text: /*
   *  linux/fs/file_table.c
   *
   *  Copyright (C) 1991, 1992  Linus Torvalds
   *  Copyright (C) 1997 David S. Miller (davem@caip.rutgers.edu)
   */
  
  #include <linux/string.h>
  #include <linux/slab.h>
  #include <linux/file.h>
  #include <linux/init.h>
  #include <linux/module.h>
  #include <linux/fs.h>
  #include <linux/security.h>
  #include <linux/eventpoll.h>
  #include <linux/rcupdate.h>
  #include <linux/mount.h>
  #include <linux/capability.h>
  #include <linux/cdev.h>
  #include <linux/fsnotify.h>
  #include <linux/sysctl.h>
  #include <linux/percpu_counter.h>
  
  #include <asm/atomic.h>
  
  /* sysctl tunables... */
  struct files_stat_struct files_stat = {
  	.max_files = NR_FILE
  };
  
  /* public. Not pretty! */
  __cacheline_aligned_in_smp DEFINE_SPINLOCK(files_lock);
  
  static struct percpu_counter nr_files __cacheline_aligned_in_smp;
  
  static inline void file_free_rcu(struct rcu_head *head)
  {
  	struct file *f =  container_of(head, struct file, f_u.fu_rcuhead);
  	kmem_cache_free(filp_cachep, f);
  }
  
  static inline void file_free(struct file *f)
  {
  	percpu_counter_dec(&nr_files);
  	call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
  }
  
  /*
   * Return the total number of open files in the system
   */
  static int get_nr_files(void)
  {
  	return percpu_counter_read_positive(&nr_files);
  }
  
  /*
   * Return the maximum number of open files in the system
   */
  int get_max_files(void)
  {
  	return files_stat.max_files;
  }
  EXPORT_SYMBOL_GPL(get_max_files);
  
  /*
   * Handle nr_files sysctl
   */
  #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
  int proc_nr_files(ctl_table *table, int write, struct file *filp,
                       void __user *buffer, size_t *lenp, loff_t *ppos)
  {
  	files_stat.nr_files = get_nr_files();
  	return proc_dointvec(table, write, filp, buffer, lenp, ppos);
  }
  #else
  int proc_nr_files(ctl_table *table, int write, struct file *filp,
                       void __user *buffer, size_t *lenp, loff_t *ppos)
  {
  	return -ENOSYS;
  }
  #endif
  
  /* Find an unused file structure and return a pointer to it.
   * Returns NULL, if there are no more free file structures or
   * we run out of memory.
   */
  struct file *get_empty_filp(void)
  {
  	struct task_struct *tsk;
  	static int old_max;
  	struct file * f;
  
  	/*
  	 * Privileged users can go above max_files
  	 */
  	if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
  		/*
  		 * percpu_counters are inaccurate.  Do an expensive check before
  		 * we go and fail.
  		 */
  		if (percpu_counter_sum(&nr_files) >= files_stat.max_files)
  			goto over;
  	}
  
  	f = kmem_cache_alloc(filp_cachep, GFP_KERNEL);
  	if (f == NULL)
  		goto fail;
  
  	percpu_counter_inc(&nr_files);
  	memset(f, 0, sizeof(*f));
  	if (security_file_alloc(f))
  		goto fail_sec;
  
  	tsk = current;
  	INIT_LIST_HEAD(&f->f_u.fu_list);
  	atomic_set(&f->f_count, 1);
  	rwlock_init(&f->f_owner.lock);
  	f->f_uid = tsk->fsuid;
  	f->f_gid = tsk->fsgid;
  	eventpoll_init_file(f);
  	/* f->f_version: 0 */
  	return f;
  
  over:
  	/* Ran out of filps - report that */
  	if (get_nr_files() > old_max) {
  		printk(KERN_INFO "VFS: file-max limit %d reached\n",
  					get_max_files());
  		old_max = get_nr_files();
  	}
  	goto fail;
  
  fail_sec:
  	file_free(f);
  fail:
  	return NULL;
  }
  
  EXPORT_SYMBOL(get_empty_filp);
  
  void fastcall fput(struct file *file)
  {
  	if (atomic_dec_and_test(&file->f_count))
  		__fput(file);
  }
  
  EXPORT_SYMBOL(fput);
  
  /* __fput is called from task context when aio completion releases the last
   * last use of a struct file *.  Do not use otherwise.
   */
  void fastcall __fput(struct file *file)
  {
  	struct dentry *dentry = file->f_path.dentry;
  	struct vfsmount *mnt = file->f_path.mnt;
  	struct inode *inode = dentry->d_inode;
  
  	might_sleep();
  
  	fsnotify_close(file);
  	/*
  	 * The function eventpoll_release() should be the first called
  	 * in the file cleanup chain.
  	 */
  	eventpoll_release(file);
  	locks_remove_flock(file);
  
  	if (file->f_op && file->f_op->release)
  		file->f_op->release(inode, file);
  	security_file_free(file);
  	if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL))
  		cdev_put(inode->i_cdev);
  	fops_put(file->f_op);
  	if (file->f_mode & FMODE_WRITE)
  		put_write_access(inode);
  	put_pid(file->f_owner.pid);
  	file_kill(file);
  	file->f_path.dentry = NULL;
  	file->f_path.mnt = NULL;
  	file_free(file);
  	dput(dentry);
  	mntput(mnt);
  }
  
  struct file fastcall *fget(unsigned int fd)
  {
  	struct file *file;
  	struct files_struct *files = current->files;
  
  	rcu_read_lock();
  	file = fcheck_files(files, fd);
  	if (file) {
  		if (!atomic_inc_not_zero(&file->f_count)) {
  			/* File object ref couldn't be taken */
  			rcu_read_unlock();
  			return NULL;
  		}
  	}
  	rcu_read_unlock();
  
  	return file;
  }
  
  EXPORT_SYMBOL(fget);
  
  /*
   * Lightweight file lookup - no refcnt increment if fd table isn't shared. 
   * You can use this only if it is guranteed that the current task already 
   * holds a refcnt to that file. That check has to be done at fget() only
   * and a flag is returned to be passed to the corresponding fput_light().
   * There must not be a cloning between an fget_light/fput_light pair.
   */
  struct file fastcall *fget_light(unsigned int fd, int *fput_needed)
  {
  	struct file *file;
  	struct files_struct *files = current->files;
  
  	*fput_needed = 0;
  	if (likely((atomic_read(&files->count) == 1))) {
  		file = fcheck_files(files, fd);
  	} else {
  		rcu_read_lock();
  		file = fcheck_files(files, fd);
  		if (file) {
  			if (atomic_inc_not_zero(&file->f_count))
  				*fput_needed = 1;
  			else
  				/* Didn't get the reference, someone's freed */
  				file = NULL;
  		}
  		rcu_read_unlock();
  	}
  
  	return file;
  }
  
  
  void put_filp(struct file *file)
  {
  	if (atomic_dec_and_test(&file->f_count)) {
  		security_file_free(file);
  		file_kill(file);
  		file_free(file);
  	}
  }
  
  void file_move(struct file *file, struct list_head *list)
  {
  	if (!list)
  		return;
  	file_list_lock();
  	list_move(&file->f_u.fu_list, list);
  	file_list_unlock();
  }
  
  void file_kill(struct file *file)
  {
  	if (!list_empty(&file->f_u.fu_list)) {
  		file_list_lock();
  		list_del_init(&file->f_u.fu_list);
  		file_list_unlock();
  	}
  }
  
  int fs_may_remount_ro(struct super_block *sb)
  {
  	struct list_head *p;
  
  	/* Check that no files are currently opened for writing. */
  	file_list_lock();
  	list_for_each(p, &sb->s_files) {
  		struct file *file = list_entry(p, struct file, f_u.fu_list);
  		struct inode *inode = file->f_path.dentry->d_inode;
  
  		/* File with pending delete? */
  		if (inode->i_nlink == 0)
  			goto too_bad;
  
  		/* Writeable file? */
  		if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE))
  			goto too_bad;
  	}
  	file_list_unlock();
  	return 1; /* Tis' cool bro. */
  too_bad:
  	file_list_unlock();
  	return 0;
  }
  
  void __init files_init(unsigned long mempages)
  { 
  	int n; 
  	/* One file with associated inode and dcache is very roughly 1K. 
  	 * Per default don't use more than 10% of our memory for files. 
  	 */ 
  
  	n = (mempages * (PAGE_SIZE / 1024)) / 10;
  	files_stat.max_files = n; 
  	if (files_stat.max_files < NR_FILE)
  		files_stat.max_files = NR_FILE;
  	files_defer_init();
  	percpu_counter_init(&nr_files, 0);
  } 
  