sys/src/vmsshmem.c

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// _Id: vmsshmem.c,v 1.7 2006-04-29 09:31:21 roart Exp $
// _Locker:  $

// Author. Roar Thronæs.
// Modified Linux source file, 2001-2004. Based on shmem.c.

/*
 * Resizable virtual memory filesystem for Linux.
 *
 * Copyright (C) 2000 Linus Torvalds.
 *               2000 Transmeta Corp.
 *               2000-2001 Christoph Rohland
 *               2000-2001 SAP AG
 * 
 * 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>

/* 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 SHMEM_SB(sb) (&sb->u.shmem_sb)

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 file_operations shmem_dir_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;
atomic_t shmem_nrpages = ATOMIC_INIT(0); /* Not used right now */

#define BLOCKS_PER_PAGE (PAGE_CACHE_SIZE/512)

/*
 * shmem_recalc_inode - recalculate the size of an inode
 *
 * @inode: inode to recalc
 * @swap:  additional swap pages freed externally
 *
 * We have to calculate the free blocks since the mm can drop pages
 * behind our back
 *
 * But we know that normally
 * inodes->i_blocks/BLOCKS_PER_PAGE == 
 *                      inode->i_mapping->nrpages + info->swapped
 *
 * So the mm freed 
 * inodes->i_blocks/BLOCKS_PER_PAGE - 
 *                      (inode->i_mapping->nrpages + info->swapped)
 *
 * It has to be called with the spinlock held.
 */

static void shmem_recalc_inode(struct _fcb * inode)
{
        unsigned long freed;

        freed = (inode->i_blocks/BLOCKS_PER_PAGE) -
                (inode->i_mapping->nrpages + SHMEM_I(inode)->swapped);
        if (freed){
                struct shmem_sb_info * sbinfo = SHMEM_SB(inode->i_sb);
                inode->i_blocks -= freed*BLOCKS_PER_PAGE;
                spin_lock (&sbinfo->stat_lock);
                sbinfo->free_blocks += freed;
                spin_unlock (&sbinfo->stat_lock);
        }
}

/*
 * 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 -ENOMEM when
 * page == 0 else it will use the page for the needed block.
 *
 * returns -EFBIG if the index is too big.
 *
 *
 * 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
 */

#define SHMEM_MAX_BLOCKS (SHMEM_NR_DIRECT + ENTRIES_PER_PAGE * ENTRIES_PER_PAGE/2*(ENTRIES_PER_PAGE+1))

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;

        index -= SHMEM_NR_DIRECT;
        offset = index % ENTRIES_PER_PAGE;
        index /= ENTRIES_PER_PAGE;

        if (!info->i_indirect) {
                info->i_indirect = (void *) page;
                return ERR_PTR(-ENOMEM);
        }

        dir = info->i_indirect + index;
        if (index >= ENTRIES_PER_PAGE/2) {
                index -= ENTRIES_PER_PAGE/2;
                dir = info->i_indirect + ENTRIES_PER_PAGE/2 
                        + index/ENTRIES_PER_PAGE;
                index %= ENTRIES_PER_PAGE;

                if(!*dir) {
                        *dir = (void *) page;
                        /* We return since we will need another page
                           in the next step */
                        return ERR_PTR(-ENOMEM);
                }
                dir = ((void **)*dir) + index;
        }
        if (!*dir) {
                if (!page)
                        return ERR_PTR(-ENOMEM);
                *dir = (void *)page;
        }
        return ((swp_entry_t *)*dir) + offset;
}

/*
 * shmem_alloc_entry - 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
 */
static inline swp_entry_t * shmem_alloc_entry (struct shmem_inode_info *info, unsigned long index)
{
        unsigned long page = 0;
        swp_entry_t * res;

        if (index >= SHMEM_MAX_BLOCKS)
                return ERR_PTR(-EFBIG);

        if (info->next_index <= index)
                info->next_index = index + 1;

        while ((res = shmem_swp_entry(info,index,page)) == ERR_PTR(-ENOMEM)) {
                page = get_zeroed_page(GFP_USER);
                if (!page)
                        break;
        }
        return res;
}

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

        for (ptr = dir; ptr < dir + count; ptr++) {
                if (!ptr->val)
                        continue;
                entry = *ptr;
                *ptr = (swp_entry_t){0};
                freed++;
#if 0
                free_swap_and_cache(entry);
#endif
        }
        return freed;
}

/*
 * shmem_truncate_direct - free the swap entries of a whole doubly
 *                         indirect block
 *
 * @dir:        pointer to the pointer to the block
 * @start:      offset to start from (in pages)
 * @len:        how many pages are stored in this block
 *
 * Returns the number of freed swap entries.
 */

static inline unsigned long 
shmem_truncate_direct(swp_entry_t *** dir, unsigned long start, unsigned long len) {
        swp_entry_t **last, **ptr;
        unsigned long off, freed = 0;
 
        if (!*dir)
                return 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++) {
                if (!*ptr) {
                        off = 0;
                        continue;
                }

                if (!off) {
                        freed += shmem_free_swp(*ptr, ENTRIES_PER_PAGE);
                        free_page ((unsigned long) *ptr);
                        *ptr = 0;
                } else {
                        freed += shmem_free_swp(*ptr+off,ENTRIES_PER_PAGE-off);
                        off = 0;
                }
        }
        
        if (!start) {
                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, len, start;
        unsigned long max = info->next_index-1;

        if (max < SHMEM_NR_DIRECT) {
                info->next_index = index;
                return shmem_free_swp(info->i_direct + index,
                                      SHMEM_NR_DIRECT - index);
        }

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

                baseidx = max & ~(ENTRIES_PER_PAGE*ENTRIES_PER_PAGE-1);
                base = (swp_entry_t ***) info->i_indirect + ENTRIES_PER_PAGE/2 + baseidx/ENTRIES_PER_PAGE/ENTRIES_PER_PAGE ;
                len = max - baseidx + 1;
                baseidx += ENTRIES_PER_PAGE*ENTRIES_PER_PAGE/2+SHMEM_NR_DIRECT;
        }

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

static void shmem_truncate (struct _fcb * inode)
{
        unsigned long index;
        unsigned long freed = 0;
        struct shmem_inode_info * info = SHMEM_I(inode);

        down(&info->sem);
        inode->i_ctime = inode->i_mtime = CURRENT_TIME;
        spin_lock (&info->lock);
        index = (inode->i_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;

        while (index < info->next_index) 
                freed += shmem_truncate_indirect(info, index);

        info->swapped -= freed;
        shmem_recalc_inode(inode);
        spin_unlock (&info->lock);
        up(&info->sem);
}

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

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

static int shmem_clear_swp (swp_entry_t entry, swp_entry_t *ptr, int size) {
        swp_entry_t *test;

        for (test = ptr; test < ptr + size; test++) {
                if (test->val == entry.val) {
#if 0
                        swap_free (entry);
#endif
                        *test = (swp_entry_t) {0};
                        return test - ptr;
                }
        }
        return -1;
}

static int shmem_unuse_inode (struct shmem_inode_info *info, swp_entry_t entry, struct page *page)
{
        swp_entry_t *ptr;
        unsigned long idx;
        int offset;
        
        idx = 0;
        spin_lock (&info->lock);
        offset = shmem_clear_swp (entry, info->i_direct, SHMEM_NR_DIRECT);
        if (offset >= 0)
                goto found;

        for (idx = SHMEM_NR_DIRECT; idx < info->next_index; 
             idx += ENTRIES_PER_PAGE) {
                ptr = shmem_swp_entry(info, idx, 0);
                if (IS_ERR(ptr))
                        continue;
                offset = shmem_clear_swp (entry, ptr, ENTRIES_PER_PAGE);
                if (offset >= 0)
                        goto found;
        }
        spin_unlock (&info->lock);
        return 0;
found:
#if 0
        delete_from_swap_cache(page);
        //add_to_page_cache(page, info->inode->i_mapping, offset + idx);
        SetPageDirty(page);
        SetPageUptodate(page);
#endif
        info->swapped--;
        spin_unlock(&info->lock);
        return 1;
}

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

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

                if (shmem_unuse_inode(info, entry, page))
                        break;
        }
        spin_unlock (&shmem_ilock);
}

/*
 * Move the page from the page cache to the swap cache.
 *
 * The page lock prevents multiple occurences of shmem_writepage at
 * once.  We still need to guard against racing with
 * shmem_getpage_locked().  
 */
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 _fcb *inode;

#if 0
        if (!PageLocked(page))
                BUG();
        if (!PageLaunder(page))
                return fail_writepage(page);
#endif

#if 0
        mapping = page->mapping;
        index = page->index;
#endif
        inode = mapping->host;
        info = SHMEM_I(inode);
#if 0
        if (info->locked)
                return fail_writepage(page);
#endif
getswap:
#if 0
        swap = get_swap_page();
        if (!swap.val)
                return fail_writepage(page);
#endif

        spin_lock(&info->lock);
        entry = shmem_swp_entry(info, index, 0);
        if (IS_ERR(entry))      /* this had been allocated on page allocation */
                BUG();
        shmem_recalc_inode(inode);
        if (entry->val)
                BUG();

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

        /* Add it to the swap cache */
#if 0
        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;
        }
#endif

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

/*
 * shmem_getpage_locked - 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
 *
 * Called with the inode locked, so it cannot race with itself, but we
 * still need to guard against racing with shm_writepage(), which might
 * be trying to move the page to the swap cache as we run.
 */
static struct page * shmem_getpage_locked(struct shmem_inode_info *info, struct _fcb * inode, unsigned long idx)
{
        struct address_space * mapping = inode->i_mapping;
        struct shmem_sb_info *sbinfo;
        struct page * page;
        swp_entry_t *entry;

repeat:
        page = 0;// find_lock_page(mapping, idx);
        if (page)
                return page;

        entry = shmem_alloc_entry (info, idx);
        if (IS_ERR(entry))
                return (void *)entry;

        spin_lock (&info->lock);
        
        /* The shmem_alloc_entry() call may have blocked, and
         * shmem_writepage may have been moving a page between the page
         * cache and swap cache.  We need to recheck the page cache
         * under the protection of the info->lock spinlock. */

        page = 0;//find_get_page(mapping, idx);
        if (page) {
#if 0
                if (TryLockPage(page))
                        goto wait_retry;
#endif
                spin_unlock (&info->lock);
                return page;
        }
        
        shmem_recalc_inode(inode);
        if (entry->val) {
                unsigned long flags;

                /* Look it up and read it in.. */
                page = 0;//find_get_page(&swapper_space, entry->val);
                if (!page) {
                        swp_entry_t swap = *entry;
                        spin_unlock (&info->lock);
#if 0
                        swapin_readahead(*entry);
                        page = read_swap_cache_async(*entry);
#endif
                        if (!page) {
                                if (entry->val != swap.val)
                                        goto repeat;
                                return ERR_PTR(-ENOMEM);
                        }
                        //wait_on_page(page);
#if 0
                        if (!Page_Uptodate(page) && entry->val == swap.val) {
                                page_cache_release(page);
                                return ERR_PTR(-EIO);
                        }
#endif  
                
                        /* Too bad we can't trust this page, because we
                         * dropped the info->lock spinlock */
                        page_cache_release(page);
                        goto repeat;
                }

                /* We have to this with page locked to prevent races */
#if 0
                if (TryLockPage(page)) 
                        goto wait_retry;

                swap_free(*entry);
                *entry = (swp_entry_t) {0};
                delete_from_swap_cache(page);
                flags = page->pfn_l_page_state & ~((1 << PG_uptodate) | (1 << PG_error) | (1 << PG_referenced) | (1 << PG_arch_1));
                page->pfn_l_page_state = flags | (1 << PG_dirty);
#endif
                //add_to_page_cache_locked(page, mapping, idx);
                info->swapped--;
                spin_unlock (&info->lock);
        } else {
                sbinfo = SHMEM_SB(inode->i_sb);
                spin_unlock (&info->lock);
                spin_lock (&sbinfo->stat_lock);
                if (sbinfo->free_blocks == 0)
                        goto no_space;
                sbinfo->free_blocks--;
                spin_unlock (&sbinfo->stat_lock);

                /* Ok, get a new page.  We don't have to worry about the
                 * info->lock spinlock here: we cannot race against
                 * shm_writepage because we have already verified that
                 * there is no page present either in memory or in the
                 * swap cache, so we are guaranteed to be populating a
                 * new shm entry.  The inode semaphore we already hold
                 * is enough to make this atomic. */
                page = page_cache_alloc(mapping);
                if (!page)
                        return ERR_PTR(-ENOMEM);
                clear_highpage(page);
                inode->i_blocks += BLOCKS_PER_PAGE;
                //add_to_page_cache (page, mapping, idx);
        }

        /* We have the page */
#if 0
        SetPageUptodate(page);
#endif
        return page;
no_space:
        spin_unlock (&sbinfo->stat_lock);
        return ERR_PTR(-ENOSPC);

wait_retry:
        spin_unlock (&info->lock);
        //wait_on_page(page);
        page_cache_release(page);
        goto repeat;
}

static int shmem_getpage(struct _fcb * inode, unsigned long idx, struct page **ptr)
{
        struct shmem_inode_info *info = SHMEM_I(inode);
        int error;

        down (&info->sem);
        *ptr = ERR_PTR(-EFAULT);
        if (inode->i_size <= (loff_t) idx * PAGE_CACHE_SIZE)
                goto failed;

        *ptr = shmem_getpage_locked(info, inode, idx);
        if (IS_ERR (*ptr))
                goto failed;

#if 0
        UnlockPage(*ptr);
#endif
        up (&info->sem);
        return 0;
failed:
        up (&info->sem);
        error = PTR_ERR(*ptr);
        *ptr = NOPAGE_SIGBUS;
        if (error == -ENOMEM)
                *ptr = NOPAGE_OOM;
        return error;
}

struct page * shmem_nopage(struct vm_area_struct * vma, unsigned long address, int unused)
{
#if 0
        struct page * page;
        unsigned int idx;
        struct _fcb * inode = vma->vm_file->f_dentry->d_inode;

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

        if (shmem_getpage(inode, idx, &page))
                return page;

        flush_page_to_ram(page);
        return(page);
#endif
        return 0;
}

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

        down(&info->sem);
        info->locked = lock;
        up(&info->sem);
}

static int shmem_mmap(struct file * file, struct vm_area_struct * vma)
{
#if 0
        struct vm_operations_struct * ops;
        struct _fcb *inode = file->f_dentry->d_inode;

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

struct _fcb *shmem_get_inode(struct super_block *sb, int mode, int dev)
{
        struct _fcb * 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);
                sema_init (&info->sem, 1);
                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 (&SHMEM_I(inode)->list, &shmem_inodes);
                        spin_unlock (&shmem_ilock);
                        break;
                case S_IFDIR:
                        inode->i_nlink++;
                        inode->i_op = &shmem_dir_inode_operations;
                        inode->i_fop = &shmem_dir_operations;
                        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;
}

static struct super_block *shmem_read_super(struct super_block * sb, void * data, int silent)
{
        struct _fcb * 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 = (unsigned long long) SHMEM_MAX_BLOCKS << PAGE_CACHE_SHIFT;
        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 = {
        writepage:      shmem_writepage,
};

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,
};

static struct file_operations shmem_dir_operations = {
        read:           generic_read_dir,
        readdir:        dcache_readdir,
#ifdef CONFIG_TMPFS
        fsync:          shmem_sync_file,
#endif
};

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_shmem_fs(void)
{
        int error;
        struct vfsmount * res;

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

        /* The internal instance should not do size checking */
        if ((error = shmem_set_size(SHMEM_SB(res->mnt_sb), ULONG_MAX, ULONG_MAX)))
                printk (KERN_ERR "could not set limits on internal tmpfs\n");

        return 0;
}

static void __exit exit_shmem_fs(void)
{
#ifdef CONFIG_TMPFS
        unregister_filesystem(&shmem_fs_type);
#endif
        unregister_filesystem(&tmpfs_fs_type);
        mntput(shm_mnt);
}

module_init(init_shmem_fs)
module_exit(exit_shmem_fs)

/*
 * shmem_file_setup - get an unlinked file living in shmem fs
 *
 * @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 _fcb * inode;
        struct dentry *dentry, *root;
        struct qstr this;
        int vm_enough_memory(long pages);

        if (size > (unsigned long long) SHMEM_MAX_BLOCKS << PAGE_CACHE_SHIFT)
                return ERR_PTR(-EINVAL);

        if (!vm_enough_memory((size) >> PAGE_CACHE_SHIFT))
                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);
        dentry->d_inode->i_size = size;
        shmem_truncate(inode);
        file->f_vfsmnt = mntget(shm_mnt);
        file->f_dentry = dentry;
        file->f_op = &shmem_file_operations;
        file->f_mode = FMODE_WRITE | FMODE_READ;
        inode->i_nlink = 0;     /* It is unlinked */
        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->rde_q_region_size;
        
        file = shmem_file_setup("dev/zero", size);
        if (IS_ERR(file))
                return PTR_ERR(file);

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

EXPORT_SYMBOL(shmem_file_setup);

---