FreeBSD/Linux Kernel Cross Reference
sys/fs/inode.c

     /*
      * linux/fs/inode.c
      *
      * (C) 1997 Linus Torvalds
      */
     
     #include <linux/config.h>
     #include <linux/fs.h>
     #include <linux/string.h>
    #include <linux/mm.h>
    #include <linux/dcache.h>
    #include <linux/init.h>
    #include <linux/quotaops.h>
    #include <linux/slab.h>
    #include <linux/cache.h>
    #include <linux/swap.h>
    #include <linux/swapctl.h>
    #include <linux/prefetch.h>
    #include <linux/locks.h>
    
    /*
     * New inode.c implementation.
     *
     * This implementation has the basic premise of trying
     * to be extremely low-overhead and SMP-safe, yet be
     * simple enough to be "obviously correct".
     *
     * Famous last words.
     */
    
    /* inode dynamic allocation 1999, Andrea Arcangeli <andrea@suse.de> */
    
    /* #define INODE_PARANOIA 1 */
    /* #define INODE_DEBUG 1 */
    
    /*
     * Inode lookup is no longer as critical as it used to be:
     * most of the lookups are going to be through the dcache.
     */
    #define I_HASHBITS      i_hash_shift
    #define I_HASHMASK      i_hash_mask
    
    static unsigned int i_hash_mask;
    static unsigned int i_hash_shift;
    
    /*
     * Each inode can be on two separate lists. One is
     * the hash list of the inode, used for lookups. The
     * other linked list is the "type" list:
     *  "in_use" - valid inode, i_count > 0, i_nlink > 0
     *  "dirty"  - as "in_use" but also dirty
     *  "unused" - valid inode, i_count = 0
     *
     * A "dirty" list is maintained for each super block,
     * allowing for low-overhead inode sync() operations.
     */
    
    static LIST_HEAD(inode_in_use);
    static LIST_HEAD(inode_unused);
    static struct list_head *inode_hashtable;
    static LIST_HEAD(anon_hash_chain); /* for inodes with NULL i_sb */
    
    /*
     * A simple spinlock to protect the list manipulations.
     *
     * NOTE! You also have to own the lock if you change
     * the i_state of an inode while it is in use..
     */
    static spinlock_t inode_lock = SPIN_LOCK_UNLOCKED;
    
    /*
     * Statistics gathering..
     */
    struct inodes_stat_t inodes_stat;
    
    static kmem_cache_t * inode_cachep;
    
    static struct inode *alloc_inode(struct super_block *sb)
    {
            static struct address_space_operations empty_aops;
            static struct inode_operations empty_iops;
            static struct file_operations empty_fops;
            struct inode *inode;
    
            if (sb->s_op->alloc_inode)
                    inode = sb->s_op->alloc_inode(sb);
            else {
                    inode = (struct inode *) kmem_cache_alloc(inode_cachep, SLAB_KERNEL);
                    /* will die */
                    if (inode)
                            memset(&inode->u, 0, sizeof(inode->u));
            }
    
            if (inode) {
                    struct address_space * const mapping = &inode->i_data;
    
                    inode->i_sb = sb;
                    inode->i_dev = sb->s_dev;
                    inode->i_blkbits = sb->s_blocksize_bits;
                   inode->i_flags = 0;
                   atomic_set(&inode->i_count, 1);
                   inode->i_sock = 0;
                   inode->i_op = &empty_iops;
                   inode->i_fop = &empty_fops;
                   inode->i_nlink = 1;
                   atomic_set(&inode->i_writecount, 0);
                   inode->i_size = 0;
                   inode->i_blocks = 0;
                   inode->i_bytes = 0;
                   inode->i_generation = 0;
                   memset(&inode->i_dquot, 0, sizeof(inode->i_dquot));
                   inode->i_pipe = NULL;
                   inode->i_bdev = NULL;
                   inode->i_cdev = NULL;
   
                   mapping->a_ops = &empty_aops;
                   mapping->host = inode;
                   mapping->gfp_mask = GFP_HIGHUSER;
                   inode->i_mapping = mapping;
           }
           return inode;
   }
   
   static void destroy_inode(struct inode *inode) 
   {
           if (inode_has_buffers(inode))
                   BUG();
           if (inode->i_sb->s_op->destroy_inode)
                   inode->i_sb->s_op->destroy_inode(inode);
           else
                   kmem_cache_free(inode_cachep, inode);
   }
   
   
   /*
    * These are initializations that only need to be done
    * once, because the fields are idempotent across use
    * of the inode, so let the slab aware of that.
    */
   void inode_init_once(struct inode *inode)
   {
           memset(inode, 0, sizeof(*inode));
           init_waitqueue_head(&inode->i_wait);
           INIT_LIST_HEAD(&inode->i_hash);
           INIT_LIST_HEAD(&inode->i_data.clean_pages);
           INIT_LIST_HEAD(&inode->i_data.dirty_pages);
           INIT_LIST_HEAD(&inode->i_data.locked_pages);
           INIT_LIST_HEAD(&inode->i_dentry);
           INIT_LIST_HEAD(&inode->i_dirty_buffers);
           INIT_LIST_HEAD(&inode->i_dirty_data_buffers);
           INIT_LIST_HEAD(&inode->i_devices);
           sema_init(&inode->i_sem, 1);
           sema_init(&inode->i_zombie, 1);
           init_rwsem(&inode->i_alloc_sem);
           spin_lock_init(&inode->i_data.i_shared_lock);
   }
   
   static void init_once(void * foo, kmem_cache_t * cachep, unsigned long flags)
   {
           struct inode * inode = (struct inode *) foo;
   
           if ((flags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) ==
               SLAB_CTOR_CONSTRUCTOR)
                   inode_init_once(inode);
   }
   
   /*
    * Put the inode on the super block's dirty list.
    *
    * CAREFUL! We mark it dirty unconditionally, but
    * move it onto the dirty list only if it is hashed.
    * If it was not hashed, it will never be added to
    * the dirty list even if it is later hashed, as it
    * will have been marked dirty already.
    *
    * In short, make sure you hash any inodes _before_
    * you start marking them dirty..
    */
    
   /**
    *      __mark_inode_dirty -    internal function
    *      @inode: inode to mark
    *      @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
    *      Mark an inode as dirty. Callers should use mark_inode_dirty or
    *      mark_inode_dirty_sync.
    */
    
   void __mark_inode_dirty(struct inode *inode, int flags)
   {
           struct super_block * sb = inode->i_sb;
   
           if (!sb)
                   return;
   
           /* Don't do this for I_DIRTY_PAGES - that doesn't actually dirty the inode itself */
           if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
                   if (sb->s_op && sb->s_op->dirty_inode)
                           sb->s_op->dirty_inode(inode);
           }
   
           /* avoid the locking if we can */
           if ((inode->i_state & flags) == flags)
                   return;
   
           spin_lock(&inode_lock);
           if ((inode->i_state & flags) != flags) {
                   inode->i_state |= flags;
                   /* Only add valid (ie hashed) inodes to the dirty list */
                   if (!(inode->i_state & I_LOCK) && !list_empty(&inode->i_hash)) {
                           list_del(&inode->i_list);
                           list_add(&inode->i_list, &sb->s_dirty);
                   }
           }
           spin_unlock(&inode_lock);
   }
   
   static void __wait_on_inode(struct inode * inode)
   {
           DECLARE_WAITQUEUE(wait, current);
   
           add_wait_queue(&inode->i_wait, &wait);
   repeat:
           set_current_state(TASK_UNINTERRUPTIBLE);
           if (inode->i_state & I_LOCK) {
                   schedule();
                   goto repeat;
           }
           remove_wait_queue(&inode->i_wait, &wait);
           current->state = TASK_RUNNING;
   }
   
   static inline void wait_on_inode(struct inode *inode)
   {
           if (inode->i_state & I_LOCK)
                   __wait_on_inode(inode);
   }
   
   
   static inline void write_inode(struct inode *inode, int sync)
   {
           if (inode->i_sb && inode->i_sb->s_op && inode->i_sb->s_op->write_inode && !is_bad_inode(inode))
                   inode->i_sb->s_op->write_inode(inode, sync);
   }
   
   static inline void __iget(struct inode * inode)
   {
           if (atomic_read(&inode->i_count)) {
                   atomic_inc(&inode->i_count);
                   return;
           }
           atomic_inc(&inode->i_count);
           if (!(inode->i_state & (I_DIRTY|I_LOCK))) {
                   list_del(&inode->i_list);
                   list_add(&inode->i_list, &inode_in_use);
           }
           inodes_stat.nr_unused--;
   }
   
   static inline void __sync_one(struct inode *inode, int sync)
   {
           unsigned dirty;
   
           list_del(&inode->i_list);
           list_add(&inode->i_list, &inode->i_sb->s_locked_inodes);
   
           if (inode->i_state & I_LOCK)
                   BUG();
   
           /* Set I_LOCK, reset I_DIRTY */
           dirty = inode->i_state & I_DIRTY;
           inode->i_state |= I_LOCK;
           inode->i_state &= ~I_DIRTY;
           spin_unlock(&inode_lock);
   
           filemap_fdatasync(inode->i_mapping);
   
           /* Don't write the inode if only I_DIRTY_PAGES was set */
           if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC))
                   write_inode(inode, sync);
   
           filemap_fdatawait(inode->i_mapping);
   
           spin_lock(&inode_lock);
           inode->i_state &= ~I_LOCK;
           if (!(inode->i_state & I_FREEING)) {
                   struct list_head *to;
                   if (inode->i_state & I_DIRTY)
                           to = &inode->i_sb->s_dirty;
                   else if (atomic_read(&inode->i_count))
                           to = &inode_in_use;
                   else
                           to = &inode_unused;
                   list_del(&inode->i_list);
                   list_add(&inode->i_list, to);
           }
           wake_up(&inode->i_wait);
   }
   
   static inline void sync_one(struct inode *inode, int sync)
   {
           while (inode->i_state & I_LOCK) {
                   __iget(inode);
                   spin_unlock(&inode_lock);
                   __wait_on_inode(inode);
                   iput(inode);
                   spin_lock(&inode_lock);
           }
   
           __sync_one(inode, sync);
   }
   
   static inline void sync_list(struct list_head *head)
   {
           struct list_head * tmp;
   
           while ((tmp = head->prev) != head) 
                   __sync_one(list_entry(tmp, struct inode, i_list), 0);
   }
   
   static inline void wait_on_locked(struct list_head *head)
   {
           struct list_head * tmp;
           while ((tmp = head->prev) != head) {
                   struct inode *inode = list_entry(tmp, struct inode, i_list);
                   __iget(inode);
                   spin_unlock(&inode_lock);
                   __wait_on_inode(inode);
                   iput(inode);
                   spin_lock(&inode_lock);
           }
   }
   
   static inline int try_to_sync_unused_list(struct list_head *head, int nr_inodes)
   {
           struct list_head *tmp = head;
           struct inode *inode;
   
           while (nr_inodes && (tmp = tmp->prev) != head) {
                   inode = list_entry(tmp, struct inode, i_list);
   
                   if (!atomic_read(&inode->i_count)) {
                           __sync_one(inode, 0);
                           nr_inodes--;
   
                           /* 
                            * __sync_one moved the inode to another list,
                            * so we have to start looking from the list head.
                            */
                           tmp = head;
                   }
           }
   
           return nr_inodes;
   }
   
   void sync_inodes_sb(struct super_block *sb)
   {
           spin_lock(&inode_lock);
           while (!list_empty(&sb->s_dirty)||!list_empty(&sb->s_locked_inodes)) {
                   sync_list(&sb->s_dirty);
                   wait_on_locked(&sb->s_locked_inodes);
           }
           spin_unlock(&inode_lock);
   }
   
   /*
    * Note:
    * We don't need to grab a reference to superblock here. If it has non-empty
    * ->s_dirty it's hadn't been killed yet and kill_super() won't proceed
    * past sync_inodes_sb() until both ->s_dirty and ->s_locked_inodes are
    * empty. Since __sync_one() regains inode_lock before it finally moves
    * inode from superblock lists we are OK.
    */
   
   void sync_unlocked_inodes(void)
   {
           struct super_block * sb;
           spin_lock(&inode_lock);
           spin_lock(&sb_lock);
           sb = sb_entry(super_blocks.next);
           for (; sb != sb_entry(&super_blocks); sb = sb_entry(sb->s_list.next)) {
                   if (!list_empty(&sb->s_dirty)) {
                           spin_unlock(&sb_lock);
                           sync_list(&sb->s_dirty);
                           spin_lock(&sb_lock);
                   }
           }
           spin_unlock(&sb_lock);
           spin_unlock(&inode_lock);
   }
   
   /*
    * Find a superblock with inodes that need to be synced
    */
   
   static struct super_block *get_super_to_sync(void)
   {
           struct list_head *p;
   restart:
           spin_lock(&inode_lock);
           spin_lock(&sb_lock);
           list_for_each(p, &super_blocks) {
                   struct super_block *s = list_entry(p,struct super_block,s_list);
                   if (list_empty(&s->s_dirty) && list_empty(&s->s_locked_inodes))
                           continue;
                   s->s_count++;
                   spin_unlock(&sb_lock);
                   spin_unlock(&inode_lock);
                   down_read(&s->s_umount);
                   if (!s->s_root) {
                           drop_super(s);
                           goto restart;
                   }
                   return s;
           }
           spin_unlock(&sb_lock);
           spin_unlock(&inode_lock);
           return NULL;
   }
   
   /**
    *      sync_inodes
    *      @dev: device to sync the inodes from.
    *
    *      sync_inodes goes through the super block's dirty list, 
    *      writes them out, and puts them back on the normal list.
    */
   
   void sync_inodes(kdev_t dev)
   {
           struct super_block * s;
   
           /*
            * Search the super_blocks array for the device(s) to sync.
            */
           if (dev) {
                   if ((s = get_super(dev)) != NULL) {
                           sync_inodes_sb(s);
                           drop_super(s);
                   }
           } else {
                   while ((s = get_super_to_sync()) != NULL) {
                           sync_inodes_sb(s);
                           drop_super(s);
                   }
           }
   }
   
   static void try_to_sync_unused_inodes(void * arg)
   {
           struct super_block * sb;
           int nr_inodes = inodes_stat.nr_unused;
   
           spin_lock(&inode_lock);
           spin_lock(&sb_lock);
           sb = sb_entry(super_blocks.next);
           for (; nr_inodes && sb != sb_entry(&super_blocks); sb = sb_entry(sb->s_list.next)) {
                   if (list_empty(&sb->s_dirty))
                           continue;
                   spin_unlock(&sb_lock);
                   nr_inodes = try_to_sync_unused_list(&sb->s_dirty, nr_inodes);
                   spin_lock(&sb_lock);
           }
           spin_unlock(&sb_lock);
           spin_unlock(&inode_lock);
   }
   
   static struct tq_struct unused_inodes_flush_task;
   
   /**
    *      write_inode_now -       write an inode to disk
    *      @inode: inode to write to disk
    *      @sync: whether the write should be synchronous or not
    *
    *      This function commits an inode to disk immediately if it is
    *      dirty. This is primarily needed by knfsd.
    */
    
   void write_inode_now(struct inode *inode, int sync)
   {
           struct super_block * sb = inode->i_sb;
   
           if (sb) {
                   spin_lock(&inode_lock);
                   while (inode->i_state & I_DIRTY)
                           sync_one(inode, sync);
                   spin_unlock(&inode_lock);
                   if (sync)
                           wait_on_inode(inode);
           }
           else
                   printk(KERN_ERR "write_inode_now: no super block\n");
   }
   
   /**
    * generic_osync_inode - flush all dirty data for a given inode to disk
    * @inode: inode to write
    * @datasync: if set, don't bother flushing timestamps
    *
    * This can be called by file_write functions for files which have the
    * O_SYNC flag set, to flush dirty writes to disk.  
    */
   
   int generic_osync_inode(struct inode *inode, int what)
   {
           int err = 0, err2 = 0, need_write_inode_now = 0;
           
           /* 
            * WARNING
            *
            * Currently, the filesystem write path does not pass the
            * filp down to the low-level write functions.  Therefore it
            * is impossible for (say) __block_commit_write to know if
            * the operation is O_SYNC or not.
            *
            * Ideally, O_SYNC writes would have the filesystem call
            * ll_rw_block as it went to kick-start the writes, and we
            * could call osync_inode_buffers() here to wait only for
            * those IOs which have already been submitted to the device
            * driver layer.  As it stands, if we did this we'd not write
            * anything to disk since our writes have not been queued by
            * this point: they are still on the dirty LRU.
            * 
            * So, currently we will call fsync_inode_buffers() instead,
            * to flush _all_ dirty buffers for this inode to disk on 
            * every O_SYNC write, not just the synchronous I/Os.  --sct
            */
   
           if (what & OSYNC_METADATA)
                   err = fsync_inode_buffers(inode);
           if (what & OSYNC_DATA)
                   err2 = fsync_inode_data_buffers(inode);
           if (!err)
                   err = err2;
   
           spin_lock(&inode_lock);
           if ((inode->i_state & I_DIRTY) &&
               ((what & OSYNC_INODE) || (inode->i_state & I_DIRTY_DATASYNC)))
                   need_write_inode_now = 1;
           spin_unlock(&inode_lock);
   
           if (need_write_inode_now)
                   write_inode_now(inode, 1);
           else
                   wait_on_inode(inode);
   
           return err;
   }
   
   /**
    * clear_inode - clear an inode
    * @inode: inode to clear
    *
    * This is called by the filesystem to tell us
    * that the inode is no longer useful. We just
    * terminate it with extreme prejudice.
    */
    
   void clear_inode(struct inode *inode)
   {
           invalidate_inode_buffers(inode);
          
           if (inode->i_data.nrpages)
                   BUG();
           if (!(inode->i_state & I_FREEING))
                   BUG();
           if (inode->i_state & I_CLEAR)
                   BUG();
           wait_on_inode(inode);
           DQUOT_DROP(inode);
           if (inode->i_sb && inode->i_sb->s_op && inode->i_sb->s_op->clear_inode)
                   inode->i_sb->s_op->clear_inode(inode);
           if (inode->i_bdev)
                   bd_forget(inode);
           else if (inode->i_cdev) {
                   cdput(inode->i_cdev);
                   inode->i_cdev = NULL;
           }
           inode->i_state = I_CLEAR;
   }
   
   /*
    * Dispose-list gets a local list with local inodes in it, so it doesn't
    * need to worry about list corruption and SMP locks.
    */
   static void dispose_list(struct list_head * head)
   {
           struct list_head * inode_entry;
           struct inode * inode;
   
           while ((inode_entry = head->next) != head)
           {
                   list_del(inode_entry);
   
                   inode = list_entry(inode_entry, struct inode, i_list);
                   if (inode->i_data.nrpages)
                           truncate_inode_pages(&inode->i_data, 0);
                   clear_inode(inode);
                   destroy_inode(inode);
                   inodes_stat.nr_inodes--;
           }
   }
   
   /*
    * Invalidate all inodes for a device.
    */
   static int invalidate_list(struct list_head *head, struct super_block * sb, struct list_head * dispose)
   {
           struct list_head *next;
           int busy = 0, count = 0;
   
           next = head->next;
           for (;;) {
                   struct list_head * tmp = next;
                   struct inode * inode;
   
                   next = next->next;
                   if (tmp == head)
                           break;
                   inode = list_entry(tmp, struct inode, i_list);
                   if (inode->i_sb != sb)
                           continue;
                   invalidate_inode_buffers(inode);
                   if (!atomic_read(&inode->i_count)) {
                           list_del_init(&inode->i_hash);
                           list_del(&inode->i_list);
                           list_add(&inode->i_list, dispose);
                           inode->i_state |= I_FREEING;
                           count++;
                           continue;
                   }
                   busy = 1;
           }
           /* only unused inodes may be cached with i_count zero */
           inodes_stat.nr_unused -= count;
           return busy;
   }
   
   /*
    * This is a two-stage process. First we collect all
    * offending inodes onto the throw-away list, and in
    * the second stage we actually dispose of them. This
    * is because we don't want to sleep while messing
    * with the global lists..
    */
    
   /**
    *      invalidate_inodes       - discard the inodes on a device
    *      @sb: superblock
    *
    *      Discard all of the inodes for a given superblock. If the discard
    *      fails because there are busy inodes then a non zero value is returned.
    *      If the discard is successful all the inodes have been discarded.
    */
    
   int invalidate_inodes(struct super_block * sb)
   {
           int busy;
           LIST_HEAD(throw_away);
   
           spin_lock(&inode_lock);
           busy = invalidate_list(&inode_in_use, sb, &throw_away);
           busy |= invalidate_list(&inode_unused, sb, &throw_away);
           busy |= invalidate_list(&sb->s_dirty, sb, &throw_away);
           busy |= invalidate_list(&sb->s_locked_inodes, sb, &throw_away);
           spin_unlock(&inode_lock);
   
           dispose_list(&throw_away);
   
           return busy;
   }
    
   int invalidate_device(kdev_t dev, int do_sync)
   {
           struct super_block *sb;
           int res;
   
           if (do_sync)
                   fsync_dev(dev);
   
           res = 0;
           sb = get_super(dev);
           if (sb) {
                   /*
                    * no need to lock the super, get_super holds the
                    * read semaphore so the filesystem cannot go away
                    * under us (->put_super runs with the write lock
                    * hold).
                    */
                   shrink_dcache_sb(sb);
                   res = invalidate_inodes(sb);
                   drop_super(sb);
           }
           invalidate_buffers(dev);
           return res;
   }
   
   
   /*
    * This is called with the inode lock held. It searches
    * the in-use for freeable inodes, which are moved to a
    * temporary list and then placed on the unused list by
    * dispose_list. 
    *
    * We don't expect to have to call this very often.
    *
    * N.B. The spinlock is released during the call to
    *      dispose_list.
    */
   #define CAN_UNUSE(inode) \
           ((((inode)->i_state | (inode)->i_data.nrpages) == 0)  && \
            !inode_has_buffers(inode))
   #define INODE(entry)    (list_entry(entry, struct inode, i_list))
   
   void prune_icache(int goal)
   {
           LIST_HEAD(list);
           struct list_head *entry, *freeable = &list;
           int count;
           struct inode * inode;
   
           spin_lock(&inode_lock);
   
           count = 0;
           entry = inode_unused.prev;
           while (entry != &inode_unused)
           {
                   struct list_head *tmp = entry;
   
                   entry = entry->prev;
                   inode = INODE(tmp);
                   if (inode->i_state & (I_FREEING|I_CLEAR|I_LOCK))
                           continue;
                   if (!CAN_UNUSE(inode))
                           continue;
                   if (atomic_read(&inode->i_count))
                           continue;
                   list_del(tmp);
                   list_del(&inode->i_hash);
                   INIT_LIST_HEAD(&inode->i_hash);
                   list_add(tmp, freeable);
                   inode->i_state |= I_FREEING;
                   count++;
                   if (!--goal)
                           break;
           }
           inodes_stat.nr_unused -= count;
           spin_unlock(&inode_lock);
   
           dispose_list(freeable);
   
           /* 
            * If we didn't freed enough clean inodes schedule
            * a sync of the dirty inodes, we cannot do it
            * from here or we're either synchronously dogslow
            * or we deadlock with oom.
            */
           if (goal)
                   schedule_task(&unused_inodes_flush_task);
   }
   
   int shrink_icache_memory(int priority, int gfp_mask)
   {
           int count = 0;
   
           /*
            * Nasty deadlock avoidance..
            *
            * We may hold various FS locks, and we don't
            * want to recurse into the FS that called us
            * in clear_inode() and friends..
            */
           if (!(gfp_mask & __GFP_FS))
                   return 0;
   
           count = inodes_stat.nr_unused / priority;
   
           prune_icache(count);
           return kmem_cache_shrink(inode_cachep);
   }
   
   /*
    * Called with the inode lock held.
    * NOTE: we are not increasing the inode-refcount, you must call __iget()
    * by hand after calling find_inode now! This simplifies iunique and won't
    * add any additional branch in the common code.
    */
   static struct inode * find_inode(struct super_block * sb, unsigned long ino, struct list_head *head, find_inode_t find_actor, void *opaque)
   {
           struct list_head *tmp;
           struct inode * inode;
   
           tmp = head;
           for (;;) {
                   tmp = tmp->next;
                   inode = NULL;
                   if (tmp == head)
                           break;
                   inode = list_entry(tmp, struct inode, i_hash);
                   if (inode->i_ino != ino)
                           continue;
                   if (inode->i_sb != sb)
                           continue;
                   if (find_actor && !find_actor(inode, ino, opaque))
                           continue;
                   break;
           }
           return inode;
   }
   
   /**
    *      new_inode       - obtain an inode
    *      @sb: superblock
    *
    *      Allocates a new inode for given superblock.
    */
    
   struct inode * new_inode(struct super_block *sb)
   {
           static unsigned long last_ino;
           struct inode * inode;
   
           spin_lock_prefetch(&inode_lock);
           
           inode = alloc_inode(sb);
           if (inode) {
                   spin_lock(&inode_lock);
                   inodes_stat.nr_inodes++;
                   list_add(&inode->i_list, &inode_in_use);
                   inode->i_ino = ++last_ino;
                   inode->i_state = 0;
                   spin_unlock(&inode_lock);
           }
           return inode;
   }
   
   /*
    * This is called without the inode lock held.. Be careful.
    *
    * We no longer cache the sb_flags in i_flags - see fs.h
    *      -- rmk@arm.uk.linux.org
    */
   static struct inode * get_new_inode(struct super_block *sb, unsigned long ino, struct list_head *head, find_inode_t find_actor, void *opaque)
   {
           struct inode * inode;
   
           inode = alloc_inode(sb);
           if (inode) {
                   struct inode * old;
   
                   spin_lock(&inode_lock);
                   /* We released the lock, so.. */
                   old = find_inode(sb, ino, head, find_actor, opaque);
                   if (!old) {
                           inodes_stat.nr_inodes++;
                           list_add(&inode->i_list, &inode_in_use);
                           list_add(&inode->i_hash, head);
                           inode->i_ino = ino;
                           inode->i_state = I_LOCK;
                           spin_unlock(&inode_lock);
   
                           /* reiserfs specific hack right here.  We don't
                           ** want this to last, and are looking for VFS changes
                           ** that will allow us to get rid of it.
                           ** -- mason@suse.com 
                           */
                           if (sb->s_op->read_inode2) {
                                   sb->s_op->read_inode2(inode, opaque) ;
                           } else {
                                   sb->s_op->read_inode(inode);
                           }
   
                           /*
                            * This is special!  We do not need the spinlock
                            * when clearing I_LOCK, because we're guaranteed
                            * that nobody else tries to do anything about the
                            * state of the inode when it is locked, as we
                            * just created it (so there can be no old holders
                            * that haven't tested I_LOCK).
                            */
                           inode->i_state &= ~I_LOCK;
                           wake_up(&inode->i_wait);
   
                           return inode;
                   }
   
                   /*
                    * Uhhuh, somebody else created the same inode under
                    * us. Use the old inode instead of the one we just
                    * allocated.
                    */
                   __iget(old);
                   spin_unlock(&inode_lock);
                   destroy_inode(inode);
                   inode = old;
                   wait_on_inode(inode);
           }
           return inode;
   }
   
   static inline unsigned long hash(struct super_block *sb, unsigned long i_ino)
   {
           unsigned long tmp = i_ino + ((unsigned long) sb / L1_CACHE_BYTES);
           tmp = tmp + (tmp >> I_HASHBITS);
           return tmp & I_HASHMASK;
   }
   
   /* Yeah, I know about quadratic hash. Maybe, later. */
   
   /**
    *      iunique - get a unique inode number
    *      @sb: superblock
    *      @max_reserved: highest reserved inode number
    *
    *      Obtain an inode number that is unique on the system for a given
    *      superblock. This is used by file systems that have no natural
    *      permanent inode numbering system. An inode number is returned that
    *      is higher than the reserved limit but unique.
    *
    *      BUGS:
    *      With a large number of inodes live on the file system this function
    *      currently becomes quite slow.
    */
    
   ino_t iunique(struct super_block *sb, ino_t max_reserved)
   {
           static ino_t counter = 0;
           struct inode *inode;
           struct list_head * head;
           ino_t res;
           spin_lock(&inode_lock);
   retry:
           if (counter > max_reserved) {
                   head = inode_hashtable + hash(sb,counter);
                   inode = find_inode(sb, res = counter++, head, NULL, NULL);
                   if (!inode) {
                           spin_unlock(&inode_lock);
                           return res;
                   }
           } else {
                   counter = max_reserved + 1;
           }
           goto retry;
           
   }
   
   struct inode *igrab(struct inode *inode)
   {
           spin_lock(&inode_lock);
           if (!(inode->i_state & I_FREEING))
                   __iget(inode);
           else
                   /*
                    * Handle the case where s_op->clear_inode is not been
                    * called yet, and somebody is calling igrab
                    * while the inode is getting freed.
                    */
                   inode = NULL;
           spin_unlock(&inode_lock);
           return inode;
   }
   
   
   struct inode *iget4(struct super_block *sb, unsigned long ino, find_inode_t find_actor, void *opaque)
   {
           struct list_head * head = inode_hashtable + hash(sb,ino);
           struct inode * inode;
   
           spin_lock(&inode_lock);
           inode = find_inode(sb, ino, head, find_actor, opaque);
           if (inode) {
                   __iget(inode);
                   spin_unlock(&inode_lock);
                   wait_on_inode(inode);
                   return inode;
           }
           spin_unlock(&inode_lock);
   
           /*
            * get_new_inode() will do the right thing, re-trying the search
            * in case it had to block at any point.
            */
           return get_new_inode(sb, ino, head, find_actor, opaque);
   }
   
   /**
    *      insert_inode_hash - hash an inode
    *      @inode: unhashed inode
    *
    *      Add an inode to the inode hash for this superblock. If the inode
    *      has no superblock it is added to a separate anonymous chain.
    */
    
   void insert_inode_hash(struct inode *inode)
   {
           struct list_head *head = &anon_hash_chain;
           if (inode->i_sb)
                   head = inode_hashtable + hash(inode->i_sb, inode->i_ino);
           spin_lock(&inode_lock);
          list_add(&inode->i_hash, head);
          spin_unlock(&inode_lock);
  }
  
  /**
   *      remove_inode_hash - remove an inode from the hash
   *      @inode: inode to unhash
   *
   *      Remove an inode from the superblock or anonymous hash.
   */
   
  void remove_inode_hash(struct inode *inode)
  {
          spin_lock(&inode_lock);
          list_del(&inode->i_hash);
          INIT_LIST_HEAD(&inode->i_hash);
          spin_unlock(&inode_lock);
  }
  
  /**
   *      iput    - put an inode 
   *      @inode: inode to put
   *
   *      Puts an inode, dropping its usage count. If the inode use count hits
   *      zero the inode is also then freed and may be destroyed.
   */
   
  void iput(struct inode *inode)
  {
          if (inode) {
                  struct super_block *sb = inode->i_sb;
                  struct super_operations *op = NULL;
  
                  if (inode->i_state == I_CLEAR)
                          BUG();
  
                  if (sb && sb->s_op)
                          op = sb->s_op;
                  if (op && op->put_inode)
                          op->put_inode(inode);
  
                  if (!atomic_dec_and_lock(&inode->i_count, &inode_lock))
                          return;
  
                  if (!inode->i_nlink) {
                          list_del(&inode->i_hash);
                          INIT_LIST_HEAD(&inode->i_hash);
                          list_del(&inode->i_list);
                          INIT_LIST_HEAD(&inode->i_list);
                          inode->i_state|=I_FREEING;
                          inodes_stat.nr_inodes--;
                          spin_unlock(&inode_lock);
  
                          if (inode->i_data.nrpages)
                                  truncate_inode_pages(&inode->i_data, 0);
  
                          if (op && op->delete_inode) {
                                  void (*delete)(struct inode *) = op->delete_inode;
                                  if (!is_bad_inode(inode))
                                          DQUOT_INIT(inode);
                                  /* s_op->delete_inode internally recalls clear_inode() */
                                  delete(inode);
                          } else
                                  clear_inode(inode);
                          if (inode->i_state != I_CLEAR)
                                  BUG();
                  } else {
                          if (!list_empty(&inode->i_hash)) {
                                  if (!(inode->i_state & (I_DIRTY|I_LOCK))) {
                                          list_del(&inode->i_list);
                                          list_add(&inode->i_list, &inode_unused);
                                  }
                                  inodes_stat.nr_unused++;
                                  spin_unlock(&inode_lock);
                                  if (!sb || (sb->s_flags & MS_ACTIVE))
                                          return;
                                  write_inode_now(inode, 1);
                                  spin_lock(&inode_lock);
                                  inodes_stat.nr_unused--;
                                  list_del_init(&inode->i_hash);
                          }
                          list_del_init(&inode->i_list);
                          inode->i_state|=I_FREEING;
                          inodes_stat.nr_inodes--;
                          spin_unlock(&inode_lock);
                          if (inode->i_data.nrpages)
                                  truncate_inode_pages(&inode->i_data, 0);
                          clear_inode(inode);
                  }
                  destroy_inode(inode);
          }
  }
  
  void force_delete(struct inode *inode)
  {
          /*
           * Kill off unused inodes ... iput() will unhash and
           * delete the inode if we set i_nlink to zero.
           */
          if (atomic_read(&inode->i_count) == 1)
                  inode->i_nlink = 0;
  }
  
  /**
   *      bmap    - find a block number in a file
   *      @inode: inode of file
   *      @block: block to find
   *
   *      Returns the block number on the device holding the inode that
   *      is the disk block number for the block of the file requested.
   *      That is, asked for block 4 of inode 1 the function will return the
   *      disk block relative to the disk start that holds that block of the 
   *      file.
   */
   
  int bmap(struct inode * inode, int block)
  {
          int res = 0;
          if (inode->i_mapping->a_ops->bmap)
                  res = inode->i_mapping->a_ops->bmap(inode->i_mapping, block);
          return res;
  }
  
  /*
   * Initialize the hash tables.
   */
  void __init inode_init(unsigned long mempages)
  {
          struct list_head *head;
          unsigned long order;
          unsigned int nr_hash;
          int i;
  
          mempages >>= (14 - PAGE_SHIFT);
          mempages *= sizeof(struct list_head);
          for (order = 0; ((1UL << order) << PAGE_SHIFT) < mempages; order++)
                  ;
  
          do {
                  unsigned long tmp;
  
                  nr_hash = (1UL << order) * PAGE_SIZE /
                          sizeof(struct list_head);
                  i_hash_mask = (nr_hash - 1);
  
                  tmp = nr_hash;
                  i_hash_shift = 0;
                  while ((tmp >>= 1UL) != 0UL)
                          i_hash_shift++;
  
                  inode_hashtable = (struct list_head *)
                          __get_free_pages(GFP_ATOMIC, order);
          } while (inode_hashtable == NULL && --order >= 0);
  
          printk(KERN_INFO "Inode cache hash table entries: %d (order: %ld, %ld bytes)\n",
                          nr_hash, order, (PAGE_SIZE << order));
  
          if (!inode_hashtable)
                  panic("Failed to allocate inode hash table\n");
  
          head = inode_hashtable;
          i = nr_hash;
          do {
                  INIT_LIST_HEAD(head);
                  head++;
                  i--;
          } while (i);
  
          /* inode slab cache */
          inode_cachep = kmem_cache_create("inode_cache", sizeof(struct inode),
                                           0, SLAB_HWCACHE_ALIGN, init_once,
                                           NULL);
          if (!inode_cachep)
                  panic("cannot create inode slab cache");
  
          unused_inodes_flush_task.routine = try_to_sync_unused_inodes;
  }
  
  /**
   *      update_atime    -       update the access time
   *      @inode: inode accessed
   *
   *      Update the accessed time on an inode and mark it for writeback.
   *      This function automatically handles read only file systems and media,
   *      as well as the "noatime" flag and inode specific "noatime" markers.
   */
   
  void update_atime (struct inode *inode)
  {
          if (inode->i_atime == CURRENT_TIME)
                  return;
          if (IS_NOATIME(inode))
                  return;
          if (IS_NODIRATIME(inode) && S_ISDIR(inode->i_mode)) 
                  return;
          if (IS_RDONLY(inode)) 
                  return;
          inode->i_atime = CURRENT_TIME;
          mark_inode_dirty_sync (inode);
  }
  
  /**
   *      update_mctime   -       update the mtime and ctime
   *      @inode: inode accessed
   *
   *      Update the modified and changed times on an inode for writes to special
   *      files such as fifos.  No change is forced if the timestamps are already
   *      up-to-date or if the filesystem is readonly.
   */
   
  void update_mctime (struct inode *inode)
  {
          if (inode->i_mtime == CURRENT_TIME && inode->i_ctime == CURRENT_TIME)
                  return;
          if (IS_RDONLY(inode))
                  return;
          inode->i_ctime = inode->i_mtime = CURRENT_TIME;
          mark_inode_dirty (inode);
  }
  
  
  /*
   *      Quota functions that want to walk the inode lists..
   */
  #ifdef CONFIG_QUOTA
  
  /* Functions back in dquot.c */
  void put_dquot_list(struct list_head *);
  int remove_inode_dquot_ref(struct inode *, short, struct list_head *);
  
  void remove_dquot_ref(struct super_block *sb, short type)
  {
          struct inode *inode;
          struct list_head *act_head;
          LIST_HEAD(tofree_head);
  
          if (!sb->dq_op)
                  return; /* nothing to do */
          /* We have to be protected against other CPUs */
          lock_kernel();          /* This lock is for quota code */
          spin_lock(&inode_lock); /* This lock is for inodes code */
   
          list_for_each(act_head, &inode_in_use) {
                  inode = list_entry(act_head, struct inode, i_list);
                  if (inode->i_sb == sb && IS_QUOTAINIT(inode))
                          remove_inode_dquot_ref(inode, type, &tofree_head);
          }
          list_for_each(act_head, &inode_unused) {
                  inode = list_entry(act_head, struct inode, i_list);
                  if (inode->i_sb == sb && IS_QUOTAINIT(inode))
                          remove_inode_dquot_ref(inode, type, &tofree_head);
          }
          list_for_each(act_head, &sb->s_dirty) {
                  inode = list_entry(act_head, struct inode, i_list);
                  if (IS_QUOTAINIT(inode))
                          remove_inode_dquot_ref(inode, type, &tofree_head);
          }
          list_for_each(act_head, &sb->s_locked_inodes) {
                  inode = list_entry(act_head, struct inode, i_list);
                  if (IS_QUOTAINIT(inode))
                          remove_inode_dquot_ref(inode, type, &tofree_head);
          }
          spin_unlock(&inode_lock);
          unlock_kernel();
  
          put_dquot_list(&tofree_head);
  }
  
  #endif

Cache object: 3cf0829203b1cb9c22637c6e9d157a07