTRIES_PER_PAGE*ENTRIES_PER_PAGE)

  #define SHMSWP_MAX_INDEX (SHMEM_NR_DIRECT + (ENTRIES_PER_PAGEPAGE/2) * (ENTRIES_PER_PAGE+1))
  #define SHMSWP_MAX_BYTES (SHMSWP_MAX_INDEX << PAGE_CACHE_SHIFT)

  #define SHMEM_MAX_BYTES  min_t(unsigned long long, SHMSWP_MAX_BYTES, MAX_LFS_FILESIZE)
  #define SHMEM_MAX_INDEX  ((unsigned long)((SHMEM_MAX_BYTES+1) >> PAGE_CACHE_SHIFT))
  
  #define BLOCKS_PER_PAGE  (PAGE_CACHE_SIZE/512)

  #define VM_ACCT(size)    (PAGE_CACHE_ALIGN(size) >> PAGE_SHIFT)
  
  /* info->flags needs VM_flags to handle pagein/truncate races efficiently */
  #define SHMEM_PAGEIN	 VM_READ
  #define SHMEM_TRUNCATE	 VM_WRITE
  
  /* Definition to limit shmem_truncate's steps between cond_rescheds */
  #define LATENCY_LIMIT	 64
  
  /* Pretend that each entry is of this size in directory's i_size */
  #define BOGO_DIRENT_SIZE 20

  /* Flag allocation requirements to shmem_getpage and shmem_swp_alloc */
  enum sgp_type {

  	SGP_READ,	/* don't exceed i_size, don't allocate page */
  	SGP_CACHE,	/* don't exceed i_size, may allocate page */

  	SGP_DIRTY,	/* like SGP_CACHE, but set new page dirty */

  	SGP_WRITE,	/* may exceed i_size, may allocate page */
  };

  #ifdef CONFIG_TMPFS

  static unsigned long shmem_default_max_blocks(void)
  {
  	return totalram_pages / 2;
  }
  
  static unsigned long shmem_default_max_inodes(void)
  {
  	return min(totalram_pages - totalhigh_pages, totalram_pages / 2);
  }

  #endif

  static int shmem_getpage(struct inode *inode, unsigned long idx,
  			 struct page **pagep, enum sgp_type sgp, int *type);

  static inline struct page *shmem_dir_alloc(gfp_t gfp_mask)

  {
  	/*
  	 * The above definition of ENTRIES_PER_PAGE, and the use of
  	 * BLOCKS_PER_PAGE on indirect pages, assume PAGE_CACHE_SIZE:
  	 * might be reconsidered if it ever diverges from PAGE_SIZE.

  	 *

  	 * Mobility flags are masked out as swap vectors cannot move

  	 */

  	return alloc_pages((gfp_mask & ~GFP_MOVABLE_MASK) | __GFP_ZERO,

  				PAGE_CACHE_SHIFT-PAGE_SHIFT);

  }
  
  static inline void shmem_dir_free(struct page *page)
  {
  	__free_pages(page, PAGE_CACHE_SHIFT-PAGE_SHIFT);
  }
  
  static struct page **shmem_dir_map(struct page *page)
  {
  	return (struct page **)kmap_atomic(page, KM_USER0);
  }
  
  static inline void shmem_dir_unmap(struct page **dir)
  {
  	kunmap_atomic(dir, KM_USER0);
  }
  
  static swp_entry_t *shmem_swp_map(struct page *page)
  {
  	return (swp_entry_t *)kmap_atomic(page, KM_USER1);
  }
  
  static inline void shmem_swp_balance_unmap(void)
  {
  	/*
  	 * When passing a pointer to an i_direct entry, to code which
  	 * also handles indirect entries and so will shmem_swp_unmap,
  	 * we must arrange for the preempt count to remain in balance.
  	 * What kmap_atomic of a lowmem page does depends on config
  	 * and architecture, so pretend to kmap_atomic some lowmem page.
  	 */
  	(void) kmap_atomic(ZERO_PAGE(0), KM_USER1);
  }
  
  static inline void shmem_swp_unmap(swp_entry_t *entry)
  {
  	kunmap_atomic(entry, KM_USER1);
  }
  
  static inline struct shmem_sb_info *SHMEM_SB(struct super_block *sb)
  {
  	return sb->s_fs_info;
  }
  
  /*
   * shmem_file_setup pre-accounts the whole fixed size of a VM object,
   * for shared memory and for shared anonymous (/dev/zero) mappings
   * (unless MAP_NORESERVE and sysctl_overcommit_memory <= 1),
   * consistent with the pre-accounting of private mappings ...
   */
  static inline int shmem_acct_size(unsigned long flags, loff_t size)
  {

  	return (flags & VM_NORESERVE) ?
  		0 : security_vm_enough_memory_kern(VM_ACCT(size));

  }
  
  static inline void shmem_unacct_size(unsigned long flags, loff_t size)
  {

  	if (!(flags & VM_NORESERVE))

  		vm_unacct_memory(VM_ACCT(size));
  }
  
  /*
   * ... whereas tmpfs objects are accounted incrementally as
   * pages are allocated, in order to allow huge sparse files.
   * shmem_getpage reports shmem_acct_block failure as -ENOSPC not -ENOMEM,
   * so that a failure on a sparse tmpfs mapping will give SIGBUS not OOM.
   */
  static inline int shmem_acct_block(unsigned long flags)
  {

  	return (flags & VM_NORESERVE) ?
  		security_vm_enough_memory_kern(VM_ACCT(PAGE_CACHE_SIZE)) : 0;

  }
  
  static inline void shmem_unacct_blocks(unsigned long flags, long pages)
  {

  	if (flags & VM_NORESERVE)

  		vm_unacct_memory(pages * VM_ACCT(PAGE_CACHE_SIZE));
  }

  static const struct super_operations shmem_ops;

  static const struct address_space_operations shmem_aops;

  static const struct file_operations shmem_file_operations;

  static const struct inode_operations shmem_inode_operations;
  static const struct inode_operations shmem_dir_inode_operations;
  static const struct inode_operations shmem_special_inode_operations;

  static const struct vm_operations_struct shmem_vm_ops;

  static struct backing_dev_info shmem_backing_dev_info  __read_mostly = {

  	.ra_pages	= 0,	/* No readahead */

  	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,

  	.unplug_io_fn	= default_unplug_io_fn,
  };
  
  static LIST_HEAD(shmem_swaplist);

  static DEFINE_MUTEX(shmem_swaplist_mutex);

  
  static void shmem_free_blocks(struct inode *inode, long pages)
  {
  	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);

  	if (sbinfo->max_blocks) {

  		percpu_counter_add(&sbinfo->used_blocks, -pages);
  		spin_lock(&inode->i_lock);

  		inode->i_blocks -= pages*BLOCKS_PER_PAGE;

  		spin_unlock(&inode->i_lock);

  	}
  }

  static int shmem_reserve_inode(struct super_block *sb)
  {
  	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
  	if (sbinfo->max_inodes) {
  		spin_lock(&sbinfo->stat_lock);
  		if (!sbinfo->free_inodes) {
  			spin_unlock(&sbinfo->stat_lock);
  			return -ENOSPC;
  		}
  		sbinfo->free_inodes--;
  		spin_unlock(&sbinfo->stat_lock);
  	}
  	return 0;
  }
  
  static void shmem_free_inode(struct super_block *sb)
  {
  	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
  	if (sbinfo->max_inodes) {
  		spin_lock(&sbinfo->stat_lock);
  		sbinfo->free_inodes++;
  		spin_unlock(&sbinfo->stat_lock);
  	}
  }

  /**

   * shmem_recalc_inode - recalculate the size of an inode

   * @inode: inode to recalc
   *
   * We have to calculate the free blocks since the mm can drop
   * undirtied hole pages behind our back.
   *
   * But normally   info->alloced == inode->i_mapping->nrpages + info->swapped
   * So mm freed is info->alloced - (inode->i_mapping->nrpages + info->swapped)
   *
   * It has to be called with the spinlock held.
   */
  static void shmem_recalc_inode(struct inode *inode)
  {
  	struct shmem_inode_info *info = SHMEM_I(inode);
  	long freed;
  
  	freed = info->alloced - info->swapped - inode->i_mapping->nrpages;
  	if (freed > 0) {
  		info->alloced -= freed;
  		shmem_unacct_blocks(info->flags, freed);
  		shmem_free_blocks(inode, freed);
  	}
  }

  /**

   * shmem_swp_entry - find the swap vector position in the info structure

   * @info:  info structure for the inode
   * @index: index of the page to find
   * @page:  optional page to add to the structure. Has to be preset to
   *         all zeros
   *
   * If there is no space allocated yet it will return NULL when
   * page is NULL, else it will use the page for the needed block,
   * setting it to NULL on return to indicate that it has been used.
   *
   * The swap vector is organized the following way:
   *
   * There are SHMEM_NR_DIRECT entries directly stored in the
   * shmem_inode_info structure. So small files do not need an addional
   * allocation.
   *
   * For pages with index > SHMEM_NR_DIRECT there is the pointer
   * i_indirect which points to a page which holds in the first half
   * doubly indirect blocks, in the second half triple indirect blocks:
   *
   * For an artificial ENTRIES_PER_PAGE = 4 this would lead to the
   * following layout (for SHMEM_NR_DIRECT == 16):
   *
   * i_indirect -> dir --> 16-19
   * 	      |	     +-> 20-23
   * 	      |
   * 	      +-->dir2 --> 24-27
   * 	      |	       +-> 28-31
   * 	      |	       +-> 32-35
   * 	      |	       +-> 36-39
   * 	      |
   * 	      +-->dir3 --> 40-43
   * 	       	       +-> 44-47
   * 	      	       +-> 48-51
   * 	      	       +-> 52-55
   */
  static swp_entry_t *shmem_swp_entry(struct shmem_inode_info *info, unsigned long index, struct page **page)
  {
  	unsigned long offset;
  	struct page **dir;
  	struct page *subdir;
  
  	if (index < SHMEM_NR_DIRECT) {
  		shmem_swp_balance_unmap();
  		return info->i_direct+index;
  	}
  	if (!info->i_indirect) {
  		if (page) {
  			info->i_indirect = *page;
  			*page = NULL;
  		}
  		return NULL;			/* need another page */
  	}
  
  	index -= SHMEM_NR_DIRECT;
  	offset = index % ENTRIES_PER_PAGE;
  	index /= ENTRIES_PER_PAGE;
  	dir = shmem_dir_map(info->i_indirect);
  
  	if (index >= ENTRIES_PER_PAGE/2) {
  		index -= ENTRIES_PER_PAGE/2;
  		dir += ENTRIES_PER_PAGE/2 + index/ENTRIES_PER_PAGE;
  		index %= ENTRIES_PER_PAGE;
  		subdir = *dir;
  		if (!subdir) {
  			if (page) {
  				*dir = *page;
  				*page = NULL;
  			}
  			shmem_dir_unmap(dir);
  			return NULL;		/* need another page */
  		}
  		shmem_dir_unmap(dir);
  		dir = shmem_dir_map(subdir);
  	}
  
  	dir += index;
  	subdir = *dir;
  	if (!subdir) {
  		if (!page || !(subdir = *page)) {
  			shmem_dir_unmap(dir);
  			return NULL;		/* need a page */
  		}
  		*dir = subdir;
  		*page = NULL;
  	}
  	shmem_dir_unmap(dir);
  	return shmem_swp_map(subdir) + offset;
  }
  
  static void shmem_swp_set(struct shmem_inode_info *info, swp_entry_t *entry, unsigned long value)
  {
  	long incdec = value? 1: -1;
  
  	entry->val = value;
  	info->swapped += incdec;

  	if ((unsigned long)(entry - info->i_direct) >= SHMEM_NR_DIRECT) {
  		struct page *page = kmap_atomic_to_page(entry);
  		set_page_private(page, page_private(page) + incdec);
  	}

  }

  /**

   * shmem_swp_alloc - get the position of the swap entry for the page.

   * @info:	info structure for the inode
   * @index:	index of the page to find
   * @sgp:	check and recheck i_size? skip allocation?

   *
   * If the entry does not exist, allocate it.

   */
  static swp_entry_t *shmem_swp_alloc(struct shmem_inode_info *info, unsigned long index, enum sgp_type sgp)
  {
  	struct inode *inode = &info->vfs_inode;
  	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
  	struct page *page = NULL;
  	swp_entry_t *entry;
  
  	if (sgp != SGP_WRITE &&
  	    ((loff_t) index << PAGE_CACHE_SHIFT) >= i_size_read(inode))
  		return ERR_PTR(-EINVAL);
  
  	while (!(entry = shmem_swp_entry(info, index, &page))) {
  		if (sgp == SGP_READ)
  			return shmem_swp_map(ZERO_PAGE(0));
  		/*

  		 * Test used_blocks against 1 less max_blocks, since we have 1 data

  		 * page (and perhaps indirect index pages) yet to allocate:
  		 * a waste to allocate index if we cannot allocate data.
  		 */

  		if (sbinfo->max_blocks) {

  			if (percpu_counter_compare(&sbinfo->used_blocks, (sbinfo->max_blocks - 1)) > 0)

  				return ERR_PTR(-ENOSPC);

  			percpu_counter_inc(&sbinfo->used_blocks);
  			spin_lock(&inode->i_lock);

  			inode->i_blocks += BLOCKS_PER_PAGE;

  			spin_unlock(&inode->i_lock);

  		}
  
  		spin_unlock(&info->lock);

  		page = shmem_dir_alloc(mapping_gfp_mask(inode->i_mapping));

  		spin_lock(&info->lock);
  
  		if (!page) {
  			shmem_free_blocks(inode, 1);
  			return ERR_PTR(-ENOMEM);
  		}
  		if (sgp != SGP_WRITE &&
  		    ((loff_t) index << PAGE_CACHE_SHIFT) >= i_size_read(inode)) {
  			entry = ERR_PTR(-EINVAL);
  			break;
  		}
  		if (info->next_index <= index)
  			info->next_index = index + 1;
  	}
  	if (page) {
  		/* another task gave its page, or truncated the file */
  		shmem_free_blocks(inode, 1);
  		shmem_dir_free(page);
  	}
  	if (info->next_index <= index && !IS_ERR(entry))
  		info->next_index = index + 1;
  	return entry;
  }

  /**

   * shmem_free_swp - free some swap entries in a directory

   * @dir:        pointer to the directory
   * @edir:       pointer after last entry of the directory
   * @punch_lock: pointer to spinlock when needed for the holepunch case

   */

  static int shmem_free_swp(swp_entry_t *dir, swp_entry_t *edir,
  						spinlock_t *punch_lock)

  {

  	spinlock_t *punch_unlock = NULL;

  	swp_entry_t *ptr;
  	int freed = 0;
  
  	for (ptr = dir; ptr < edir; ptr++) {
  		if (ptr->val) {

  			if (unlikely(punch_lock)) {
  				punch_unlock = punch_lock;
  				punch_lock = NULL;
  				spin_lock(punch_unlock);
  				if (!ptr->val)
  					continue;
  			}

  			free_swap_and_cache(*ptr);
  			*ptr = (swp_entry_t){0};
  			freed++;
  		}
  	}

  	if (punch_unlock)
  		spin_unlock(punch_unlock);

  	return freed;
  }

  static int shmem_map_and_free_swp(struct page *subdir, int offset,
  		int limit, struct page ***dir, spinlock_t *punch_lock)

  {
  	swp_entry_t *ptr;
  	int freed = 0;
  
  	ptr = shmem_swp_map(subdir);
  	for (; offset < limit; offset += LATENCY_LIMIT) {
  		int size = limit - offset;
  		if (size > LATENCY_LIMIT)
  			size = LATENCY_LIMIT;

  		freed += shmem_free_swp(ptr+offset, ptr+offset+size,
  							punch_lock);

  		if (need_resched()) {
  			shmem_swp_unmap(ptr);
  			if (*dir) {
  				shmem_dir_unmap(*dir);
  				*dir = NULL;
  			}
  			cond_resched();
  			ptr = shmem_swp_map(subdir);
  		}
  	}
  	shmem_swp_unmap(ptr);
  	return freed;
  }
  
  static void shmem_free_pages(struct list_head *next)
  {
  	struct page *page;
  	int freed = 0;
  
  	do {
  		page = container_of(next, struct page, lru);
  		next = next->next;
  		shmem_dir_free(page);
  		freed++;
  		if (freed >= LATENCY_LIMIT) {
  			cond_resched();
  			freed = 0;
  		}
  	} while (next);
  }

  static void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end)

  {
  	struct shmem_inode_info *info = SHMEM_I(inode);
  	unsigned long idx;
  	unsigned long size;
  	unsigned long limit;
  	unsigned long stage;
  	unsigned long diroff;
  	struct page **dir;
  	struct page *topdir;
  	struct page *middir;
  	struct page *subdir;
  	swp_entry_t *ptr;
  	LIST_HEAD(pages_to_free);
  	long nr_pages_to_free = 0;
  	long nr_swaps_freed = 0;
  	int offset;
  	int freed;

  	int punch_hole;

  	spinlock_t *needs_lock;
  	spinlock_t *punch_lock;

  	unsigned long upper_limit;

  
  	inode->i_ctime = inode->i_mtime = CURRENT_TIME;

  	idx = (start + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;

  	if (idx >= info->next_index)
  		return;
  
  	spin_lock(&info->lock);
  	info->flags |= SHMEM_TRUNCATE;

  	if (likely(end == (loff_t) -1)) {
  		limit = info->next_index;

  		upper_limit = SHMEM_MAX_INDEX;

  		info->next_index = idx;

  		needs_lock = NULL;

  		punch_hole = 0;

  	} else {

  		if (end + 1 >= inode->i_size) {	/* we may free a little more */
  			limit = (inode->i_size + PAGE_CACHE_SIZE - 1) >>
  							PAGE_CACHE_SHIFT;
  			upper_limit = SHMEM_MAX_INDEX;
  		} else {
  			limit = (end + 1) >> PAGE_CACHE_SHIFT;
  			upper_limit = limit;
  		}

  		needs_lock = &info->lock;

  		punch_hole = 1;
  	}

  	topdir = info->i_indirect;

  	if (topdir && idx <= SHMEM_NR_DIRECT && !punch_hole) {

  		info->i_indirect = NULL;
  		nr_pages_to_free++;
  		list_add(&topdir->lru, &pages_to_free);
  	}
  	spin_unlock(&info->lock);
  
  	if (info->swapped && idx < SHMEM_NR_DIRECT) {
  		ptr = info->i_direct;
  		size = limit;
  		if (size > SHMEM_NR_DIRECT)
  			size = SHMEM_NR_DIRECT;

  		nr_swaps_freed = shmem_free_swp(ptr+idx, ptr+size, needs_lock);

  	}

  
  	/*
  	 * If there are no indirect blocks or we are punching a hole
  	 * below indirect blocks, nothing to be done.
  	 */

  	if (!topdir || limit <= SHMEM_NR_DIRECT)

  		goto done2;

  	/*
  	 * The truncation case has already dropped info->lock, and we're safe
  	 * because i_size and next_index have already been lowered, preventing
  	 * access beyond.  But in the punch_hole case, we still need to take
  	 * the lock when updating the swap directory, because there might be
  	 * racing accesses by shmem_getpage(SGP_CACHE), shmem_unuse_inode or
  	 * shmem_writepage.  However, whenever we find we can remove a whole
  	 * directory page (not at the misaligned start or end of the range),
  	 * we first NULLify its pointer in the level above, and then have no
  	 * need to take the lock when updating its contents: needs_lock and
  	 * punch_lock (either pointing to info->lock or NULL) manage this.
  	 */

  	upper_limit -= SHMEM_NR_DIRECT;

  	limit -= SHMEM_NR_DIRECT;
  	idx = (idx > SHMEM_NR_DIRECT)? (idx - SHMEM_NR_DIRECT): 0;
  	offset = idx % ENTRIES_PER_PAGE;
  	idx -= offset;
  
  	dir = shmem_dir_map(topdir);
  	stage = ENTRIES_PER_PAGEPAGE/2;
  	if (idx < ENTRIES_PER_PAGEPAGE/2) {
  		middir = topdir;
  		diroff = idx/ENTRIES_PER_PAGE;
  	} else {
  		dir += ENTRIES_PER_PAGE/2;
  		dir += (idx - ENTRIES_PER_PAGEPAGE/2)/ENTRIES_PER_PAGEPAGE;
  		while (stage <= idx)
  			stage += ENTRIES_PER_PAGEPAGE;
  		middir = *dir;
  		if (*dir) {
  			diroff = ((idx - ENTRIES_PER_PAGEPAGE/2) %
  				ENTRIES_PER_PAGEPAGE) / ENTRIES_PER_PAGE;

  			if (!diroff && !offset && upper_limit >= stage) {

  				if (needs_lock) {
  					spin_lock(needs_lock);
  					*dir = NULL;
  					spin_unlock(needs_lock);
  					needs_lock = NULL;
  				} else
  					*dir = NULL;

  				nr_pages_to_free++;
  				list_add(&middir->lru, &pages_to_free);
  			}
  			shmem_dir_unmap(dir);
  			dir = shmem_dir_map(middir);
  		} else {
  			diroff = 0;
  			offset = 0;
  			idx = stage;
  		}
  	}
  
  	for (; idx < limit; idx += ENTRIES_PER_PAGE, diroff++) {
  		if (unlikely(idx == stage)) {
  			shmem_dir_unmap(dir);
  			dir = shmem_dir_map(topdir) +
  			    ENTRIES_PER_PAGE/2 + idx/ENTRIES_PER_PAGEPAGE;
  			while (!*dir) {
  				dir++;
  				idx += ENTRIES_PER_PAGEPAGE;
  				if (idx >= limit)
  					goto done1;
  			}
  			stage = idx + ENTRIES_PER_PAGEPAGE;
  			middir = *dir;

  			if (punch_hole)
  				needs_lock = &info->lock;

  			if (upper_limit >= stage) {

  				if (needs_lock) {
  					spin_lock(needs_lock);
  					*dir = NULL;
  					spin_unlock(needs_lock);
  					needs_lock = NULL;
  				} else
  					*dir = NULL;

  				nr_pages_to_free++;
  				list_add(&middir->lru, &pages_to_free);
  			}

  			shmem_dir_unmap(dir);
  			cond_resched();
  			dir = shmem_dir_map(middir);
  			diroff = 0;
  		}

  		punch_lock = needs_lock;

  		subdir = dir[diroff];

  		if (subdir && !offset && upper_limit-idx >= ENTRIES_PER_PAGE) {
  			if (needs_lock) {
  				spin_lock(needs_lock);
  				dir[diroff] = NULL;
  				spin_unlock(needs_lock);
  				punch_lock = NULL;
  			} else
  				dir[diroff] = NULL;
  			nr_pages_to_free++;
  			list_add(&subdir->lru, &pages_to_free);
  		}
  		if (subdir && page_private(subdir) /* has swap entries */) {

  			size = limit - idx;
  			if (size > ENTRIES_PER_PAGE)
  				size = ENTRIES_PER_PAGE;
  			freed = shmem_map_and_free_swp(subdir,

  					offset, size, &dir, punch_lock);

  			if (!dir)
  				dir = shmem_dir_map(middir);
  			nr_swaps_freed += freed;

  			if (offset || punch_lock) {

  				spin_lock(&info->lock);

  				set_page_private(subdir,
  					page_private(subdir) - freed);

  				spin_unlock(&info->lock);

  			} else
  				BUG_ON(page_private(subdir) != freed);

  		}

  		offset = 0;

  	}
  done1:
  	shmem_dir_unmap(dir);
  done2:
  	if (inode->i_mapping->nrpages && (info->flags & SHMEM_PAGEIN)) {
  		/*
  		 * Call truncate_inode_pages again: racing shmem_unuse_inode

  		 * may have swizzled a page in from swap since
  		 * truncate_pagecache or generic_delete_inode did it, before we
  		 * lowered next_index.  Also, though shmem_getpage checks
  		 * i_size before adding to cache, no recheck after: so fix the
  		 * narrow window there too.

  		 *
  		 * Recalling truncate_inode_pages_range and unmap_mapping_range
  		 * every time for punch_hole (which never got a chance to clear
  		 * SHMEM_PAGEIN at the start of vmtruncate_range) is expensive,
  		 * yet hardly ever necessary: try to optimize them out later.

  		 */

  		truncate_inode_pages_range(inode->i_mapping, start, end);

  		if (punch_hole)
  			unmap_mapping_range(inode->i_mapping, start,
  							end - start, 1);

  	}
  
  	spin_lock(&info->lock);
  	info->flags &= ~SHMEM_TRUNCATE;
  	info->swapped -= nr_swaps_freed;
  	if (nr_pages_to_free)
  		shmem_free_blocks(inode, nr_pages_to_free);
  	shmem_recalc_inode(inode);
  	spin_unlock(&info->lock);
  
  	/*
  	 * Empty swap vector directory pages to be freed?
  	 */
  	if (!list_empty(&pages_to_free)) {
  		pages_to_free.prev->next = NULL;
  		shmem_free_pages(pages_to_free.next);
  	}
  }
  
  static int shmem_notify_change(struct dentry *dentry, struct iattr *attr)
  {
  	struct inode *inode = dentry->d_inode;

  	loff_t newsize = attr->ia_size;

  	int error;

  	error = inode_change_ok(inode, attr);
  	if (error)
  		return error;

  	if (S_ISREG(inode->i_mode) && (attr->ia_valid & ATTR_SIZE)
  					&& newsize != inode->i_size) {

  		struct page *page = NULL;
  
  		if (newsize < inode->i_size) {

  			/*
  			 * If truncating down to a partial page, then
  			 * if that page is already allocated, hold it
  			 * in memory until the truncation is over, so
  			 * truncate_partial_page cannnot miss it were
  			 * it assigned to swap.
  			 */

  			if (newsize & (PAGE_CACHE_SIZE-1)) {

  				(void) shmem_getpage(inode,

  					newsize >> PAGE_CACHE_SHIFT,

  						&page, SGP_READ, NULL);

  				if (page)
  					unlock_page(page);

  			}
  			/*
  			 * Reset SHMEM_PAGEIN flag so that shmem_truncate can
  			 * detect if any pages might have been added to cache
  			 * after truncate_inode_pages.  But we needn't bother
  			 * if it's being fully truncated to zero-length: the
  			 * nrpages check is efficient enough in that case.
  			 */

  			if (newsize) {

  				struct shmem_inode_info *info = SHMEM_I(inode);
  				spin_lock(&info->lock);
  				info->flags &= ~SHMEM_PAGEIN;
  				spin_unlock(&info->lock);
  			}
  		}

  		/* XXX(truncate): truncate_setsize should be called last */
  		truncate_setsize(inode, newsize);

  		if (page)
  			page_cache_release(page);

  		shmem_truncate_range(inode, newsize, (loff_t)-1);

  	}

  	setattr_copy(inode, attr);

  #ifdef CONFIG_TMPFS_POSIX_ACL

  	if (attr->ia_valid & ATTR_MODE)

  		error = generic_acl_chmod(inode);

  #endif

  	return error;
  }

  static void shmem_evict_inode(struct inode *inode)

  {

  	struct shmem_inode_info *info = SHMEM_I(inode);

  	if (inode->i_mapping->a_ops == &shmem_aops) {

  		truncate_inode_pages(inode->i_mapping, 0);

  		shmem_unacct_size(info->flags, inode->i_size);
  		inode->i_size = 0;

  		shmem_truncate_range(inode, 0, (loff_t)-1);

  		if (!list_empty(&info->swaplist)) {

  			mutex_lock(&shmem_swaplist_mutex);

  			list_del_init(&info->swaplist);

  			mutex_unlock(&shmem_swaplist_mutex);

  		}
  	}

  	BUG_ON(inode->i_blocks);

  	shmem_free_inode(inode->i_sb);

  	end_writeback(inode);

  }
  
  static inline int shmem_find_swp(swp_entry_t entry, swp_entry_t *dir, swp_entry_t *edir)
  {
  	swp_entry_t *ptr;
  
  	for (ptr = dir; ptr < edir; ptr++) {
  		if (ptr->val == entry.val)
  			return ptr - dir;
  	}
  	return -1;
  }
  
  static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, struct page *page)
  {
  	struct inode *inode;
  	unsigned long idx;
  	unsigned long size;
  	unsigned long limit;
  	unsigned long stage;
  	struct page **dir;
  	struct page *subdir;
  	swp_entry_t *ptr;
  	int offset;

  	int error;

  
  	idx = 0;
  	ptr = info->i_direct;
  	spin_lock(&info->lock);

  	if (!info->swapped) {
  		list_del_init(&info->swaplist);
  		goto lost2;
  	}

  	limit = info->next_index;
  	size = limit;
  	if (size > SHMEM_NR_DIRECT)
  		size = SHMEM_NR_DIRECT;
  	offset = shmem_find_swp(entry, ptr, ptr+size);

  	if (offset >= 0)

  		goto found;

  	if (!info->i_indirect)
  		goto lost2;
  
  	dir = shmem_dir_map(info->i_indirect);
  	stage = SHMEM_NR_DIRECT + ENTRIES_PER_PAGEPAGE/2;
  
  	for (idx = SHMEM_NR_DIRECT; idx < limit; idx += ENTRIES_PER_PAGE, dir++) {
  		if (unlikely(idx == stage)) {
  			shmem_dir_unmap(dir-1);

  			if (cond_resched_lock(&info->lock)) {
  				/* check it has not been truncated */
  				if (limit > info->next_index) {
  					limit = info->next_index;
  					if (idx >= limit)
  						goto lost2;
  				}
  			}

  			dir = shmem_dir_map(info->i_indirect) +
  			    ENTRIES_PER_PAGE/2 + idx/ENTRIES_PER_PAGEPAGE;
  			while (!*dir) {
  				dir++;
  				idx += ENTRIES_PER_PAGEPAGE;
  				if (idx >= limit)
  					goto lost1;
  			}
  			stage = idx + ENTRIES_PER_PAGEPAGE;
  			subdir = *dir;
  			shmem_dir_unmap(dir);
  			dir = shmem_dir_map(subdir);
  		}
  		subdir = *dir;

  		if (subdir && page_private(subdir)) {

  			ptr = shmem_swp_map(subdir);
  			size = limit - idx;
  			if (size > ENTRIES_PER_PAGE)
  				size = ENTRIES_PER_PAGE;
  			offset = shmem_find_swp(entry, ptr, ptr+size);

  			shmem_swp_unmap(ptr);

  			if (offset >= 0) {
  				shmem_dir_unmap(dir);
  				goto found;
  			}

  		}
  	}
  lost1:
  	shmem_dir_unmap(dir-1);
  lost2:
  	spin_unlock(&info->lock);
  	return 0;
  found:
  	idx += offset;

  	inode = igrab(&info->vfs_inode);
  	spin_unlock(&info->lock);

  	/*
  	 * Move _head_ to start search for next from here.

  	 * But be careful: shmem_evict_inode checks list_empty without taking

  	 * mutex, and there's an instant in list_move_tail when info->swaplist
  	 * would appear empty, if it were the only one on shmem_swaplist.  We
  	 * could avoid doing it if inode NULL; or use this minor optimization.
  	 */
  	if (shmem_swaplist.next != &info->swaplist)
  		list_move_tail(&shmem_swaplist, &info->swaplist);

  	mutex_unlock(&shmem_swaplist_mutex);
  
  	error = 1;
  	if (!inode)
  		goto out;

  	/*

  	 * Charge page using GFP_KERNEL while we can wait.
  	 * Charged back to the user(not to caller) when swap account is used.
  	 * add_to_page_cache() will be called with GFP_NOWAIT.

  	 */

  	error = mem_cgroup_cache_charge(page, current->mm, GFP_KERNEL);

  	if (error)
  		goto out;

  	error = radix_tree_preload(GFP_KERNEL);

  	if (error) {
  		mem_cgroup_uncharge_cache_page(page);
  		goto out;
  	}

  	error = 1;

  
  	spin_lock(&info->lock);
  	ptr = shmem_swp_entry(info, idx, NULL);

  	if (ptr && ptr->val == entry.val) {

  		error = add_to_page_cache_locked(page, inode->i_mapping,

  						idx, GFP_NOWAIT);

  		/* does mem_cgroup_uncharge_cache_page on error */
  	} else	/* we must compensate for our precharge above */
  		mem_cgroup_uncharge_cache_page(page);

  	if (error == -EEXIST) {
  		struct page *filepage = find_get_page(inode->i_mapping, idx);

  		error = 1;

  		if (filepage) {
  			/*
  			 * There might be a more uptodate page coming down
  			 * from a stacked writepage: forget our swappage if so.
  			 */
  			if (PageUptodate(filepage))
  				error = 0;
  			page_cache_release(filepage);
  		}
  	}
  	if (!error) {

  		delete_from_swap_cache(page);
  		set_page_dirty(page);

  		info->flags |= SHMEM_PAGEIN;

  		shmem_swp_set(info, ptr, 0);
  		swap_free(entry);
  		error = 1;	/* not an error, but entry was found */

  	}

  	if (ptr)
  		shmem_swp_unmap(ptr);

  	spin_unlock(&info->lock);

  	radix_tree_preload_end();

  out:
  	unlock_page(page);
  	page_cache_release(page);
  	iput(inode);		/* allows for NULL */
  	return error;

  }
  
  /*
   * shmem_unuse() search for an eventually swapped out shmem page.
   */
  int shmem_unuse(swp_entry_t entry, struct page *page)
  {
  	struct list_head *p, *next;
  	struct shmem_inode_info *info;
  	int found = 0;

  	mutex_lock(&shmem_swaplist_mutex);

  	list_for_each_safe(p, next, &shmem_swaplist) {
  		info = list_entry(p, struct shmem_inode_info, swaplist);

  		found = shmem_unuse_inode(info, entry, page);

  		cond_resched();

  		if (found)
  			goto out;

  	}

  	mutex_unlock(&shmem_swaplist_mutex);

  	/*
  	 * Can some race bring us here?  We've been holding page lock,
  	 * so I think not; but would rather try again later than BUG()
  	 */
  	unlock_page(page);
  	page_cache_release(page);
  out:
  	return (found < 0) ? found : 0;

  }
  
  /*
   * Move the page from the page cache to the swap cache.
   */
  static int shmem_writepage(struct page *page, struct writeback_control *wbc)
  {
  	struct shmem_inode_info *info;
  	swp_entry_t *entry, swap;
  	struct address_space *mapping;
  	unsigned long index;
  	struct inode *inode;
  
  	BUG_ON(!PageLocked(page));

  	mapping = page->mapping;
  	index = page->index;
  	inode = mapping->host;
  	info = SHMEM_I(inode);
  	if (info->flags & VM_LOCKED)
  		goto redirty;

  	if (!total_swap_pages)

  		goto redirty;

  	/*
  	 * shmem_backing_dev_info's capabilities prevent regular writeback or
  	 * sync from ever calling shmem_writepage; but a stacking filesystem
  	 * may use the ->writepage of its underlying filesystem, in which case
  	 * tmpfs should write out to swap only in response to memory pressure,

  	 * and not for the writeback threads or sync.  However, in those cases,
  	 * we do still want to check if there's a redundant swappage to be
  	 * discarded.

  	 */
  	if (wbc->for_reclaim)
  		swap = get_swap_page();
  	else
  		swap.val = 0;

  	spin_lock(&info->lock);

  	if (index >= info->next_index) {
  		BUG_ON(!(info->flags & SHMEM_TRUNCATE));
  		goto unlock;
  	}
  	entry = shmem_swp_entry(info, index, NULL);

  	if (entry->val) {
  		/*
  		 * The more uptodate page coming down from a stacked
  		 * writepage should replace our old swappage.
  		 */
  		free_swap_and_cache(*entry);
  		shmem_swp_set(info, entry, 0);
  	}
  	shmem_recalc_inode(inode);

  	if (swap.val && add_to_swap_cache(page, swap, GFP_ATOMIC) == 0) {

  		remove_from_page_cache(page);

  		shmem_swp_set(info, entry, swap.val);
  		shmem_swp_unmap(entry);

  		if (list_empty(&info->swaplist))
  			inode = igrab(inode);
  		else
  			inode = NULL;

  		spin_unlock(&info->lock);

  		swap_shmem_alloc(swap);

  		BUG_ON(page_mapped(page));

  		page_cache_release(page);	/* pagecache ref */

  		swap_writepage(page, wbc);

  		if (inode) {
  			mutex_lock(&shmem_swaplist_mutex);
  			/* move instead of add in case we're racing */
  			list_move_tail(&info->swaplist, &shmem_swaplist);
  			mutex_unlock(&shmem_swaplist_mutex);
  			iput(inode);
  		}

  		return 0;
  	}
  
  	shmem_swp_unmap(entry);
  unlock:
  	spin_unlock(&info->lock);

  	/*
  	 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
  	 * clear SWAP_HAS_CACHE flag.
  	 */

  	swapcache_free(swap, NULL);

  redirty:
  	set_page_dirty(page);

  	if (wbc->for_reclaim)
  		return AOP_WRITEPAGE_ACTIVATE;	/* Return with page locked */
  	unlock_page(page);
  	return 0;

  }
  
  #ifdef CONFIG_NUMA

  #ifdef CONFIG_TMPFS

  static void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)

  {

  	char buffer[64];

  	if (!mpol || mpol->mode == MPOL_DEFAULT)

  		return;		/* show nothing */

  	mpol_to_str(buffer, sizeof(buffer), mpol, 1);

  
  	seq_printf(seq, ",mpol=%s", buffer);

  }

  
  static struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
  {
  	struct mempolicy *mpol = NULL;
  	if (sbinfo->mpol) {
  		spin_lock(&sbinfo->stat_lock);	/* prevent replace/use races */
  		mpol = sbinfo->mpol;
  		mpol_get(mpol);
  		spin_unlock(&sbinfo->stat_lock);
  	}
  	return mpol;
  }

  #endif /* CONFIG_TMPFS */

  static struct page *shmem_swapin(swp_entry_t entry, gfp_t gfp,
  			struct shmem_inode_info *info, unsigned long idx)

  {

  	struct mempolicy mpol, *spol;

  	struct vm_area_struct pvma;

  	struct page *page;

  	spol = mpol_cond_copy(&mpol,
  				mpol_shared_policy_lookup(&info->policy, idx));

  	/* Create a pseudo vma that just contains the policy */

  	pvma.vm_start = 0;

  	pvma.vm_pgoff = idx;

  	pvma.vm_ops = NULL;

  	pvma.vm_policy = spol;

  	page = swapin_readahead(entry, gfp, &pvma, 0);

  	return page;
  }

  static struct page *shmem_alloc_page(gfp_t gfp,
  			struct shmem_inode_info *info, unsigned long idx)

  {
  	struct vm_area_struct pvma;

  	/* Create a pseudo vma that just contains the policy */
  	pvma.vm_start = 0;

  	pvma.vm_pgoff = idx;

  	pvma.vm_ops = NULL;
  	pvma.vm_policy = mpol_shared_policy_lookup(&info->policy, idx);

  
  	/*
  	 * alloc_page_vma() will drop the shared policy reference
  	 */
  	return alloc_page_vma(gfp, &pvma, 0);

  }

  #else /* !CONFIG_NUMA */
  #ifdef CONFIG_TMPFS

  static inline void shmem_show_mpol(struct seq_file *seq, struct mempolicy *p)

  {
  }
  #endif /* CONFIG_TMPFS */

  static inline struct page *shmem_swapin(swp_entry_t entry, gfp_t gfp,
  			struct shmem_inode_info *info, unsigned long idx)

  {

  	return swapin_readahead(entry, gfp, NULL, 0);

  }

  static inline struct page *shmem_alloc_page(gfp_t gfp,
  			struct shmem_inode_info *info, unsigned long idx)

  {

  	return alloc_page(gfp);

  }

  #endif /* CONFIG_NUMA */

  #if !defined(CONFIG_NUMA) || !defined(CONFIG_TMPFS)
  static inline struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
  {
  	return NULL;
  }
  #endif

  /*
   * shmem_getpage - either get the page from swap or allocate a new one
   *
   * If we allocate a new one we do not mark it dirty. That's up to the
   * vm. If we swap it in we mark it dirty since we also free the swap
   * entry since a page cannot live in both the swap and page cache
   */
  static int shmem_getpage(struct inode *inode, unsigned long idx,
  			struct page **pagep, enum sgp_type sgp, int *type)
  {
  	struct address_space *mapping = inode->i_mapping;
  	struct shmem_inode_info *info = SHMEM_I(inode);
  	struct shmem_sb_info *sbinfo;
  	struct page *filepage = *pagep;
  	struct page *swappage;

  	struct page *prealloc_page = NULL;

  	swp_entry_t *entry;
  	swp_entry_t swap;

  	gfp_t gfp;

  	int error;
  
  	if (idx >= SHMEM_MAX_INDEX)
  		return -EFBIG;

  
  	if (type)

  		*type = 0;

  	/*
  	 * Normally, filepage is NULL on entry, and either found
  	 * uptodate immediately, or allocated and zeroed, or read
  	 * in under swappage, which is then assigned to filepage.

  	 * But shmem_readpage (required for splice) passes in a locked

  	 * filepage, which may be found not uptodate by other callers
  	 * too, and may need to be copied from the swappage read in.

  	 */
  repeat:
  	if (!filepage)
  		filepage = find_lock_page(mapping, idx);
  	if (filepage && PageUptodate(filepage))
  		goto done;

  	gfp = mapping_gfp_mask(mapping);

  	if (!filepage) {
  		/*
  		 * Try to preload while we can wait, to not make a habit of
  		 * draining atomic reserves; but don't latch on to this cpu.
  		 */
  		error = radix_tree_preload(gfp & ~__GFP_HIGHMEM);
  		if (error)
  			goto failed;
  		radix_tree_preload_end();

  		if (sgp != SGP_READ && !prealloc_page) {
  			/* We don't care if this fails */
  			prealloc_page = shmem_alloc_page(gfp, info, idx);
  			if (prealloc_page) {
  				if (mem_cgroup_cache_charge(prealloc_page,
  						current->mm, GFP_KERNEL)) {
  					page_cache_release(prealloc_page);
  					prealloc_page = NULL;
  				}
  			}
  		}

  	}

  	error = 0;

  
  	spin_lock(&info->lock);
  	shmem_recalc_inode(inode);
  	entry = shmem_swp_alloc(info, idx, sgp);
  	if (IS_ERR(entry)) {
  		spin_unlock(&info->lock);
  		error = PTR_ERR(entry);
  		goto failed;
  	}
  	swap = *entry;
  
  	if (swap.val) {
  		/* Look it up and read it in.. */
  		swappage = lookup_swap_cache(swap);
  		if (!swappage) {
  			shmem_swp_unmap(entry);

  			/* here we actually do the io */

  			if (type && !(*type & VM_FAULT_MAJOR)) {

  				__count_vm_event(PGMAJFAULT);

  				*type |= VM_FAULT_MAJOR;

  			}

  			spin_unlock(&info->lock);

  			swappage = shmem_swapin(swap, gfp, info, idx);

  			if (!swappage) {
  				spin_lock(&info->lock);
  				entry = shmem_swp_alloc(info, idx, sgp);
  				if (IS_ERR(entry))
  					error = PTR_ERR(entry);
  				else {
  					if (entry->val == swap.val)
  						error = -ENOMEM;
  					shmem_swp_unmap(entry);
  				}
  				spin_unlock(&info->lock);
  				if (error)
  					goto failed;
  				goto repeat;
  			}
  			wait_on_page_locked(swappage);
  			page_cache_release(swappage);
  			goto repeat;
  		}
  
  		/* We have to do this with page locked to prevent races */

  		if (!trylock_page(swappage)) {

  			shmem_swp_unmap(entry);
  			spin_unlock(&info->lock);
  			wait_on_page_locked(swappage);
  			page_cache_release(swappage);
  			goto repeat;
  		}
  		if (PageWriteback(swappage)) {
  			shmem_swp_unmap(entry);
  			spin_unlock(&info->lock);
  			wait_on_page_writeback(swappage);
  			unlock_page(swappage);
  			page_cache_release(swappage);
  			goto repeat;
  		}
  		if (!PageUptodate(swappage)) {
  			shmem_swp_unmap(entry);
  			spin_unlock(&info->lock);
  			unlock_page(swappage);
  			page_cache_release(swappage);
  			error = -EIO;
  			goto failed;
  		}
  
  		if (filepage) {
  			shmem_swp_set(info, entry, 0);
  			shmem_swp_unmap(entry);
  			delete_from_swap_cache(swappage);
  			spin_unlock(&info->lock);
  			copy_highpage(filepage, swappage);
  			unlock_page(swappage);
  			page_cache_release(swappage);
  			flush_dcache_page(filepage);
  			SetPageUptodate(filepage);
  			set_page_dirty(filepage);
  			swap_free(swap);

  		} else if (!(error = add_to_page_cache_locked(swappage, mapping,
  					idx, GFP_NOWAIT))) {

  			info->flags |= SHMEM_PAGEIN;
  			shmem_swp_set(info, entry, 0);
  			shmem_swp_unmap(entry);

  			delete_from_swap_cache(swappage);

  			spin_unlock(&info->lock);
  			filepage = swappage;

  			set_page_dirty(filepage);

  			swap_free(swap);
  		} else {
  			shmem_swp_unmap(entry);
  			spin_unlock(&info->lock);

  			if (error == -ENOMEM) {

  				/*
  				 * reclaim from proper memory cgroup and
  				 * call memcg's OOM if needed.
  				 */
  				error = mem_cgroup_shmem_charge_fallback(
  								swappage,

  								current->mm,

  								gfp);

  				if (error) {
  					unlock_page(swappage);
  					page_cache_release(swappage);

  					goto failed;

  				}

  			}

  			unlock_page(swappage);
  			page_cache_release(swappage);

  			goto repeat;
  		}
  	} else if (sgp == SGP_READ && !filepage) {
  		shmem_swp_unmap(entry);
  		filepage = find_get_page(mapping, idx);
  		if (filepage &&

  		    (!PageUptodate(filepage) || !trylock_page(filepage))) {

  			spin_unlock(&info->lock);
  			wait_on_page_locked(filepage);
  			page_cache_release(filepage);
  			filepage = NULL;
  			goto repeat;
  		}
  		spin_unlock(&info->lock);
  	} else {
  		shmem_swp_unmap(entry);
  		sbinfo = SHMEM_SB(inode->i_sb);

  		if (sbinfo->max_blocks) {

  			if ((percpu_counter_compare(&sbinfo->used_blocks, sbinfo->max_blocks) > 0) ||

  			    shmem_acct_block(info->flags)) {

  				spin_unlock(&info->lock);
  				error = -ENOSPC;
  				goto failed;
  			}

  			percpu_counter_inc(&sbinfo->used_blocks);
  			spin_lock(&inode->i_lock);

  			inode->i_blocks += BLOCKS_PER_PAGE;

  			spin_unlock(&inode->i_lock);

  		} else if (shmem_acct_block(info->flags)) {
  			spin_unlock(&info->lock);
  			error = -ENOSPC;
  			goto failed;
  		}
  
  		if (!filepage) {

  			int ret;

  			if (!prealloc_page) {
  				spin_unlock(&info->lock);
  				filepage = shmem_alloc_page(gfp, info, idx);
  				if (!filepage) {
  					shmem_unacct_blocks(info->flags, 1);
  					shmem_free_blocks(inode, 1);
  					error = -ENOMEM;
  					goto failed;
  				}
  				SetPageSwapBacked(filepage);

  				/*
  				 * Precharge page while we can wait, compensate
  				 * after
  				 */
  				error = mem_cgroup_cache_charge(filepage,
  					current->mm, GFP_KERNEL);
  				if (error) {
  					page_cache_release(filepage);
  					shmem_unacct_blocks(info->flags, 1);
  					shmem_free_blocks(inode, 1);
  					filepage = NULL;
  					goto failed;
  				}
  
  				spin_lock(&info->lock);
  			} else {
  				filepage = prealloc_page;
  				prealloc_page = NULL;
  				SetPageSwapBacked(filepage);

  			}

  			entry = shmem_swp_alloc(info, idx, sgp);
  			if (IS_ERR(entry))
  				error = PTR_ERR(entry);
  			else {
  				swap = *entry;
  				shmem_swp_unmap(entry);
  			}

  			ret = error || swap.val;
  			if (ret)
  				mem_cgroup_uncharge_cache_page(filepage);
  			else
  				ret = add_to_page_cache_lru(filepage, mapping,
  						idx, GFP_NOWAIT);
  			/*
  			 * At add_to_page_cache_lru() failure, uncharge will
  			 * be done automatically.
  			 */
  			if (ret) {

  				spin_unlock(&info->lock);
  				page_cache_release(filepage);
  				shmem_unacct_blocks(info->flags, 1);
  				shmem_free_blocks(inode, 1);
  				filepage = NULL;
  				if (error)
  					goto failed;
  				goto repeat;
  			}
  			info->flags |= SHMEM_PAGEIN;
  		}
  
  		info->alloced++;
  		spin_unlock(&info->lock);

  		clear_highpage(filepage);

  		flush_dcache_page(filepage);
  		SetPageUptodate(filepage);

  		if (sgp == SGP_DIRTY)
  			set_page_dirty(filepage);

  	}
  done:

  	*pagep = filepage;

  	error = 0;
  	goto out;

  
  failed:
  	if (*pagep != filepage) {
  		unlock_page(filepage);
  		page_cache_release(filepage);
  	}

  out:
  	if (prealloc_page) {
  		mem_cgroup_uncharge_cache_page(prealloc_page);
  		page_cache_release(prealloc_page);
  	}

  	return error;
  }

  static int shmem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)

  {

  	struct inode *inode = vma->vm_file->f_path.dentry->d_inode;

  	int error;

  	int ret;

  	if (((loff_t)vmf->pgoff << PAGE_CACHE_SHIFT) >= i_size_read(inode))
  		return VM_FAULT_SIGBUS;

  	error = shmem_getpage(inode, vmf->pgoff, &vmf->page, SGP_CACHE, &ret);

  	if (error)
  		return ((error == -ENOMEM) ? VM_FAULT_OOM : VM_FAULT_SIGBUS);

  	return ret | VM_FAULT_LOCKED;

  }

  #ifdef CONFIG_NUMA

  static int shmem_set_policy(struct vm_area_struct *vma, struct mempolicy *new)

  {

  	struct inode *i = vma->vm_file->f_path.dentry->d_inode;

  	return mpol_set_shared_policy(&SHMEM_I(i)->policy, vma, new);
  }

  static struct mempolicy *shmem_get_policy(struct vm_area_struct *vma,
  					  unsigned long addr)

  {

  	struct inode *i = vma->vm_file->f_path.dentry->d_inode;

  	unsigned long idx;
  
  	idx = ((addr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
  	return mpol_shared_policy_lookup(&SHMEM_I(i)->policy, idx);
  }
  #endif
  
  int shmem_lock(struct file *file, int lock, struct user_struct *user)
  {

  	struct inode *inode = file->f_path.dentry->d_inode;

  	struct shmem_inode_info *info = SHMEM_I(inode);
  	int retval = -ENOMEM;
  
  	spin_lock(&info->lock);
  	if (lock && !(info->flags & VM_LOCKED)) {
  		if (!user_shm_lock(inode->i_size, user))
  			goto out_nomem;
  		info->flags |= VM_LOCKED;

  		mapping_set_unevictable(file->f_mapping);

  	}
  	if (!lock && (info->flags & VM_LOCKED) && user) {
  		user_shm_unlock(inode->i_size, user);
  		info->flags &= ~VM_LOCKED;

  		mapping_clear_unevictable(file->f_mapping);
  		scan_mapping_unevictable_pages(file->f_mapping);

  	}
  	retval = 0;

  out_nomem:
  	spin_unlock(&info->lock);
  	return retval;
  }

  static int shmem_mmap(struct file *file, struct vm_area_struct *vma)

  {
  	file_accessed(file);
  	vma->vm_ops = &shmem_vm_ops;

  	vma->vm_flags |= VM_CAN_NONLINEAR;

  	return 0;
  }

  static struct inode *shmem_get_inode(struct super_block *sb, const struct inode *dir,
  				     int mode, dev_t dev, unsigned long flags)

  {
  	struct inode *inode;
  	struct shmem_inode_info *info;
  	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);

  	if (shmem_reserve_inode(sb))
  		return NULL;

  
  	inode = new_inode(sb);
  	if (inode) {

  		inode_init_owner(inode, dir, mode);

  		inode->i_blocks = 0;

  		inode->i_mapping->backing_dev_info = &shmem_backing_dev_info;
  		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;

  		inode->i_generation = get_seconds();

  		info = SHMEM_I(inode);
  		memset(info, 0, (char *)inode - (char *)info);
  		spin_lock_init(&info->lock);

  		info->flags = flags & VM_NORESERVE;

  		INIT_LIST_HEAD(&info->swaplist);

  		cache_no_acl(inode);

  
  		switch (mode & S_IFMT) {
  		default:

  			inode->i_op = &shmem_special_inode_operations;

  			init_special_inode(inode, mode, dev);
  			break;
  		case S_IFREG:

  			inode->i_mapping->a_ops = &shmem_aops;

  			inode->i_op = &shmem_inode_operations;
  			inode->i_fop = &shmem_file_operations;

  			mpol_shared_policy_init(&info->policy,
  						 shmem_get_sbmpol(sbinfo));

  			break;
  		case S_IFDIR:

  			inc_nlink(inode);

  			/* Some things misbehave if size == 0 on a directory */
  			inode->i_size = 2 * BOGO_DIRENT_SIZE;
  			inode->i_op = &shmem_dir_inode_operations;
  			inode->i_fop = &simple_dir_operations;
  			break;
  		case S_IFLNK:
  			/*
  			 * Must not load anything in the rbtree,
  			 * mpol_free_shared_policy will not be called.
  			 */

  			mpol_shared_policy_init(&info->policy, NULL);

  			break;
  		}

  	} else
  		shmem_free_inode(sb);

  	return inode;
  }
  
  #ifdef CONFIG_TMPFS

  static const struct inode_operations shmem_symlink_inode_operations;
  static const struct inode_operations shmem_symlink_inline_operations;

  
  /*

   * Normally tmpfs avoids the use of shmem_readpage and shmem_write_begin;

   * but providing them allows a tmpfs file to be used for splice, sendfile, and
   * below the loop driver, in the generic fashion that many filesystems support.

   */

  static int shmem_readpage(struct file *file, struct page *page)
  {
  	struct inode *inode = page->mapping->host;
  	int error = shmem_getpage(inode, page->index, &page, SGP_CACHE, NULL);
  	unlock_page(page);
  	return error;
  }

  static int

  shmem_write_begin(struct file *file, struct address_space *mapping,
  			loff_t pos, unsigned len, unsigned flags,
  			struct page **pagep, void **fsdata)

  {

  	struct inode *inode = mapping->host;
  	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
  	*pagep = NULL;
  	return shmem_getpage(inode, index, pagep, SGP_WRITE, NULL);
  }
  
  static int
  shmem_write_end(struct file *file, struct address_space *mapping,
  			loff_t pos, unsigned len, unsigned copied,
  			struct page *page, void *fsdata)
  {
  	struct inode *inode = mapping->host;

  	if (pos + copied > inode->i_size)
  		i_size_write(inode, pos + copied);

  	set_page_dirty(page);

  	unlock_page(page);

  	page_cache_release(page);

  	return copied;

  }

  static void do_shmem_file_read(struct file *filp, loff_t *ppos, read_descriptor_t *desc, read_actor_t actor)
  {

  	struct inode *inode = filp->f_path.dentry->d_inode;

  	struct address_space *mapping = inode->i_mapping;
  	unsigned long index, offset;

  	enum sgp_type sgp = SGP_READ;
  
  	/*
  	 * Might this read be for a stacking filesystem?  Then when reading
  	 * holes of a sparse file, we actually need to allocate those pages,
  	 * and even mark them dirty, so it cannot exceed the max_blocks limit.
  	 */
  	if (segment_eq(get_fs(), KERNEL_DS))
  		sgp = SGP_DIRTY;

  
  	index = *ppos >> PAGE_CACHE_SHIFT;
  	offset = *ppos & ~PAGE_CACHE_MASK;
  
  	for (;;) {
  		struct page *page = NULL;
  		unsigned long end_index, nr, ret;
  		loff_t i_size = i_size_read(inode);
  
  		end_index = i_size >> PAGE_CACHE_SHIFT;
  		if (index > end_index)
  			break;
  		if (index == end_index) {
  			nr = i_size & ~PAGE_CACHE_MASK;
  			if (nr <= offset)
  				break;
  		}

  		desc->error = shmem_getpage(inode, index, &page, sgp, NULL);

  		if (desc->error) {
  			if (desc->error == -EINVAL)
  				desc->error = 0;
  			break;
  		}

  		if (page)
  			unlock_page(page);

  
  		/*
  		 * We must evaluate after, since reads (unlike writes)

  		 * are called without i_mutex protection against truncate

  		 */
  		nr = PAGE_CACHE_SIZE;
  		i_size = i_size_read(inode);
  		end_index = i_size >> PAGE_CACHE_SHIFT;
  		if (index == end_index) {
  			nr = i_size & ~PAGE_CACHE_MASK;
  			if (nr <= offset) {
  				if (page)
  					page_cache_release(page);
  				break;
  			}
  		}
  		nr -= offset;
  
  		if (page) {
  			/*
  			 * If users can be writing to this page using arbitrary
  			 * virtual addresses, take care about potential aliasing
  			 * before reading the page on the kernel side.
  			 */
  			if (mapping_writably_mapped(mapping))
  				flush_dcache_page(page);
  			/*
  			 * Mark the page accessed if we read the beginning.
  			 */
  			if (!offset)
  				mark_page_accessed(page);

  		} else {

  			page = ZERO_PAGE(0);

  			page_cache_get(page);
  		}

  
  		/*
  		 * Ok, we have the page, and it's up-to-date, so
  		 * now we can copy it to user space...
  		 *
  		 * The actor routine returns how many bytes were actually used..
  		 * NOTE! This may not be the same as how much of a user buffer
  		 * we filled up (we may be padding etc), so we can only update
  		 * "pos" here (the actor routine has to update the user buffer
  		 * pointers and the remaining count).
  		 */
  		ret = actor(desc, page, offset, nr);
  		offset += ret;
  		index += offset >> PAGE_CACHE_SHIFT;
  		offset &= ~PAGE_CACHE_MASK;
  
  		page_cache_release(page);
  		if (ret != nr || !desc->count)
  			break;
  
  		cond_resched();
  	}
  
  	*ppos = ((loff_t) index << PAGE_CACHE_SHIFT) + offset;
  	file_accessed(filp);
  }

  static ssize_t shmem_file_aio_read(struct kiocb *iocb,
  		const struct iovec *iov, unsigned long nr_segs, loff_t pos)
  {
  	struct file *filp = iocb->ki_filp;
  	ssize_t retval;
  	unsigned long seg;
  	size_t count;
  	loff_t *ppos = &iocb->ki_pos;
  
  	retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
  	if (retval)
  		return retval;
  
  	for (seg = 0; seg < nr_segs; seg++) {
  		read_descriptor_t desc;
  
  		desc.written = 0;
  		desc.arg.buf = iov[seg].iov_base;
  		desc.count = iov[seg].iov_len;
  		if (desc.count == 0)
  			continue;
  		desc.error = 0;
  		do_shmem_file_read(filp, ppos, &desc, file_read_actor);
  		retval += desc.written;
  		if (desc.error) {
  			retval = retval ?: desc.error;
  			break;
  		}
  		if (desc.count > 0)
  			break;
  	}
  	return retval;

  }

  static int shmem_statfs(struct dentry *dentry, struct kstatfs *buf)

  {

  	struct shmem_sb_info *sbinfo = SHMEM_SB(dentry->d_sb);

  
  	buf->f_type = TMPFS_MAGIC;
  	buf->f_bsize = PAGE_CACHE_SIZE;
  	buf->f_namelen = NAME_MAX;

  	if (sbinfo->max_blocks) {

  		buf->f_blocks = sbinfo->max_blocks;

  		buf->f_bavail = buf->f_bfree =
  				sbinfo->max_blocks - percpu_counter_sum(&sbinfo->used_blocks);

  	}
  	if (sbinfo->max_inodes) {

  		buf->f_files = sbinfo->max_inodes;
  		buf->f_ffree = sbinfo->free_inodes;

  	}
  	/* else leave those fields 0 like simple_statfs */
  	return 0;
  }
  
  /*
   * File creation. Allocate an inode, and we're done..
   */
  static int
  shmem_mknod(struct inode *dir, struct dentry *dentry, int mode, dev_t dev)
  {

  	struct inode *inode;

  	int error = -ENOSPC;

  	inode = shmem_get_inode(dir->i_sb, dir, mode, dev, VM_NORESERVE);

  	if (inode) {

  		error = security_inode_init_security(inode, dir, NULL, NULL,
  						     NULL);
  		if (error) {
  			if (error != -EOPNOTSUPP) {
  				iput(inode);
  				return error;
  			}

  		}

  #ifdef CONFIG_TMPFS_POSIX_ACL
  		error = generic_acl_init(inode, dir);

  		if (error) {
  			iput(inode);
  			return error;

  		}

  #else
  		error = 0;

  #endif

  		dir->i_size += BOGO_DIRENT_SIZE;
  		dir->i_ctime = dir->i_mtime = CURRENT_TIME;
  		d_instantiate(dentry, inode);
  		dget(dentry); /* Extra count - pin the dentry in core */

  	}
  	return error;
  }
  
  static int shmem_mkdir(struct inode *dir, struct dentry *dentry, int mode)
  {
  	int error;
  
  	if ((error = shmem_mknod(dir, dentry, mode | S_IFDIR, 0)))
  		return error;

  	inc_nlink(dir);

  	return 0;
  }
  
  static int shmem_create(struct inode *dir, struct dentry *dentry, int mode,
  		struct nameidata *nd)
  {
  	return shmem_mknod(dir, dentry, mode | S_IFREG, 0);
  }
  
  /*
   * Link a file..
   */
  static int shmem_link(struct dentry *old_dentry, struct inode *dir, struct dentry *dentry)
  {
  	struct inode *inode = old_dentry->d_inode;

  	int ret;

  
  	/*
  	 * No ordinary (disk based) filesystem counts links as inodes;
  	 * but each new link needs a new dentry, pinning lowmem, and
  	 * tmpfs dentries cannot be pruned until they are unlinked.
  	 */

  	ret = shmem_reserve_inode(inode->i_sb);
  	if (ret)
  		goto out;

  
  	dir->i_size += BOGO_DIRENT_SIZE;
  	inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;

  	inc_nlink(inode);

  	atomic_inc(&inode->i_count);	/* New dentry reference */
  	dget(dentry);		/* Extra pinning count for the created dentry */
  	d_instantiate(dentry, inode);

  out:
  	return ret;

  }
  
  static int shmem_unlink(struct inode *dir, struct dentry *dentry)
  {
  	struct inode *inode = dentry->d_inode;

  	if (inode->i_nlink > 1 && !S_ISDIR(inode->i_mode))
  		shmem_free_inode(inode->i_sb);

  
  	dir->i_size -= BOGO_DIRENT_SIZE;
  	inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;

  	drop_nlink(inode);

  	dput(dentry);	/* Undo the count from "create" - this does all the work */
  	return 0;
  }
  
  static int shmem_rmdir(struct inode *dir, struct dentry *dentry)
  {
  	if (!simple_empty(dentry))
  		return -ENOTEMPTY;

  	drop_nlink(dentry->d_inode);
  	drop_nlink(dir);

  	return shmem_unlink(dir, dentry);
  }
  
  /*
   * The VFS layer already does all the dentry stuff for rename,
   * we just have to decrement the usage count for the target if
   * it exists so that the VFS layer correctly free's it when it
   * gets overwritten.
   */
  static int shmem_rename(struct inode *old_dir, struct dentry *old_dentry, struct inode *new_dir, struct dentry *new_dentry)
  {
  	struct inode *inode = old_dentry->d_inode;
  	int they_are_dirs = S_ISDIR(inode->i_mode);
  
  	if (!simple_empty(new_dentry))
  		return -ENOTEMPTY;
  
  	if (new_dentry->d_inode) {
  		(void) shmem_unlink(new_dir, new_dentry);
  		if (they_are_dirs)

  			drop_nlink(old_dir);

  	} else if (they_are_dirs) {

  		drop_nlink(old_dir);

  		inc_nlink(new_dir);

  	}
  
  	old_dir->i_size -= BOGO_DIRENT_SIZE;
  	new_dir->i_size += BOGO_DIRENT_SIZE;
  	old_dir->i_ctime = old_dir->i_mtime =
  	new_dir->i_ctime = new_dir->i_mtime =
  	inode->i_ctime = CURRENT_TIME;
  	return 0;
  }
  
  static int shmem_symlink(struct inode *dir, struct dentry *dentry, const char *symname)
  {
  	int error;
  	int len;
  	struct inode *inode;
  	struct page *page = NULL;
  	char *kaddr;
  	struct shmem_inode_info *info;
  
  	len = strlen(symname) + 1;
  	if (len > PAGE_CACHE_SIZE)
  		return -ENAMETOOLONG;

  	inode = shmem_get_inode(dir->i_sb, dir, S_IFLNK|S_IRWXUGO, 0, VM_NORESERVE);

  	if (!inode)
  		return -ENOSPC;

  	error = security_inode_init_security(inode, dir, NULL, NULL,
  					     NULL);
  	if (error) {
  		if (error != -EOPNOTSUPP) {
  			iput(inode);
  			return error;
  		}
  		error = 0;
  	}

  	info = SHMEM_I(inode);
  	inode->i_size = len-1;
  	if (len <= (char *)inode - (char *)info) {
  		/* do it inline */
  		memcpy(info, symname, len);
  		inode->i_op = &shmem_symlink_inline_operations;
  	} else {
  		error = shmem_getpage(inode, 0, &page, SGP_WRITE, NULL);
  		if (error) {
  			iput(inode);
  			return error;
  		}

  		inode->i_mapping->a_ops = &shmem_aops;

  		inode->i_op = &shmem_symlink_inode_operations;
  		kaddr = kmap_atomic(page, KM_USER0);
  		memcpy(kaddr, symname, len);
  		kunmap_atomic(kaddr, KM_USER0);
  		set_page_dirty(page);

  		unlock_page(page);

  		page_cache_release(page);
  	}

  	dir->i_size += BOGO_DIRENT_SIZE;
  	dir->i_ctime = dir->i_mtime = CURRENT_TIME;
  	d_instantiate(dentry, inode);
  	dget(dentry);
  	return 0;
  }

  static void *shmem_follow_link_inline(struct dentry *dentry, struct nameidata *nd)

  {
  	nd_set_link(nd, (char *)SHMEM_I(dentry->d_inode));

  	return NULL;

  }

  static void *shmem_follow_link(struct dentry *dentry, struct nameidata *nd)

  {
  	struct page *page = NULL;
  	int res = shmem_getpage(dentry->d_inode, 0, &page, SGP_READ, NULL);
  	nd_set_link(nd, res ? ERR_PTR(res) : kmap(page));

  	if (page)
  		unlock_page(page);

  	return page;

  }

  static void shmem_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)

  {
  	if (!IS_ERR(nd_get_link(nd))) {

  		struct page *page = cookie;

  		kunmap(page);
  		mark_page_accessed(page);
  		page_cache_release(page);

  	}
  }

  static const struct inode_operations shmem_symlink_inline_operations = {

  	.readlink	= generic_readlink,
  	.follow_link	= shmem_follow_link_inline,

  };

  static const struct inode_operations shmem_symlink_inode_operations = {

  	.readlink	= generic_readlink,
  	.follow_link	= shmem_follow_link,
  	.put_link	= shmem_put_link,

  };

  #ifdef CONFIG_TMPFS_POSIX_ACL

  /*

   * Superblocks without xattr inode operations will get security.* xattr
   * support from the VFS "for free". As soon as we have any other xattrs
   * like ACLs, we also need to implement the security.* handlers at
   * filesystem level, though.
   */

  static size_t shmem_xattr_security_list(struct dentry *dentry, char *list,

  					size_t list_len, const char *name,

  					size_t name_len, int handler_flags)

  {

  	return security_inode_listsecurity(dentry->d_inode, list, list_len);

  }

  static int shmem_xattr_security_get(struct dentry *dentry, const char *name,
  		void *buffer, size_t size, int handler_flags)

  {
  	if (strcmp(name, "") == 0)
  		return -EINVAL;

  	return xattr_getsecurity(dentry->d_inode, name, buffer, size);

  }

  static int shmem_xattr_security_set(struct dentry *dentry, const char *name,
  		const void *value, size_t size, int flags, int handler_flags)

  {
  	if (strcmp(name, "") == 0)
  		return -EINVAL;

  	return security_inode_setsecurity(dentry->d_inode, name, value,
  					  size, flags);

  }

  static const struct xattr_handler shmem_xattr_security_handler = {

  	.prefix = XATTR_SECURITY_PREFIX,
  	.list   = shmem_xattr_security_list,
  	.get    = shmem_xattr_security_get,
  	.set    = shmem_xattr_security_set,
  };

  static const struct xattr_handler *shmem_xattr_handlers[] = {

  	&generic_acl_access_handler,
  	&generic_acl_default_handler,

  	&shmem_xattr_security_handler,
  	NULL
  };
  #endif

  static struct dentry *shmem_get_parent(struct dentry *child)
  {
  	return ERR_PTR(-ESTALE);
  }
  
  static int shmem_match(struct inode *ino, void *vfh)
  {
  	__u32 *fh = vfh;
  	__u64 inum = fh[2];
  	inum = (inum << 32) | fh[1];
  	return ino->i_ino == inum && fh[0] == ino->i_generation;
  }

  static struct dentry *shmem_fh_to_dentry(struct super_block *sb,
  		struct fid *fid, int fh_len, int fh_type)

  {

  	struct inode *inode;

  	struct dentry *dentry = NULL;
  	u64 inum = fid->raw[2];
  	inum = (inum << 32) | fid->raw[1];
  
  	if (fh_len < 3)
  		return NULL;

  	inode = ilookup5(sb, (unsigned long)(inum + fid->raw[0]),
  			shmem_match, fid->raw);

  	if (inode) {

  		dentry = d_find_alias(inode);

  		iput(inode);
  	}

  	return dentry;

  }
  
  static int shmem_encode_fh(struct dentry *dentry, __u32 *fh, int *len,
  				int connectable)
  {
  	struct inode *inode = dentry->d_inode;
  
  	if (*len < 3)
  		return 255;
  
  	if (hlist_unhashed(&inode->i_hash)) {
  		/* Unfortunately insert_inode_hash is not idempotent,
  		 * so as we hash inodes here rather than at creation
  		 * time, we need a lock to ensure we only try
  		 * to do it once
  		 */
  		static DEFINE_SPINLOCK(lock);
  		spin_lock(&lock);
  		if (hlist_unhashed(&inode->i_hash))
  			__insert_inode_hash(inode,
  					    inode->i_ino + inode->i_generation);
  		spin_unlock(&lock);
  	}
  
  	fh[0] = inode->i_generation;
  	fh[1] = inode->i_ino;
  	fh[2] = ((__u64)inode->i_ino) >> 32;
  
  	*len = 3;
  	return 1;
  }

  static const struct export_operations shmem_export_ops = {

  	.get_parent     = shmem_get_parent,

  	.encode_fh      = shmem_encode_fh,

  	.fh_to_dentry	= shmem_fh_to_dentry,

  };

  static int shmem_parse_options(char *options, struct shmem_sb_info *sbinfo,
  			       bool remount)

  {
  	char *this_char, *value, *rest;

  	while (options != NULL) {
  		this_char = options;
  		for (;;) {
  			/*
  			 * NUL-terminate this option: unfortunately,
  			 * mount options form a comma-separated list,
  			 * but mpol's nodelist may also contain commas.
  			 */
  			options = strchr(options, ',');
  			if (options == NULL)
  				break;
  			options++;
  			if (!isdigit(*options)) {
  				options[-1] = '\0';
  				break;
  			}
  		}

  		if (!*this_char)
  			continue;
  		if ((value = strchr(this_char,'=')) != NULL) {
  			*value++ = 0;
  		} else {
  			printk(KERN_ERR
  			    "tmpfs: No value for mount option '%s'
  ",
  			    this_char);
  			return 1;
  		}
  
  		if (!strcmp(this_char,"size")) {
  			unsigned long long size;
  			size = memparse(value,&rest);
  			if (*rest == '%') {
  				size <<= PAGE_SHIFT;
  				size *= totalram_pages;
  				do_div(size, 100);
  				rest++;
  			}
  			if (*rest)
  				goto bad_val;

  			sbinfo->max_blocks =
  				DIV_ROUND_UP(size, PAGE_CACHE_SIZE);

  		} else if (!strcmp(this_char,"nr_blocks")) {

  			sbinfo->max_blocks = memparse(value, &rest);

  			if (*rest)
  				goto bad_val;
  		} else if (!strcmp(this_char,"nr_inodes")) {

  			sbinfo->max_inodes = memparse(value, &rest);

  			if (*rest)
  				goto bad_val;
  		} else if (!strcmp(this_char,"mode")) {

  			if (remount)

  				continue;

  			sbinfo->mode = simple_strtoul(value, &rest, 8) & 07777;

  			if (*rest)
  				goto bad_val;
  		} else if (!strcmp(this_char,"uid")) {

  			if (remount)

  				continue;

  			sbinfo->uid = simple_strtoul(value, &rest, 0);

  			if (*rest)
  				goto bad_val;
  		} else if (!strcmp(this_char,"gid")) {

  			if (remount)

  				continue;

  			sbinfo->gid = simple_strtoul(value, &rest, 0);

  			if (*rest)
  				goto bad_val;

  		} else if (!strcmp(this_char,"mpol")) {

  			if (mpol_parse_str(value, &sbinfo->mpol, 1))

  				goto bad_val;

  		} else {
  			printk(KERN_ERR "tmpfs: Bad mount option %s
  ",
  			       this_char);
  			return 1;
  		}
  	}
  	return 0;
  
  bad_val:
  	printk(KERN_ERR "tmpfs: Bad value '%s' for mount option '%s'
  ",
  	       value, this_char);
  	return 1;
  
  }
  
  static int shmem_remount_fs(struct super_block *sb, int *flags, char *data)
  {
  	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);

  	struct shmem_sb_info config = *sbinfo;

  	unsigned long inodes;
  	int error = -EINVAL;

  	if (shmem_parse_options(data, &config, true))

  		return error;

  	spin_lock(&sbinfo->stat_lock);

  	inodes = sbinfo->max_inodes - sbinfo->free_inodes;

  	if (percpu_counter_compare(&sbinfo->used_blocks, config.max_blocks) > 0)

  		goto out;

  	if (config.max_inodes < inodes)

  		goto out;
  	/*
  	 * Those tests also disallow limited->unlimited while any are in
  	 * use, so i_blocks will always be zero when max_blocks is zero;
  	 * but we must separately disallow unlimited->limited, because
  	 * in that case we have no record of how much is already in use.
  	 */

  	if (config.max_blocks && !sbinfo->max_blocks)

  		goto out;

  	if (config.max_inodes && !sbinfo->max_inodes)

  		goto out;
  
  	error = 0;

  	sbinfo->max_blocks  = config.max_blocks;

  	sbinfo->max_inodes  = config.max_inodes;
  	sbinfo->free_inodes = config.max_inodes - inodes;

  
  	mpol_put(sbinfo->mpol);
  	sbinfo->mpol        = config.mpol;	/* transfers initial ref */

  out:
  	spin_unlock(&sbinfo->stat_lock);
  	return error;

  }