ClabureDB: Classified Bug-Reports Database

   /*
    * 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/xattr.h>
  #include <linux/exportfs.h>
  #include <linux/generic_acl.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 <linux/highmem.h>
  #include <linux/seq_file.h>
  #include <linux/magic.h>
  
  #include <asm/uaccess.h>
  #include <asm/div64.h>
  #include <asm/pgtable.h>
  
  #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_READ,        /* don't exceed i_size, don't allocate page */
          SGP_CACHE,        /* don't exceed i_size, may allocate page */
          SGP_DIRTY,        /* like SGP_CACHE, but set new page dirty */
          SGP_WRITE,        /* may exceed i_size, may allocate page */
  };
  
  #ifdef CONFIG_TMPFS
  static unsigned long shmem_default_max_blocks(void)
  {
          return totalram_pages / 2;
  }
  
  static unsigned long shmem_default_max_inodes(void)
  {
          return min(totalram_pages - totalhigh_pages, totalram_pages / 2);
  }
  #endif
  
  static int shmem_getpage(struct inode *inode, unsigned long idx,
                           struct page **pagep, enum sgp_type sgp, int *type);
 
 static inline struct page *shmem_dir_alloc(gfp_t gfp_mask)
 {
         /*
          * The above definition of ENTRIES_PER_PAGE, and the use of
          * BLOCKS_PER_PAGE on indirect pages, assume PAGE_CACHE_SIZE:
          * might be reconsidered if it ever diverges from PAGE_SIZE.
          *
          * Mobility flags are masked out as swap vectors cannot move
          */
         return alloc_pages((gfp_mask & ~GFP_MOVABLE_MASK) | __GFP_ZERO,
                                 PAGE_CACHE_SHIFT-PAGE_SHIFT);
 }
 
 static inline void shmem_dir_free(struct page *page)
 {
         __free_pages(page, PAGE_CACHE_SHIFT-PAGE_SHIFT);
 }
 
 static struct page **shmem_dir_map(struct page *page)
 {
         return (struct page **)kmap_atomic(page, KM_USER0);
 }
 
 static inline void shmem_dir_unmap(struct page **dir)
 {
         kunmap_atomic(dir, KM_USER0);
 }
 
 static swp_entry_t *shmem_swp_map(struct page *page)
 {
         return (swp_entry_t *)kmap_atomic(page, KM_USER1);
 }
 
 static inline void shmem_swp_balance_unmap(void)
 {
         /*
          * When passing a pointer to an i_direct entry, to code which
          * also handles indirect entries and so will shmem_swp_unmap,
          * we must arrange for the preempt count to remain in balance.
          * What kmap_atomic of a lowmem page does depends on config
          * and architecture, so pretend to kmap_atomic some lowmem page.
          */
         (void) kmap_atomic(ZERO_PAGE(0), KM_USER1);
 }
 
 static inline void shmem_swp_unmap(swp_entry_t *entry)
 {
         kunmap_atomic(entry, KM_USER1);
 }
 
 static inline struct shmem_sb_info *SHMEM_SB(struct super_block *sb)
 {
         return sb->s_fs_info;
 }
 
 /*
  * shmem_file_setup pre-accounts the whole fixed size of a VM object,
  * for shared memory and for shared anonymous (/dev/zero) mappings
  * (unless MAP_NORESERVE and sysctl_overcommit_memory <= 1),
  * consistent with the pre-accounting of private mappings ...
  */
 static inline int shmem_acct_size(unsigned long flags, loff_t size)
 {
         return (flags & VM_ACCOUNT) ?
                 security_vm_enough_memory_kern(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_kern(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 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 struct vm_operations_struct shmem_vm_ops;
 
 static struct backing_dev_info shmem_backing_dev_info  __read_mostly = {
         .ra_pages        = 0,        /* No readahead */
         .capabilities        = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
         .unplug_io_fn        = default_unplug_io_fn,
 };
 
 static LIST_HEAD(shmem_swaplist);
 static DEFINE_MUTEX(shmem_swaplist_mutex);
 
 static void shmem_free_blocks(struct inode *inode, long pages)
 {
         struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
         if (sbinfo->max_blocks) {
                 spin_lock(&sbinfo->stat_lock);
                 sbinfo->free_blocks += pages;
                 inode->i_blocks -= pages*BLOCKS_PER_PAGE;
                 spin_unlock(&sbinfo->stat_lock);
         }
 }
 
 static int shmem_reserve_inode(struct super_block *sb)
 {
         struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
         if (sbinfo->max_inodes) {
                 spin_lock(&sbinfo->stat_lock);
                 if (!sbinfo->free_inodes) {
                         spin_unlock(&sbinfo->stat_lock);
                         return -ENOSPC;
                 }
                 sbinfo->free_inodes--;
                 spin_unlock(&sbinfo->stat_lock);
         }
         return 0;
 }
 
 static void shmem_free_inode(struct super_block *sb)
 {
         struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
         if (sbinfo->max_inodes) {
                 spin_lock(&sbinfo->stat_lock);
                 sbinfo->free_inodes++;
                 spin_unlock(&sbinfo->stat_lock);
         }
 }
 
 /**
  * shmem_recalc_inode - recalculate the size of an inode
  * @inode: inode to recalc
  *
  * We have to calculate the free blocks since the mm can drop
  * undirtied hole pages behind our back.
  *
  * But normally   info->alloced == inode->i_mapping->nrpages + info->swapped
  * So mm freed is info->alloced - (inode->i_mapping->nrpages + info->swapped)
  *
  * It has to be called with the spinlock held.
  */
 static void shmem_recalc_inode(struct inode *inode)
 {
         struct shmem_inode_info *info = SHMEM_I(inode);
         long freed;
 
         freed = info->alloced - info->swapped - inode->i_mapping->nrpages;
         if (freed > 0) {
                 info->alloced -= freed;
                 shmem_unacct_blocks(info->flags, freed);
                 shmem_free_blocks(inode, freed);
         }
 }
 
 /**
  * shmem_swp_entry - find the swap vector position in the info structure
  * @info:  info structure for the inode
  * @index: index of the page to find
  * @page:  optional page to add to the structure. Has to be preset to
  *         all zeros
  *
  * If there is no space allocated yet it will return NULL when
  * page is NULL, else it will use the page for the needed block,
  * setting it to NULL on return to indicate that it has been used.
  *
  * The swap vector is organized the following way:
  *
  * There are SHMEM_NR_DIRECT entries directly stored in the
  * shmem_inode_info structure. So small files do not need an addional
  * allocation.
  *
  * For pages with index > SHMEM_NR_DIRECT there is the pointer
  * i_indirect which points to a page which holds in the first half
  * doubly indirect blocks, in the second half triple indirect blocks:
  *
  * For an artificial ENTRIES_PER_PAGE = 4 this would lead to the
  * following layout (for SHMEM_NR_DIRECT == 16):
  *
  * i_indirect -> dir --> 16-19
  *               |             +-> 20-23
  *               |
  *               +-->dir2 --> 24-27
  *               |               +-> 28-31
  *               |               +-> 32-35
  *               |               +-> 36-39
  *               |
  *               +-->dir3 --> 40-43
  *                               +-> 44-47
  *                              +-> 48-51
  *                              +-> 52-55
  */
 static swp_entry_t *shmem_swp_entry(struct shmem_inode_info *info, unsigned long index, struct page **page)
 {
         unsigned long offset;
         struct page **dir;
         struct page *subdir;
 
         if (index < SHMEM_NR_DIRECT) {
                 shmem_swp_balance_unmap();
                 return info->i_direct+index;
         }
         if (!info->i_indirect) {
                 if (page) {
                         info->i_indirect = *page;
                         *page = NULL;
                 }
                 return NULL;                        /* need another page */
         }
 
         index -= SHMEM_NR_DIRECT;
         offset = index % ENTRIES_PER_PAGE;
         index /= ENTRIES_PER_PAGE;
         dir = shmem_dir_map(info->i_indirect);
 
         if (index >= ENTRIES_PER_PAGE/2) {
                 index -= ENTRIES_PER_PAGE/2;
                 dir += ENTRIES_PER_PAGE/2 + index/ENTRIES_PER_PAGE;
                 index %= ENTRIES_PER_PAGE;
                 subdir = *dir;
                 if (!subdir) {
                         if (page) {
                                 *dir = *page;
                                 *page = NULL;
                         }
                         shmem_dir_unmap(dir);
                         return NULL;                /* need another page */
                 }
                 shmem_dir_unmap(dir);
                 dir = shmem_dir_map(subdir);
         }
 
         dir += index;
         subdir = *dir;
         if (!subdir) {
                 if (!page || !(subdir = *page)) {
                         shmem_dir_unmap(dir);
                         return NULL;                /* need a page */
                 }
                 *dir = subdir;
                 *page = NULL;
         }
         shmem_dir_unmap(dir);
         return shmem_swp_map(subdir) + offset;
 }
 
 static void shmem_swp_set(struct shmem_inode_info *info, swp_entry_t *entry, unsigned long value)
 {
         long incdec = value? 1: -1;
 
         entry->val = value;
         info->swapped += incdec;
         if ((unsigned long)(entry - info->i_direct) >= SHMEM_NR_DIRECT) {
                 struct page *page = kmap_atomic_to_page(entry);
                 set_page_private(page, page_private(page) + incdec);
         }
 }
 
 /**
  * shmem_swp_alloc - get the position of the swap entry for the page.
  * @info:        info structure for the inode
  * @index:        index of the page to find
  * @sgp:        check and recheck i_size? skip allocation?
  *
  * If the entry does not exist, allocate it.
  */
 static swp_entry_t *shmem_swp_alloc(struct shmem_inode_info *info, unsigned long index, enum sgp_type sgp)
 {
         struct inode *inode = &info->vfs_inode;
         struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
         struct page *page = NULL;
         swp_entry_t *entry;
 
         if (sgp != SGP_WRITE &&
             ((loff_t) index << PAGE_CACHE_SHIFT) >= i_size_read(inode))
                 return ERR_PTR(-EINVAL);
 
         while (!(entry = shmem_swp_entry(info, index, &page))) {
                 if (sgp == SGP_READ)
                         return shmem_swp_map(ZERO_PAGE(0));
                 /*
                  * Test 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));
                 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
  * @punch_lock: pointer to spinlock when needed for the holepunch case
  */
 static int shmem_free_swp(swp_entry_t *dir, swp_entry_t *edir,
                                                 spinlock_t *punch_lock)
 {
         spinlock_t *punch_unlock = NULL;
         swp_entry_t *ptr;
         int freed = 0;
 
         for (ptr = dir; ptr < edir; ptr++) {
                 if (ptr->val) {
                         if (unlikely(punch_lock)) {
                                 punch_unlock = punch_lock;
                                 punch_lock = NULL;
                                 spin_lock(punch_unlock);
                                 if (!ptr->val)
                                         continue;
                         }
                         free_swap_and_cache(*ptr);
                         *ptr = (swp_entry_t){0};
                         freed++;
                 }
         }
         if (punch_unlock)
                 spin_unlock(punch_unlock);
         return freed;
 }
 
 static int shmem_map_and_free_swp(struct page *subdir, int offset,
                 int limit, struct page ***dir, spinlock_t *punch_lock)
 {
         swp_entry_t *ptr;
         int freed = 0;
 
         ptr = shmem_swp_map(subdir);
         for (; offset < limit; offset += LATENCY_LIMIT) {
                 int size = limit - offset;
                 if (size > LATENCY_LIMIT)
                         size = LATENCY_LIMIT;
                 freed += shmem_free_swp(ptr+offset, ptr+offset+size,
                                                         punch_lock);
                 if (need_resched()) {
                         shmem_swp_unmap(ptr);
                         if (*dir) {
                                 shmem_dir_unmap(*dir);
                                 *dir = NULL;
                         }
                         cond_resched();
                         ptr = shmem_swp_map(subdir);
                 }
         }
         shmem_swp_unmap(ptr);
         return freed;
 }
 
 static void shmem_free_pages(struct list_head *next)
 {
         struct page *page;
         int freed = 0;
 
         do {
                 page = container_of(next, struct page, lru);
                 next = next->next;
                 shmem_dir_free(page);
                 freed++;
                 if (freed >= LATENCY_LIMIT) {
                         cond_resched();
                         freed = 0;
                 }
         } while (next);
 }
 
 static void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end)
 {
         struct shmem_inode_info *info = SHMEM_I(inode);
         unsigned long idx;
         unsigned long size;
         unsigned long limit;
         unsigned long stage;
         unsigned long diroff;
         struct page **dir;
         struct page *topdir;
         struct page *middir;
         struct page *subdir;
         swp_entry_t *ptr;
         LIST_HEAD(pages_to_free);
         long nr_pages_to_free = 0;
         long nr_swaps_freed = 0;
         int offset;
         int freed;
         int punch_hole;
         spinlock_t *needs_lock;
         spinlock_t *punch_lock;
         unsigned long upper_limit;
 
         inode->i_ctime = inode->i_mtime = CURRENT_TIME;
         idx = (start + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
         if (idx >= info->next_index)
                 return;
 
         spin_lock(&info->lock);
         info->flags |= SHMEM_TRUNCATE;
         if (likely(end == (loff_t) -1)) {
                 limit = info->next_index;
                 upper_limit = SHMEM_MAX_INDEX;
                 info->next_index = idx;
                 needs_lock = NULL;
                 punch_hole = 0;
         } else {
                 if (end + 1 >= inode->i_size) {        /* we may free a little more */
                         limit = (inode->i_size + PAGE_CACHE_SIZE - 1) >>
                                                         PAGE_CACHE_SHIFT;
                         upper_limit = SHMEM_MAX_INDEX;
                 } else {
                         limit = (end + 1) >> PAGE_CACHE_SHIFT;
                         upper_limit = limit;
                 }
                 needs_lock = &info->lock;
                 punch_hole = 1;
         }
 
         topdir = info->i_indirect;
         if (topdir && idx <= SHMEM_NR_DIRECT && !punch_hole) {
                 info->i_indirect = NULL;
                 nr_pages_to_free++;
                 list_add(&topdir->lru, &pages_to_free);
         }
         spin_unlock(&info->lock);
 
         if (info->swapped && idx < SHMEM_NR_DIRECT) {
                 ptr = info->i_direct;
                 size = limit;
                 if (size > SHMEM_NR_DIRECT)
                         size = SHMEM_NR_DIRECT;
                 nr_swaps_freed = shmem_free_swp(ptr+idx, ptr+size, needs_lock);
         }
 
         /*
          * If there are no indirect blocks or we are punching a hole
          * below indirect blocks, nothing to be done.
          */
         if (!topdir || limit <= SHMEM_NR_DIRECT)
                 goto done2;
 
         /*
          * The truncation case has already dropped info->lock, and we're safe
          * because i_size and next_index have already been lowered, preventing
          * access beyond.  But in the punch_hole case, we still need to take
          * the lock when updating the swap directory, because there might be
          * racing accesses by shmem_getpage(SGP_CACHE), shmem_unuse_inode or
          * shmem_writepage.  However, whenever we find we can remove a whole
          * directory page (not at the misaligned start or end of the range),
          * we first NULLify its pointer in the level above, and then have no
          * need to take the lock when updating its contents: needs_lock and
          * punch_lock (either pointing to info->lock or NULL) manage this.
          */
 
         upper_limit -= SHMEM_NR_DIRECT;
         limit -= SHMEM_NR_DIRECT;
         idx = (idx > SHMEM_NR_DIRECT)? (idx - SHMEM_NR_DIRECT): 0;
         offset = idx % ENTRIES_PER_PAGE;
         idx -= offset;
 
         dir = shmem_dir_map(topdir);
         stage = ENTRIES_PER_PAGEPAGE/2;
         if (idx < ENTRIES_PER_PAGEPAGE/2) {
                 middir = topdir;
                 diroff = idx/ENTRIES_PER_PAGE;
         } else {
                 dir += ENTRIES_PER_PAGE/2;
                 dir += (idx - ENTRIES_PER_PAGEPAGE/2)/ENTRIES_PER_PAGEPAGE;
                 while (stage <= idx)
                         stage += ENTRIES_PER_PAGEPAGE;
                 middir = *dir;
                 if (*dir) {
                         diroff = ((idx - ENTRIES_PER_PAGEPAGE/2) %
                                 ENTRIES_PER_PAGEPAGE) / ENTRIES_PER_PAGE;
                         if (!diroff && !offset && upper_limit >= stage) {
                                 if (needs_lock) {
                                         spin_lock(needs_lock);
                                         *dir = NULL;
                                         spin_unlock(needs_lock);
                                         needs_lock = NULL;
                                 } else
                                         *dir = NULL;
                                 nr_pages_to_free++;
                                 list_add(&middir->lru, &pages_to_free);
                         }
                         shmem_dir_unmap(dir);
                         dir = shmem_dir_map(middir);
                 } else {
                         diroff = 0;
                         offset = 0;
                         idx = stage;
                 }
         }
 
         for (; idx < limit; idx += ENTRIES_PER_PAGE, diroff++) {
                 if (unlikely(idx == stage)) {
                         shmem_dir_unmap(dir);
                         dir = shmem_dir_map(topdir) +
                             ENTRIES_PER_PAGE/2 + idx/ENTRIES_PER_PAGEPAGE;
                         while (!*dir) {
                                 dir++;
                                 idx += ENTRIES_PER_PAGEPAGE;
                                 if (idx >= limit)
                                         goto done1;
                         }
                         stage = idx + ENTRIES_PER_PAGEPAGE;
                         middir = *dir;
                         if (punch_hole)
                                 needs_lock = &info->lock;
                         if (upper_limit >= stage) {
                                 if (needs_lock) {
                                         spin_lock(needs_lock);
                                         *dir = NULL;
                                         spin_unlock(needs_lock);
                                         needs_lock = NULL;
                                 } else
                                         *dir = NULL;
                                 nr_pages_to_free++;
                                 list_add(&middir->lru, &pages_to_free);
                         }
                         shmem_dir_unmap(dir);
                         cond_resched();
                         dir = shmem_dir_map(middir);
                         diroff = 0;
                 }
                 punch_lock = needs_lock;
                 subdir = dir[diroff];
                 if (subdir && !offset && upper_limit-idx >= ENTRIES_PER_PAGE) {
                         if (needs_lock) {
                                 spin_lock(needs_lock);
                                 dir[diroff] = NULL;
                                 spin_unlock(needs_lock);
                                 punch_lock = NULL;
                         } else
                                 dir[diroff] = NULL;
                         nr_pages_to_free++;
                         list_add(&subdir->lru, &pages_to_free);
                 }
                 if (subdir && page_private(subdir) /* has swap entries */) {
                         size = limit - idx;
                         if (size > ENTRIES_PER_PAGE)
                                 size = ENTRIES_PER_PAGE;
                         freed = shmem_map_and_free_swp(subdir,
                                         offset, size, &dir, punch_lock);
                         if (!dir)
                                 dir = shmem_dir_map(middir);
                         nr_swaps_freed += freed;
                         if (offset || punch_lock) {
                                 spin_lock(&info->lock);
                                 set_page_private(subdir,
                                         page_private(subdir) - freed);
                                 spin_unlock(&info->lock);
                         } else
                                 BUG_ON(page_private(subdir) != freed);
                 }
                 offset = 0;
         }
 done1:
         shmem_dir_unmap(dir);
 done2:
         if (inode->i_mapping->nrpages && (info->flags & SHMEM_PAGEIN)) {
                 /*
                  * Call truncate_inode_pages again: racing shmem_unuse_inode
                  * may have swizzled a page in from swap since 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.
                  *
                  * Recalling truncate_inode_pages_range and unmap_mapping_range
                  * every time for punch_hole (which never got a chance to clear
                  * SHMEM_PAGEIN at the start of vmtruncate_range) is expensive,
                  * yet hardly ever necessary: try to optimize them out later.
                  */
                 truncate_inode_pages_range(inode->i_mapping, start, end);
                 if (punch_hole)
                         unmap_mapping_range(inode->i_mapping, start,
                                                         end - start, 1);
         }
 
         spin_lock(&info->lock);
         info->flags &= ~SHMEM_TRUNCATE;
         info->swapped -= nr_swaps_freed;
         if (nr_pages_to_free)
                 shmem_free_blocks(inode, nr_pages_to_free);
         shmem_recalc_inode(inode);
         spin_unlock(&info->lock);
 
         /*
          * Empty swap vector directory pages to be freed?
          */
         if (!list_empty(&pages_to_free)) {
                 pages_to_free.prev->next = NULL;
                 shmem_free_pages(pages_to_free.next);
         }
 }
 
 static 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 (S_ISREG(inode->i_mode) && (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);
                                 if (page)
                                         unlock_page(page);
                         }
                         /*
                          * Reset SHMEM_PAGEIN flag so that shmem_truncate can
                          * detect if any pages might have been added to cache
                          * after truncate_inode_pages.  But we needn't bother
                          * if it's being fully truncated to zero-length: the
                          * nrpages check is efficient enough in that case.
                          */
                         if (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);
 #ifdef CONFIG_TMPFS_POSIX_ACL
         if (!error && (attr->ia_valid & ATTR_MODE))
                 error = generic_acl_chmod(inode, &shmem_acl_ops);
 #endif
         if (page)
                 page_cache_release(page);
         return error;
 }
 
 static void shmem_delete_inode(struct inode *inode)
 {
         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)) {
                         mutex_lock(&shmem_swaplist_mutex);
                         list_del_init(&info->swaplist);
                         mutex_unlock(&shmem_swaplist_mutex);
                 }
         }
         BUG_ON(inode->i_blocks);
         shmem_free_inode(inode->i_sb);
         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;
         int error;
 
         idx = 0;
         ptr = info->i_direct;
         spin_lock(&info->lock);
         if (!info->swapped) {
                 list_del_init(&info->swaplist);
                 goto lost2;
         }
         limit = info->next_index;
         size = limit;
         if (size > SHMEM_NR_DIRECT)
                 size = SHMEM_NR_DIRECT;
         offset = shmem_find_swp(entry, ptr, ptr+size);
         if (offset >= 0)
                 goto found;
         if (!info->i_indirect)
                 goto lost2;
 
         dir = shmem_dir_map(info->i_indirect);
         stage = SHMEM_NR_DIRECT + ENTRIES_PER_PAGEPAGE/2;
 
         for (idx = SHMEM_NR_DIRECT; idx < limit; idx += ENTRIES_PER_PAGE, dir++) {
                 if (unlikely(idx == stage)) {
                         shmem_dir_unmap(dir-1);
                         if (cond_resched_lock(&info->lock)) {
                                 /* check it has not been truncated */
                                 if (limit > info->next_index) {
                                         limit = info->next_index;
                                         if (idx >= limit)
                                                 goto lost2;
                                 }
                         }
                         dir = shmem_dir_map(info->i_indirect) +
                             ENTRIES_PER_PAGE/2 + idx/ENTRIES_PER_PAGEPAGE;
                         while (!*dir) {
                                 dir++;
                                 idx += ENTRIES_PER_PAGEPAGE;
                                 if (idx >= limit)
                                         goto lost1;
                         }
                         stage = idx + ENTRIES_PER_PAGEPAGE;
                         subdir = *dir;
                         shmem_dir_unmap(dir);
                         dir = shmem_dir_map(subdir);
                 }
                 subdir = *dir;
                 if (subdir && page_private(subdir)) {
                         ptr = shmem_swp_map(subdir);
                         size = limit - idx;
                         if (size > ENTRIES_PER_PAGE)
                                 size = ENTRIES_PER_PAGE;
                         offset = shmem_find_swp(entry, ptr, ptr+size);
                         shmem_swp_unmap(ptr);
                         if (offset >= 0) {
                                 shmem_dir_unmap(dir);
                                 goto found;
                         }
                 }
         }
 lost1:
         shmem_dir_unmap(dir-1);
 lost2:
         spin_unlock(&info->lock);
         return 0;
 found:
         idx += offset;
         inode = igrab(&info->vfs_inode);
         spin_unlock(&info->lock);
 
         /*
          * Move _head_ to start search for next from here.
          * But be careful: shmem_delete_inode checks list_empty without taking
          * mutex, and there's an instant in list_move_tail when info->swaplist
          * would appear empty, if it were the only one on shmem_swaplist.  We
          * could avoid doing it if inode NULL; or use this minor optimization.
          */
         if (shmem_swaplist.next != &info->swaplist)
                 list_move_tail(&shmem_swaplist, &info->swaplist);
         mutex_unlock(&shmem_swaplist_mutex);
 
         error = 1;
         if (!inode)
                 goto out;
         /* Precharge page using GFP_KERNEL while we can wait */
         error = mem_cgroup_cache_charge(page, current->mm, GFP_KERNEL);
         if (error)
                 goto out;
         error = radix_tree_preload(GFP_KERNEL);
         if (error) {
                 mem_cgroup_uncharge_cache_page(page);
                 goto out;
         }
         error = 1;
 
         spin_lock(&info->lock);
         ptr = shmem_swp_entry(info, idx, NULL);
         if (ptr && ptr->val == entry.val) {
                 error = add_to_page_cache_locked(page, inode->i_mapping,
                                                 idx, GFP_NOWAIT);
                 /* does mem_cgroup_uncharge_cache_page on error */
         } else        /* we must compensate for our precharge above */
                 mem_cgroup_uncharge_cache_page(page);
 
         if (error == -EEXIST) {
                 struct page *filepage = find_get_page(inode->i_mapping, idx);
                 error = 1;
                 if (filepage) {
                         /*
                          * There might be a more uptodate page coming down
                          * from a stacked writepage: forget our swappage if so.
                          */
                         if (PageUptodate(filepage))
                                 error = 0;
                         page_cache_release(filepage);
                 }
         }
         if (!error) {
                 delete_from_swap_cache(page);
                 set_page_dirty(page);
                 info->flags |= SHMEM_PAGEIN;
                 shmem_swp_set(info, ptr, 0);
                 swap_free(entry);
                 error = 1;        /* not an error, but entry was found */
         }
         if (ptr)
                 shmem_swp_unmap(ptr);
         spin_unlock(&info->lock);
         radix_tree_preload_end();
 out:
         unlock_page(page);
         page_cache_release(page);
         iput(inode);                /* allows for NULL */
         return error;
 }
 
 /*
  * shmem_unuse() search for an eventually swapped out shmem page.
  */
 int shmem_unuse(swp_entry_t entry, struct page *page)
 {
         struct list_head *p, *next;
         struct shmem_inode_info *info;
         int found = 0;
 
         mutex_lock(&shmem_swaplist_mutex);
         list_for_each_safe(p, next, &shmem_swaplist) {
                 info = list_entry(p, struct shmem_inode_info, swaplist);
                 found = shmem_unuse_inode(info, entry, page);
                 cond_resched();
                 if (found)
                         goto out;
         }
         mutex_unlock(&shmem_swaplist_mutex);
 out:        return found;        /* 0 or 1 or -ENOMEM */
 }
 
 /*
  * Move the page from the page cache to the swap cache.
  */
 static int shmem_writepage(struct page *page, struct writeback_control *wbc)
{
        struct shmem_inode_info *info;
        swp_entry_t *entry, swap;
        struct address_space *mapping;
        unsigned long index;
        struct inode *inode;

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

        /*
         * shmem_backing_dev_info's capabilities prevent regular writeback or
         * sync from ever calling shmem_writepage; but a stacking filesystem
         * may use the ->writepage of its underlying filesystem, in which case
         * tmpfs should write out to swap only in response to memory pressure,
         * and not for pdflush or sync.  However, in those cases, we do still
         * want to check if there's a redundant swappage to be discarded.
         */
        if (wbc->for_reclaim)
                swap = get_swap_page();
        else
                swap.val = 0;

        spin_lock(&info->lock);
        if (index >= info->next_index) {
                BUG_ON(!(info->flags & SHMEM_TRUNCATE));
                goto unlock;
        }
        entry = shmem_swp_entry(info, index, NULL);
        if (entry->val) {
                /*
                 * The more uptodate page coming down from a stacked
                 * writepage should replace our old swappage.
                 */
                free_swap_and_cache(*entry);
                shmem_swp_set(info, entry, 0);
        }
        shmem_recalc_inode(inode);

        if (swap.val && add_to_swap_cache(page, swap, GFP_ATOMIC) == 0) {
                remove_from_page_cache(page);
                shmem_swp_set(info, entry, swap.val);
                shmem_swp_unmap(entry);
                if (list_empty(&info->swaplist))
                        inode = igrab(inode);
                else
                        inode = NULL;
                spin_unlock(&info->lock);
                swap_duplicate(swap);
                BUG_ON(page_mapped(page));
                page_cache_release(page);        /* pagecache ref */
                set_page_dirty(page);
                unlock_page(page);
                if (inode) {
                        mutex_lock(&shmem_swaplist_mutex);
                        /* move instead of add in case we're racing */
                        list_move_tail(&info->swaplist, &shmem_swaplist);
                        mutex_unlock(&shmem_swaplist_mutex);
                        iput(inode);
                }
                return 0;
        }

        shmem_swp_unmap(entry);
unlock:
        spin_unlock(&info->lock);
        swap_free(swap);
redirty:
        set_page_dirty(page);
        if (wbc->for_reclaim)
                return AOP_WRITEPAGE_ACTIVATE;        /* Return with page locked */
        unlock_page(page);
        return 0;
}

#ifdef CONFIG_NUMA
#ifdef CONFIG_TMPFS
static void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
{
        char buffer[64];

        if (!mpol || mpol->mode == MPOL_DEFAULT)
                return;                /* show nothing */

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

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

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

static struct page *shmem_swapin(swp_entry_t entry, gfp_t gfp,
                        struct shmem_inode_info *info, unsigned long idx)
{
        struct mempolicy mpol, *spol;
        struct vm_area_struct pvma;
        struct page *page;

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

        /* Create a pseudo vma that just contains the policy */
        pvma.vm_start = 0;
        pvma.vm_pgoff = idx;
        pvma.vm_ops = NULL;
        pvma.vm_policy = spol;
        page = swapin_readahead(entry, gfp, &pvma, 0);
        return page;
}

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

        /* Create a pseudo vma that just contains the policy */
        pvma.vm_start = 0;
        pvma.vm_pgoff = idx;
        pvma.vm_ops = NULL;
        pvma.vm_policy = mpol_shared_policy_lookup(&info->policy, idx);

        /*
         * alloc_page_vma() will drop the shared policy reference
         */
        return alloc_page_vma(gfp, &pvma, 0);
}
#else /* !CONFIG_NUMA */
#ifdef CONFIG_TMPFS
static inline void shmem_show_mpol(struct seq_file *seq, struct mempolicy *p)
{
}
#endif /* CONFIG_TMPFS */

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

static inline struct page *shmem_alloc_page(gfp_t gfp,
                        struct shmem_inode_info *info, unsigned long idx)
{
        return alloc_page(gfp);
}
#endif /* CONFIG_NUMA */

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

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

        if (idx >= SHMEM_MAX_INDEX)
                return -EFBIG;

        if (type)
                *type = 0;

        /*
         * Normally, filepage is NULL on entry, and either found
         * uptodate immediately, or allocated and zeroed, or read
         * in under swappage, which is then assigned to filepage.
         * But shmem_readpage (required for splice) passes in a locked
         * filepage, which may be found not uptodate by other callers
         * too, and may need to be copied from the swappage read in.
         */
repeat:
        if (!filepage)
                filepage = find_lock_page(mapping, idx);
        if (filepage && PageUptodate(filepage))
                goto done;
        error = 0;
        gfp = mapping_gfp_mask(mapping);
        if (!filepage) {
                /*
                 * Try to preload while we can wait, to not make a habit of
                 * draining atomic reserves; but don't latch on to this cpu.
                 */
                error = radix_tree_preload(gfp & ~__GFP_HIGHMEM);
                if (error)
                        goto failed;
                radix_tree_preload_end();
        }

        spin_lock(&info->lock);
        shmem_recalc_inode(inode);
        entry = shmem_swp_alloc(info, idx, sgp);
        if (IS_ERR(entry)) {
                spin_unlock(&info->lock);
                error = PTR_ERR(entry);
                goto failed;
        }
        swap = *entry;

        if (swap.val) {
                /* Look it up and read it in.. */
                swappage = lookup_swap_cache(swap);
                if (!swappage) {
                        shmem_swp_unmap(entry);
                        /* here we actually do the io */
                        if (type && !(*type & VM_FAULT_MAJOR)) {
                                __count_vm_event(PGMAJFAULT);
                                *type |= VM_FAULT_MAJOR;
                        }
                        spin_unlock(&info->lock);
                        swappage = shmem_swapin(swap, gfp, info, idx);
                        if (!swappage) {
                                spin_lock(&info->lock);
                                entry = shmem_swp_alloc(info, idx, sgp);
                                if (IS_ERR(entry))
                                        error = PTR_ERR(entry);
                                else {
                                        if (entry->val == swap.val)
                                                error = -ENOMEM;
                                        shmem_swp_unmap(entry);
                                }
                                spin_unlock(&info->lock);
                                if (error)
                                        goto failed;
                                goto repeat;
                        }
                        wait_on_page_locked(swappage);
                        page_cache_release(swappage);
                        goto repeat;
                }

                /* We have to do this with page locked to prevent races */
                if (!trylock_page(swappage)) {
                        shmem_swp_unmap(entry);
                        spin_unlock(&info->lock);
                        wait_on_page_locked(swappage);
                        page_cache_release(swappage);
                        goto repeat;
                }
                if (PageWriteback(swappage)) {
                        shmem_swp_unmap(entry);
                        spin_unlock(&info->lock);
                        wait_on_page_writeback(swappage);
                        unlock_page(swappage);
                        page_cache_release(swappage);
                        goto repeat;
                }
                if (!PageUptodate(swappage)) {
                        shmem_swp_unmap(entry);
                        spin_unlock(&info->lock);
                        unlock_page(swappage);
                        page_cache_release(swappage);
                        error = -EIO;
                        goto failed;
                }

                if (filepage) {
                        shmem_swp_set(info, entry, 0);
                        shmem_swp_unmap(entry);
                        delete_from_swap_cache(swappage);
                        spin_unlock(&info->lock);
                        copy_highpage(filepage, swappage);
                        unlock_page(swappage);
                        page_cache_release(swappage);
                        flush_dcache_page(filepage);
                        SetPageUptodate(filepage);
                        set_page_dirty(filepage);
                        swap_free(swap);
                } else if (!(error = add_to_page_cache_locked(swappage, mapping,
                                        idx, GFP_NOWAIT))) {
                        info->flags |= SHMEM_PAGEIN;
                        shmem_swp_set(info, entry, 0);
                        shmem_swp_unmap(entry);
                        delete_from_swap_cache(swappage);
                        spin_unlock(&info->lock);
                        filepage = swappage;
                        set_page_dirty(filepage);
                        swap_free(swap);
                } else {
                        shmem_swp_unmap(entry);
                        spin_unlock(&info->lock);
                        unlock_page(swappage);
                        page_cache_release(swappage);
                        if (error == -ENOMEM) {
                                /* allow reclaim from this memory cgroup */
                                error = mem_cgroup_shrink_usage(current->mm,
                                                                gfp);
                                if (error)
                                        goto failed;
                        }
                        goto repeat;
                }
        } else if (sgp == SGP_READ && !filepage) {
                shmem_swp_unmap(entry);
                filepage = find_get_page(mapping, idx);
                if (filepage &&
                    (!PageUptodate(filepage) || !trylock_page(filepage))) {
                        spin_unlock(&info->lock);
                        wait_on_page_locked(filepage);
                        page_cache_release(filepage);
                        filepage = NULL;
                        goto repeat;
                }
                spin_unlock(&info->lock);
        } else {
                shmem_swp_unmap(entry);
                sbinfo = SHMEM_SB(inode->i_sb);
                if (sbinfo->max_blocks) {
                        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) {
                        int ret;

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

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

                        spin_lock(&info->lock);
                        entry = shmem_swp_alloc(info, idx, sgp);
                        if (IS_ERR(entry))
                                error = PTR_ERR(entry);
                        else {
                                swap = *entry;
                                shmem_swp_unmap(entry);
                        }
                        ret = error || swap.val;
                        if (ret)
                                mem_cgroup_uncharge_cache_page(filepage);
                        else
                                ret = add_to_page_cache_lru(filepage, mapping,
                                                idx, GFP_NOWAIT);
                        /*
                         * At add_to_page_cache_lru() failure, uncharge will
                         * be done automatically.
                         */
                        if (ret) {
                                spin_unlock(&info->lock);
                                page_cache_release(filepage);
                                shmem_unacct_blocks(info->flags, 1);
                                shmem_free_blocks(inode, 1);
                                filepage = NULL;
                                if (error)
                                        goto failed;
                                goto repeat;
                        }
                        info->flags |= SHMEM_PAGEIN;
                }

                info->alloced++;
                spin_unlock(&info->lock);
                clear_highpage(filepage);
                flush_dcache_page(filepage);
                SetPageUptodate(filepage);
                if (sgp == SGP_DIRTY)
                        set_page_dirty(filepage);
        }
done:
        *pagep = filepage;
        return 0;

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

static int shmem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
{
        struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
        int error;
        int ret;

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

        error = shmem_getpage(inode, vmf->pgoff, &vmf->page, SGP_CACHE, &ret);
        if (error)
                return ((error == -ENOMEM) ? VM_FAULT_OOM : VM_FAULT_SIGBUS);

        mark_page_accessed(vmf->page);
        return ret | VM_FAULT_LOCKED;
}

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

static struct mempolicy *shmem_get_policy(struct vm_area_struct *vma,
                                          unsigned long addr)
{
        struct inode *i = vma->vm_file->f_path.dentry->d_inode;
        unsigned long idx;

        idx = ((addr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
        return mpol_shared_policy_lookup(&SHMEM_I(i)->policy, idx);
}
#endif

int shmem_lock(struct file *file, int lock, struct user_struct *user)
{
        struct inode *inode = file->f_path.dentry->d_inode;
        struct shmem_inode_info *info = SHMEM_I(inode);
        int retval = -ENOMEM;

        spin_lock(&info->lock);
        if (lock && !(info->flags & VM_LOCKED)) {
                if (!user_shm_lock(inode->i_size, user))
                        goto out_nomem;
                info->flags |= VM_LOCKED;
                mapping_set_unevictable(file->f_mapping);
        }
        if (!lock && (info->flags & VM_LOCKED) && user) {
                user_shm_unlock(inode->i_size, user);
                info->flags &= ~VM_LOCKED;
                mapping_clear_unevictable(file->f_mapping);
                scan_mapping_unevictable_pages(file->f_mapping);
        }
        retval = 0;

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

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

static struct inode *
shmem_get_inode(struct super_block *sb, int mode, dev_t dev)
{
        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_mode = mode;
                inode->i_uid = current->fsuid;
                inode->i_gid = current->fsgid;
                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);
                INIT_LIST_HEAD(&info->swaplist);

                switch (mode & S_IFMT) {
                default:
                        inode->i_op = &shmem_special_inode_operations;
                        init_special_inode(inode, mode, dev);
                        break;
                case S_IFREG:
                        inode->i_mapping->a_ops = &shmem_aops;
                        inode->i_op = &shmem_inode_operations;
                        inode->i_fop = &shmem_file_operations;
                        mpol_shared_policy_init(&info->policy,
                                                 shmem_get_sbmpol(sbinfo));
                        break;
                case S_IFDIR:
                        inc_nlink(inode);
                        /* Some things misbehave if size == 0 on a directory */
                        inode->i_size = 2 * BOGO_DIRENT_SIZE;
                        inode->i_op = &shmem_dir_inode_operations;
                        inode->i_fop = &simple_dir_operations;
                        break;
                case S_IFLNK:
                        /*
                         * Must not load anything in the rbtree,
                         * mpol_free_shared_policy will not be called.
                         */
                        mpol_shared_policy_init(&info->policy, NULL);
                        break;
                }
        } else
                shmem_free_inode(sb);
        return inode;
}

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

/*
 * Normally tmpfs avoids the use of shmem_readpage and shmem_write_begin;
 * but providing them allows a tmpfs file to be used for splice, sendfile, and
 * below the loop driver, in the generic fashion that many filesystems support.
 */
static int shmem_readpage(struct file *file, struct page *page)
{
        struct inode *inode = page->mapping->host;
        int error = shmem_getpage(inode, page->index, &page, SGP_CACHE, NULL);
        unlock_page(page);
        return error;
}

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

static int
shmem_write_end(struct file *file, struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned copied,
                        struct page *page, void *fsdata)
{
        struct inode *inode = mapping->host;

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

        unlock_page(page);
        set_page_dirty(page);
        page_cache_release(page);

        return copied;
}

static void do_shmem_file_read(struct file *filp, loff_t *ppos, read_descriptor_t *desc, read_actor_t actor)
{
        struct inode *inode = filp->f_path.dentry->d_inode;
        struct address_space *mapping = inode->i_mapping;
        unsigned long index, offset;
        enum sgp_type sgp = SGP_READ;

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

        index = *ppos >> PAGE_CACHE_SHIFT;
        offset = *ppos & ~PAGE_CACHE_MASK;

        for (;;) {
                struct page *page = NULL;
                unsigned long end_index, nr, ret;
                loff_t i_size = i_size_read(inode);

                end_index = i_size >> PAGE_CACHE_SHIFT;
                if (index > end_index)
                        break;
                if (index == end_index) {
                        nr = i_size & ~PAGE_CACHE_MASK;
                        if (nr <= offset)
                                break;
                }

                desc->error = shmem_getpage(inode, index, &page, sgp, NULL);
                if (desc->error) {
                        if (desc->error == -EINVAL)
                                desc->error = 0;
                        break;
                }
                if (page)
                        unlock_page(page);

                /*
                 * We must evaluate after, since reads (unlike writes)
                 * are called without i_mutex protection against truncate
                 */
                nr = PAGE_CACHE_SIZE;
                i_size = i_size_read(inode);
                end_index = i_size >> PAGE_CACHE_SHIFT;
                if (index == end_index) {
                        nr = i_size & ~PAGE_CACHE_MASK;
                        if (nr <= offset) {
                                if (page)
                                        page_cache_release(page);
                                break;
                        }
                }
                nr -= offset;

                if (page) {
                        /*
                         * If users can be writing to this page using arbitrary
                         * virtual addresses, take care about potential aliasing
                         * before reading the page on the kernel side.
                         */
                        if (mapping_writably_mapped(mapping))
                                flush_dcache_page(page);
                        /*
                         * Mark the page accessed if we read the beginning.
                         */
                        if (!offset)
                                mark_page_accessed(page);
                } else {
                        page = ZERO_PAGE(0);
                        page_cache_get(page);
                }

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

                page_cache_release(page);
                if (ret != nr || !desc->count)
                        break;

                cond_resched();
        }

        *ppos = ((loff_t) index << PAGE_CACHE_SHIFT) + offset;
        file_accessed(filp);
}

static ssize_t shmem_file_aio_read(struct kiocb *iocb,
                const struct iovec *iov, unsigned long nr_segs, loff_t pos)
{
        struct file *filp = iocb->ki_filp;
        ssize_t retval;
        unsigned long seg;
        size_t count;
        loff_t *ppos = &iocb->ki_pos;

        retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
        if (retval)
                return retval;

        for (seg = 0; seg < nr_segs; seg++) {
                read_descriptor_t desc;

                desc.written = 0;
                desc.arg.buf = iov[seg].iov_base;
                desc.count = iov[seg].iov_len;
                if (desc.count == 0)
                        continue;
                desc.error = 0;
                do_shmem_file_read(filp, ppos, &desc, file_read_actor);
                retval += desc.written;
                if (desc.error) {
                        retval = retval ?: desc.error;
                        break;
                }
                if (desc.count > 0)
                        break;
        }
        return retval;
}

static int shmem_statfs(struct dentry *dentry, struct kstatfs *buf)
{
        struct shmem_sb_info *sbinfo = SHMEM_SB(dentry->d_sb);

        buf->f_type = TMPFS_MAGIC;
        buf->f_bsize = PAGE_CACHE_SIZE;
        buf->f_namelen = NAME_MAX;
        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 = shmem_acl_init(inode, dir);
                if (error) {
                        iput(inode);
                        return error;
                }
                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;
        inc_nlink(dir);
        return 0;
}

static int shmem_create(struct inode *dir, struct dentry *dentry, int mode,
                struct nameidata *nd)
{
        return shmem_mknod(dir, dentry, mode | S_IFREG, 0);
}

/*
 * Link a file..
 */
static int shmem_link(struct dentry *old_dentry, struct inode *dir, struct dentry *dentry)
{
        struct inode *inode = old_dentry->d_inode;
        int ret;

        /*
         * No ordinary (disk based) filesystem counts links as inodes;
         * but each new link needs a new dentry, pinning lowmem, and
         * tmpfs dentries cannot be pruned until they are unlinked.
         */
        ret = shmem_reserve_inode(inode->i_sb);
        if (ret)
                goto out;

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

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

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

        dir->i_size -= BOGO_DIRENT_SIZE;
        inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;
        drop_nlink(inode);
        dput(dentry);        /* Undo the count from "create" - this does all the work */
        return 0;
}

static int shmem_rmdir(struct inode *dir, struct dentry *dentry)
{
        if (!simple_empty(dentry))
                return -ENOTEMPTY;

        drop_nlink(dentry->d_inode);
        drop_nlink(dir);
        return shmem_unlink(dir, dentry);
}

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

        if (!simple_empty(new_dentry))
                return -ENOTEMPTY;

        if (new_dentry->d_inode) {
                (void) shmem_unlink(new_dir, new_dentry);
                if (they_are_dirs)
                        drop_nlink(old_dir);
        } else if (they_are_dirs) {
                drop_nlink(old_dir);
                inc_nlink(new_dir);
        }

        old_dir->i_size -= BOGO_DIRENT_SIZE;
        new_dir->i_size += BOGO_DIRENT_SIZE;
        old_dir->i_ctime = old_dir->i_mtime =
        new_dir->i_ctime = new_dir->i_mtime =
        inode->i_ctime = CURRENT_TIME;
        return 0;
}

static int shmem_symlink(struct inode *dir, struct dentry *dentry, const char *symname)
{
        int error;
        int len;
        struct inode *inode;
        struct page *page = NULL;
        char *kaddr;
        struct shmem_inode_info *info;

        len = strlen(symname) + 1;
        if (len > PAGE_CACHE_SIZE)
                return -ENAMETOOLONG;

        inode = shmem_get_inode(dir->i_sb, 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;
                }
                unlock_page(page);
                inode->i_mapping->a_ops = &shmem_aops;
                inode->i_op = &shmem_symlink_inode_operations;
                kaddr = kmap_atomic(page, KM_USER0);
                memcpy(kaddr, symname, len);
                kunmap_atomic(kaddr, KM_USER0);
                set_page_dirty(page);
                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));
        if (page)
                unlock_page(page);
        return page;
}

static void shmem_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
{
        if (!IS_ERR(nd_get_link(nd))) {
                struct page *page = cookie;
                kunmap(page);
                mark_page_accessed(page);
                page_cache_release(page);
        }
}

static const struct inode_operations shmem_symlink_inline_operations = {
        .readlink        = generic_readlink,
        .follow_link        = shmem_follow_link_inline,
};

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

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

static size_t shmem_xattr_security_list(struct inode *inode, char *list,
                                        size_t list_len, const char *name,
                                        size_t name_len)
{
        return security_inode_listsecurity(inode, list, list_len);
}

static int shmem_xattr_security_get(struct inode *inode, const char *name,
                                    void *buffer, size_t size)
{
        if (strcmp(name, "") == 0)
                return -EINVAL;
        return xattr_getsecurity(inode, name, buffer, size);
}

static int shmem_xattr_security_set(struct inode *inode, const char *name,
                                    const void *value, size_t size, int flags)
{
        if (strcmp(name, "") == 0)
                return -EINVAL;
        return security_inode_setsecurity(inode, name, value, size, flags);
}

static struct xattr_handler shmem_xattr_security_handler = {
        .prefix = XATTR_SECURITY_PREFIX,
        .list   = shmem_xattr_security_list,
        .get    = shmem_xattr_security_get,
        .set    = shmem_xattr_security_set,
};

static struct xattr_handler *shmem_xattr_handlers[] = {
        &shmem_xattr_acl_access_handler,
        &shmem_xattr_acl_default_handler,
        &shmem_xattr_security_handler,
        NULL
};
#endif

static struct dentry *shmem_get_parent(struct dentry *child)
{
        return ERR_PTR(-ESTALE);
}

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

static struct dentry *shmem_fh_to_dentry(struct super_block *sb,
                struct fid *fid, int fh_len, int fh_type)
{
        struct inode *inode;
        struct dentry *dentry = NULL;
        u64 inum = fid->raw[2];
        inum = (inum << 32) | fid->raw[1];

        if (fh_len < 3)
                return NULL;

        inode = ilookup5(sb, (unsigned long)(inum + fid->raw[0]),
                        shmem_match, fid->raw);
        if (inode) {
                dentry = d_find_alias(inode);
                iput(inode);
        }

        return dentry;
}

static int shmem_encode_fh(struct dentry *dentry, __u32 *fh, int *len,
                                int connectable)
{
        struct inode *inode = dentry->d_inode;

        if (*len < 3)
                return 255;

        if (hlist_unhashed(&inode->i_hash)) {
                /* Unfortunately insert_inode_hash is not idempotent,
                 * so as we hash inodes here rather than at creation
                 * time, we need a lock to ensure we only try
                 * to do it once
                 */
                static DEFINE_SPINLOCK(lock);
                spin_lock(&lock);
                if (hlist_unhashed(&inode->i_hash))
                        __insert_inode_hash(inode,
                                            inode->i_ino + inode->i_generation);
                spin_unlock(&lock);
        }

        fh[0] = inode->i_generation;
        fh[1] = inode->i_ino;
        fh[2] = ((__u64)inode->i_ino) >> 32;

        *len = 3;
        return 1;
}

static const struct export_operations shmem_export_ops = {
        .get_parent     = shmem_get_parent,
        .encode_fh      = shmem_encode_fh,
        .fh_to_dentry        = shmem_fh_to_dentry,
};

static int shmem_parse_options(char *options, struct shmem_sb_info *sbinfo,
                               bool remount)
{
        char *this_char, *value, *rest;

        while (options != NULL) {
                this_char = options;
                for (;;) {
                        /*
                         * NUL-terminate this option: unfortunately,
                         * mount options form a comma-separated list,
                         * but mpol's nodelist may also contain commas.
                         */
                        options = strchr(options, ',');
                        if (options == NULL)
                                break;
                        options++;
                        if (!isdigit(*options)) {
                                options[-1] = '\0';
                                break;
                        }
                }
                if (!*this_char)
                        continue;
                if ((value = strchr(this_char,'=')) != NULL) {
                        *value++ = 0;
                } else {
                        printk(KERN_ERR
                            "tmpfs: No value for mount option '%s'\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;
                        sbinfo->max_blocks =
                                DIV_ROUND_UP(size, PAGE_CACHE_SIZE);
                } else if (!strcmp(this_char,"nr_blocks")) {
                        sbinfo->max_blocks = memparse(value, &rest);
                        if (*rest)
                                goto bad_val;
                } else if (!strcmp(this_char,"nr_inodes")) {
                        sbinfo->max_inodes = memparse(value, &rest);
                        if (*rest)
                                goto bad_val;
                } else if (!strcmp(this_char,"mode")) {
                        if (remount)
                                continue;
                        sbinfo->mode = simple_strtoul(value, &rest, 8) & 07777;
                        if (*rest)
                                goto bad_val;
                } else if (!strcmp(this_char,"uid")) {
                        if (remount)
                                continue;
                        sbinfo->uid = simple_strtoul(value, &rest, 0);
                        if (*rest)
                                goto bad_val;
                } else if (!strcmp(this_char,"gid")) {
                        if (remount)
                                continue;
                        sbinfo->gid = simple_strtoul(value, &rest, 0);
                        if (*rest)
                                goto bad_val;
                } else if (!strcmp(this_char,"mpol")) {
                        if (mpol_parse_str(value, &sbinfo->mpol, 1))
                                goto bad_val;
                } else {
                        printk(KERN_ERR "tmpfs: Bad mount option %s\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);
        struct shmem_sb_info config = *sbinfo;
        unsigned long blocks;
        unsigned long inodes;
        int error = -EINVAL;

        if (shmem_parse_options(data, &config, true))
                return error;

        spin_lock(&sbinfo->stat_lock);
        blocks = sbinfo->max_blocks - sbinfo->free_blocks;
        inodes = sbinfo->max_inodes - sbinfo->free_inodes;
        if (config.max_blocks < blocks)
                goto out;
        if (config.max_inodes < inodes)
                goto out;
        /*
         * Those tests also disallow limited->unlimited while any are in
         * use, so i_blocks will always be zero when max_blocks is zero;
         * but we must separately disallow unlimited->limited, because
         * in that case we have no record of how much is already in use.
         */
        if (config.max_blocks && !sbinfo->max_blocks)
                goto out;
        if (config.max_inodes && !sbinfo->max_inodes)
                goto out;

        error = 0;
        sbinfo->max_blocks  = config.max_blocks;
        sbinfo->free_blocks = config.max_blocks - blocks;
        sbinfo->max_inodes  = config.max_inodes;
        sbinfo->free_inodes = config.max_inodes - inodes;

        mpol_put(sbinfo->mpol);
        sbinfo->mpol        = config.mpol;        /* transfers initial ref */
out:
        spin_unlock(&sbinfo->stat_lock);
        return error;
}

static int shmem_show_options(struct seq_file *seq, struct vfsmount *vfs)
{
        struct shmem_sb_info *sbinfo = SHMEM_SB(vfs->mnt_sb);

        if (sbinfo->max_blocks != shmem_default_max_blocks())
                seq_printf(seq, ",size=%luk",
                        sbinfo->max_blocks << (PAGE_CACHE_SHIFT - 10));
        if (sbinfo->max_inodes != shmem_default_max_inodes())
                seq_printf(seq, ",nr_inodes=%lu", sbinfo->max_inodes);
        if (sbinfo->mode != (S_IRWXUGO | S_ISVTX))
                seq_printf(seq, ",mode=%03o", sbinfo->mode);
        if (sbinfo->uid != 0)
                seq_printf(seq, ",uid=%u", sbinfo->uid);
        if (sbinfo->gid != 0)
                seq_printf(seq, ",gid=%u", sbinfo->gid);
        shmem_show_mpol(seq, sbinfo->mpol);
        return 0;
}
#endif /* CONFIG_TMPFS */

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;
        struct shmem_sb_info *sbinfo;
        int err = -ENOMEM;

        /* 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;

        sbinfo->max_blocks = 0;
        sbinfo->max_inodes = 0;
        sbinfo->mode = S_IRWXUGO | S_ISVTX;
        sbinfo->uid = current->fsuid;
        sbinfo->gid = current->fsgid;
        sbinfo->mpol = NULL;
        sb->s_fs_info = sbinfo;

#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)) {
                sbinfo->max_blocks = shmem_default_max_blocks();
                sbinfo->max_inodes = shmem_default_max_inodes();
                if (shmem_parse_options(data, sbinfo, false)) {
                        err = -EINVAL;
                        goto failed;
                }
        }
        sb->s_export_op = &shmem_export_ops;
#else
        sb->s_flags |= MS_NOUSER;
#endif

        spin_lock_init(&sbinfo->stat_lock);
        sbinfo->free_blocks = sbinfo->max_blocks;
        sbinfo->free_inodes = sbinfo->max_inodes;

        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;
#ifdef CONFIG_TMPFS_POSIX_ACL
        sb->s_xattr = shmem_xattr_handlers;
        sb->s_flags |= MS_POSIXACL;
#endif

        inode = shmem_get_inode(sb, S_IFDIR | sbinfo->mode, 0);
        if (!inode)
                goto failed;
        inode->i_uid = sbinfo->uid;
        inode->i_gid = sbinfo->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, GFP_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);
        }
        shmem_acl_destroy_inode(inode);
        kmem_cache_free(shmem_inode_cachep, SHMEM_I(inode));
}

static void init_once(void *foo)
{
        struct shmem_inode_info *p = (struct shmem_inode_info *) foo;

        inode_init_once(&p->vfs_inode);
#ifdef CONFIG_TMPFS_POSIX_ACL
        p->i_acl = NULL;
        p->i_default_acl = NULL;
#endif
}

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

static void destroy_inodecache(void)
{
        kmem_cache_destroy(shmem_inode_cachep);
}

static const struct address_space_operations shmem_aops = {
        .writepage        = shmem_writepage,
        .set_page_dirty        = __set_page_dirty_no_writeback,
#ifdef CONFIG_TMPFS
        .readpage        = shmem_readpage,
        .write_begin        = shmem_write_begin,
        .write_end        = shmem_write_end,
#endif
        .migratepage        = migrate_page,
};

static const struct file_operations shmem_file_operations = {
        .mmap                = shmem_mmap,
#ifdef CONFIG_TMPFS
        .llseek                = generic_file_llseek,
        .read                = do_sync_read,
        .write                = do_sync_write,
        .aio_read        = shmem_file_aio_read,
        .aio_write        = generic_file_aio_write,
        .fsync                = simple_sync_file,
        .splice_read        = generic_file_splice_read,
        .splice_write        = generic_file_splice_write,
#endif
};

static const struct inode_operations shmem_inode_operations = {
        .truncate        = shmem_truncate,
        .setattr        = shmem_notify_change,
        .truncate_range        = shmem_truncate_range,
#ifdef CONFIG_TMPFS_POSIX_ACL
        .setxattr        = generic_setxattr,
        .getxattr        = generic_getxattr,
        .listxattr        = generic_listxattr,
        .removexattr        = generic_removexattr,
        .permission        = shmem_permission,
#endif

};

static const 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
#ifdef CONFIG_TMPFS_POSIX_ACL
        .setattr        = shmem_notify_change,
        .setxattr        = generic_setxattr,
        .getxattr        = generic_getxattr,
        .listxattr        = generic_listxattr,
        .removexattr        = generic_removexattr,
        .permission        = shmem_permission,
#endif
};

static const struct inode_operations shmem_special_inode_operations = {
#ifdef CONFIG_TMPFS_POSIX_ACL
        .setattr        = shmem_notify_change,
        .setxattr        = generic_setxattr,
        .getxattr        = generic_getxattr,
        .listxattr        = generic_listxattr,
        .removexattr        = generic_removexattr,
        .permission        = shmem_permission,
#endif
};

static const 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,
        .show_options        = shmem_show_options,
#endif
        .delete_inode        = shmem_delete_inode,
        .drop_inode        = generic_delete_inode,
        .put_super        = shmem_put_super,
};

static struct vm_operations_struct shmem_vm_ops = {
        .fault                = shmem_fault,
#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 = bdi_init(&shmem_backing_dev_info);
        if (error)
                goto out4;

        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:
        bdi_destroy(&shmem_backing_dev_info);
out4:
        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
 * @flags: vm_flags
 */
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 */
        init_file(file, shm_mnt, dentry, FMODE_WRITE | FMODE_READ,
                        &shmem_file_operations);
        return file;

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

/**
 * 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;
}