/*
   * 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) 2002-2011 Hugh Dickins.
   * Copyright (C) 2011 Google Inc.

   * 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/export.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/pagevec.h>

  #include <linux/percpu_counter.h>

  #include <linux/splice.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/pgtable.h>

  #define BLOCKS_PER_PAGE  (PAGE_CACHE_SIZE/512)

  #define VM_ACCT(size)    (PAGE_CACHE_ALIGN(size) >> PAGE_SHIFT)

  /* Pretend that each entry is of this size in directory's i_size */
  #define BOGO_DIRENT_SIZE 20

  /* Symlink up to this size is kmalloc'ed instead of using a swappable page */
  #define SHORT_SYMLINK_LEN 128

  struct shmem_xattr {
  	struct list_head list;	/* anchored by shmem_inode_info->xattr_list */
  	char *name;		/* xattr name */
  	size_t size;
  	char value[0];
  };

  /* Flag allocation requirements to shmem_getpage */

  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_gfp(struct inode *inode, pgoff_t index,
  	struct page **pagep, enum sgp_type sgp, gfp_t gfp, int *fault_type);
  
  static inline int shmem_getpage(struct inode *inode, pgoff_t index,
  	struct page **pagep, enum sgp_type sgp, int *fault_type)
  {
  	return shmem_getpage_gfp(inode, index, pagep, sgp,
  			mapping_gfp_mask(inode->i_mapping), fault_type);
  }

  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_mm(current->mm, 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_mm(current->mm, 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,

  };
  
  static LIST_HEAD(shmem_swaplist);

  static DEFINE_MUTEX(shmem_swaplist_mutex);

  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 block usage 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) {

  		struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
  		if (sbinfo->max_blocks)
  			percpu_counter_add(&sbinfo->used_blocks, -freed);

  		info->alloced -= freed;

  		inode->i_blocks -= freed * BLOCKS_PER_PAGE;

  		shmem_unacct_blocks(info->flags, freed);

  	}
  }

  /*
   * Replace item expected in radix tree by a new item, while holding tree lock.
   */
  static int shmem_radix_tree_replace(struct address_space *mapping,
  			pgoff_t index, void *expected, void *replacement)
  {
  	void **pslot;
  	void *item = NULL;
  
  	VM_BUG_ON(!expected);
  	pslot = radix_tree_lookup_slot(&mapping->page_tree, index);
  	if (pslot)
  		item = radix_tree_deref_slot_protected(pslot,
  							&mapping->tree_lock);
  	if (item != expected)
  		return -ENOENT;
  	if (replacement)
  		radix_tree_replace_slot(pslot, replacement);
  	else
  		radix_tree_delete(&mapping->page_tree, index);
  	return 0;
  }
  
  /*

   * Like add_to_page_cache_locked, but error if expected item has gone.
   */
  static int shmem_add_to_page_cache(struct page *page,
  				   struct address_space *mapping,
  				   pgoff_t index, gfp_t gfp, void *expected)
  {

  	int error = 0;

  
  	VM_BUG_ON(!PageLocked(page));
  	VM_BUG_ON(!PageSwapBacked(page));

  	if (!expected)
  		error = radix_tree_preload(gfp & GFP_RECLAIM_MASK);
  	if (!error) {
  		page_cache_get(page);
  		page->mapping = mapping;
  		page->index = index;
  
  		spin_lock_irq(&mapping->tree_lock);
  		if (!expected)
  			error = radix_tree_insert(&mapping->page_tree,
  							index, page);
  		else
  			error = shmem_radix_tree_replace(mapping, index,
  							expected, page);
  		if (!error) {
  			mapping->nrpages++;
  			__inc_zone_page_state(page, NR_FILE_PAGES);
  			__inc_zone_page_state(page, NR_SHMEM);
  			spin_unlock_irq(&mapping->tree_lock);
  		} else {
  			page->mapping = NULL;
  			spin_unlock_irq(&mapping->tree_lock);
  			page_cache_release(page);
  		}
  		if (!expected)
  			radix_tree_preload_end();
  	}
  	if (error)
  		mem_cgroup_uncharge_cache_page(page);

  	return error;
  }
  
  /*

   * Like delete_from_page_cache, but substitutes swap for page.
   */
  static void shmem_delete_from_page_cache(struct page *page, void *radswap)
  {
  	struct address_space *mapping = page->mapping;
  	int error;
  
  	spin_lock_irq(&mapping->tree_lock);
  	error = shmem_radix_tree_replace(mapping, page->index, page, radswap);
  	page->mapping = NULL;
  	mapping->nrpages--;
  	__dec_zone_page_state(page, NR_FILE_PAGES);
  	__dec_zone_page_state(page, NR_SHMEM);
  	spin_unlock_irq(&mapping->tree_lock);
  	page_cache_release(page);
  	BUG_ON(error);
  }
  
  /*

   * Like find_get_pages, but collecting swap entries as well as pages.
   */
  static unsigned shmem_find_get_pages_and_swap(struct address_space *mapping,
  					pgoff_t start, unsigned int nr_pages,
  					struct page **pages, pgoff_t *indices)
  {
  	unsigned int i;
  	unsigned int ret;
  	unsigned int nr_found;
  
  	rcu_read_lock();
  restart:
  	nr_found = radix_tree_gang_lookup_slot(&mapping->page_tree,
  				(void ***)pages, indices, start, nr_pages);
  	ret = 0;
  	for (i = 0; i < nr_found; i++) {
  		struct page *page;
  repeat:
  		page = radix_tree_deref_slot((void **)pages[i]);
  		if (unlikely(!page))
  			continue;
  		if (radix_tree_exception(page)) {

  			if (radix_tree_deref_retry(page))
  				goto restart;
  			/*
  			 * Otherwise, we must be storing a swap entry
  			 * here as an exceptional entry: so return it
  			 * without attempting to raise page count.
  			 */
  			goto export;

  		}
  		if (!page_cache_get_speculative(page))
  			goto repeat;
  
  		/* Has the page moved? */
  		if (unlikely(page != *((void **)pages[i]))) {
  			page_cache_release(page);
  			goto repeat;
  		}
  export:
  		indices[ret] = indices[i];
  		pages[ret] = page;
  		ret++;
  	}
  	if (unlikely(!ret && nr_found))
  		goto restart;
  	rcu_read_unlock();
  	return ret;
  }
  
  /*
   * Remove swap entry from radix tree, free the swap and its page cache.
   */
  static int shmem_free_swap(struct address_space *mapping,
  			   pgoff_t index, void *radswap)
  {
  	int error;
  
  	spin_lock_irq(&mapping->tree_lock);
  	error = shmem_radix_tree_replace(mapping, index, radswap, NULL);
  	spin_unlock_irq(&mapping->tree_lock);
  	if (!error)
  		free_swap_and_cache(radix_to_swp_entry(radswap));
  	return error;
  }
  
  /*
   * Pagevec may contain swap entries, so shuffle up pages before releasing.
   */

  static void shmem_deswap_pagevec(struct pagevec *pvec)

  {
  	int i, j;
  
  	for (i = 0, j = 0; i < pagevec_count(pvec); i++) {
  		struct page *page = pvec->pages[i];
  		if (!radix_tree_exceptional_entry(page))
  			pvec->pages[j++] = page;
  	}
  	pvec->nr = j;

  }
  
  /*
   * SysV IPC SHM_UNLOCK restore Unevictable pages to their evictable lists.
   */
  void shmem_unlock_mapping(struct address_space *mapping)
  {
  	struct pagevec pvec;
  	pgoff_t indices[PAGEVEC_SIZE];
  	pgoff_t index = 0;
  
  	pagevec_init(&pvec, 0);
  	/*
  	 * Minor point, but we might as well stop if someone else SHM_LOCKs it.
  	 */
  	while (!mapping_unevictable(mapping)) {
  		/*
  		 * Avoid pagevec_lookup(): find_get_pages() returns 0 as if it
  		 * has finished, if it hits a row of PAGEVEC_SIZE swap entries.
  		 */
  		pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
  					PAGEVEC_SIZE, pvec.pages, indices);
  		if (!pvec.nr)
  			break;
  		index = indices[pvec.nr - 1] + 1;
  		shmem_deswap_pagevec(&pvec);
  		check_move_unevictable_pages(pvec.pages, pvec.nr);
  		pagevec_release(&pvec);
  		cond_resched();
  	}

  }
  
  /*
   * Remove range of pages and swap entries from radix tree, and free them.
   */

  void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)

  {

  	struct address_space *mapping = inode->i_mapping;

  	struct shmem_inode_info *info = SHMEM_I(inode);

  	pgoff_t start = (lstart + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;

  	unsigned partial = lstart & (PAGE_CACHE_SIZE - 1);

  	pgoff_t end = (lend >> PAGE_CACHE_SHIFT);

  	struct pagevec pvec;

  	pgoff_t indices[PAGEVEC_SIZE];
  	long nr_swaps_freed = 0;

  	pgoff_t index;

  	int i;
  
  	BUG_ON((lend & (PAGE_CACHE_SIZE - 1)) != (PAGE_CACHE_SIZE - 1));
  
  	pagevec_init(&pvec, 0);
  	index = start;

  	while (index <= end) {
  		pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
  			min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1,
  							pvec.pages, indices);
  		if (!pvec.nr)
  			break;

  		mem_cgroup_uncharge_start();
  		for (i = 0; i < pagevec_count(&pvec); i++) {
  			struct page *page = pvec.pages[i];

  			index = indices[i];

  			if (index > end)
  				break;

  			if (radix_tree_exceptional_entry(page)) {
  				nr_swaps_freed += !shmem_free_swap(mapping,
  								index, page);

  				continue;

  			}
  
  			if (!trylock_page(page))

  				continue;

  			if (page->mapping == mapping) {
  				VM_BUG_ON(PageWriteback(page));
  				truncate_inode_page(mapping, page);

  			}

  			unlock_page(page);
  		}

  		shmem_deswap_pagevec(&pvec);
  		pagevec_release(&pvec);

  		mem_cgroup_uncharge_end();
  		cond_resched();
  		index++;
  	}

  	if (partial) {
  		struct page *page = NULL;
  		shmem_getpage(inode, start - 1, &page, SGP_READ, NULL);
  		if (page) {
  			zero_user_segment(page, partial, PAGE_CACHE_SIZE);
  			set_page_dirty(page);
  			unlock_page(page);
  			page_cache_release(page);
  		}
  	}
  
  	index = start;
  	for ( ; ; ) {
  		cond_resched();

  		pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
  			min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1,
  							pvec.pages, indices);
  		if (!pvec.nr) {

  			if (index == start)
  				break;
  			index = start;
  			continue;
  		}

  		if (index == start && indices[0] > end) {

  			shmem_deswap_pagevec(&pvec);
  			pagevec_release(&pvec);

  			break;
  		}
  		mem_cgroup_uncharge_start();
  		for (i = 0; i < pagevec_count(&pvec); i++) {
  			struct page *page = pvec.pages[i];

  			index = indices[i];

  			if (index > end)
  				break;

  			if (radix_tree_exceptional_entry(page)) {
  				nr_swaps_freed += !shmem_free_swap(mapping,
  								index, page);
  				continue;
  			}

  			lock_page(page);

  			if (page->mapping == mapping) {
  				VM_BUG_ON(PageWriteback(page));
  				truncate_inode_page(mapping, page);
  			}

  			unlock_page(page);
  		}

  		shmem_deswap_pagevec(&pvec);
  		pagevec_release(&pvec);

  		mem_cgroup_uncharge_end();
  		index++;
  	}

  	spin_lock(&info->lock);

  	info->swapped -= nr_swaps_freed;

  	shmem_recalc_inode(inode);
  	spin_unlock(&info->lock);

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

  }

  EXPORT_SYMBOL_GPL(shmem_truncate_range);

  static int shmem_setattr(struct dentry *dentry, struct iattr *attr)

  {
  	struct inode *inode = dentry->d_inode;

  	int error;

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

  	if (S_ISREG(inode->i_mode) && (attr->ia_valid & ATTR_SIZE)) {
  		loff_t oldsize = inode->i_size;
  		loff_t newsize = attr->ia_size;

  		if (newsize != oldsize) {
  			i_size_write(inode, newsize);
  			inode->i_ctime = inode->i_mtime = CURRENT_TIME;
  		}
  		if (newsize < oldsize) {
  			loff_t holebegin = round_up(newsize, PAGE_SIZE);
  			unmap_mapping_range(inode->i_mapping, holebegin, 0, 1);
  			shmem_truncate_range(inode, newsize, (loff_t)-1);
  			/* unmap again to remove racily COWed private pages */
  			unmap_mapping_range(inode->i_mapping, holebegin, 0, 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);

  	struct shmem_xattr *xattr, *nxattr;

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

  		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);

  		}

  	} else
  		kfree(info->symlink);

  
  	list_for_each_entry_safe(xattr, nxattr, &info->xattr_list, list) {
  		kfree(xattr->name);
  		kfree(xattr);
  	}

  	BUG_ON(inode->i_blocks);

  	shmem_free_inode(inode->i_sb);

  	clear_inode(inode);

  }

  /*
   * If swap found in inode, free it and move page from swapcache to filecache.
   */

  static int shmem_unuse_inode(struct shmem_inode_info *info,
  			     swp_entry_t swap, struct page *page)

  {

  	struct address_space *mapping = info->vfs_inode.i_mapping;

  	void *radswap;

  	pgoff_t index;

  	int error;

  	radswap = swp_to_radix_entry(swap);

  	index = radix_tree_locate_item(&mapping->page_tree, radswap);

  	if (index == -1)

  		return 0;

  	/*
  	 * 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.

  	 */
  	if (shmem_swaplist.next != &info->swaplist)
  		list_move_tail(&shmem_swaplist, &info->swaplist);

  	/*

  	 * We rely on shmem_swaplist_mutex, not only to protect the swaplist,
  	 * but also to hold up shmem_evict_inode(): so inode cannot be freed
  	 * beneath us (pagelock doesn't help until the page is in pagecache).

  	 */

  	error = shmem_add_to_page_cache(page, mapping, index,
  						GFP_NOWAIT, radswap);

  	/* which does mem_cgroup_uncharge_cache_page on error */

  	if (error != -ENOMEM) {

  		/*
  		 * Truncation and eviction use free_swap_and_cache(), which
  		 * only does trylock page: if we raced, best clean up here.
  		 */

  		delete_from_swap_cache(page);
  		set_page_dirty(page);

  		if (!error) {
  			spin_lock(&info->lock);
  			info->swapped--;
  			spin_unlock(&info->lock);
  			swap_free(swap);
  		}

  		error = 1;	/* not an error, but entry was found */

  	}

  	return error;

  }
  
  /*

   * Search through swapped inodes to find and replace swap by page.

   */

  int shmem_unuse(swp_entry_t swap, struct page *page)

  {

  	struct list_head *this, *next;

  	struct shmem_inode_info *info;
  	int found = 0;

  	int error;
  
  	/*
  	 * Charge page using GFP_KERNEL while we can wait, before taking
  	 * the shmem_swaplist_mutex which might hold up shmem_writepage().
  	 * Charged back to the user (not to caller) when swap account is used.

  	 */
  	error = mem_cgroup_cache_charge(page, current->mm, GFP_KERNEL);
  	if (error)
  		goto out;

  	/* No radix_tree_preload: swap entry keeps a place for page in tree */

  	mutex_lock(&shmem_swaplist_mutex);

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

  		if (info->swapped)

  			found = shmem_unuse_inode(info, swap, page);

  		else
  			list_del_init(&info->swaplist);

  		cond_resched();

  		if (found)

  			break;

  	}

  	mutex_unlock(&shmem_swaplist_mutex);

  	if (!found)
  		mem_cgroup_uncharge_cache_page(page);
  	if (found < 0)
  		error = found;
  out:

  	unlock_page(page);
  	page_cache_release(page);

  	return error;

  }
  
  /*
   * 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;

  	struct address_space *mapping;

  	struct inode *inode;

  	swp_entry_t swap;
  	pgoff_t index;

  
  	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

  	 * might use ->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.

  	 */

  	if (!wbc->for_reclaim) {
  		WARN_ON_ONCE(1);	/* Still happens? Tell us about it! */
  		goto redirty;
  	}
  	swap = get_swap_page();
  	if (!swap.val)
  		goto redirty;

  	/*
  	 * Add inode to shmem_unuse()'s list of swapped-out inodes,

  	 * if it's not already there.  Do it now before the page is
  	 * moved to swap cache, when its pagelock no longer protects

  	 * the inode from eviction.  But don't unlock the mutex until

  	 * we've incremented swapped, because shmem_unuse_inode() will
  	 * prune a !swapped inode from the swaplist under this mutex.

  	 */

  	mutex_lock(&shmem_swaplist_mutex);
  	if (list_empty(&info->swaplist))
  		list_add_tail(&info->swaplist, &shmem_swaplist);

  	if (add_to_swap_cache(page, swap, GFP_ATOMIC) == 0) {

  		swap_shmem_alloc(swap);

  		shmem_delete_from_page_cache(page, swp_to_radix_entry(swap));
  
  		spin_lock(&info->lock);
  		info->swapped++;
  		shmem_recalc_inode(inode);

  		spin_unlock(&info->lock);

  
  		mutex_unlock(&shmem_swaplist_mutex);

  		BUG_ON(page_mapped(page));

  		swap_writepage(page, wbc);

  		return 0;
  	}

  	mutex_unlock(&shmem_swaplist_mutex);

  	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 swap, gfp_t gfp,
  			struct shmem_inode_info *info, pgoff_t index)

  {

  	struct mempolicy mpol, *spol;

  	struct vm_area_struct pvma;

  	spol = mpol_cond_copy(&mpol,

  			mpol_shared_policy_lookup(&info->policy, index));

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

  	pvma.vm_start = 0;

  	pvma.vm_pgoff = index;

  	pvma.vm_ops = NULL;

  	pvma.vm_policy = spol;

  	return swapin_readahead(swap, gfp, &pvma, 0);

  }

  static struct page *shmem_alloc_page(gfp_t gfp,

  			struct shmem_inode_info *info, pgoff_t index)

  {
  	struct vm_area_struct pvma;

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

  	pvma.vm_pgoff = index;

  	pvma.vm_ops = NULL;

  	pvma.vm_policy = mpol_shared_policy_lookup(&info->policy, index);

  
  	/*
  	 * 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 *mpol)

  {
  }
  #endif /* CONFIG_TMPFS */

  static inline struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp,
  			struct shmem_inode_info *info, pgoff_t index)

  {

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

  }

  static inline struct page *shmem_alloc_page(gfp_t gfp,

  			struct shmem_inode_info *info, pgoff_t index)

  {

  	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_gfp - find page in cache, or get from swap, or allocate

   *
   * 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_gfp(struct inode *inode, pgoff_t index,

  	struct page **pagep, enum sgp_type sgp, gfp_t gfp, int *fault_type)

  {
  	struct address_space *mapping = inode->i_mapping;

  	struct shmem_inode_info *info;

  	struct shmem_sb_info *sbinfo;

  	struct page *page;

  	swp_entry_t swap;
  	int error;

  	int once = 0;

  	if (index > (MAX_LFS_FILESIZE >> PAGE_CACHE_SHIFT))

  		return -EFBIG;

  repeat:

  	swap.val = 0;

  	page = find_lock_page(mapping, index);

  	if (radix_tree_exceptional_entry(page)) {
  		swap = radix_to_swp_entry(page);
  		page = NULL;
  	}
  
  	if (sgp != SGP_WRITE &&
  	    ((loff_t)index << PAGE_CACHE_SHIFT) >= i_size_read(inode)) {
  		error = -EINVAL;
  		goto failed;
  	}
  
  	if (page || (sgp == SGP_READ && !swap.val)) {

  		/*

  		 * Once we can get the page lock, it must be uptodate:
  		 * if there were an error in reading back from swap,
  		 * the page would not be inserted into the filecache.

  		 */

  		BUG_ON(page && !PageUptodate(page));
  		*pagep = page;
  		return 0;

  	}
  
  	/*

  	 * Fast cache lookup did not find it:
  	 * bring it back from swap or allocate.

  	 */

  	info = SHMEM_I(inode);
  	sbinfo = SHMEM_SB(inode->i_sb);

  	if (swap.val) {
  		/* Look it up and read it in.. */

  		page = lookup_swap_cache(swap);
  		if (!page) {

  			/* here we actually do the io */

  			if (fault_type)
  				*fault_type |= VM_FAULT_MAJOR;

  			page = shmem_swapin(swap, gfp, info, index);

  			if (!page) {

  				error = -ENOMEM;
  				goto failed;

  			}

  		}
  
  		/* We have to do this with page locked to prevent races */

  		lock_page(page);

  		if (!PageUptodate(page)) {

  			error = -EIO;

  			goto failed;

  		}

  		wait_on_page_writeback(page);
  
  		/* Someone may have already done it for us */
  		if (page->mapping) {
  			if (page->mapping == mapping &&
  			    page->index == index)
  				goto done;
  			error = -EEXIST;
  			goto failed;

  		}

  		error = mem_cgroup_cache_charge(page, current->mm,
  						gfp & GFP_RECLAIM_MASK);
  		if (!error)
  			error = shmem_add_to_page_cache(page, mapping, index,
  						gfp, swp_to_radix_entry(swap));

  		if (error)
  			goto failed;
  
  		spin_lock(&info->lock);

  		info->swapped--;

  		shmem_recalc_inode(inode);

  		spin_unlock(&info->lock);

  
  		delete_from_swap_cache(page);

  		set_page_dirty(page);
  		swap_free(swap);

  	} else {
  		if (shmem_acct_block(info->flags)) {
  			error = -ENOSPC;
  			goto failed;

  		}

  		if (sbinfo->max_blocks) {

  			if (percpu_counter_compare(&sbinfo->used_blocks,

  						sbinfo->max_blocks) >= 0) {
  				error = -ENOSPC;
  				goto unacct;
  			}

  			percpu_counter_inc(&sbinfo->used_blocks);

  		}

  		page = shmem_alloc_page(gfp, info, index);
  		if (!page) {
  			error = -ENOMEM;
  			goto decused;

  		}

  		SetPageSwapBacked(page);
  		__set_page_locked(page);

  		error = mem_cgroup_cache_charge(page, current->mm,
  						gfp & GFP_RECLAIM_MASK);
  		if (!error)
  			error = shmem_add_to_page_cache(page, mapping, index,
  						gfp, NULL);

  		if (error)
  			goto decused;
  		lru_cache_add_anon(page);
  
  		spin_lock(&info->lock);

  		info->alloced++;

  		inode->i_blocks += BLOCKS_PER_PAGE;
  		shmem_recalc_inode(inode);

  		spin_unlock(&info->lock);

  		clear_highpage(page);
  		flush_dcache_page(page);
  		SetPageUptodate(page);

  		if (sgp == SGP_DIRTY)

  			set_page_dirty(page);

  	}
  done:

  	/* Perhaps the file has been truncated since we checked */
  	if (sgp != SGP_WRITE &&
  	    ((loff_t)index << PAGE_CACHE_SHIFT) >= i_size_read(inode)) {
  		error = -EINVAL;
  		goto trunc;

  	}

  	*pagep = page;
  	return 0;

  	/*

  	 * Error recovery.

  	 */

  trunc:
  	ClearPageDirty(page);
  	delete_from_page_cache(page);
  	spin_lock(&info->lock);
  	info->alloced--;
  	inode->i_blocks -= BLOCKS_PER_PAGE;

  	spin_unlock(&info->lock);

  decused:
  	if (sbinfo->max_blocks)
  		percpu_counter_add(&sbinfo->used_blocks, -1);
  unacct:
  	shmem_unacct_blocks(info->flags, 1);
  failed:
  	if (swap.val && error != -EINVAL) {
  		struct page *test = find_get_page(mapping, index);
  		if (test && !radix_tree_exceptional_entry(test))
  			page_cache_release(test);
  		/* Have another try if the entry has changed */
  		if (test != swp_to_radix_entry(swap))
  			error = -EEXIST;
  	}

  	if (page) {

  		unlock_page(page);

  		page_cache_release(page);

  	}
  	if (error == -ENOSPC && !once++) {
  		info = SHMEM_I(inode);
  		spin_lock(&info->lock);
  		shmem_recalc_inode(inode);
  		spin_unlock(&info->lock);

  		goto repeat;

  	}

  	if (error == -EEXIST)
  		goto repeat;
  	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 = VM_FAULT_LOCKED;

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

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

  	if (ret & VM_FAULT_MAJOR) {
  		count_vm_event(PGMAJFAULT);
  		mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
  	}

  	return ret;

  }

  #ifdef CONFIG_NUMA

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

  {

  	struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
  	return mpol_set_shared_policy(&SHMEM_I(inode)->policy, vma, mpol);

  }

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

  {

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

  	index = ((addr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
  	return mpol_shared_policy_lookup(&SHMEM_I(inode)->policy, index);

  }
  #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);

  	}
  	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,

  				     umode_t 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->i_ino = get_next_ino();

  		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);

  		INIT_LIST_HEAD(&info->xattr_list);

  		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_short_symlink_operations;

  #ifdef CONFIG_TMPFS_XATTR
  static int shmem_initxattrs(struct inode *, const struct xattr *, void *);
  #else
  #define shmem_initxattrs NULL
  #endif

  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;

  	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;

  	pgoff_t index;
  	unsigned long 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;

  		pgoff_t end_index;
  		unsigned long 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 ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
  				struct pipe_inode_info *pipe, size_t len,
  				unsigned int flags)
  {
  	struct address_space *mapping = in->f_mapping;

  	struct inode *inode = mapping->host;

  	unsigned int loff, nr_pages, req_pages;
  	struct page *pages[PIPE_DEF_BUFFERS];
  	struct partial_page partial[PIPE_DEF_BUFFERS];
  	struct page *page;
  	pgoff_t index, end_index;
  	loff_t isize, left;
  	int error, page_nr;
  	struct splice_pipe_desc spd = {
  		.pages = pages,
  		.partial = partial,
  		.flags = flags,
  		.ops = &page_cache_pipe_buf_ops,
  		.spd_release = spd_release_page,
  	};

  	isize = i_size_read(inode);

  	if (unlikely(*ppos >= isize))
  		return 0;
  
  	left = isize - *ppos;
  	if (unlikely(left < len))
  		len = left;
  
  	if (splice_grow_spd(pipe, &spd))
  		return -ENOMEM;
  
  	index = *ppos >> PAGE_CACHE_SHIFT;
  	loff = *ppos & ~PAGE_CACHE_MASK;
  	req_pages = (len + loff + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
  	nr_pages = min(req_pages, pipe->buffers);

  	spd.nr_pages = find_get_pages_contig(mapping, index,
  						nr_pages, spd.pages);
  	index += spd.nr_pages;

  	error = 0;

  	while (spd.nr_pages < nr_pages) {

  		error = shmem_getpage(inode, index, &page, SGP_CACHE, NULL);
  		if (error)
  			break;
  		unlock_page(page);

  		spd.pages[spd.nr_pages++] = page;
  		index++;
  	}

  	index = *ppos >> PAGE_CACHE_SHIFT;
  	nr_pages = spd.nr_pages;
  	spd.nr_pages = 0;

  	for (page_nr = 0; page_nr < nr_pages; page_nr++) {
  		unsigned int this_len;
  
  		if (!len)
  			break;

  		this_len = min_t(unsigned long, len, PAGE_CACHE_SIZE - loff);
  		page = spd.pages[page_nr];

  		if (!PageUptodate(page) || page->mapping != mapping) {

  			error = shmem_getpage(inode, index, &page,
  							SGP_CACHE, NULL);
  			if (error)

  				break;

  			unlock_page(page);
  			page_cache_release(spd.pages[page_nr]);
  			spd.pages[page_nr] = page;

  		}

  
  		isize = i_size_read(inode);

  		end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
  		if (unlikely(!isize || index > end_index))
  			break;

  		if (end_index == index) {
  			unsigned int plen;

  			plen = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
  			if (plen <= loff)
  				break;

  			this_len = min(this_len, plen - loff);
  			len = this_len;
  		}
  
  		spd.partial[page_nr].offset = loff;
  		spd.partial[page_nr].len = this_len;
  		len -= this_len;
  		loff = 0;
  		spd.nr_pages++;
  		index++;
  	}

  	while (page_nr < nr_pages)
  		page_cache_release(spd.pages[page_nr++]);

  
  	if (spd.nr_pages)
  		error = splice_to_pipe(pipe, &spd);
  
  	splice_shrink_spd(pipe, &spd);
  
  	if (error > 0) {
  		*ppos += error;
  		file_accessed(in);
  	}
  	return error;
  }

  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, umode_t 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,

  						     &dentry->d_name,

  						     shmem_initxattrs, 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, umode_t 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, umode_t 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);

  	ihold(inode);	/* 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;

  	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, &dentry->d_name,

  					     shmem_initxattrs, NULL);

  	if (error) {
  		if (error != -EOPNOTSUPP) {
  			iput(inode);
  			return error;
  		}
  		error = 0;
  	}

  	info = SHMEM_I(inode);
  	inode->i_size = len-1;

  	if (len <= SHORT_SYMLINK_LEN) {
  		info->symlink = kmemdup(symname, len, GFP_KERNEL);
  		if (!info->symlink) {
  			iput(inode);
  			return -ENOMEM;
  		}
  		inode->i_op = &shmem_short_symlink_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);

  		memcpy(kaddr, symname, len);

  		kunmap_atomic(kaddr);

  		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_short_symlink(struct dentry *dentry, struct nameidata *nd)

  {

  	nd_set_link(nd, SHMEM_I(dentry->d_inode)->symlink);

  	return NULL;

  }

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

  {
  	struct page *page = NULL;

  	int error = shmem_getpage(dentry->d_inode, 0, &page, SGP_READ, NULL);
  	nd_set_link(nd, error ? ERR_PTR(error) : 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);

  	}
  }

  #ifdef CONFIG_TMPFS_XATTR

  /*

   * Superblocks without xattr inode operations may get some security.* xattr
   * support from the LSM "for free". As soon as we have any other xattrs

   * like ACLs, we also need to implement the security.* handlers at
   * filesystem level, though.
   */

  /*
   * Allocate new xattr and copy in the value; but leave the name to callers.
   */
  static struct shmem_xattr *shmem_xattr_alloc(const void *value, size_t size)
  {
  	struct shmem_xattr *new_xattr;
  	size_t len;
  
  	/* wrap around? */
  	len = sizeof(*new_xattr) + size;
  	if (len <= sizeof(*new_xattr))
  		return NULL;
  
  	new_xattr = kmalloc(len, GFP_KERNEL);
  	if (!new_xattr)
  		return NULL;
  
  	new_xattr->size = size;
  	memcpy(new_xattr->value, value, size);
  	return new_xattr;
  }
  
  /*
   * Callback for security_inode_init_security() for acquiring xattrs.
   */
  static int shmem_initxattrs(struct inode *inode,
  			    const struct xattr *xattr_array,
  			    void *fs_info)
  {
  	struct shmem_inode_info *info = SHMEM_I(inode);
  	const struct xattr *xattr;
  	struct shmem_xattr *new_xattr;
  	size_t len;
  
  	for (xattr = xattr_array; xattr->name != NULL; xattr++) {
  		new_xattr = shmem_xattr_alloc(xattr->value, xattr->value_len);
  		if (!new_xattr)
  			return -ENOMEM;
  
  		len = strlen(xattr->name) + 1;
  		new_xattr->name = kmalloc(XATTR_SECURITY_PREFIX_LEN + len,
  					  GFP_KERNEL);
  		if (!new_xattr->name) {
  			kfree(new_xattr);
  			return -ENOMEM;
  		}
  
  		memcpy(new_xattr->name, XATTR_SECURITY_PREFIX,
  		       XATTR_SECURITY_PREFIX_LEN);
  		memcpy(new_xattr->name + XATTR_SECURITY_PREFIX_LEN,
  		       xattr->name, len);
  
  		spin_lock(&info->lock);
  		list_add(&new_xattr->list, &info->xattr_list);
  		spin_unlock(&info->lock);
  	}
  
  	return 0;
  }

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

  {

  	struct shmem_inode_info *info;
  	struct shmem_xattr *xattr;
  	int ret = -ENODATA;

  	info = SHMEM_I(dentry->d_inode);
  
  	spin_lock(&info->lock);
  	list_for_each_entry(xattr, &info->xattr_list, list) {
  		if (strcmp(name, xattr->name))
  			continue;
  
  		ret = xattr->size;
  		if (buffer) {
  			if (size < xattr->size)
  				ret = -ERANGE;
  			else
  				memcpy(buffer, xattr->value, xattr->size);
  		}
  		break;
  	}
  	spin_unlock(&info->lock);
  	return ret;

  }

  static int shmem_xattr_set(struct inode *inode, const char *name,

  			   const void *value, size_t size, int flags)

  {

  	struct shmem_inode_info *info = SHMEM_I(inode);
  	struct shmem_xattr *xattr;
  	struct shmem_xattr *new_xattr = NULL;

  	int err = 0;
  
  	/* value == NULL means remove */
  	if (value) {

  		new_xattr = shmem_xattr_alloc(value, size);

  		if (!new_xattr)
  			return -ENOMEM;
  
  		new_xattr->name = kstrdup(name, GFP_KERNEL);
  		if (!new_xattr->name) {
  			kfree(new_xattr);
  			return -ENOMEM;
  		}

  	}
  
  	spin_lock(&info->lock);
  	list_for_each_entry(xattr, &info->xattr_list, list) {
  		if (!strcmp(name, xattr->name)) {
  			if (flags & XATTR_CREATE) {
  				xattr = new_xattr;
  				err = -EEXIST;
  			} else if (new_xattr) {
  				list_replace(&xattr->list, &new_xattr->list);
  			} else {
  				list_del(&xattr->list);
  			}
  			goto out;
  		}
  	}
  	if (flags & XATTR_REPLACE) {
  		xattr = new_xattr;
  		err = -ENODATA;
  	} else {
  		list_add(&new_xattr->list, &info->xattr_list);
  		xattr = NULL;
  	}
  out:
  	spin_unlock(&info->lock);
  	if (xattr)
  		kfree(xattr->name);
  	kfree(xattr);
  	return err;

  }

  static const struct xattr_handler *shmem_xattr_handlers[] = {

  #ifdef CONFIG_TMPFS_POSIX_ACL

  	&generic_acl_access_handler,
  	&generic_acl_default_handler,

  #endif

  	NULL
  };

  
  static int shmem_xattr_validate(const char *name)
  {
  	struct { const char *prefix; size_t len; } arr[] = {
  		{ XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN },
  		{ XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN }
  	};
  	int i;
  
  	for (i = 0; i < ARRAY_SIZE(arr); i++) {
  		size_t preflen = arr[i].len;
  		if (strncmp(name, arr[i].prefix, preflen) == 0) {
  			if (!name[preflen])
  				return -EINVAL;
  			return 0;
  		}
  	}
  	return -EOPNOTSUPP;
  }
  
  static ssize_t shmem_getxattr(struct dentry *dentry, const char *name,
  			      void *buffer, size_t size)
  {
  	int err;
  
  	/*
  	 * If this is a request for a synthetic attribute in the system.*
  	 * namespace use the generic infrastructure to resolve a handler
  	 * for it via sb->s_xattr.
  	 */
  	if (!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
  		return generic_getxattr(dentry, name, buffer, size);
  
  	err = shmem_xattr_validate(name);
  	if (err)
  		return err;
  
  	return shmem_xattr_get(dentry, name, buffer, size);
  }
  
  static int shmem_setxattr(struct dentry *dentry, const char *name,
  			  const void *value, size_t size, int flags)
  {
  	int err;
  
  	/*
  	 * If this is a request for a synthetic attribute in the system.*
  	 * namespace use the generic infrastructure to resolve a handler
  	 * for it via sb->s_xattr.
  	 */
  	if (!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
  		return generic_setxattr(dentry, name, value, size, flags);
  
  	err = shmem_xattr_validate(name);
  	if (err)
  		return err;
  
  	if (size == 0)
  		value = "";  /* empty EA, do not remove */

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

  
  }
  
  static int shmem_removexattr(struct dentry *dentry, const char *name)
  {
  	int err;
  
  	/*
  	 * If this is a request for a synthetic attribute in the system.*
  	 * namespace use the generic infrastructure to resolve a handler
  	 * for it via sb->s_xattr.
  	 */
  	if (!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
  		return generic_removexattr(dentry, name);
  
  	err = shmem_xattr_validate(name);
  	if (err)
  		return err;

  	return shmem_xattr_set(dentry->d_inode, name, NULL, 0, XATTR_REPLACE);

  }
  
  static bool xattr_is_trusted(const char *name)
  {
  	return !strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN);
  }
  
  static ssize_t shmem_listxattr(struct dentry *dentry, char *buffer, size_t size)
  {
  	bool trusted = capable(CAP_SYS_ADMIN);
  	struct shmem_xattr *xattr;
  	struct shmem_inode_info *info;
  	size_t used = 0;
  
  	info = SHMEM_I(dentry->d_inode);
  
  	spin_lock(&info->lock);
  	list_for_each_entry(xattr, &info->xattr_list, list) {
  		size_t len;
  
  		/* skip "trusted." attributes for unprivileged callers */
  		if (!trusted && xattr_is_trusted(xattr->name))
  			continue;
  
  		len = strlen(xattr->name) + 1;
  		used += len;
  		if (buffer) {
  			if (size < used) {
  				used = -ERANGE;
  				break;
  			}
  			memcpy(buffer, xattr->name, len);
  			buffer += len;
  		}
  	}
  	spin_unlock(&info->lock);
  
  	return used;
  }
  #endif /* CONFIG_TMPFS_XATTR */

  static const struct inode_operations shmem_short_symlink_operations = {

  	.readlink	= generic_readlink,

  	.follow_link	= shmem_follow_short_symlink,

  #ifdef CONFIG_TMPFS_XATTR
  	.setxattr	= shmem_setxattr,
  	.getxattr	= shmem_getxattr,
  	.listxattr	= shmem_listxattr,
  	.removexattr	= shmem_removexattr,
  #endif
  };
  
  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_XATTR
  	.setxattr	= shmem_setxattr,
  	.getxattr	= shmem_getxattr,
  	.listxattr	= shmem_listxattr,
  	.removexattr	= shmem_removexattr,

  #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;