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shmem.c

/*
 * 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>
 *
 * This file is released under the GPL.
 */

/*
 * 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/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/file.h>
#include <linux/swap.h>
#include <linux/pagemap.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/backing-dev.h>
#include <linux/shmem_fs.h>
#include <linux/mount.h>
#include <linux/writeback.h>
#include <linux/vfs.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 <asm/uaccess.h>
#include <asm/div64.h>
#include <asm/pgtable.h>

/* This magic number is used in glibc for posix shared memory */
#define TMPFS_MAGIC     0x01021994

#define ENTRIES_PER_PAGE (PAGE_CACHE_SIZE/sizeof(unsigned long))
#define ENTRIES_PER_PAGEPAGE (ENTRIES_PER_PAGE*ENTRIES_PER_PAGE)
#define BLOCKS_PER_PAGE  (PAGE_CACHE_SIZE/512)

#define SHMEM_MAX_INDEX  (SHMEM_NR_DIRECT + (ENTRIES_PER_PAGEPAGE/2) * (ENTRIES_PER_PAGE+1))
#define SHMEM_MAX_BYTES  ((unsigned long long)SHMEM_MAX_INDEX << PAGE_CACHE_SHIFT)

#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_QUICK,  /* don't try more than file page cache lookup */
      SGP_READ,   /* don't exceed i_size, don't allocate page */
      SGP_CACHE,  /* don't exceed i_size, may allocate page */
      SGP_WRITE,  /* may exceed i_size, may allocate page */
};

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.
       */
      return alloc_pages(gfp_mask, 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_ACCOUNT)?
            security_vm_enough_memory(VM_ACCT(size)): 0;
}

static inline void shmem_unacct_size(unsigned long flags, loff_t size)
{
      if (flags & VM_ACCOUNT)
            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_ACCOUNT)?
            0: security_vm_enough_memory(VM_ACCT(PAGE_CACHE_SIZE));
}

static inline void shmem_unacct_blocks(unsigned long flags, long pages)
{
      if (!(flags & VM_ACCOUNT))
            vm_unacct_memory(pages * VM_ACCT(PAGE_CACHE_SIZE));
}

static struct super_operations shmem_ops;
static const struct address_space_operations shmem_aops;
static struct file_operations shmem_file_operations;
static struct inode_operations shmem_inode_operations;
static struct inode_operations shmem_dir_inode_operations;
static 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_DIRTY | BDI_CAP_NO_WRITEBACK,
      .unplug_io_fn     = default_unplug_io_fn,
};

static LIST_HEAD(shmem_swaplist);
static DEFINE_SPINLOCK(shmem_swaplist_lock);

static void shmem_free_blocks(struct inode *inode, long pages)
{
      struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
      if (sbinfo->max_blocks) {
            spin_lock(&sbinfo->stat_lock);
            sbinfo->free_blocks += pages;
            inode->i_blocks -= pages*BLOCKS_PER_PAGE;
            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.
 *                   If it does not exist allocate the entry.
 *
 * @info:   info structure for the inode
 * @index:  index of the page to find
 * @sgp:    check and recheck i_size? skip allocation?
 */
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 free_blocks against 1 not 0, 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) {
                  spin_lock(&sbinfo->stat_lock);
                  if (sbinfo->free_blocks <= 1) {
                        spin_unlock(&sbinfo->stat_lock);
                        return ERR_PTR(-ENOSPC);
                  }
                  sbinfo->free_blocks--;
                  inode->i_blocks += BLOCKS_PER_PAGE;
                  spin_unlock(&sbinfo->stat_lock);
            }

            spin_unlock(&info->lock);
            page = shmem_dir_alloc(mapping_gfp_mask(inode->i_mapping) | __GFP_ZERO);
            if (page)
                  set_page_private(page, 0);
            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
 */
static int shmem_free_swp(swp_entry_t *dir, swp_entry_t *edir)
{
      swp_entry_t *ptr;
      int freed = 0;

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

static int shmem_map_and_free_swp(struct page *subdir,
            int offset, int limit, struct page ***dir)
{
      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);
            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 = 0;

      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;
            info->next_index = idx;
      } else {
            limit = (end + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
            if (limit > info->next_index)
                  limit = info->next_index;
            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);
      }
      if (!topdir)
            goto done2;

      BUG_ON(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) {
                        *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;
                  *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;
            }
            subdir = dir[diroff];
            if (subdir && page_private(subdir)) {
                  size = limit - idx;
                  if (size > ENTRIES_PER_PAGE)
                        size = ENTRIES_PER_PAGE;
                  freed = shmem_map_and_free_swp(subdir,
                                    offset, size, &dir);
                  if (!dir)
                        dir = shmem_dir_map(middir);
                  nr_swaps_freed += freed;
                  if (offset)
                        spin_lock(&info->lock);
                  set_page_private(subdir, page_private(subdir) - freed);
                  if (offset)
                        spin_unlock(&info->lock);
                  if (!punch_hole)
                        BUG_ON(page_private(subdir) > offset);
            }
            if (offset)
                  offset = 0;
            else if (subdir && !page_private(subdir)) {
                  dir[diroff] = NULL;
                  nr_pages_to_free++;
                  list_add(&subdir->lru, &pages_to_free);
            }
      }
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 vmtruncate 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.
             */
            truncate_inode_pages_range(inode->i_mapping, start, end);
      }

      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 void shmem_truncate(struct inode *inode)
{
      shmem_truncate_range(inode, inode->i_size, (loff_t)-1);
}

static int shmem_notify_change(struct dentry *dentry, struct iattr *attr)
{
      struct inode *inode = dentry->d_inode;
      struct page *page = NULL;
      int error;

      if (attr->ia_valid & ATTR_SIZE) {
            if (attr->ia_size < 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 (attr->ia_size & (PAGE_CACHE_SIZE-1)) {
                        (void) shmem_getpage(inode,
                              attr->ia_size>>PAGE_CACHE_SHIFT,
                                    &page, SGP_READ, NULL);
                  }
                  /*
                   * 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 (attr->ia_size) {
                        struct shmem_inode_info *info = SHMEM_I(inode);
                        spin_lock(&info->lock);
                        info->flags &= ~SHMEM_PAGEIN;
                        spin_unlock(&info->lock);
                  }
            }
      }

      error = inode_change_ok(inode, attr);
      if (!error)
            error = inode_setattr(inode, attr);
      if (page)
            page_cache_release(page);
      return error;
}

static void shmem_delete_inode(struct inode *inode)
{
      struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
      struct shmem_inode_info *info = SHMEM_I(inode);

      if (inode->i_op->truncate == shmem_truncate) {
            truncate_inode_pages(inode->i_mapping, 0);
            shmem_unacct_size(info->flags, inode->i_size);
            inode->i_size = 0;
            shmem_truncate(inode);
            if (!list_empty(&info->swaplist)) {
                  spin_lock(&shmem_swaplist_lock);
                  list_del_init(&info->swaplist);
                  spin_unlock(&shmem_swaplist_lock);
            }
      }
      BUG_ON(inode->i_blocks);
      if (sbinfo->max_inodes) {
            spin_lock(&sbinfo->stat_lock);
            sbinfo->free_inodes++;
            spin_unlock(&sbinfo->stat_lock);
      }
      clear_inode(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;

      idx = 0;
      ptr = info->i_direct;
      spin_lock(&info->lock);
      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) {
            shmem_swp_balance_unmap();
            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);
                  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);
                  if (offset >= 0) {
                        shmem_dir_unmap(dir);
                        goto found;
                  }
                  shmem_swp_unmap(ptr);
            }
      }
lost1:
      shmem_dir_unmap(dir-1);
lost2:
      spin_unlock(&info->lock);
      return 0;
found:
      idx += offset;
      inode = &info->vfs_inode;
      if (move_from_swap_cache(page, idx, inode->i_mapping) == 0) {
            info->flags |= SHMEM_PAGEIN;
            shmem_swp_set(info, ptr + offset, 0);
      }
      shmem_swp_unmap(ptr);
      spin_unlock(&info->lock);
      /*
       * Decrement swap count even when the entry is left behind:
       * try_to_unuse will skip over mms, then reincrement count.
       */
      swap_free(entry);
      return 1;
}

/*
 * 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;

      spin_lock(&shmem_swaplist_lock);
      list_for_each_safe(p, next, &shmem_swaplist) {
            info = list_entry(p, struct shmem_inode_info, swaplist);
            if (!info->swapped)
                  list_del_init(&info->swaplist);
            else if (shmem_unuse_inode(info, entry, page)) {
                  /* move head to start search for next from here */
                  list_move_tail(&shmem_swaplist, &info->swaplist);
                  found = 1;
                  break;
            }
      }
      spin_unlock(&shmem_swaplist_lock);
      return found;
}

/*
 * 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));
      BUG_ON(page_mapped(page));

      mapping = page->mapping;
      index = page->index;
      inode = mapping->host;
      info = SHMEM_I(inode);
      if (info->flags & VM_LOCKED)
            goto redirty;
      swap = get_swap_page();
      if (!swap.val)
            goto redirty;

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

      if (move_to_swap_cache(page, swap) == 0) {
            shmem_swp_set(info, entry, swap.val);
            shmem_swp_unmap(entry);
            spin_unlock(&info->lock);
            if (list_empty(&info->swaplist)) {
                  spin_lock(&shmem_swaplist_lock);
                  /* move instead of add in case we're racing */
                  list_move_tail(&info->swaplist, &shmem_swaplist);
                  spin_unlock(&shmem_swaplist_lock);
            }
            unlock_page(page);
            return 0;
      }

      shmem_swp_unmap(entry);
unlock:
      spin_unlock(&info->lock);
      swap_free(swap);
redirty:
      set_page_dirty(page);
      return AOP_WRITEPAGE_ACTIVATE;      /* Return with the page locked */
}

#ifdef CONFIG_NUMA
static inline int shmem_parse_mpol(char *value, int *policy, nodemask_t *policy_nodes)
{
      char *nodelist = strchr(value, ':');
      int err = 1;

      if (nodelist) {
            /* NUL-terminate policy string */
            *nodelist++ = '\0';
            if (nodelist_parse(nodelist, *policy_nodes))
                  goto out;
      }
      if (!strcmp(value, "default")) {
            *policy = MPOL_DEFAULT;
            /* Don't allow a nodelist */
            if (!nodelist)
                  err = 0;
      } else if (!strcmp(value, "prefer")) {
            *policy = MPOL_PREFERRED;
            /* Insist on a nodelist of one node only */
            if (nodelist) {
                  char *rest = nodelist;
                  while (isdigit(*rest))
                        rest++;
                  if (!*rest)
                        err = 0;
            }
      } else if (!strcmp(value, "bind")) {
            *policy = MPOL_BIND;
            /* Insist on a nodelist */
            if (nodelist)
                  err = 0;
      } else if (!strcmp(value, "interleave")) {
            *policy = MPOL_INTERLEAVE;
            /* Default to nodes online if no nodelist */
            if (!nodelist)
                  *policy_nodes = node_online_map;
            err = 0;
      }
out:
      /* Restore string for error message */
      if (nodelist)
            *--nodelist = ':';
      return err;
}

static struct page *shmem_swapin_async(struct shared_policy *p,
                               swp_entry_t entry, unsigned long idx)
{
      struct page *page;
      struct vm_area_struct pvma;

      /* Create a pseudo vma that just contains the policy */
      memset(&pvma, 0, sizeof(struct vm_area_struct));
      pvma.vm_end = PAGE_SIZE;
      pvma.vm_pgoff = idx;
      pvma.vm_policy = mpol_shared_policy_lookup(p, idx);
      page = read_swap_cache_async(entry, &pvma, 0);
      mpol_free(pvma.vm_policy);
      return page;
}

struct page *shmem_swapin(struct shmem_inode_info *info, swp_entry_t entry,
                    unsigned long idx)
{
      struct shared_policy *p = &info->policy;
      int i, num;
      struct page *page;
      unsigned long offset;

      num = valid_swaphandles(entry, &offset);
      for (i = 0; i < num; offset++, i++) {
            page = shmem_swapin_async(p,
                        swp_entry(swp_type(entry), offset), idx);
            if (!page)
                  break;
            page_cache_release(page);
      }
      lru_add_drain();  /* Push any new pages onto the LRU now */
      return shmem_swapin_async(p, entry, idx);
}

static struct page *
shmem_alloc_page(gfp_t gfp, struct shmem_inode_info *info,
             unsigned long idx)
{
      struct vm_area_struct pvma;
      struct page *page;

      memset(&pvma, 0, sizeof(struct vm_area_struct));
      pvma.vm_policy = mpol_shared_policy_lookup(&info->policy, idx);
      pvma.vm_pgoff = idx;
      pvma.vm_end = PAGE_SIZE;
      page = alloc_page_vma(gfp | __GFP_ZERO, &pvma, 0);
      mpol_free(pvma.vm_policy);
      return page;
}
#else
static inline int shmem_parse_mpol(char *value, int *policy, nodemask_t *policy_nodes)
{
      return 1;
}

static inline struct page *
shmem_swapin(struct shmem_inode_info *info,swp_entry_t entry,unsigned long idx)
{
      swapin_readahead(entry, 0, NULL);
      return read_swap_cache_async(entry, NULL, 0);
}

static inline struct page *
shmem_alloc_page(gfp_t gfp,struct shmem_inode_info *info, unsigned long idx)
{
      return alloc_page(gfp | __GFP_ZERO);
}
#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;
      swp_entry_t *entry;
      swp_entry_t swap;
      int error;

      if (idx >= SHMEM_MAX_INDEX)
            return -EFBIG;
      /*
       * 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_prepare_write 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;
      error = 0;
      if (sgp == SGP_QUICK)
            goto failed;

      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_MINOR) {
                        __count_vm_event(PGMAJFAULT);
                        *type = VM_FAULT_MAJOR;
                  }
                  spin_unlock(&info->lock);
                  swappage = shmem_swapin(info, swap, 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 (TestSetPageLocked(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 = move_from_swap_cache(
                        swappage, idx, mapping))) {
                  info->flags |= SHMEM_PAGEIN;
                  shmem_swp_set(info, entry, 0);
                  shmem_swp_unmap(entry);
                  spin_unlock(&info->lock);
                  filepage = swappage;
                  swap_free(swap);
            } else {
                  shmem_swp_unmap(entry);
                  spin_unlock(&info->lock);
                  unlock_page(swappage);
                  page_cache_release(swappage);
                  if (error == -ENOMEM) {
                        /* let kswapd refresh zone for GFP_ATOMICs */
                        blk_congestion_wait(WRITE, HZ/50);
                  }
                  goto repeat;
            }
      } else if (sgp == SGP_READ && !filepage) {
            shmem_swp_unmap(entry);
            filepage = find_get_page(mapping, idx);
            if (filepage &&
                (!PageUptodate(filepage) || TestSetPageLocked(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) {
                  spin_lock(&sbinfo->stat_lock);
                  if (sbinfo->free_blocks == 0 ||
                      shmem_acct_block(info->flags)) {
                        spin_unlock(&sbinfo->stat_lock);
                        spin_unlock(&info->lock);
                        error = -ENOSPC;
                        goto failed;
                  }
                  sbinfo->free_blocks--;
                  inode->i_blocks += BLOCKS_PER_PAGE;
                  spin_unlock(&sbinfo->stat_lock);
            } else if (shmem_acct_block(info->flags)) {
                  spin_unlock(&info->lock);
                  error = -ENOSPC;
                  goto failed;
            }

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

                  spin_lock(&info->lock);
                  entry = shmem_swp_alloc(info, idx, sgp);
                  if (IS_ERR(entry))
                        error = PTR_ERR(entry);
                  else {
                        swap = *entry;
                        shmem_swp_unmap(entry);
                  }
                  if (error || swap.val || 0 != add_to_page_cache_lru(
                              filepage, mapping, idx, GFP_ATOMIC)) {
                        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);
            flush_dcache_page(filepage);
            SetPageUptodate(filepage);
      }
done:
      if (*pagep != filepage) {
            unlock_page(filepage);
            *pagep = filepage;
      }
      return 0;

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

struct page *shmem_nopage(struct vm_area_struct *vma, unsigned long address, int *type)
{
      struct inode *inode = vma->vm_file->f_dentry->d_inode;
      struct page *page = NULL;
      unsigned long idx;
      int error;

      idx = (address - vma->vm_start) >> PAGE_SHIFT;
      idx += vma->vm_pgoff;
      idx >>= PAGE_CACHE_SHIFT - PAGE_SHIFT;
      if (((loff_t) idx << PAGE_CACHE_SHIFT) >= i_size_read(inode))
            return NOPAGE_SIGBUS;

      error = shmem_getpage(inode, idx, &page, SGP_CACHE, type);
      if (error)
            return (error == -ENOMEM)? NOPAGE_OOM: NOPAGE_SIGBUS;

      mark_page_accessed(page);
      return page;
}

static int shmem_populate(struct vm_area_struct *vma,
      unsigned long addr, unsigned long len,
      pgprot_t prot, unsigned long pgoff, int nonblock)
{
      struct inode *inode = vma->vm_file->f_dentry->d_inode;
      struct mm_struct *mm = vma->vm_mm;
      enum sgp_type sgp = nonblock? SGP_QUICK: SGP_CACHE;
      unsigned long size;

      size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
      if (pgoff >= size || pgoff + (len >> PAGE_SHIFT) > size)
            return -EINVAL;

      while ((long) len > 0) {
            struct page *page = NULL;
            int err;
            /*
             * Will need changing if PAGE_CACHE_SIZE != PAGE_SIZE
             */
            err = shmem_getpage(inode, pgoff, &page, sgp, NULL);
            if (err)
                  return err;
            /* Page may still be null, but only if nonblock was set. */
            if (page) {
                  mark_page_accessed(page);
                  err = install_page(mm, vma, addr, page, prot);
                  if (err) {
                        page_cache_release(page);
                        return err;
                  }
            } else if (vma->vm_flags & VM_NONLINEAR) {
                  /* No page was found just because we can't read it in
                   * now (being here implies nonblock != 0), but the page
                   * may exist, so set the PTE to fault it in later. */
                  err = install_file_pte(mm, vma, addr, pgoff, prot);
                  if (err)
                        return err;
            }

            len -= PAGE_SIZE;
            addr += PAGE_SIZE;
            pgoff++;
      }
      return 0;
}

#ifdef CONFIG_NUMA
int shmem_set_policy(struct vm_area_struct *vma, struct mempolicy *new)
{
      struct inode *i = vma->vm_file->f_dentry->d_inode;
      return mpol_set_shared_policy(&SHMEM_I(i)->policy, vma, new);
}

struct mempolicy *
shmem_get_policy(struct vm_area_struct *vma, unsigned long addr)
{
      struct inode *i = vma->vm_file->f_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_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;
      }
      if (!lock && (info->flags & VM_LOCKED) && user) {
            user_shm_unlock(inode->i_size, user);
            info->flags &= ~VM_LOCKED;
      }
      retval = 0;
out_nomem:
      spin_unlock(&info->lock);
      return retval;
}

int shmem_mmap(struct file *file, struct vm_area_struct *vma)
{
      file_accessed(file);
      vma->vm_ops = &shmem_vm_ops;
      return 0;
}

static struct inode *
shmem_get_inode(struct super_block *sb, int mode, dev_t dev)
{
      struct inode *inode;
      struct shmem_inode_info *info;
      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 NULL;
            }
            sbinfo->free_inodes--;
            spin_unlock(&sbinfo->stat_lock);
      }

      inode = new_inode(sb);
      if (inode) {
            inode->i_mode = mode;
            inode->i_uid = current->fsuid;
            inode->i_gid = current->fsgid;
            inode->i_blksize = PAGE_CACHE_SIZE;
            inode->i_blocks = 0;
            inode->i_mapping->a_ops = &shmem_aops;
            inode->i_mapping->backing_dev_info = &shmem_backing_dev_info;
            inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
            info = SHMEM_I(inode);
            memset(info, 0, (char *)inode - (char *)info);
            spin_lock_init(&info->lock);
            INIT_LIST_HEAD(&info->swaplist);

            switch (mode & S_IFMT) {
            default:
                  init_special_inode(inode, mode, dev);
                  break;
            case S_IFREG:
                  inode->i_op = &shmem_inode_operations;
                  inode->i_fop = &shmem_file_operations;
                  mpol_shared_policy_init(&info->policy, sbinfo->policy,
                                          &sbinfo->policy_nodes);
                  break;
            case S_IFDIR:
                  inode->i_nlink++;
                  /* 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, MPOL_DEFAULT,
                                    NULL);
                  break;
            }
      } else if (sbinfo->max_inodes) {
            spin_lock(&sbinfo->stat_lock);
            sbinfo->free_inodes++;
            spin_unlock(&sbinfo->stat_lock);
      }
      return inode;
}

#ifdef CONFIG_TMPFS
static struct inode_operations shmem_symlink_inode_operations;
static struct inode_operations shmem_symlink_inline_operations;

/*
 * Normally tmpfs makes no use of shmem_prepare_write, but it
 * lets a tmpfs file be used read-write below the loop driver.
 */
static int
shmem_prepare_write(struct file *file, struct page *page, unsigned offset, unsigned to)
{
      struct inode *inode = page->mapping->host;
      return shmem_getpage(inode, page->index, &page, SGP_WRITE, NULL);
}

static ssize_t
shmem_file_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
{
      struct inode      *inode = file->f_dentry->d_inode;
      loff_t            pos;
      unsigned long     written;
      ssize_t           err;

      if ((ssize_t) count < 0)
            return -EINVAL;

      if (!access_ok(VERIFY_READ, buf, count))
            return -EFAULT;

      mutex_lock(&inode->i_mutex);

      pos = *ppos;
      written = 0;

      err = generic_write_checks(file, &pos, &count, 0);
      if (err || !count)
            goto out;

      err = remove_suid(file->f_dentry);
      if (err)
            goto out;

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

      do {
            struct page *page = NULL;
            unsigned long bytes, index, offset;
            char *kaddr;
            int left;

            offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
            index = pos >> PAGE_CACHE_SHIFT;
            bytes = PAGE_CACHE_SIZE - offset;
            if (bytes > count)
                  bytes = count;

            /*
             * We don't hold page lock across copy from user -
             * what would it guard against? - so no deadlock here.
             * But it still may be a good idea to prefault below.
             */

            err = shmem_getpage(inode, index, &page, SGP_WRITE, NULL);
            if (err)
                  break;

            left = bytes;
            if (PageHighMem(page)) {
                  volatile unsigned char dummy;
                  __get_user(dummy, buf);
                  __get_user(dummy, buf + bytes - 1);

                  kaddr = kmap_atomic(page, KM_USER0);
                  left = __copy_from_user_inatomic(kaddr + offset,
                                          buf, bytes);
                  kunmap_atomic(kaddr, KM_USER0);
            }
            if (left) {
                  kaddr = kmap(page);
                  left = __copy_from_user(kaddr + offset, buf, bytes);
                  kunmap(page);
            }

            written += bytes;
            count -= bytes;
            pos += bytes;
            buf += bytes;
            if (pos > inode->i_size)
                  i_size_write(inode, pos);

            flush_dcache_page(page);
            set_page_dirty(page);
            mark_page_accessed(page);
            page_cache_release(page);

            if (left) {
                  pos -= left;
                  written -= left;
                  err = -EFAULT;
                  break;
            }

            /*
             * Our dirty pages are not counted in nr_dirty,
             * and we do not attempt to balance dirty pages.
             */

            cond_resched();
      } while (count);

      *ppos = pos;
      if (written)
            err = written;
out:
      mutex_unlock(&inode->i_mutex);
      return err;
}

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

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

            /*
             * 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_read(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
{
      read_descriptor_t desc;

      if ((ssize_t) count < 0)
            return -EINVAL;
      if (!access_ok(VERIFY_WRITE, buf, count))
            return -EFAULT;
      if (!count)
            return 0;

      desc.written = 0;
      desc.count = count;
      desc.arg.buf = buf;
      desc.error = 0;

      do_shmem_file_read(filp, ppos, &desc, file_read_actor);
      if (desc.written)
            return desc.written;
      return desc.error;
}

static ssize_t shmem_file_sendfile(struct file *in_file, loff_t *ppos,
                   size_t count, read_actor_t actor, void *target)
{
      read_descriptor_t desc;

      if (!count)
            return 0;

      desc.written = 0;
      desc.count = count;
      desc.arg.data = target;
      desc.error = 0;

      do_shmem_file_read(in_file, ppos, &desc, actor);
      if (desc.written)
            return desc.written;
      return desc.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;
      spin_lock(&sbinfo->stat_lock);
      if (sbinfo->max_blocks) {
            buf->f_blocks = sbinfo->max_blocks;
            buf->f_bavail = buf->f_bfree = sbinfo->free_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 */
      spin_unlock(&sbinfo->stat_lock);
      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 = shmem_get_inode(dir->i_sb, mode, dev);
      int error = -ENOSPC;

      if (inode) {
            error = security_inode_init_security(inode, dir, NULL, NULL,
                                         NULL);
            if (error) {
                  if (error != -EOPNOTSUPP) {
                        iput(inode);
                        return error;
                  }
                  error = 0;
            }
            if (dir->i_mode & S_ISGID) {
                  inode->i_gid = dir->i_gid;
                  if (S_ISDIR(mode))
                        inode->i_mode |= S_ISGID;
            }
            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;
      dir->i_nlink++;
      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;
      struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);

      /*
       * 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.
       */
      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);
      }

      dir->i_size += BOGO_DIRENT_SIZE;
      inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;
      inode->i_nlink++;
      atomic_inc(&inode->i_count);  /* New dentry reference */
      dget(dentry);           /* Extra pinning count for the created dentry */
      d_instantiate(dentry, inode);
      return 0;
}

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)) {
            struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
            if (sbinfo->max_inodes) {
                  spin_lock(&sbinfo->stat_lock);
                  sbinfo->free_inodes++;
                  spin_unlock(&sbinfo->stat_lock);
            }
      }

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

      dentry->d_inode->i_nlink--;
      dir->i_nlink--;
      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)
                  old_dir->i_nlink--;
      } else if (they_are_dirs) {
            old_dir->i_nlink--;
            new_dir->i_nlink++;
      }

      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, S_IFLNK|S_IRWXUGO, 0);
      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_op = &shmem_symlink_inode_operations;
            kaddr = kmap_atomic(page, KM_USER0);
            memcpy(kaddr, symname, len);
            kunmap_atomic(kaddr, KM_USER0);
            set_page_dirty(page);
            page_cache_release(page);
      }
      if (dir->i_mode & S_ISGID)
            inode->i_gid = dir->i_gid;
      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));
      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 struct inode_operations shmem_symlink_inline_operations = {
      .readlink   = generic_readlink,
      .follow_link      = shmem_follow_link_inline,
};

static struct inode_operations shmem_symlink_inode_operations = {
      .truncate   = shmem_truncate,
      .readlink   = generic_readlink,
      .follow_link      = shmem_follow_link,
      .put_link   = shmem_put_link,
};

static int shmem_parse_options(char *options, int *mode, uid_t *uid,
      gid_t *gid, unsigned long *blocks, unsigned long *inodes,
      int *policy, nodemask_t *policy_nodes)
{
      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'\n",
                      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;
                  *blocks = size >> PAGE_CACHE_SHIFT;
            } else if (!strcmp(this_char,"nr_blocks")) {
                  *blocks = memparse(value,&rest);
                  if (*rest)
                        goto bad_val;
            } else if (!strcmp(this_char,"nr_inodes")) {
                  *inodes = memparse(value,&rest);
                  if (*rest)
                        goto bad_val;
            } else if (!strcmp(this_char,"mode")) {
                  if (!mode)
                        continue;
                  *mode = simple_strtoul(value,&rest,8);
                  if (*rest)
                        goto bad_val;
            } else if (!strcmp(this_char,"uid")) {
                  if (!uid)
                        continue;
                  *uid = simple_strtoul(value,&rest,0);
                  if (*rest)
                        goto bad_val;
            } else if (!strcmp(this_char,"gid")) {
                  if (!gid)
                        continue;
                  *gid = simple_strtoul(value,&rest,0);
                  if (*rest)
                        goto bad_val;
            } else if (!strcmp(this_char,"mpol")) {
                  if (shmem_parse_mpol(value,policy,policy_nodes))
                        goto bad_val;
            } else {
                  printk(KERN_ERR "tmpfs: Bad mount option %s\n",
                         this_char);
                  return 1;
            }
      }
      return 0;

bad_val:
      printk(KERN_ERR "tmpfs: Bad value '%s' for mount option '%s'\n",
             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);
      unsigned long max_blocks = sbinfo->max_blocks;
      unsigned long max_inodes = sbinfo->max_inodes;
      int policy = sbinfo->policy;
      nodemask_t policy_nodes = sbinfo->policy_nodes;
      unsigned long blocks;
      unsigned long inodes;
      int error = -EINVAL;

      if (shmem_parse_options(data, NULL, NULL, NULL, &max_blocks,
                        &max_inodes, &policy, &policy_nodes))
            return error;

      spin_lock(&sbinfo->stat_lock);
      blocks = sbinfo->max_blocks - sbinfo->free_blocks;
      inodes = sbinfo->max_inodes - sbinfo->free_inodes;
      if (max_blocks < blocks)
            goto out;
      if (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 (max_blocks && !sbinfo->max_blocks)
            goto out;
      if (max_inodes && !sbinfo->max_inodes)
            goto out;

      error = 0;
      sbinfo->max_blocks  = max_blocks;
      sbinfo->free_blocks = max_blocks - blocks;
      sbinfo->max_inodes  = max_inodes;
      sbinfo->free_inodes = max_inodes - inodes;
      sbinfo->policy = policy;
      sbinfo->policy_nodes = policy_nodes;
out:
      spin_unlock(&sbinfo->stat_lock);
      return error;
}
#endif

static void shmem_put_super(struct super_block *sb)
{
      kfree(sb->s_fs_info);
      sb->s_fs_info = NULL;
}

static int shmem_fill_super(struct super_block *sb,
                      void *data, int silent)
{
      struct inode *inode;
      struct dentry *root;
      int mode   = S_IRWXUGO | S_ISVTX;
      uid_t uid = current->fsuid;
      gid_t gid = current->fsgid;
      int err = -ENOMEM;
      struct shmem_sb_info *sbinfo;
      unsigned long blocks = 0;
      unsigned long inodes = 0;
      int policy = MPOL_DEFAULT;
      nodemask_t policy_nodes = node_online_map;

#ifdef CONFIG_TMPFS
      /*
       * Per default we only allow half of the physical ram per
       * tmpfs instance, limiting inodes to one per page of lowmem;
       * but the internal instance is left unlimited.
       */
      if (!(sb->s_flags & MS_NOUSER)) {
            blocks = totalram_pages / 2;
            inodes = totalram_pages - totalhigh_pages;
            if (inodes > blocks)
                  inodes = blocks;
            if (shmem_parse_options(data, &mode, &uid, &gid, &blocks,
                              &inodes, &policy, &policy_nodes))
                  return -EINVAL;
      }
#else
      sb->s_flags |= MS_NOUSER;
#endif

      /* Round up to L1_CACHE_BYTES to resist false sharing */
      sbinfo = kmalloc(max((int)sizeof(struct shmem_sb_info),
                        L1_CACHE_BYTES), GFP_KERNEL);
      if (!sbinfo)
            return -ENOMEM;

      spin_lock_init(&sbinfo->stat_lock);
      sbinfo->max_blocks = blocks;
      sbinfo->free_blocks = blocks;
      sbinfo->max_inodes = inodes;
      sbinfo->free_inodes = inodes;
      sbinfo->policy = policy;
      sbinfo->policy_nodes = policy_nodes;

      sb->s_fs_info = sbinfo;
      sb->s_maxbytes = SHMEM_MAX_BYTES;
      sb->s_blocksize = PAGE_CACHE_SIZE;
      sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
      sb->s_magic = TMPFS_MAGIC;
      sb->s_op = &shmem_ops;
      sb->s_time_gran = 1;

      inode = shmem_get_inode(sb, S_IFDIR | mode, 0);
      if (!inode)
            goto failed;
      inode->i_uid = uid;
      inode->i_gid = gid;
      root = d_alloc_root(inode);
      if (!root)
            goto failed_iput;
      sb->s_root = root;
      return 0;

failed_iput:
      iput(inode);
failed:
      shmem_put_super(sb);
      return err;
}

static struct kmem_cache *shmem_inode_cachep;

static struct inode *shmem_alloc_inode(struct super_block *sb)
{
      struct shmem_inode_info *p;
      p = (struct shmem_inode_info *)kmem_cache_alloc(shmem_inode_cachep, SLAB_KERNEL);
      if (!p)
            return NULL;
      return &p->vfs_inode;
}

static void shmem_destroy_inode(struct inode *inode)
{
      if ((inode->i_mode & S_IFMT) == S_IFREG) {
            /* only struct inode is valid if it's an inline symlink */
            mpol_free_shared_policy(&SHMEM_I(inode)->policy);
      }
      kmem_cache_free(shmem_inode_cachep, SHMEM_I(inode));
}

static void init_once(void *foo, struct kmem_cache *cachep,
                  unsigned long flags)
{
      struct shmem_inode_info *p = (struct shmem_inode_info *) foo;

      if ((flags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) ==
          SLAB_CTOR_CONSTRUCTOR) {
            inode_init_once(&p->vfs_inode);
      }
}

static int init_inodecache(void)
{
      shmem_inode_cachep = kmem_cache_create("shmem_inode_cache",
                        sizeof(struct shmem_inode_info),
                        0, 0, init_once, NULL);
      if (shmem_inode_cachep == NULL)
            return -ENOMEM;
      return 0;
}

static void destroy_inodecache(void)
{
      if (kmem_cache_destroy(shmem_inode_cachep))
            printk(KERN_INFO "shmem_inode_cache: not all structures were freed\n");
}

static const struct address_space_operations shmem_aops = {
      .writepage  = shmem_writepage,
      .set_page_dirty   = __set_page_dirty_nobuffers,
#ifdef CONFIG_TMPFS
      .prepare_write    = shmem_prepare_write,
      .commit_write     = simple_commit_write,
#endif
      .migratepage      = migrate_page,
};

static struct file_operations shmem_file_operations = {
      .mmap       = shmem_mmap,
#ifdef CONFIG_TMPFS
      .llseek           = generic_file_llseek,
      .read       = shmem_file_read,
      .write            = shmem_file_write,
      .fsync            = simple_sync_file,
      .sendfile   = shmem_file_sendfile,
#endif
};

static struct inode_operations shmem_inode_operations = {
      .truncate   = shmem_truncate,
      .setattr    = shmem_notify_change,
      .truncate_range   = shmem_truncate_range,
};

static struct inode_operations shmem_dir_inode_operations = {
#ifdef CONFIG_TMPFS
      .create           = shmem_create,
      .lookup           = simple_lookup,
      .link       = shmem_link,
      .unlink           = shmem_unlink,
      .symlink    = shmem_symlink,
      .mkdir            = shmem_mkdir,
      .rmdir            = shmem_rmdir,
      .mknod            = shmem_mknod,
      .rename           = shmem_rename,
#endif
};

static struct super_operations shmem_ops = {
      .alloc_inode      = shmem_alloc_inode,
      .destroy_inode    = shmem_destroy_inode,
#ifdef CONFIG_TMPFS
      .statfs           = shmem_statfs,
      .remount_fs = shmem_remount_fs,
#endif
      .delete_inode     = shmem_delete_inode,
      .drop_inode = generic_delete_inode,
      .put_super  = shmem_put_super,
};

static struct vm_operations_struct shmem_vm_ops = {
      .nopage           = shmem_nopage,
      .populate   = shmem_populate,
#ifdef CONFIG_NUMA
      .set_policy     = shmem_set_policy,
      .get_policy     = shmem_get_policy,
#endif
};


static int shmem_get_sb(struct file_system_type *fs_type,
      int flags, const char *dev_name, void *data, struct vfsmount *mnt)
{
      return get_sb_nodev(fs_type, flags, data, shmem_fill_super, mnt);
}

static struct file_system_type tmpfs_fs_type = {
      .owner            = THIS_MODULE,
      .name       = "tmpfs",
      .get_sb           = shmem_get_sb,
      .kill_sb    = kill_litter_super,
};
static struct vfsmount *shm_mnt;

static int __init init_tmpfs(void)
{
      int error;

      error = init_inodecache();
      if (error)
            goto out3;

      error = register_filesystem(&tmpfs_fs_type);
      if (error) {
            printk(KERN_ERR "Could not register tmpfs\n");
            goto out2;
      }

      shm_mnt = vfs_kern_mount(&tmpfs_fs_type, MS_NOUSER,
                        tmpfs_fs_type.name, NULL);
      if (IS_ERR(shm_mnt)) {
            error = PTR_ERR(shm_mnt);
            printk(KERN_ERR "Could not kern_mount tmpfs\n");
            goto out1;
      }
      return 0;

out1:
      unregister_filesystem(&tmpfs_fs_type);
out2:
      destroy_inodecache();
out3:
      shm_mnt = ERR_PTR(error);
      return error;
}
module_init(init_tmpfs)

/*
 * shmem_file_setup - get an unlinked file living in tmpfs
 *
 * @name: name for dentry (to be seen in /proc/<pid>/maps
 * @size: size to be set for the file
 *
 */
struct file *shmem_file_setup(char *name, loff_t size, unsigned long flags)
{
      int error;
      struct file *file;
      struct inode *inode;
      struct dentry *dentry, *root;
      struct qstr this;

      if (IS_ERR(shm_mnt))
            return (void *)shm_mnt;

      if (size < 0 || size > SHMEM_MAX_BYTES)
            return ERR_PTR(-EINVAL);

      if (shmem_acct_size(flags, size))
            return ERR_PTR(-ENOMEM);

      error = -ENOMEM;
      this.name = name;
      this.len = strlen(name);
      this.hash = 0; /* will go */
      root = shm_mnt->mnt_root;
      dentry = d_alloc(root, &this);
      if (!dentry)
            goto put_memory;

      error = -ENFILE;
      file = get_empty_filp();
      if (!file)
            goto put_dentry;

      error = -ENOSPC;
      inode = shmem_get_inode(root->d_sb, S_IFREG | S_IRWXUGO, 0);
      if (!inode)
            goto close_file;

      SHMEM_I(inode)->flags = flags & VM_ACCOUNT;
      d_instantiate(dentry, inode);
      inode->i_size = size;
      inode->i_nlink = 0;     /* It is unlinked */
      file->f_vfsmnt = mntget(shm_mnt);
      file->f_dentry = dentry;
      file->f_mapping = inode->i_mapping;
      file->f_op = &shmem_file_operations;
      file->f_mode = FMODE_WRITE | FMODE_READ;
      return file;

close_file:
      put_filp(file);
put_dentry:
      dput(dentry);
put_memory:
      shmem_unacct_size(flags, size);
      return ERR_PTR(error);
}

/*
 * shmem_zero_setup - setup a shared anonymous mapping
 *
 * @vma: the vma to be mmapped is prepared by do_mmap_pgoff
 */
int shmem_zero_setup(struct vm_area_struct *vma)
{
      struct file *file;
      loff_t size = vma->vm_end - vma->vm_start;

      file = shmem_file_setup("dev/zero", size, vma->vm_flags);
      if (IS_ERR(file))
            return PTR_ERR(file);

      if (vma->vm_file)
            fput(vma->vm_file);
      vma->vm_file = file;
      vma->vm_ops = &shmem_vm_ops;
      return 0;
}

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