shmem.c

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/*
 * Resizable virtual memory filesystem for Linux.
 *
 * Copyright (C) 2000 Linus Torvalds.
 *       2000 Transmeta Corp.
 *       2000-2001 Christoph Rohland
 *       2000-2001 SAP AG
 *       2002 Red Hat Inc.
 * Copyright (C) 2002-2011 Hugh Dickins.
 * Copyright (C) 2011 Google Inc.
 * Copyright (C) 2002-2005 VERITAS Software Corporation.
 * Copyright (C) 2004 Andi Kleen, SuSE Labs
 *
 * Extended attribute support for tmpfs:
 * Copyright (c) 2004, Luke Kenneth Casson Leighton <[email protected]>
 * Copyright (c) 2004 Red Hat, Inc., James Morris <[email protected]>
 *
 * tiny-shmem:
 * Copyright (c) 2004, 2008 Matt Mackall <[email protected]>
 *
 * This file is released under the GPL.
 */

#include <linux/fs.h>
#include <linux/init.h>
#include <linux/vfs.h>
#include <linux/mount.h>
#include <linux/pagemap.h>
#include <linux/file.h>
#include <linux/mm.h>
#include <linux/export.h>
#include <linux/swap.h>

static struct vfsmount *shm_mnt;

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

#include <linux/xattr.h>
#include <linux/exportfs.h>
#include <linux/posix_acl.h>
#include <linux/generic_acl.h>
#include <linux/mman.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/backing-dev.h>
#include <linux/shmem_fs.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
#include <linux/pagevec.h>
#include <linux/percpu_counter.h>
#include <linux/falloc.h>
#include <linux/splice.h>
#include <linux/security.h>
#include <linux/swapops.h>
#include <linux/mempolicy.h>
#include <linux/namei.h>
#include <linux/ctype.h>
#include <linux/migrate.h>
#include <linux/highmem.h>
#include <linux/seq_file.h>
#include <linux/magic.h>

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

#define BLOCKS_PER_PAGE  (PAGE_CACHE_SIZE/512)
#define VM_ACCT(size)    (PAGE_CACHE_ALIGN(size) >> PAGE_SHIFT)

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

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

/*
 * shmem_fallocate and shmem_writepage communicate via inode->i_private
 * (with i_mutex making sure that it has only one user at a time):
 * we would prefer not to enlarge the shmem inode just for that.
 */
struct shmem_falloc {
    pgoff_t start;      /* start of range currently being fallocated */
    pgoff_t next;       /* the next page offset to be fallocated */
    pgoff_t nr_falloced;    /* how many new pages have been fallocated */
    pgoff_t nr_unswapped;   /* how often writepage refused to swap out */
};

/* Flag allocation requirements to shmem_getpage */
enum sgp_type {
    SGP_READ,   /* don't exceed i_size, don't allocate page */
    SGP_CACHE,  /* don't exceed i_size, may allocate page */
    SGP_DIRTY,  /* like SGP_CACHE, but set new page dirty */
    SGP_WRITE,  /* may exceed i_size, may allocate !Uptodate page */
    SGP_FALLOC, /* like SGP_WRITE, but make existing page Uptodate */
};

#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 bool shmem_should_replace_page(struct page *page, gfp_t gfp);
static int shmem_replace_page(struct page **pagep, gfp_t gfp,
                struct shmem_inode_info *info, pgoff_t index);
static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
    struct page **pagep, enum sgp_type sgp, gfp_t gfp, int *fault_type);

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

static inline struct shmem_sb_info *SHMEM_SB(struct super_block *sb)
{
    return sb->s_fs_info;
}

/*
 * shmem_file_setup pre-accounts the whole fixed size of a VM object,
 * for shared memory and for shared anonymous (/dev/zero) mappings
 * (unless MAP_NORESERVE and sysctl_overcommit_memory <= 1),
 * consistent with the pre-accounting of private mappings ...
 */
static inline int shmem_acct_size(unsigned long flags, loff_t size)
{
    return (flags & VM_NORESERVE) ?
        0 : security_vm_enough_memory_mm(current->mm, VM_ACCT(size));
}

static inline void shmem_unacct_size(unsigned long flags, loff_t size)
{
    if (!(flags & VM_NORESERVE))
        vm_unacct_memory(VM_ACCT(size));
}

/*
 * ... whereas tmpfs objects are accounted incrementally as
 * pages are allocated, in order to allow huge sparse files.
 * shmem_getpage reports shmem_acct_block failure as -ENOSPC not -ENOMEM,
 * so that a failure on a sparse tmpfs mapping will give SIGBUS not OOM.
 */
static inline int shmem_acct_block(unsigned long flags)
{
    return (flags & VM_NORESERVE) ?
        security_vm_enough_memory_mm(current->mm, VM_ACCT(PAGE_CACHE_SIZE)) : 0;
}

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

static const struct super_operations shmem_ops;
static const struct address_space_operations shmem_aops;
static const struct file_operations shmem_file_operations;
static const struct inode_operations shmem_inode_operations;
static const struct inode_operations shmem_dir_inode_operations;
static const struct inode_operations shmem_special_inode_operations;
static const struct vm_operations_struct shmem_vm_ops;

static struct backing_dev_info shmem_backing_dev_info  __read_mostly = {
    .ra_pages   = 0,    /* No readahead */
    .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
};

static LIST_HEAD(shmem_swaplist);
static DEFINE_MUTEX(shmem_swaplist_mutex);

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

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

static void shmem_recalc_inode(struct inode *inode)
{
    struct shmem_inode_info *info = SHMEM_I(inode);
    long freed;

    freed = info->alloced - info->swapped - inode->i_mapping->nrpages;
    if (freed > 0) {
        struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
        if (sbinfo->max_blocks)
            percpu_counter_add(&sbinfo->used_blocks, -freed);
        info->alloced -= freed;
        inode->i_blocks -= freed * BLOCKS_PER_PAGE;
        shmem_unacct_blocks(info->flags, freed);
    }
}

/*
 * Replace item expected in radix tree by a new item, while holding tree lock.
 */
static int shmem_radix_tree_replace(struct address_space *mapping,
            pgoff_t index, void *expected, void *replacement)
{
    void **pslot;
    void *item = NULL;

    VM_BUG_ON(!expected);
    pslot = radix_tree_lookup_slot(&mapping->page_tree, index);
    if (pslot)
        item = radix_tree_deref_slot_protected(pslot,
                            &mapping->tree_lock);
    if (item != expected)
        return -ENOENT;
    if (replacement)
        radix_tree_replace_slot(pslot, replacement);
    else
        radix_tree_delete(&mapping->page_tree, index);
    return 0;
}

/*
 * Sometimes, before we decide whether to proceed or to fail, we must check
 * that an entry was not already brought back from swap by a racing thread.
 *
 * Checking page is not enough: by the time a SwapCache page is locked, it
 * might be reused, and again be SwapCache, using the same swap as before.
 */
static bool shmem_confirm_swap(struct address_space *mapping,
                   pgoff_t index, swp_entry_t swap)
{
    void *item;

    rcu_read_lock();
    item = radix_tree_lookup(&mapping->page_tree, index);
    rcu_read_unlock();
    return item == swp_to_radix_entry(swap);
}

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

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

    page_cache_get(page);
    page->mapping = mapping;
    page->index = index;

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

/*
 * Like delete_from_page_cache, but substitutes swap for page.
 */
static void shmem_delete_from_page_cache(struct page *page, void *radswap)
{
    struct address_space *mapping = page->mapping;
    int error;

    spin_lock_irq(&mapping->tree_lock);
    error = shmem_radix_tree_replace(mapping, page->index, page, radswap);
    page->mapping = NULL;
    mapping->nrpages--;
    __dec_zone_page_state(page, NR_FILE_PAGES);
    __dec_zone_page_state(page, NR_SHMEM);
    spin_unlock_irq(&mapping->tree_lock);
    page_cache_release(page);
    BUG_ON(error);
}

/*
 * Like find_get_pages, but collecting swap entries as well as pages.
 */
static unsigned shmem_find_get_pages_and_swap(struct address_space *mapping,
                    pgoff_t start, unsigned int nr_pages,
                    struct page **pages, pgoff_t *indices)
{
    unsigned int i;
    unsigned int ret;
    unsigned int nr_found;

    rcu_read_lock();
restart:
    nr_found = radix_tree_gang_lookup_slot(&mapping->page_tree,
                (void ***)pages, indices, start, nr_pages);
    ret = 0;
    for (i = 0; i < nr_found; i++) {
        struct page *page;
repeat:
        page = radix_tree_deref_slot((void **)pages[i]);
        if (unlikely(!page))
            continue;
        if (radix_tree_exception(page)) {
            if (radix_tree_deref_retry(page))
                goto restart;
            /*
             * Otherwise, we must be storing a swap entry
             * here as an exceptional entry: so return it
             * without attempting to raise page count.
             */
            goto export;
        }
        if (!page_cache_get_speculative(page))
            goto repeat;

        /* Has the page moved? */
        if (unlikely(page != *((void **)pages[i]))) {
            page_cache_release(page);
            goto repeat;
        }
export:
        indices[ret] = indices[i];
        pages[ret] = page;
        ret++;
    }
    if (unlikely(!ret && nr_found))
        goto restart;
    rcu_read_unlock();
    return ret;
}

/*
 * Remove swap entry from radix tree, free the swap and its page cache.
 */
static int shmem_free_swap(struct address_space *mapping,
               pgoff_t index, void *radswap)
{
    int error;

    spin_lock_irq(&mapping->tree_lock);
    error = shmem_radix_tree_replace(mapping, index, radswap, NULL);
    spin_unlock_irq(&mapping->tree_lock);
    if (!error)
        free_swap_and_cache(radix_to_swp_entry(radswap));
    return error;
}

/*
 * Pagevec may contain swap entries, so shuffle up pages before releasing.
 */
static void shmem_deswap_pagevec(struct pagevec *pvec)
{
    int i, j;

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

/*
 * SysV IPC SHM_UNLOCK restore Unevictable pages to their evictable lists.
 */
void shmem_unlock_mapping(struct address_space *mapping)
{
    struct pagevec pvec;
    pgoff_t indices[PAGEVEC_SIZE];
    pgoff_t index = 0;

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

/*
 * Remove range of pages and swap entries from radix tree, and free them.
 * If !unfalloc, truncate or punch hole; if unfalloc, undo failed fallocate.
 */
static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
                                 bool unfalloc)
{
    struct address_space *mapping = inode->i_mapping;
    struct shmem_inode_info *info = SHMEM_I(inode);
    pgoff_t start = (lstart + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
    pgoff_t end = (lend + 1) >> PAGE_CACHE_SHIFT;
    unsigned int partial_start = lstart & (PAGE_CACHE_SIZE - 1);
    unsigned int partial_end = (lend + 1) & (PAGE_CACHE_SIZE - 1);
    struct pagevec pvec;
    pgoff_t indices[PAGEVEC_SIZE];
    long nr_swaps_freed = 0;
    pgoff_t index;
    int i;

    if (lend == -1)
        end = -1;   /* unsigned, so actually very big */

    pagevec_init(&pvec, 0);
    index = start;
    while (index < end) {
        pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
                min(end - index, (pgoff_t)PAGEVEC_SIZE),
                            pvec.pages, indices);
        if (!pvec.nr)
            break;
        mem_cgroup_uncharge_start();
        for (i = 0; i < pagevec_count(&pvec); i++) {
            struct page *page = pvec.pages[i];

            index = indices[i];
            if (index >= end)
                break;

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

            if (!trylock_page(page))
                continue;
            if (!unfalloc || !PageUptodate(page)) {
                if (page->mapping == mapping) {
                    VM_BUG_ON(PageWriteback(page));
                    truncate_inode_page(mapping, page);
                }
            }
            unlock_page(page);
        }
        shmem_deswap_pagevec(&pvec);
        pagevec_release(&pvec);
        mem_cgroup_uncharge_end();
        cond_resched();
        index++;
    }

    if (partial_start) {
        struct page *page = NULL;
        shmem_getpage(inode, start - 1, &page, SGP_READ, NULL);
        if (page) {
            unsigned int top = PAGE_CACHE_SIZE;
            if (start > end) {
                top = partial_end;
                partial_end = 0;
            }
            zero_user_segment(page, partial_start, top);
            set_page_dirty(page);
            unlock_page(page);
            page_cache_release(page);
        }
    }
    if (partial_end) {
        struct page *page = NULL;
        shmem_getpage(inode, end, &page, SGP_READ, NULL);
        if (page) {
            zero_user_segment(page, 0, partial_end);
            set_page_dirty(page);
            unlock_page(page);
            page_cache_release(page);
        }
    }
    if (start >= end)
        return;

    index = start;
    for ( ; ; ) {
        cond_resched();
        pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
                min(end - index, (pgoff_t)PAGEVEC_SIZE),
                            pvec.pages, indices);
        if (!pvec.nr) {
            if (index == start || unfalloc)
                break;
            index = start;
            continue;
        }
        if ((index == start || unfalloc) && indices[0] >= end) {
            shmem_deswap_pagevec(&pvec);
            pagevec_release(&pvec);
            break;
        }
        mem_cgroup_uncharge_start();
        for (i = 0; i < pagevec_count(&pvec); i++) {
            struct page *page = pvec.pages[i];

            index = indices[i];
            if (index >= end)
                break;

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

            lock_page(page);
            if (!unfalloc || !PageUptodate(page)) {
                if (page->mapping == mapping) {
                    VM_BUG_ON(PageWriteback(page));
                    truncate_inode_page(mapping, page);
                }
            }
            unlock_page(page);
        }
        shmem_deswap_pagevec(&pvec);
        pagevec_release(&pvec);
        mem_cgroup_uncharge_end();
        index++;
    }

    spin_lock(&info->lock);
    info->swapped -= nr_swaps_freed;
    shmem_recalc_inode(inode);
    spin_unlock(&info->lock);
}

void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
{
    shmem_undo_range(inode, lstart, lend, false);
    inode->i_ctime = inode->i_mtime = CURRENT_TIME;
}
EXPORT_SYMBOL_GPL(shmem_truncate_range);

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

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

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

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

    setattr_copy(inode, attr);
#ifdef CONFIG_TMPFS_POSIX_ACL
    if (attr->ia_valid & ATTR_MODE)
        error = generic_acl_chmod(inode);
#endif
    return error;
}

static void shmem_evict_inode(struct inode *inode)
{
    struct shmem_inode_info *info = SHMEM_I(inode);

    if (inode->i_mapping->a_ops == &shmem_aops) {
        shmem_unacct_size(info->flags, inode->i_size);
        inode->i_size = 0;
        shmem_truncate_range(inode, 0, (loff_t)-1);
        if (!list_empty(&info->swaplist)) {
            mutex_lock(&shmem_swaplist_mutex);
            list_del_init(&info->swaplist);
            mutex_unlock(&shmem_swaplist_mutex);
        }
    } else
        kfree(info->symlink);

    simple_xattrs_free(&info->xattrs);
    WARN_ON(inode->i_blocks);
    shmem_free_inode(inode->i_sb);
    clear_inode(inode);
}

/*
 * If swap found in inode, free it and move page from swapcache to filecache.
 */
static int shmem_unuse_inode(struct shmem_inode_info *info,
                 swp_entry_t swap, struct page **pagep)
{
    struct address_space *mapping = info->vfs_inode.i_mapping;
    void *radswap;
    pgoff_t index;
    gfp_t gfp;
    int error = 0;

    radswap = swp_to_radix_entry(swap);
    index = radix_tree_locate_item(&mapping->page_tree, radswap);
    if (index == -1)
        return 0;

    /*
     * Move _head_ to start search for next from here.
     * But be careful: shmem_evict_inode checks list_empty without taking
     * mutex, and there's an instant in list_move_tail when info->swaplist
     * would appear empty, if it were the only one on shmem_swaplist.
     */
    if (shmem_swaplist.next != &info->swaplist)
        list_move_tail(&shmem_swaplist, &info->swaplist);

    gfp = mapping_gfp_mask(mapping);
    if (shmem_should_replace_page(*pagep, gfp)) {
        mutex_unlock(&shmem_swaplist_mutex);
        error = shmem_replace_page(pagep, gfp, info, index);
        mutex_lock(&shmem_swaplist_mutex);
        /*
         * We needed to drop mutex to make that restrictive page
         * allocation, but the inode might have been freed while we
         * dropped it: although a racing shmem_evict_inode() cannot
         * complete without emptying the radix_tree, our page lock
         * on this swapcache page is not enough to prevent that -
         * free_swap_and_cache() of our swap entry will only
         * trylock_page(), removing swap from radix_tree whatever.
         *
         * We must not proceed to shmem_add_to_page_cache() if the
         * inode has been freed, but of course we cannot rely on
         * inode or mapping or info to check that.  However, we can
         * safely check if our swap entry is still in use (and here
         * it can't have got reused for another page): if it's still
         * in use, then the inode cannot have been freed yet, and we
         * can safely proceed (if it's no longer in use, that tells
         * nothing about the inode, but we don't need to unuse swap).
         */
        if (!page_swapcount(*pagep))
            error = -ENOENT;
    }

    /*
     * We rely on shmem_swaplist_mutex, not only to protect the swaplist,
     * but also to hold up shmem_evict_inode(): so inode cannot be freed
     * beneath us (pagelock doesn't help until the page is in pagecache).
     */
    if (!error)
        error = shmem_add_to_page_cache(*pagep, mapping, index,
                        GFP_NOWAIT, radswap);
    if (error != -ENOMEM) {
        /*
         * Truncation and eviction use free_swap_and_cache(), which
         * only does trylock page: if we raced, best clean up here.
         */
        delete_from_swap_cache(*pagep);
        set_page_dirty(*pagep);
        if (!error) {
            spin_lock(&info->lock);
            info->swapped--;
            spin_unlock(&info->lock);
            swap_free(swap);
        }
        error = 1;  /* not an error, but entry was found */
    }
    return error;
}

/*
 * Search through swapped inodes to find and replace swap by page.
 */
int shmem_unuse(swp_entry_t swap, struct page *page)
{
    struct list_head *this, *next;
    struct shmem_inode_info *info;
    int found = 0;
    int error = 0;

    /*
     * There's a faint possibility that swap page was replaced before
     * caller locked it: caller will come back later with the right page.
     */
    if (unlikely(!PageSwapCache(page) || page_private(page) != swap.val))
        goto out;

    /*
     * Charge page using GFP_KERNEL while we can wait, before taking
     * the shmem_swaplist_mutex which might hold up shmem_writepage().
     * Charged back to the user (not to caller) when swap account is used.
     */
    error = mem_cgroup_cache_charge(page, current->mm, GFP_KERNEL);
    if (error)
        goto out;
    /* No radix_tree_preload: swap entry keeps a place for page in tree */

    mutex_lock(&shmem_swaplist_mutex);
    list_for_each_safe(this, next, &shmem_swaplist) {
        info = list_entry(this, struct shmem_inode_info, swaplist);
        if (info->swapped)
            found = shmem_unuse_inode(info, swap, &page);
        else
            list_del_init(&info->swaplist);
        cond_resched();
        if (found)
            break;
    }
    mutex_unlock(&shmem_swaplist_mutex);

    if (found < 0)
        error = found;
out:
    unlock_page(page);
    page_cache_release(page);
    return error;
}

/*
 * Move the page from the page cache to the swap cache.
 */
static int shmem_writepage(struct page *page, struct writeback_control *wbc)
{
    struct shmem_inode_info *info;
    struct address_space *mapping;
    struct inode *inode;
    swp_entry_t swap;
    pgoff_t index;

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

    /*
     * shmem_backing_dev_info's capabilities prevent regular writeback or
     * sync from ever calling shmem_writepage; but a stacking filesystem
     * might use ->writepage of its underlying filesystem, in which case
     * tmpfs should write out to swap only in response to memory pressure,
     * and not for the writeback threads or sync.
     */
    if (!wbc->for_reclaim) {
        WARN_ON_ONCE(1);    /* Still happens? Tell us about it! */
        goto redirty;
    }

    /*
     * This is somewhat ridiculous, but without plumbing a SWAP_MAP_FALLOC
     * value into swapfile.c, the only way we can correctly account for a
     * fallocated page arriving here is now to initialize it and write it.
     *
     * That's okay for a page already fallocated earlier, but if we have
     * not yet completed the fallocation, then (a) we want to keep track
     * of this page in case we have to undo it, and (b) it may not be a
     * good idea to continue anyway, once we're pushing into swap.  So
     * reactivate the page, and let shmem_fallocate() quit when too many.
     */
    if (!PageUptodate(page)) {
        if (inode->i_private) {
            struct shmem_falloc *shmem_falloc;
            spin_lock(&inode->i_lock);
            shmem_falloc = inode->i_private;
            if (shmem_falloc &&
                index >= shmem_falloc->start &&
                index < shmem_falloc->next)
                shmem_falloc->nr_unswapped++;
            else
                shmem_falloc = NULL;
            spin_unlock(&inode->i_lock);
            if (shmem_falloc)
                goto redirty;
        }
        clear_highpage(page);
        flush_dcache_page(page);
        SetPageUptodate(page);
    }

    swap = get_swap_page();
    if (!swap.val)
        goto redirty;

    /*
     * Add inode to shmem_unuse()'s list of swapped-out inodes,
     * if it's not already there.  Do it now before the page is
     * moved to swap cache, when its pagelock no longer protects
     * the inode from eviction.  But don't unlock the mutex until
     * we've incremented swapped, because shmem_unuse_inode() will
     * prune a !swapped inode from the swaplist under this mutex.
     */
    mutex_lock(&shmem_swaplist_mutex);
    if (list_empty(&info->swaplist))
        list_add_tail(&info->swaplist, &shmem_swaplist);

    if (add_to_swap_cache(page, swap, GFP_ATOMIC) == 0) {
        swap_shmem_alloc(swap);
        shmem_delete_from_page_cache(page, swp_to_radix_entry(swap));

        spin_lock(&info->lock);
        info->swapped++;
        shmem_recalc_inode(inode);
        spin_unlock(&info->lock);

        mutex_unlock(&shmem_swaplist_mutex);
        BUG_ON(page_mapped(page));
        swap_writepage(page, wbc);
        return 0;
    }

    mutex_unlock(&shmem_swaplist_mutex);
    swapcache_free(swap, NULL);
redirty:
    set_page_dirty(page);
    if (wbc->for_reclaim)
        return AOP_WRITEPAGE_ACTIVATE;  /* Return with page locked */
    unlock_page(page);
    return 0;
}

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

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

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

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

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

static struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp,
            struct shmem_inode_info *info, pgoff_t index)
{
    struct vm_area_struct pvma;
    struct page *page;

    /* Create a pseudo vma that just contains the policy */
    pvma.vm_start = 0;
    /* Bias interleave by inode number to distribute better across nodes */
    pvma.vm_pgoff = index + info->vfs_inode.i_ino;
    pvma.vm_ops = NULL;
    pvma.vm_policy = mpol_shared_policy_lookup(&info->policy, index);

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

    /* Drop reference taken by mpol_shared_policy_lookup() */
    mpol_cond_put(pvma.vm_policy);

    return page;
}

static struct page *shmem_alloc_page(gfp_t gfp,
            struct shmem_inode_info *info, pgoff_t index)
{
    struct vm_area_struct pvma;
    struct page *page;

    /* Create a pseudo vma that just contains the policy */
    pvma.vm_start = 0;
    /* Bias interleave by inode number to distribute better across nodes */
    pvma.vm_pgoff = index + info->vfs_inode.i_ino;
    pvma.vm_ops = NULL;
    pvma.vm_policy = mpol_shared_policy_lookup(&info->policy, index);

    page = alloc_page_vma(gfp, &pvma, 0);

    /* Drop reference taken by mpol_shared_policy_lookup() */
    mpol_cond_put(pvma.vm_policy);

    return page;
}
#else /* !CONFIG_NUMA */
#ifdef CONFIG_TMPFS
static inline void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
{
}
#endif /* CONFIG_TMPFS */

static inline struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp,
            struct shmem_inode_info *info, pgoff_t index)
{
    return swapin_readahead(swap, gfp, NULL, 0);
}

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

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

/*
 * When a page is moved from swapcache to shmem filecache (either by the
 * usual swapin of shmem_getpage_gfp(), or by the less common swapoff of
 * shmem_unuse_inode()), it may have been read in earlier from swap, in
 * ignorance of the mapping it belongs to.  If that mapping has special
 * constraints (like the gma500 GEM driver, which requires RAM below 4GB),
 * we may need to copy to a suitable page before moving to filecache.
 *
 * In a future release, this may well be extended to respect cpuset and
 * NUMA mempolicy, and applied also to anonymous pages in do_swap_page();
 * but for now it is a simple matter of zone.
 */
static bool shmem_should_replace_page(struct page *page, gfp_t gfp)
{
    return page_zonenum(page) > gfp_zone(gfp);
}

static int shmem_replace_page(struct page **pagep, gfp_t gfp,
                struct shmem_inode_info *info, pgoff_t index)
{
    struct page *oldpage, *newpage;
    struct address_space *swap_mapping;
    pgoff_t swap_index;
    int error;

    oldpage = *pagep;
    swap_index = page_private(oldpage);
    swap_mapping = page_mapping(oldpage);

    /*
     * We have arrived here because our zones are constrained, so don't
     * limit chance of success by further cpuset and node constraints.
     */
    gfp &= ~GFP_CONSTRAINT_MASK;
    newpage = shmem_alloc_page(gfp, info, index);
    if (!newpage)
        return -ENOMEM;

    page_cache_get(newpage);
    copy_highpage(newpage, oldpage);
    flush_dcache_page(newpage);

    __set_page_locked(newpage);
    SetPageUptodate(newpage);
    SetPageSwapBacked(newpage);
    set_page_private(newpage, swap_index);
    SetPageSwapCache(newpage);

    /*
     * Our caller will very soon move newpage out of swapcache, but it's
     * a nice clean interface for us to replace oldpage by newpage there.
     */
    spin_lock_irq(&swap_mapping->tree_lock);
    error = shmem_radix_tree_replace(swap_mapping, swap_index, oldpage,
                                   newpage);
    if (!error) {
        __inc_zone_page_state(newpage, NR_FILE_PAGES);
        __dec_zone_page_state(oldpage, NR_FILE_PAGES);
    }
    spin_unlock_irq(&swap_mapping->tree_lock);

    if (unlikely(error)) {
        /*
         * Is this possible?  I think not, now that our callers check
         * both PageSwapCache and page_private after getting page lock;
         * but be defensive.  Reverse old to newpage for clear and free.
         */
        oldpage = newpage;
    } else {
        mem_cgroup_replace_page_cache(oldpage, newpage);
        lru_cache_add_anon(newpage);
        *pagep = newpage;
    }

    ClearPageSwapCache(oldpage);
    set_page_private(oldpage, 0);

    unlock_page(oldpage);
    page_cache_release(oldpage);
    page_cache_release(oldpage);
    return error;
}

/*
 * shmem_getpage_gfp - find page in cache, or get from swap, or allocate
 *
 * If we allocate a new one we do not mark it dirty. That's up to the
 * vm. If we swap it in we mark it dirty since we also free the swap
 * entry since a page cannot live in both the swap and page cache
 */
static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
    struct page **pagep, enum sgp_type sgp, gfp_t gfp, int *fault_type)
{
    struct address_space *mapping = inode->i_mapping;
    struct shmem_inode_info *info;
    struct shmem_sb_info *sbinfo;
    struct page *page;
    swp_entry_t swap;
    int error;
    int once = 0;
    int alloced = 0;

    if (index > (MAX_LFS_FILESIZE >> PAGE_CACHE_SHIFT))
        return -EFBIG;
repeat:
    swap.val = 0;
    page = find_lock_page(mapping, index);
    if (radix_tree_exceptional_entry(page)) {
        swap = radix_to_swp_entry(page);
        page = NULL;
    }

    if (sgp != SGP_WRITE && sgp != SGP_FALLOC &&
        ((loff_t)index << PAGE_CACHE_SHIFT) >= i_size_read(inode)) {
        error = -EINVAL;
        goto failed;
    }

    /* fallocated page? */
    if (page && !PageUptodate(page)) {
        if (sgp != SGP_READ)
            goto clear;
        unlock_page(page);
        page_cache_release(page);
        page = NULL;
    }
    if (page || (sgp == SGP_READ && !swap.val)) {
        *pagep = page;
        return 0;
    }

    /*
     * Fast cache lookup did not find it:
     * bring it back from swap or allocate.
     */
    info = SHMEM_I(inode);
    sbinfo = SHMEM_SB(inode->i_sb);

    if (swap.val) {
        /* Look it up and read it in.. */
        page = lookup_swap_cache(swap);
        if (!page) {
            /* here we actually do the io */
            if (fault_type)
                *fault_type |= VM_FAULT_MAJOR;
            page = shmem_swapin(swap, gfp, info, index);
            if (!page) {
                error = -ENOMEM;
                goto failed;
            }
        }

        /* We have to do this with page locked to prevent races */
        lock_page(page);
        if (!PageSwapCache(page) || page_private(page) != swap.val ||
            !shmem_confirm_swap(mapping, index, swap)) {
            error = -EEXIST;    /* try again */
            goto unlock;
        }
        if (!PageUptodate(page)) {
            error = -EIO;
            goto failed;
        }
        wait_on_page_writeback(page);

        if (shmem_should_replace_page(page, gfp)) {
            error = shmem_replace_page(&page, gfp, info, index);
            if (error)
                goto failed;
        }

        error = mem_cgroup_cache_charge(page, current->mm,
                        gfp & GFP_RECLAIM_MASK);
        if (!error) {
            error = shmem_add_to_page_cache(page, mapping, index,
                        gfp, swp_to_radix_entry(swap));
            /*
             * We already confirmed swap under page lock, and make
             * no memory allocation here, so usually no possibility
             * of error; but free_swap_and_cache() only trylocks a
             * page, so it is just possible that the entry has been
             * truncated or holepunched since swap was confirmed.
             * shmem_undo_range() will have done some of the
             * unaccounting, now delete_from_swap_cache() will do
             * the rest (including mem_cgroup_uncharge_swapcache).
             * Reset swap.val? No, leave it so "failed" goes back to
             * "repeat": reading a hole and writing should succeed.
             */
            if (error)
                delete_from_swap_cache(page);
        }
        if (error)
            goto failed;

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

        delete_from_swap_cache(page);
        set_page_dirty(page);
        swap_free(swap);

    } else {
        if (shmem_acct_block(info->flags)) {
            error = -ENOSPC;
            goto failed;
        }
        if (sbinfo->max_blocks) {
            if (percpu_counter_compare(&sbinfo->used_blocks,
                        sbinfo->max_blocks) >= 0) {
                error = -ENOSPC;
                goto unacct;
            }
            percpu_counter_inc(&sbinfo->used_blocks);
        }

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

        SetPageSwapBacked(page);
        __set_page_locked(page);
        error = mem_cgroup_cache_charge(page, current->mm,
                        gfp & GFP_RECLAIM_MASK);
        if (error)
            goto decused;
        error = radix_tree_preload(gfp & GFP_RECLAIM_MASK);
        if (!error) {
            error = shmem_add_to_page_cache(page, mapping, index,
                            gfp, NULL);
            radix_tree_preload_end();
        }
        if (error) {
            mem_cgroup_uncharge_cache_page(page);
            goto decused;
        }
        lru_cache_add_anon(page);

        spin_lock(&info->lock);
        info->alloced++;
        inode->i_blocks += BLOCKS_PER_PAGE;
        shmem_recalc_inode(inode);
        spin_unlock(&info->lock);
        alloced = true;

        /*
         * Let SGP_FALLOC use the SGP_WRITE optimization on a new page.
         */
        if (sgp == SGP_FALLOC)
            sgp = SGP_WRITE;
clear:
        /*
         * Let SGP_WRITE caller clear ends if write does not fill page;
         * but SGP_FALLOC on a page fallocated earlier must initialize
         * it now, lest undo on failure cancel our earlier guarantee.
         */
        if (sgp != SGP_WRITE) {
            clear_highpage(page);
            flush_dcache_page(page);
            SetPageUptodate(page);
        }
        if (sgp == SGP_DIRTY)
            set_page_dirty(page);
    }

    /* Perhaps the file has been truncated since we checked */
    if (sgp != SGP_WRITE && sgp != SGP_FALLOC &&
        ((loff_t)index << PAGE_CACHE_SHIFT) >= i_size_read(inode)) {
        error = -EINVAL;
        if (alloced)
            goto trunc;
        else
            goto failed;
    }
    *pagep = page;
    return 0;

    /*
     * Error recovery.
     */
trunc:
    info = SHMEM_I(inode);
    ClearPageDirty(page);
    delete_from_page_cache(page);
    spin_lock(&info->lock);
    info->alloced--;
    inode->i_blocks -= BLOCKS_PER_PAGE;
    spin_unlock(&info->lock);
decused:
    sbinfo = SHMEM_SB(inode->i_sb);
    if (sbinfo->max_blocks)
        percpu_counter_add(&sbinfo->used_blocks, -1);
unacct:
    shmem_unacct_blocks(info->flags, 1);
failed:
    if (swap.val && error != -EINVAL &&
        !shmem_confirm_swap(mapping, index, swap))
        error = -EEXIST;
unlock:
    if (page) {
        unlock_page(page);
        page_cache_release(page);
    }
    if (error == -ENOSPC && !once++) {
        info = SHMEM_I(inode);
        spin_lock(&info->lock);
        shmem_recalc_inode(inode);
        spin_unlock(&info->lock);
        goto repeat;
    }
    if (error == -EEXIST)   /* from above or from radix_tree_insert */
        goto repeat;
    return error;
}

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

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

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

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

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

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

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

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

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

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

static struct inode *shmem_get_inode(struct super_block *sb, const struct inode *dir,
                     umode_t mode, dev_t dev, unsigned long flags)
{
    struct inode *inode;
    struct shmem_inode_info *info;
    struct shmem_sb_info *sbinfo = SHMEM_SB(sb);

    if (shmem_reserve_inode(sb))
        return NULL;

    inode = new_inode(sb);
    if (inode) {
        inode->i_ino = get_next_ino();
        inode_init_owner(inode, dir, mode);
        inode->i_blocks = 0;
        inode->i_mapping->backing_dev_info = &shmem_backing_dev_info;
        inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
        inode->i_generation = get_seconds();
        info = SHMEM_I(inode);
        memset(info, 0, (char *)inode - (char *)info);
        spin_lock_init(&info->lock);
        info->flags = flags & VM_NORESERVE;
        INIT_LIST_HEAD(&info->swaplist);
        simple_xattrs_init(&info->xattrs);
        cache_no_acl(inode);

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

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

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

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

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

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

    if (!PageUptodate(page)) {
        if (copied < PAGE_CACHE_SIZE) {
            unsigned from = pos & (PAGE_CACHE_SIZE - 1);
            zero_user_segments(page, 0, from,
                    from + copied, PAGE_CACHE_SIZE);
        }
        SetPageUptodate(page);
    }
    set_page_dirty(page);
    unlock_page(page);
    page_cache_release(page);

    return copied;
}

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

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

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

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

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

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

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

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

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

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

        cond_resched();
    }

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

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

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

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

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

static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
                struct pipe_inode_info *pipe, size_t len,
                unsigned int flags)
{
    struct address_space *mapping = in->f_mapping;
    struct inode *inode = mapping->host;
    unsigned int loff, nr_pages, req_pages;
    struct page *pages[PIPE_DEF_BUFFERS];
    struct partial_page partial[PIPE_DEF_BUFFERS];
    struct page *page;
    pgoff_t index, end_index;
    loff_t isize, left;
    int error, page_nr;
    struct splice_pipe_desc spd = {
        .pages = pages,
        .partial = partial,
        .nr_pages_max = PIPE_DEF_BUFFERS,
        .flags = flags,
        .ops = &page_cache_pipe_buf_ops,
        .spd_release = spd_release_page,
    };

    isize = i_size_read(inode);
    if (unlikely(*ppos >= isize))
        return 0;

    left = isize - *ppos;
    if (unlikely(left < len))
        len = left;

    if (splice_grow_spd(pipe, &spd))
        return -ENOMEM;

    index = *ppos >> PAGE_CACHE_SHIFT;
    loff = *ppos & ~PAGE_CACHE_MASK;
    req_pages = (len + loff + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
    nr_pages = min(req_pages, pipe->buffers);

    spd.nr_pages = find_get_pages_contig(mapping, index,
                        nr_pages, spd.pages);
    index += spd.nr_pages;
    error = 0;

    while (spd.nr_pages < nr_pages) {
        error = shmem_getpage(inode, index, &page, SGP_CACHE, NULL);
        if (error)
            break;
        unlock_page(page);
        spd.pages[spd.nr_pages++] = page;
        index++;
    }

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

    for (page_nr = 0; page_nr < nr_pages; page_nr++) {
        unsigned int this_len;

        if (!len)
            break;

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

        if (!PageUptodate(page) || page->mapping != mapping) {
            error = shmem_getpage(inode, index, &page,
                            SGP_CACHE, NULL);
            if (error)
                break;
            unlock_page(page);
            page_cache_release(spd.pages[page_nr]);
            spd.pages[page_nr] = page;
        }

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

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

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

            this_len = min(this_len, plen - loff);
            len = this_len;
        }

        spd.partial[page_nr].offset = loff;
        spd.partial[page_nr].len = this_len;
        len -= this_len;
        loff = 0;
        spd.nr_pages++;
        index++;
    }

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

    if (spd.nr_pages)
        error = splice_to_pipe(pipe, &spd);

    splice_shrink_spd(&spd);

    if (error > 0) {
        *ppos += error;
        file_accessed(in);
    }
    return error;
}

static long shmem_fallocate(struct file *file, int mode, loff_t offset,
                             loff_t len)
{
    struct inode *inode = file->f_path.dentry->d_inode;
    struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
    struct shmem_falloc shmem_falloc;
    pgoff_t start, index, end;
    int error;

    mutex_lock(&inode->i_mutex);

    if (mode & FALLOC_FL_PUNCH_HOLE) {
        struct address_space *mapping = file->f_mapping;
        loff_t unmap_start = round_up(offset, PAGE_SIZE);
        loff_t unmap_end = round_down(offset + len, PAGE_SIZE) - 1;

        if ((u64)unmap_end > (u64)unmap_start)
            unmap_mapping_range(mapping, unmap_start,
                        1 + unmap_end - unmap_start, 0);
        shmem_truncate_range(inode, offset, offset + len - 1);
        /* No need to unmap again: hole-punching leaves COWed pages */
        error = 0;
        goto out;
    }

    /* We need to check rlimit even when FALLOC_FL_KEEP_SIZE */
    error = inode_newsize_ok(inode, offset + len);
    if (error)
        goto out;

    start = offset >> PAGE_CACHE_SHIFT;
    end = (offset + len + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
    /* Try to avoid a swapstorm if len is impossible to satisfy */
    if (sbinfo->max_blocks && end - start > sbinfo->max_blocks) {
        error = -ENOSPC;
        goto out;
    }

    shmem_falloc.start = start;
    shmem_falloc.next  = start;
    shmem_falloc.nr_falloced = 0;
    shmem_falloc.nr_unswapped = 0;
    spin_lock(&inode->i_lock);
    inode->i_private = &shmem_falloc;
    spin_unlock(&inode->i_lock);

    for (index = start; index < end; index++) {
        struct page *page;

        /*
         * Good, the fallocate(2) manpage permits EINTR: we may have
         * been interrupted because we are using up too much memory.
         */
        if (signal_pending(current))
            error = -EINTR;
        else if (shmem_falloc.nr_unswapped > shmem_falloc.nr_falloced)
            error = -ENOMEM;
        else
            error = shmem_getpage(inode, index, &page, SGP_FALLOC,
                                    NULL);
        if (error) {
            /* Remove the !PageUptodate pages we added */
            shmem_undo_range(inode,
                (loff_t)start << PAGE_CACHE_SHIFT,
                (loff_t)index << PAGE_CACHE_SHIFT, true);
            goto undone;
        }

        /*
         * Inform shmem_writepage() how far we have reached.
         * No need for lock or barrier: we have the page lock.
         */
        shmem_falloc.next++;
        if (!PageUptodate(page))
            shmem_falloc.nr_falloced++;

        /*
         * If !PageUptodate, leave it that way so that freeable pages
         * can be recognized if we need to rollback on error later.
         * But set_page_dirty so that memory pressure will swap rather
         * than free the pages we are allocating (and SGP_CACHE pages
         * might still be clean: we now need to mark those dirty too).
         */
        set_page_dirty(page);
        unlock_page(page);
        page_cache_release(page);
        cond_resched();
    }

    if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > inode->i_size)
        i_size_write(inode, offset + len);
    inode->i_ctime = CURRENT_TIME;
undone:
    spin_lock(&inode->i_lock);
    inode->i_private = NULL;
    spin_unlock(&inode->i_lock);
out:
    mutex_unlock(&inode->i_mutex);
    return error;
}

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

    buf->f_type = TMPFS_MAGIC;
    buf->f_bsize = PAGE_CACHE_SIZE;
    buf->f_namelen = NAME_MAX;
    if (sbinfo->max_blocks) {
        buf->f_blocks = sbinfo->max_blocks;
        buf->f_bavail =
        buf->f_bfree  = sbinfo->max_blocks -
                percpu_counter_sum(&sbinfo->used_blocks);
    }
    if (sbinfo->max_inodes) {
        buf->f_files = sbinfo->max_inodes;
        buf->f_ffree = sbinfo->free_inodes;
    }
    /* else leave those fields 0 like simple_statfs */
    return 0;
}

/*
 * File creation. Allocate an inode, and we're done..
 */
static int
shmem_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
{
    struct inode *inode;
    int error = -ENOSPC;

    inode = shmem_get_inode(dir->i_sb, dir, mode, dev, VM_NORESERVE);
    if (inode) {
        error = security_inode_init_security(inode, dir,
                             &dentry->d_name,
                             shmem_initxattrs, NULL);
        if (error) {
            if (error != -EOPNOTSUPP) {
                iput(inode);
                return error;
            }
        }
#ifdef CONFIG_TMPFS_POSIX_ACL
        error = generic_acl_init(inode, dir);
        if (error) {
            iput(inode);
            return error;
        }
#else
        error = 0;
#endif
        dir->i_size += BOGO_DIRENT_SIZE;
        dir->i_ctime = dir->i_mtime = CURRENT_TIME;
        d_instantiate(dentry, inode);
        dget(dentry); /* Extra count - pin the dentry in core */
    }
    return error;
}

static int shmem_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
{
    int error;

    if ((error = shmem_mknod(dir, dentry, mode | S_IFDIR, 0)))
        return error;
    inc_nlink(dir);
    return 0;
}

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    error = security_inode_init_security(inode, dir, &dentry->d_name,
                         shmem_initxattrs, NULL);
    if (error) {
        if (error != -EOPNOTSUPP) {
            iput(inode);
            return error;
        }
        error = 0;
    }

    info = SHMEM_I(inode);
    inode->i_size = len-1;
    if (len <= SHORT_SYMLINK_LEN) {
        info->symlink = kmemdup(symname, len, GFP_KERNEL);
        if (!info->symlink) {
            iput(inode);
            return -ENOMEM;
        }
        inode->i_op = &shmem_short_symlink_operations;
    } else {
        error = shmem_getpage(inode, 0, &page, SGP_WRITE, NULL);
        if (error) {
            iput(inode);
            return error;
        }
        inode->i_mapping->a_ops = &shmem_aops;
        inode->i_op = &shmem_symlink_inode_operations;
        kaddr = kmap_atomic(page);
        memcpy(kaddr, symname, len);
        kunmap_atomic(kaddr);
        SetPageUptodate(page);
        set_page_dirty(page);
        unlock_page(page);
        page_cache_release(page);
    }
    dir->i_size += BOGO_DIRENT_SIZE;
    dir->i_ctime = dir->i_mtime = CURRENT_TIME;
    d_instantiate(dentry, inode);
    dget(dentry);
    return 0;
}

static void *shmem_follow_short_symlink(struct dentry *dentry, struct nameidata *nd)
{
    nd_set_link(nd, SHMEM_I(dentry->d_inode)->symlink);
    return NULL;
}

static void *shmem_follow_link(struct dentry *dentry, struct nameidata *nd)
{
    struct page *page = NULL;
    int error = shmem_getpage(dentry->d_inode, 0, &page, SGP_READ, NULL);
    nd_set_link(nd, error ? ERR_PTR(error) : kmap(page));
    if (page)
        unlock_page(page);
    return page;
}

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

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

/*
 * Callback for security_inode_init_security() for acquiring xattrs.
 */
static int shmem_initxattrs(struct inode *inode,
                const struct xattr *xattr_array,
                void *fs_info)
{
    struct shmem_inode_info *info = SHMEM_I(inode);
    const struct xattr *xattr;
    struct simple_xattr *new_xattr;
    size_t len;

    for (xattr = xattr_array; xattr->name != NULL; xattr++) {
        new_xattr = simple_xattr_alloc(xattr->value, xattr->value_len);
        if (!new_xattr)
            return -ENOMEM;

        len = strlen(xattr->name) + 1;
        new_xattr->name = kmalloc(XATTR_SECURITY_PREFIX_LEN + len,
                      GFP_KERNEL);
        if (!new_xattr->name) {
            kfree(new_xattr);
            return -ENOMEM;
        }

        memcpy(new_xattr->name, XATTR_SECURITY_PREFIX,
               XATTR_SECURITY_PREFIX_LEN);
        memcpy(new_xattr->name + XATTR_SECURITY_PREFIX_LEN,
               xattr->name, len);

        simple_xattr_list_add(&info->xattrs, new_xattr);
    }

    return 0;
}

static const struct xattr_handler *shmem_xattr_handlers[] = {
#ifdef CONFIG_TMPFS_POSIX_ACL
    &generic_acl_access_handler,
    &generic_acl_default_handler,
#endif
    NULL
};

static int shmem_xattr_validate(const char *name)
{
    struct { const char *prefix; size_t len; } arr[] = {
        { XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN },
        { XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN }
    };
    int i;

    for (i = 0; i < ARRAY_SIZE(arr); i++) {
        size_t preflen = arr[i].len;
        if (strncmp(name, arr[i].prefix, preflen) == 0) {
            if (!name[preflen])
                return -EINVAL;
            return 0;
        }
    }
    return -EOPNOTSUPP;
}

static ssize_t shmem_getxattr(struct dentry *dentry, const char *name,
                  void *buffer, size_t size)
{
    struct shmem_inode_info *info = SHMEM_I(dentry->d_inode);
    int err;

    /*
     * If this is a request for a synthetic attribute in the system.*
     * namespace use the generic infrastructure to resolve a handler
     * for it via sb->s_xattr.
     */
    if (!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
        return generic_getxattr(dentry, name, buffer, size);

    err = shmem_xattr_validate(name);
    if (err)
        return err;

    return simple_xattr_get(&info->xattrs, name, buffer, size);
}

static int shmem_setxattr(struct dentry *dentry, const char *name,
              const void *value, size_t size, int flags)
{
    struct shmem_inode_info *info = SHMEM_I(dentry->d_inode);
    int err;

    /*
     * If this is a request for a synthetic attribute in the system.*
     * namespace use the generic infrastructure to resolve a handler
     * for it via sb->s_xattr.
     */
    if (!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
        return generic_setxattr(dentry, name, value, size, flags);

    err = shmem_xattr_validate(name);
    if (err)
        return err;

    return simple_xattr_set(&info->xattrs, name, value, size, flags);
}

static int shmem_removexattr(struct dentry *dentry, const char *name)
{
    struct shmem_inode_info *info = SHMEM_I(dentry->d_inode);
    int err;

    /*
     * If this is a request for a synthetic attribute in the system.*
     * namespace use the generic infrastructure to resolve a handler
     * for it via sb->s_xattr.
     */
    if (!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
        return generic_removexattr(dentry, name);

    err = shmem_xattr_validate(name);
    if (err)
        return err;

    return simple_xattr_remove(&info->xattrs, name);
}

static ssize_t shmem_listxattr(struct dentry *dentry, char *buffer, size_t size)
{
    struct shmem_inode_info *info = SHMEM_I(dentry->d_inode);
    return simple_xattr_list(&info->xattrs, buffer, size);
}
#endif /* CONFIG_TMPFS_XATTR */

static const struct inode_operations shmem_short_symlink_operations = {
    .readlink   = generic_readlink,
    .follow_link    = shmem_follow_short_symlink,
#ifdef CONFIG_TMPFS_XATTR
    .setxattr   = shmem_setxattr,
    .getxattr   = shmem_getxattr,
    .listxattr  = shmem_listxattr,
    .removexattr    = shmem_removexattr,
#endif
};

static const struct inode_operations shmem_symlink_inode_operations = {
    .readlink   = generic_readlink,
    .follow_link    = shmem_follow_link,
    .put_link   = shmem_put_link,
#ifdef CONFIG_TMPFS_XATTR
    .setxattr   = shmem_setxattr,
    .getxattr   = shmem_getxattr,
    .listxattr  = shmem_listxattr,
    .removexattr    = shmem_removexattr,
#endif
};

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

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

static struct dentry *shmem_fh_to_dentry(struct super_block *sb,
        struct fid *fid, int fh_len, int fh_type)
{
    struct inode *inode;
    struct dentry *dentry = NULL;
    u64 inum;

    if (fh_len < 3)
        return NULL;

    inum = fid->raw[2];
    inum = (inum << 32) | fid->raw[1];

    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 inode *inode, __u32 *fh, int *len,
                struct inode *parent)
{
    if (*len < 3) {
        *len = 3;
        return 255;
    }

    if (inode_unhashed(inode)) {
        /* 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 (inode_unhashed(inode))
            __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;
    uid_t uid;
    gid_t gid;

    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;
            uid = simple_strtoul(value, &rest, 0);
            if (*rest)
                goto bad_val;
            sbinfo->uid = make_kuid(current_user_ns(), uid);
            if (!uid_valid(sbinfo->uid))
                goto bad_val;
        } else if (!strcmp(this_char,"gid")) {
            if (remount)
                continue;
            gid = simple_strtoul(value, &rest, 0);
            if (*rest)
                goto bad_val;
            sbinfo->gid = make_kgid(current_user_ns(), gid);
            if (!gid_valid(sbinfo->gid))
                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 inodes;
    int error = -EINVAL;

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

    spin_lock(&sbinfo->stat_lock);
    inodes = sbinfo->max_inodes - sbinfo->free_inodes;
    if (percpu_counter_compare(&sbinfo->used_blocks, config.max_blocks) > 0)
        goto out;
    if (config.max_inodes < inodes)
        goto out;
    /*
     * Those tests disallow limited->unlimited while any are in use;
     * but we must separately disallow unlimited->limited, because
     * in that case we have no record of how much is already in use.
     */
    if (config.max_blocks && !sbinfo->max_blocks)
        goto out;
    if (config.max_inodes && !sbinfo->max_inodes)
        goto out;

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

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

static int shmem_show_options(struct seq_file *seq, struct dentry *root)
{
    struct shmem_sb_info *sbinfo = SHMEM_SB(root->d_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=%03ho", sbinfo->mode);
    if (!uid_eq(sbinfo->uid, GLOBAL_ROOT_UID))
        seq_printf(seq, ",uid=%u",
                from_kuid_munged(&init_user_ns, sbinfo->uid));
    if (!gid_eq(sbinfo->gid, GLOBAL_ROOT_GID))
        seq_printf(seq, ",gid=%u",
                from_kgid_munged(&init_user_ns, sbinfo->gid));
    shmem_show_mpol(seq, sbinfo->mpol);
    return 0;
}
#endif /* CONFIG_TMPFS */

static void shmem_put_super(struct super_block *sb)
{
    struct shmem_sb_info *sbinfo = SHMEM_SB(sb);

    percpu_counter_destroy(&sbinfo->used_blocks);
    kfree(sbinfo);
    sb->s_fs_info = NULL;
}

int shmem_fill_super(struct super_block *sb, void *data, int silent)
{
    struct inode *inode;
    struct shmem_sb_info *sbinfo;
    int err = -ENOMEM;

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

    sbinfo->mode = S_IRWXUGO | S_ISVTX;
    sbinfo->uid = current_fsuid();
    sbinfo->gid = current_fsgid();
    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;
    sb->s_flags |= MS_NOSEC;
#else
    sb->s_flags |= MS_NOUSER;
#endif

    spin_lock_init(&sbinfo->stat_lock);
    if (percpu_counter_init(&sbinfo->used_blocks, 0))
        goto failed;
    sbinfo->free_inodes = sbinfo->max_inodes;

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

    inode = shmem_get_inode(sb, NULL, S_IFDIR | sbinfo->mode, 0, VM_NORESERVE);
    if (!inode)
        goto failed;
    inode->i_uid = sbinfo->uid;
    inode->i_gid = sbinfo->gid;
    sb->s_root = d_make_root(inode);
    if (!sb->s_root)
        goto failed;
    return 0;

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 *info;
    info = kmem_cache_alloc(shmem_inode_cachep, GFP_KERNEL);
    if (!info)
        return NULL;
    return &info->vfs_inode;
}

static void shmem_destroy_callback(struct rcu_head *head)
{
    struct inode *inode = container_of(head, struct inode, i_rcu);
    kmem_cache_free(shmem_inode_cachep, SHMEM_I(inode));
}

static void shmem_destroy_inode(struct inode *inode)
{
    if (S_ISREG(inode->i_mode))
        mpol_free_shared_policy(&SHMEM_I(inode)->policy);
    call_rcu(&inode->i_rcu, shmem_destroy_callback);
}

static void shmem_init_inode(void *foo)
{
    struct shmem_inode_info *info = foo;
    inode_init_once(&info->vfs_inode);
}

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

static void shmem_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
    .write_begin    = shmem_write_begin,
    .write_end  = shmem_write_end,
#endif
    .migratepage    = migrate_page,
    .error_remove_page = generic_error_remove_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      = noop_fsync,
    .splice_read    = shmem_file_splice_read,
    .splice_write   = generic_file_splice_write,
    .fallocate  = shmem_fallocate,
#endif
};

static const struct inode_operations shmem_inode_operations = {
    .setattr    = shmem_setattr,
#ifdef CONFIG_TMPFS_XATTR
    .setxattr   = shmem_setxattr,
    .getxattr   = shmem_getxattr,
    .listxattr  = shmem_listxattr,
    .removexattr    = shmem_removexattr,
#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_XATTR
    .setxattr   = shmem_setxattr,
    .getxattr   = shmem_getxattr,
    .listxattr  = shmem_listxattr,
    .removexattr    = shmem_removexattr,
#endif
#ifdef CONFIG_TMPFS_POSIX_ACL
    .setattr    = shmem_setattr,
#endif
};

static const struct inode_operations shmem_special_inode_operations = {
#ifdef CONFIG_TMPFS_XATTR
    .setxattr   = shmem_setxattr,
    .getxattr   = shmem_getxattr,
    .listxattr  = shmem_listxattr,
    .removexattr    = shmem_removexattr,
#endif
#ifdef CONFIG_TMPFS_POSIX_ACL
    .setattr    = shmem_setattr,
#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
    .evict_inode    = shmem_evict_inode,
    .drop_inode = generic_delete_inode,
    .put_super  = shmem_put_super,
};

static const struct vm_operations_struct shmem_vm_ops = {
    .fault      = shmem_fault,
#ifdef CONFIG_NUMA
    .set_policy     = shmem_set_policy,
    .get_policy     = shmem_get_policy,
#endif
    .remap_pages    = generic_file_remap_pages,
};

static struct dentry *shmem_mount(struct file_system_type *fs_type,
    int flags, const char *dev_name, void *data)
{
    return mount_nodev(fs_type, flags, data, shmem_fill_super);
}

static struct file_system_type shmem_fs_type = {
    .owner      = THIS_MODULE,
    .name       = "tmpfs",
    .mount      = shmem_mount,
    .kill_sb    = kill_litter_super,
};

int __init shmem_init(void)
{
    int error;

    error = bdi_init(&shmem_backing_dev_info);
    if (error)
        goto out4;

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

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

    shm_mnt = vfs_kern_mount(&shmem_fs_type, MS_NOUSER,
                 shmem_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(&shmem_fs_type);
out2:
    shmem_destroy_inodecache();
out3:
    bdi_destroy(&shmem_backing_dev_info);
out4:
    shm_mnt = ERR_PTR(error);
    return error;
}

#else /* !CONFIG_SHMEM */

/*
 * tiny-shmem: simple shmemfs and tmpfs using ramfs code
 *
 * This is intended for small system where the benefits of the full
 * shmem code (swap-backed and resource-limited) are outweighed by
 * their complexity. On systems without swap this code should be
 * effectively equivalent, but much lighter weight.
 */

#include <linux/ramfs.h>

static struct file_system_type shmem_fs_type = {
    .name       = "tmpfs",
    .mount      = ramfs_mount,
    .kill_sb    = kill_litter_super,
};

int __init shmem_init(void)
{
    BUG_ON(register_filesystem(&shmem_fs_type) != 0);

    shm_mnt = kern_mount(&shmem_fs_type);
    BUG_ON(IS_ERR(shm_mnt));

    return 0;
}

int shmem_unuse(swp_entry_t swap, struct page *page)
{
    return 0;
}

int shmem_lock(struct file *file, int lock, struct user_struct *user)
{
    return 0;
}

void shmem_unlock_mapping(struct address_space *mapping)
{
}

void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
{
    truncate_inode_pages_range(inode->i_mapping, lstart, lend);
}
EXPORT_SYMBOL_GPL(shmem_truncate_range);

#define shmem_vm_ops                generic_file_vm_ops
#define shmem_file_operations           ramfs_file_operations
#define shmem_get_inode(sb, dir, mode, dev, flags)  ramfs_get_inode(sb, dir, mode, dev)
#define shmem_acct_size(flags, size)        0
#define shmem_unacct_size(flags, size)      do {} while (0)

#endif /* CONFIG_SHMEM */

/* common code */

struct file *shmem_file_setup(const char *name, loff_t size, unsigned long flags)
{
    int error;
    struct file *file;
    struct inode *inode;
    struct path path;
    struct dentry *root;
    struct qstr this;

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

    if (size < 0 || size > MAX_LFS_FILESIZE)
        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;
    path.dentry = d_alloc(root, &this);
    if (!path.dentry)
        goto put_memory;
    path.mnt = mntget(shm_mnt);

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

    d_instantiate(path.dentry, inode);
    inode->i_size = size;
    clear_nlink(inode); /* It is unlinked */
#ifndef CONFIG_MMU
    error = ramfs_nommu_expand_for_mapping(inode, size);
    if (error)
        goto put_dentry;
#endif

    error = -ENFILE;
    file = alloc_file(&path, FMODE_WRITE | FMODE_READ,
          &shmem_file_operations);
    if (!file)
        goto put_dentry;

    return file;

put_dentry:
    path_put(&path);
put_memory:
    shmem_unacct_size(flags, size);
    return ERR_PTR(error);
}
EXPORT_SYMBOL_GPL(shmem_file_setup);

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;
}

struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
                     pgoff_t index, gfp_t gfp)
{
#ifdef CONFIG_SHMEM
    struct inode *inode = mapping->host;
    struct page *page;
    int error;

    BUG_ON(mapping->a_ops != &shmem_aops);
    error = shmem_getpage_gfp(inode, index, &page, SGP_CACHE, gfp, NULL);
    if (error)
        page = ERR_PTR(error);
    else
        unlock_page(page);
    return page;
#else
    /*
     * The tiny !SHMEM case uses ramfs without swap
     */
    return read_cache_page_gfp(mapping, index, gfp);
#endif
}
EXPORT_SYMBOL_GPL(shmem_read_mapping_page_gfp);