/*
 * 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) 2002-2003 Hugh Dickins.
 * Copyright (C) 2002-2003 VERITAS Software Corporation.
 *
 * 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/config.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/devfs_fs_kernel.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/file.h>
#include <linux/swap.h>
#include <linux/pagemap.h>
#include <linux/string.h>
#include <linux/locks.h>
#include <linux/smp_lock.h>

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

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

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

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

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

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

#define SHMEM_SB(sb) (&sb->u.shmem_sb)

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

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

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

LIST_HEAD(shmem_inodes);
static spinlock_t shmem_ilock = SPIN_LOCK_UNLOCKED;

static void shmem_free_block(struct inode *inode)
{
        struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
        spin_lock(&sbinfo->stat_lock);
        sbinfo->free_blocks++;
        inode->i_blocks -= BLOCKS_PER_PAGE;
        spin_unlock(&sbinfo->stat_lock);
}

static void shmem_removepage(struct page *page)
{
        if (!PageLaunder(page))
                shmem_free_block(page->mapping->host);
}

/*
 * 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 0, else it will use the page for the needed block,
 * setting it to 0 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, unsigned long *page)
{
        unsigned long offset;
        void **dir;

        if (index < SHMEM_NR_DIRECT)
                return info->i_direct+index;
        if (!info->i_indirect) {
                if (page) {
                        info->i_indirect = (void **) *page;
                        *page = 0;
                }
                return NULL;                    /* need another page */
        }

        index -= SHMEM_NR_DIRECT;
        offset = index % ENTRIES_PER_PAGE;
        index /= ENTRIES_PER_PAGE;
        dir = 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;
                if (!*dir) {
                        if (page) {
                                *dir = (void *) *page;
                                *page = 0;
                        }
                        return NULL;            /* need another page */
                }
                dir = (void **) *dir;
        }

        dir += index;
        if (!*dir) {
                if (!page || !*page)
                        return NULL;            /* need a page */
                *dir = (void *) *page;
                *page = 0;
        }
        return (swp_entry_t *) *dir + offset;
}

/*
 * shmem_swp_alloc - get the position of the swap entry for the page.
 *                   If it does not exist allocate the entry.
 *
 * @info:       info structure for the inode
 * @index:      index of the page to find
 * @sgp:        check and recheck i_size? skip allocation?
 */
static swp_entry_t *shmem_swp_alloc(struct shmem_inode_info *info, unsigned long index, enum sgp_type sgp)
{
        struct inode *inode = info->inode;
        struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
        unsigned long page = 0;
        swp_entry_t *entry;
        static const swp_entry_t unswapped = {0};

        if (sgp != SGP_WRITE &&
            ((loff_t) index << PAGE_CACHE_SHIFT) >= inode->i_size)
                return ERR_PTR(-EINVAL);

        while (!(entry = shmem_swp_entry(info, index, &page))) {
                if (sgp == SGP_READ)
                        return (swp_entry_t *) &unswapped;
                /*
                 * 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.
                 */
                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 = get_zeroed_page(GFP_USER);
                spin_lock(&info->lock);

                if (!page) {
                        shmem_free_block(inode);
                        return ERR_PTR(-ENOMEM);
                }
                if (sgp != SGP_WRITE &&
                    ((loff_t) index << PAGE_CACHE_SHIFT) >= inode->i_size) {
                        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_block(inode);
                free_page(page);
        }
        if (info->next_index <= index && !IS_ERR(entry))
                info->next_index = index + 1;
        return entry;
}

/*
 * shmem_free_swp - free some swap entries in a directory
 *
 * @dir:   pointer to the directory
 * @edir:  pointer after last entry of the directory
 */
static int shmem_free_swp(swp_entry_t *dir, swp_entry_t *edir)
{
        swp_entry_t *ptr;
        int freed = 0;

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

/*
 * shmem_truncate_direct - free the swap entries of a whole doubly
 *                         indirect block
 *
 * @info:       the info structure of the inode
 * @dir:        pointer to the pointer to the block
 * @start:      offset to start from (in pages)
 * @len:        how many pages are stored in this block
 */
static inline unsigned long
shmem_truncate_direct(struct shmem_inode_info *info, swp_entry_t ***dir, unsigned long start, unsigned long len)
{
        swp_entry_t **last, **ptr;
        unsigned long off, freed_swp, freed = 0;

        last = *dir + (len + ENTRIES_PER_PAGE - 1) / ENTRIES_PER_PAGE;
        off = start % ENTRIES_PER_PAGE;

        for (ptr = *dir + start/ENTRIES_PER_PAGE; ptr < last; ptr++, off = 0) {
                if (!*ptr)
                        continue;

                if (info->swapped) {
                        freed_swp = shmem_free_swp(*ptr + off,
                                                *ptr + ENTRIES_PER_PAGE);
                        info->swapped -= freed_swp;
                        freed += freed_swp;
                }

                if (!off) {
                        freed++;
                        free_page((unsigned long) *ptr);
                        *ptr = 0;
                }
        }

        if (!start) {
                freed++;
                free_page((unsigned long) *dir);
                *dir = 0;
        }
        return freed;
}

/*
 * shmem_truncate_indirect - truncate an inode
 *
 * @info:  the info structure of the inode
 * @index: the index to truncate
 *
 * This function locates the last doubly indirect block and calls
 * then shmem_truncate_direct to do the real work
 */
static inline unsigned long
shmem_truncate_indirect(struct shmem_inode_info *info, unsigned long index)
{
        swp_entry_t ***base;
        unsigned long baseidx, start;
        unsigned long len = info->next_index;
        unsigned long freed;

        if (len <= SHMEM_NR_DIRECT) {
                info->next_index = index;
                if (!info->swapped)
                        return 0;
                freed = shmem_free_swp(info->i_direct + index,
                                        info->i_direct + len);
                info->swapped -= freed;
                return freed;
        }

        if (len <= ENTRIES_PER_PAGEPAGE/2 + SHMEM_NR_DIRECT) {
                len -= SHMEM_NR_DIRECT;
                base = (swp_entry_t ***) &info->i_indirect;
                baseidx = SHMEM_NR_DIRECT;
        } else {
                len -= ENTRIES_PER_PAGEPAGE/2 + SHMEM_NR_DIRECT;
                BUG_ON(len > ENTRIES_PER_PAGEPAGE*ENTRIES_PER_PAGE/2);
                baseidx = len - 1;
                baseidx -= baseidx % ENTRIES_PER_PAGEPAGE;
                base = (swp_entry_t ***) info->i_indirect +
                        ENTRIES_PER_PAGE/2 + baseidx/ENTRIES_PER_PAGEPAGE;
                len -= baseidx;
                baseidx += ENTRIES_PER_PAGEPAGE/2 + SHMEM_NR_DIRECT;
        }

        if (index > baseidx) {
                info->next_index = index;
                start = index - baseidx;
        } else {
                info->next_index = baseidx;
                start = 0;
        }
        return *base? shmem_truncate_direct(info, base, start, len): 0;
}

static void shmem_truncate(struct inode *inode)
{
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
        unsigned long freed = 0;
        unsigned long index;

        inode->i_ctime = inode->i_mtime = CURRENT_TIME;
        index = (inode->i_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
        if (index >= info->next_index)
                return;

        spin_lock(&info->lock);
        while (index < info->next_index)
                freed += shmem_truncate_indirect(info, index);
        BUG_ON(info->swapped > info->next_index);
        spin_unlock(&info->lock);

        spin_lock(&sbinfo->stat_lock);
        sbinfo->free_blocks += freed;
        inode->i_blocks -= freed*BLOCKS_PER_PAGE;
        spin_unlock(&sbinfo->stat_lock);
}

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

        if (attr->ia_valid & ATTR_SIZE) {
                if (attr->ia_size < inode->i_size) {
                        /*
                         * If truncating down to a partial page, then
                         * if that page is already allocated, hold it
                         * in memory until the truncation is over, so
                         * truncate_partial_page cannnot miss it were
                         * it assigned to swap.
                         */
                        if (attr->ia_size & (PAGE_CACHE_SIZE-1)) {
                                (void) shmem_getpage(inode,
                                        attr->ia_size>>PAGE_CACHE_SHIFT,
                                                &page, SGP_READ);
                        }
                }
        }

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

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

        if (inode->i_op->truncate == shmem_truncate) {
                spin_lock(&shmem_ilock);
                list_del(&info->list);
                spin_unlock(&shmem_ilock);
                inode->i_size = 0;
                shmem_truncate(inode);
        }
        BUG_ON(inode->i_blocks);
        spin_lock(&sbinfo->stat_lock);
        sbinfo->free_inodes++;
        spin_unlock(&sbinfo->stat_lock);
        clear_inode(inode);
}

static inline int shmem_find_swp(swp_entry_t entry, swp_entry_t *dir, swp_entry_t *edir)
{
        swp_entry_t *ptr;

        for (ptr = dir; ptr < edir; ptr++) {
                if (ptr->val == entry.val)
                        return ptr - dir;
        }
        return -1;
}

static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, struct page *page)
{
        struct inode *inode;
        struct address_space *mapping;
        swp_entry_t *ptr;
        unsigned long idx;
        unsigned long limit;
        int offset;

        idx = 0;
        ptr = info->i_direct;
        spin_lock(&info->lock);
        offset = info->next_index;
        if (offset > SHMEM_NR_DIRECT)
                offset = SHMEM_NR_DIRECT;
        offset = shmem_find_swp(entry, ptr, ptr + offset);
        if (offset >= 0)
                goto found;

        for (idx = SHMEM_NR_DIRECT; idx < info->next_index;
             idx += ENTRIES_PER_PAGE) {
                ptr = shmem_swp_entry(info, idx, NULL);
                if (!ptr)
                        continue;
                offset = info->next_index - idx;
                if (offset > ENTRIES_PER_PAGE)
                        offset = ENTRIES_PER_PAGE;
                offset = shmem_find_swp(entry, ptr, ptr + offset);
                if (offset >= 0)
                        goto found;
        }
        spin_unlock(&info->lock);
        return 0;
found:
        idx += offset;
        inode = info->inode;
        mapping = inode->i_mapping;
        delete_from_swap_cache(page);

        /* Racing against delete or truncate? Must leave out of page cache */
        limit = (inode->i_state & I_FREEING)? 0:
                (inode->i_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;

        if (idx >= limit || add_to_page_cache_unique(page,
                        mapping, idx, page_hash(mapping, idx)) == 0) {
                ptr[offset].val = 0;
                info->swapped--;
        } else if (add_to_swap_cache(page, entry) != 0)
                BUG();
        spin_unlock(&info->lock);
        SetPageUptodate(page);
        /*
         * Decrement swap count even when the entry is left behind:
         * try_to_unuse will skip over mms, then reincrement count.
         */
        swap_free(entry);
        return 1;
}

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

        spin_lock(&shmem_ilock);
        list_for_each(p, &shmem_inodes) {
                info = list_entry(p, struct shmem_inode_info, list);

                if (info->swapped && shmem_unuse_inode(info, entry, page)) {
                        /* move head to start search for next from here */
                        list_move_tail(&shmem_inodes, &info->list);
                        found = 1;
                        break;
                }
        }
        spin_unlock(&shmem_ilock);
        return found;
}

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

        BUG_ON(!PageLocked(page));
        if (!PageLaunder(page))
                return fail_writepage(page);

        mapping = page->mapping;
        index = page->index;
        inode = mapping->host;
        info = SHMEM_I(inode);
        if (info->flags & VM_LOCKED)
                return fail_writepage(page);
getswap:
        swap = get_swap_page();
        if (!swap.val)
                return fail_writepage(page);

        spin_lock(&info->lock);
        BUG_ON(index >= info->next_index);
        entry = shmem_swp_entry(info, index, NULL);
        BUG_ON(!entry);
        BUG_ON(entry->val);

        /* Remove it from the page cache */
        remove_inode_page(page);
        page_cache_release(page);

        /* Add it to the swap cache */
        if (add_to_swap_cache(page, swap) != 0) {
                /*
                 * Raced with "speculative" read_swap_cache_async.
                 * Add page back to page cache, unref swap, try again.
                 */
                add_to_page_cache_locked(page, mapping, index);
                spin_unlock(&info->lock);
                swap_free(swap);
                goto getswap;
        }

        *entry = swap;
        info->swapped++;
        spin_unlock(&info->lock);
        SetPageUptodate(page);
        set_page_dirty(page);
        UnlockPage(page);
        return 0;
}

/*
 * 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)
{
        struct address_space *mapping = inode->i_mapping;
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct shmem_sb_info *sbinfo;
        struct page *filepage = *pagep;
        struct page *swappage;
        swp_entry_t *entry;
        swp_entry_t swap;
        int error = 0;

        if (idx >= SHMEM_MAX_INDEX)
                return -EFBIG;
        /*
         * Normally, filepage is NULL on entry, and either found
         * uptodate immediately, or allocated and zeroed, or read
         * in under swappage, which is then assigned to filepage.
         * But shmem_readpage and shmem_prepare_write pass 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 && Page_Uptodate(filepage))
                goto done;

        spin_lock(&info->lock);
        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) {
                        spin_unlock(&info->lock);
                        swapin_readahead(swap);
                        swappage = read_swap_cache_async(swap);
                        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;
                                spin_unlock(&info->lock);
                                if (error)
                                        goto failed;
                                goto repeat;
                        }
                        wait_on_page(swappage);
                        page_cache_release(swappage);
                        goto repeat;
                }

                /* We have to do this with page locked to prevent races */
                if (TryLockPage(swappage)) {
                        spin_unlock(&info->lock);
                        wait_on_page(swappage);
                        page_cache_release(swappage);
                        goto repeat;
                }
                if (!Page_Uptodate(swappage)) {
                        spin_unlock(&info->lock);
                        UnlockPage(swappage);
                        page_cache_release(swappage);
                        error = -EIO;
                        goto failed;
                }

                delete_from_swap_cache(swappage);
                if (filepage) {
                        entry->val = 0;
                        info->swapped--;
                        spin_unlock(&info->lock);
                        flush_page_to_ram(swappage);
                        copy_highpage(filepage, swappage);
                        UnlockPage(swappage);
                        page_cache_release(swappage);
                        flush_dcache_page(filepage);
                        SetPageUptodate(filepage);
                        SetPageDirty(filepage);
                        swap_free(swap);
                } else if (add_to_page_cache_unique(swappage,
                        mapping, idx, page_hash(mapping, idx)) == 0) {
                        entry->val = 0;
                        info->swapped--;
                        spin_unlock(&info->lock);
                        filepage = swappage;
                        SetPageUptodate(filepage);
                        SetPageDirty(filepage);
                        swap_free(swap);
                } else {
                        if (add_to_swap_cache(swappage, swap) != 0)
                                BUG();
                        spin_unlock(&info->lock);
                        SetPageUptodate(swappage);
                        SetPageDirty(swappage);
                        UnlockPage(swappage);
                        page_cache_release(swappage);
                        goto repeat;
                }
        } else if (sgp == SGP_READ && !filepage) {
                filepage = find_get_page(mapping, idx);
                if (filepage &&
                    (!Page_Uptodate(filepage) || TryLockPage(filepage))) {
                        spin_unlock(&info->lock);
                        wait_on_page(filepage);
                        page_cache_release(filepage);
                        filepage = NULL;
                        goto repeat;
                }
                spin_unlock(&info->lock);
        } else {
                sbinfo = SHMEM_SB(inode->i_sb);
                spin_lock(&sbinfo->stat_lock);
                if (sbinfo->free_blocks == 0) {
                        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);

                if (!filepage) {
                        spin_unlock(&info->lock);
                        filepage = page_cache_alloc(mapping);
                        if (!filepage) {
                                shmem_free_block(inode);
                                error = -ENOMEM;
                                goto failed;
                        }

                        spin_lock(&info->lock);
                        entry = shmem_swp_alloc(info, idx, sgp);
                        if (IS_ERR(entry))
                                error = PTR_ERR(entry);
                        if (error || entry->val ||
                            add_to_page_cache_unique(filepage,
                            mapping, idx, page_hash(mapping, idx)) != 0) {
                                spin_unlock(&info->lock);
                                page_cache_release(filepage);
                                shmem_free_block(inode);
                                filepage = NULL;
                                if (error)
                                        goto failed;
                                goto repeat;
                        }
                }

                spin_unlock(&info->lock);
                clear_highpage(filepage);
                flush_dcache_page(filepage);
                SetPageUptodate(filepage);
        }
done:
        if (!*pagep) {
                if (filepage) {
                        UnlockPage(filepage);
                        *pagep = filepage;
                } else
                        *pagep = ZERO_PAGE(0);
        }
        return 0;

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

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

        idx = (address - vma->vm_start) >> PAGE_SHIFT;
        idx += vma->vm_pgoff;
        idx >>= PAGE_CACHE_SHIFT - PAGE_SHIFT;

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

        mark_page_accessed(page);
        flush_page_to_ram(page);
        return page;
}

void shmem_lock(struct file *file, int lock)
{
        struct inode *inode = file->f_dentry->d_inode;
        struct shmem_inode_info *info = SHMEM_I(inode);

        spin_lock(&info->lock);
        if (lock)
                info->flags |= VM_LOCKED;
        else
                info->flags &= ~VM_LOCKED;
        spin_unlock(&info->lock);
}

static int shmem_mmap(struct file *file, struct vm_area_struct *vma)
{
        struct vm_operations_struct *ops;
        struct inode *inode = file->f_dentry->d_inode;

        ops = &shmem_vm_ops;
        if (!S_ISREG(inode->i_mode))
                return -EACCES;
        UPDATE_ATIME(inode);
        vma->vm_ops = ops;
        return 0;
}

static struct inode *shmem_get_inode(struct super_block *sb, int mode, int dev)
{
        struct inode *inode;
        struct shmem_inode_info *info;
        struct shmem_sb_info *sbinfo = SHMEM_SB(sb);

        spin_lock(&sbinfo->stat_lock);
        if (!sbinfo->free_inodes) {
                spin_unlock(&sbinfo->stat_lock);
                return NULL;
        }
        sbinfo->free_inodes--;
        spin_unlock(&sbinfo->stat_lock);

        inode = new_inode(sb);
        if (inode) {
                inode->i_mode = mode;
                inode->i_uid = current->fsuid;
                inode->i_gid = current->fsgid;
                inode->i_blksize = PAGE_CACHE_SIZE;
                inode->i_blocks = 0;
                inode->i_rdev = NODEV;
                inode->i_mapping->a_ops = &shmem_aops;
                inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
                info = SHMEM_I(inode);
                info->inode = inode;
                spin_lock_init(&info->lock);
                switch (mode & S_IFMT) {
                default:
                        init_special_inode(inode, mode, dev);
                        break;
                case S_IFREG:
                        inode->i_op = &shmem_inode_operations;
                        inode->i_fop = &shmem_file_operations;
                        spin_lock(&shmem_ilock);
                        list_add_tail(&info->list, &shmem_inodes);
                        spin_unlock(&shmem_ilock);
                        break;
                case S_IFDIR:
                        inode->i_nlink++;
                        /* Some things misbehave if size == 0 on a directory */
                        inode->i_size = 2 * BOGO_DIRENT_SIZE;
                        inode->i_op = &shmem_dir_inode_operations;
                        inode->i_fop = &dcache_dir_ops;
                        break;
                case S_IFLNK:
                        break;
                }
        }
        return inode;
}

static int shmem_set_size(struct shmem_sb_info *info,
                          unsigned long max_blocks, unsigned long max_inodes)
{
        int error;
        unsigned long blocks, inodes;

        spin_lock(&info->stat_lock);
        blocks = info->max_blocks - info->free_blocks;
        inodes = info->max_inodes - info->free_inodes;
        error = -EINVAL;
        if (max_blocks < blocks)
                goto out;
        if (max_inodes < inodes)
                goto out;
        error = 0;
        info->max_blocks  = max_blocks;
        info->free_blocks = max_blocks - blocks;
        info->max_inodes  = max_inodes;
        info->free_inodes = max_inodes - inodes;
out:
        spin_unlock(&info->stat_lock);
        return error;
}

#ifdef CONFIG_TMPFS

static struct inode_operations shmem_symlink_inode_operations;
static struct inode_operations shmem_symlink_inline_operations;

/*
 * tmpfs itself makes no use of generic_file_read, generic_file_mmap
 * or generic_file_write; but shmem_readpage, shmem_prepare_write and
 * shmem_commit_write let a tmpfs file be used below the loop driver,
 * and shmem_readpage lets a tmpfs file be used by sendfile.
 */
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);
        UnlockPage(page);
        return error;
}

static int
shmem_prepare_write(struct file *file, struct page *page, unsigned offset, unsigned to)
{
        struct inode *inode = page->mapping->host;
        return shmem_getpage(inode, page->index, &page, SGP_WRITE);
}

static int
shmem_commit_write(struct file *file, struct page *page, unsigned offset, unsigned to)
{
        struct inode *inode = page->mapping->host;
        loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;

        if (pos > inode->i_size)
                inode->i_size = pos;
        SetPageDirty(page);
        return 0;
}

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

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

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

        down(&inode->i_sem);

        pos = *ppos;
        written = 0;

        err = precheck_file_write(file, inode, &count, &pos);
        if (err || !count)
                goto out;

        remove_suid(inode);
        inode->i_ctime = inode->i_mtime = CURRENT_TIME;

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

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

                /*
                 * We don't hold page lock across copy from user -
                 * what would it guard against? - so no deadlock here.
                 */

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

                kaddr = kmap(page);
                left = __copy_from_user(kaddr + offset, buf, bytes);
                kunmap(page);

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

                flush_dcache_page(page);
                SetPageDirty(page);
                SetPageReferenced(page);
                page_cache_release(page);

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

        *ppos = pos;
        if (written)
                err = written;
out:
        up(&inode->i_sem);
        return err;

}

static void do_shmem_file_read(struct file *filp, loff_t *ppos, read_descriptor_t *desc)
{
        struct inode *inode = filp->f_dentry->d_inode;
        struct address_space *mapping = inode->i_mapping;
        unsigned long index, offset;

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

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

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

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

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

                if (page != ZERO_PAGE(0)) {
                        /*
                         * 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->i_mmap_shared != NULL)
                                flush_dcache_page(page);
                        /*
                         * Mark the page accessed if we read the
                         * beginning or we just did an lseek.
                         */
                        if (!offset || !filp->f_reada)
                                mark_page_accessed(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 = file_read_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;
        }

        *ppos = ((loff_t) index << PAGE_CACHE_SHIFT) + offset;
        filp->f_reada = 1;
        UPDATE_ATIME(inode);
}

static ssize_t shmem_file_read(struct file *filp, char *buf, size_t count, loff_t *ppos)
{
        read_descriptor_t desc;

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

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

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

static int shmem_statfs(struct super_block *sb, struct statfs *buf)
{
        struct shmem_sb_info *sbinfo = SHMEM_SB(sb);

        buf->f_type = TMPFS_MAGIC;
        buf->f_bsize = PAGE_CACHE_SIZE;
        spin_lock(&sbinfo->stat_lock);
        buf->f_blocks = sbinfo->max_blocks;
        buf->f_bavail = buf->f_bfree = sbinfo->free_blocks;
        buf->f_files = sbinfo->max_inodes;
        buf->f_ffree = sbinfo->free_inodes;
        spin_unlock(&sbinfo->stat_lock);
        buf->f_namelen = NAME_MAX;
        return 0;
}

/*
 * Lookup the data. This is trivial - if the dentry didn't already
 * exist, we know it is negative.
 */
static struct dentry *shmem_lookup(struct inode *dir, struct dentry *dentry)
{
        d_add(dentry, NULL);
        return NULL;
}

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

        if (inode) {
                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 */
                error = 0;
        }
        return error;
}

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

        if ((error = shmem_mknod(dir, dentry, mode | S_IFDIR, 0)))
                return error;
        dir->i_nlink++;
        return 0;
}

static int shmem_create(struct inode *dir, struct dentry *dentry, int mode)
{
        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;

        if (S_ISDIR(inode->i_mode))
                return -EPERM;

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

static inline int shmem_positive(struct dentry *dentry)
{
        return dentry->d_inode && !d_unhashed(dentry);
}

/*
 * Check that a directory is empty (this works
 * for regular files too, they'll just always be
 * considered empty..).
 *
 * Note that an empty directory can still have
 * children, they just all have to be negative..
 */
static int shmem_empty(struct dentry *dentry)
{
        struct list_head *list;

        spin_lock(&dcache_lock);
        list = dentry->d_subdirs.next;

        while (list != &dentry->d_subdirs) {
                struct dentry *de = list_entry(list, struct dentry, d_child);

                if (shmem_positive(de)) {
                        spin_unlock(&dcache_lock);
                        return 0;
                }
                list = list->next;
        }
        spin_unlock(&dcache_lock);
        return 1;
}

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

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

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

        dir->i_nlink--;
        return shmem_unlink(dir, dentry);
}

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

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

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

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

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

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

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

        info = SHMEM_I(inode);
        inode->i_size = len-1;
        if (len <= sizeof(struct shmem_inode_info)) {
                /* do it inline */
                memcpy(info, symname, len);
                inode->i_op = &shmem_symlink_inline_operations;
        } else {
                error = shmem_getpage(inode, 0, &page, SGP_WRITE);
                if (error) {
                        iput(inode);
                        return error;
                }
                inode->i_op = &shmem_symlink_inode_operations;
                spin_lock(&shmem_ilock);
                list_add_tail(&info->list, &shmem_inodes);
                spin_unlock(&shmem_ilock);
                kaddr = kmap(page);
                memcpy(kaddr, symname, len);
                kunmap(page);
                SetPageDirty(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 int shmem_readlink_inline(struct dentry *dentry, char *buffer, int buflen)
{
        return vfs_readlink(dentry, buffer, buflen, (const char *)SHMEM_I(dentry->d_inode));
}

static int shmem_follow_link_inline(struct dentry *dentry, struct nameidata *nd)
{
        return vfs_follow_link(nd, (const char *)SHMEM_I(dentry->d_inode));
}

static int shmem_readlink(struct dentry *dentry, char *buffer, int buflen)
{
        struct page *page = NULL;
        int res = shmem_getpage(dentry->d_inode, 0, &page, SGP_READ);
        if (res)
                return res;
        res = vfs_readlink(dentry, buffer, buflen, kmap(page));
        kunmap(page);
        mark_page_accessed(page);
        page_cache_release(page);
        return res;
}

static int shmem_follow_link(struct dentry *dentry, struct nameidata *nd)
{
        struct page *page = NULL;
        int res = shmem_getpage(dentry->d_inode, 0, &page, SGP_READ);
        if (res)
                return res;
        res = vfs_follow_link(nd, kmap(page));
        kunmap(page);
        mark_page_accessed(page);
        page_cache_release(page);
        return res;
}

static struct inode_operations shmem_symlink_inline_operations = {
        readlink:       shmem_readlink_inline,
        follow_link:    shmem_follow_link_inline,
};

static struct inode_operations shmem_symlink_inode_operations = {
        truncate:       shmem_truncate,
        readlink:       shmem_readlink,
        follow_link:    shmem_follow_link,
};

static int shmem_parse_options(char *options, int *mode, uid_t *uid, gid_t *gid, unsigned long *blocks, unsigned long *inodes)
{
        char *this_char, *value, *rest;

        while ((this_char = strsep(&options, ",")) != NULL) {
                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 == '%') {
                                struct sysinfo si;
                                si_meminfo(&si);
                                size <<= PAGE_SHIFT;
                                size *= si.totalram;
                                do_div(size, 100);
                                rest++;
                        }
                        if (*rest)
                                goto bad_val;
                        *blocks = size >> PAGE_CACHE_SHIFT;
                } else if (!strcmp(this_char,"nr_blocks")) {
                        *blocks = memparse(value,&rest);
                        if (*rest)
                                goto bad_val;
                } else if (!strcmp(this_char,"nr_inodes")) {
                        *inodes = memparse(value,&rest);
                        if (*rest)
                                goto bad_val;
                } else if (!strcmp(this_char,"mode")) {
                        if (!mode)
                                continue;
                        *mode = simple_strtoul(value,&rest,8);
                        if (*rest)
                                goto bad_val;
                } else if (!strcmp(this_char,"uid")) {
                        if (!uid)
                                continue;
                        *uid = simple_strtoul(value,&rest,0);
                        if (*rest)
                                goto bad_val;
                } else if (!strcmp(this_char,"gid")) {
                        if (!gid)
                                continue;
                        *gid = simple_strtoul(value,&rest,0);
                        if (*rest)
                                goto bad_val;
                } else {
                        printk(KERN_ERR "tmpfs: Bad mount option %s\n",
                               this_char);
                        return 1;
                }
        }
        return 0;

bad_val:
        printk(KERN_ERR "tmpfs: Bad value '%s' for mount option '%s'\n",
               value, this_char);
        return 1;
}

static int shmem_remount_fs(struct super_block *sb, int *flags, char *data)
{
        struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
        unsigned long max_blocks = sbinfo->max_blocks;
        unsigned long max_inodes = sbinfo->max_inodes;

        if (shmem_parse_options(data, NULL, NULL, NULL, &max_blocks, &max_inodes))
                return -EINVAL;
        return shmem_set_size(sbinfo, max_blocks, max_inodes);
}

static int shmem_sync_file(struct file *file, struct dentry *dentry, int datasync)
{
        return 0;
}
#endif

static struct super_block *shmem_read_super(struct super_block *sb, void *data, int silent)
{
        struct inode *inode;
        struct dentry *root;
        unsigned long blocks, inodes;
        int mode   = S_IRWXUGO | S_ISVTX;
        uid_t uid = current->fsuid;
        gid_t gid = current->fsgid;
        struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
        struct sysinfo si;

        /*
         * Per default we only allow half of the physical ram per
         * tmpfs instance
         */
        si_meminfo(&si);
        blocks = inodes = si.totalram / 2;

#ifdef CONFIG_TMPFS
        if (shmem_parse_options(data, &mode, &uid, &gid, &blocks, &inodes))
                return NULL;
#endif

        spin_lock_init(&sbinfo->stat_lock);
        sbinfo->max_blocks = blocks;
        sbinfo->free_blocks = blocks;
        sbinfo->max_inodes = inodes;
        sbinfo->free_inodes = 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;
        inode = shmem_get_inode(sb, S_IFDIR | mode, 0);
        if (!inode)
                return NULL;

        inode->i_uid = uid;
        inode->i_gid = gid;
        root = d_alloc_root(inode);
        if (!root) {
                iput(inode);
                return NULL;
        }
        sb->s_root = root;
        return sb;
}

static struct address_space_operations shmem_aops = {
        removepage:     shmem_removepage,
        writepage:      shmem_writepage,
#ifdef CONFIG_TMPFS
        readpage:       shmem_readpage,
        prepare_write:  shmem_prepare_write,
        commit_write:   shmem_commit_write,
#endif
};

static struct file_operations shmem_file_operations = {
        mmap:           shmem_mmap,
#ifdef CONFIG_TMPFS
        read:           shmem_file_read,
        write:          shmem_file_write,
        fsync:          shmem_sync_file,
#endif
};

static struct inode_operations shmem_inode_operations = {
        truncate:       shmem_truncate,
        setattr:        shmem_notify_change,
};

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

static struct super_operations shmem_ops = {
#ifdef CONFIG_TMPFS
        statfs:         shmem_statfs,
        remount_fs:     shmem_remount_fs,
#endif
        delete_inode:   shmem_delete_inode,
        put_inode:      force_delete,
};

static struct vm_operations_struct shmem_vm_ops = {
        nopage:         shmem_nopage,
};

#ifdef CONFIG_TMPFS
/* type "shm" will be tagged obsolete in 2.5 */
static DECLARE_FSTYPE(shmem_fs_type, "shm", shmem_read_super, FS_LITTER);
static DECLARE_FSTYPE(tmpfs_fs_type, "tmpfs", shmem_read_super, FS_LITTER);
#else
static DECLARE_FSTYPE(tmpfs_fs_type, "tmpfs", shmem_read_super, FS_LITTER|FS_NOMOUNT);
#endif
static struct vfsmount *shm_mnt;

static int __init init_tmpfs(void)
{
        int error;

        error = register_filesystem(&tmpfs_fs_type);
        if (error) {
                printk(KERN_ERR "Could not register tmpfs\n");
                goto out3;
        }
#ifdef CONFIG_TMPFS
        error = register_filesystem(&shmem_fs_type);
        if (error) {
                printk(KERN_ERR "Could not register shm fs\n");
                goto out2;
        }
        devfs_mk_dir(NULL, "shm", NULL);
#endif
        shm_mnt = kern_mount(&tmpfs_fs_type);
        if (IS_ERR(shm_mnt)) {
                error = PTR_ERR(shm_mnt);
                printk(KERN_ERR "Could not kern_mount tmpfs\n");
                goto out1;
        }

        /* The internal instance should not do size checking */
        shmem_set_size(SHMEM_SB(shm_mnt->mnt_sb), ULONG_MAX, ULONG_MAX);
        return 0;

out1:
#ifdef CONFIG_TMPFS
        unregister_filesystem(&shmem_fs_type);
out2:
#endif
        unregister_filesystem(&tmpfs_fs_type);
out3:
        shm_mnt = ERR_PTR(error);
        return error;
}
module_init(init_tmpfs)

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

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

        if (size > SHMEM_MAX_BYTES)
                return ERR_PTR(-EINVAL);

        if (!vm_enough_memory(VM_ACCT(size)))
                return ERR_PTR(-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)
                return ERR_PTR(-ENOMEM);

        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;

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

close_file:
        put_filp(file);
put_dentry:
        dput(dentry);
        return ERR_PTR(error);
}

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

        file = shmem_file_setup("dev/zero", size);
        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;
}

EXPORT_SYMBOL(shmem_file_setup);