/*
   *  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/fdtable.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 <linux/ima.h>

  
  #include <asm/atomic.h>

  #include "internal.h"

  /* sysctl tunables... */
  struct files_stat_struct files_stat = {
  	.max_files = NR_FILE
  };

  /* public. Not pretty! */

  __cacheline_aligned_in_smp DEFINE_SPINLOCK(files_lock);

  /* SLAB cache for file structures */
  static struct kmem_cache *filp_cachep __read_mostly;

  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);
  
  	put_cred(f->f_cred);

  	kmem_cache_free(filp_cachep, f);

  }

  static inline void file_free(struct file *f)

  {

  	percpu_counter_dec(&nr_files);

  	file_check_state(f);

  	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,

                       void __user *buffer, size_t *lenp, loff_t *ppos)
  {
  	files_stat.nr_files = get_nr_files();

  	return proc_dointvec(table, write, buffer, lenp, ppos);

  }
  #else

  int proc_nr_files(ctl_table *table, int write,

                       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.

   *
   * Be very careful using this.  You are responsible for
   * getting write access to any mount that you might assign
   * to this filp, if it is opened for write.  If this is not
   * done, you will imbalance int the mount's writer count
   * and a warning at __fput() time.

   */
  struct file *get_empty_filp(void)
  {

  	const struct cred *cred = current_cred();

  	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_positive(&nr_files) >= files_stat.max_files)

  			goto over;
  	}

  	f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);

  	if (f == NULL)
  		goto fail;

  	percpu_counter_inc(&nr_files);

  	if (security_file_alloc(f))
  		goto fail_sec;

  	INIT_LIST_HEAD(&f->f_u.fu_list);

  	atomic_long_set(&f->f_count, 1);

  	rwlock_init(&f->f_owner.lock);

  	f->f_cred = get_cred(cred);

  	spin_lock_init(&f->f_lock);

  	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
  ",

  					get_max_files());
  		old_max = get_nr_files();

  	}

  	goto fail;
  
  fail_sec:
  	file_free(f);

  fail:
  	return NULL;
  }

  /**
   * alloc_file - allocate and initialize a 'struct file'
   * @mnt: the vfsmount on which the file will reside
   * @dentry: the dentry representing the new file
   * @mode: the mode with which the new file will be opened
   * @fop: the 'struct file_operations' for the new file
   *
   * Use this instead of get_empty_filp() to get a new
   * 'struct file'.  Do so because of the same initialization
   * pitfalls reasons listed for init_file().  This is a
   * preferred interface to using init_file().
   *
   * If all the callers of init_file() are eliminated, its
   * code should be moved into this function.
   */

  struct file *alloc_file(struct path *path, fmode_t mode,
  		const struct file_operations *fop)

  {
  	struct file *file;

  
  	file = get_empty_filp();
  	if (!file)
  		return NULL;

  	file->f_path = *path;
  	file->f_mapping = path->dentry->d_inode->i_mapping;

  	file->f_mode = mode;
  	file->f_op = fop;

  
  	/*
  	 * These mounts don't really matter in practice
  	 * for r/o bind mounts.  They aren't userspace-
  	 * visible.  We do this for consistency, and so
  	 * that we can do debugging checks at __fput()
  	 */

  	if ((mode & FMODE_WRITE) && !special_file(path->dentry->d_inode->i_mode)) {

  		file_take_write(file);

  		WARN_ON(mnt_clone_write(path->mnt));

  	}

  	ima_counts_get(file);

  	return file;

  }

  EXPORT_SYMBOL(alloc_file);

  void fput(struct file *file)

  {

  	if (atomic_long_dec_and_test(&file->f_count))

  		__fput(file);
  }
  
  EXPORT_SYMBOL(fput);

  /**
   * drop_file_write_access - give up ability to write to a file
   * @file: the file to which we will stop writing
   *
   * This is a central place which will give up the ability
   * to write to @file, along with access to write through
   * its vfsmount.
   */
  void drop_file_write_access(struct file *file)
  {

  	struct vfsmount *mnt = file->f_path.mnt;

  	struct dentry *dentry = file->f_path.dentry;
  	struct inode *inode = dentry->d_inode;
  
  	put_write_access(inode);

  
  	if (special_file(inode->i_mode))
  		return;
  	if (file_check_writeable(file) != 0)
  		return;
  	mnt_drop_write(mnt);
  	file_release_write(file);

  }
  EXPORT_SYMBOL_GPL(drop_file_write_access);

  /* __fput is called from task context when aio completion releases the last
   * last use of a struct file *.  Do not use otherwise.
   */

  void __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 (unlikely(file->f_flags & FASYNC)) {
  		if (file->f_op && file->f_op->fasync)
  			file->f_op->fasync(-1, file, 0);
  	}

  	if (file->f_op && file->f_op->release)
  		file->f_op->release(inode, file);
  	security_file_free(file);

  	ima_file_free(file);

  	if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL))

  		cdev_put(inode->i_cdev);
  	fops_put(file->f_op);

  	put_pid(file->f_owner.pid);

  	file_kill(file);

  	if (file->f_mode & FMODE_WRITE)
  		drop_file_write_access(file);

  	file->f_path.dentry = NULL;
  	file->f_path.mnt = NULL;

  	file_free(file);
  	dput(dentry);
  	mntput(mnt);
  }

  struct file *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_long_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 *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_long_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_long_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 file *file;

  
  	/* Check that no files are currently opened for writing. */
  	file_list_lock();

  	list_for_each_entry(file, &sb->s_files, 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;
  }

  /**
   *	mark_files_ro - mark all files read-only
   *	@sb: superblock in question
   *
   *	All files are marked read-only.  We don't care about pending
   *	delete files so this should be used in 'force' mode only.
   */
  void mark_files_ro(struct super_block *sb)
  {
  	struct file *f;
  
  retry:
  	file_list_lock();
  	list_for_each_entry(f, &sb->s_files, f_u.fu_list) {
  		struct vfsmount *mnt;
  		if (!S_ISREG(f->f_path.dentry->d_inode->i_mode))
  		       continue;
  		if (!file_count(f))
  			continue;
  		if (!(f->f_mode & FMODE_WRITE))
  			continue;

  		spin_lock(&f->f_lock);

  		f->f_mode &= ~FMODE_WRITE;

  		spin_unlock(&f->f_lock);

  		if (file_check_writeable(f) != 0)
  			continue;
  		file_release_write(f);
  		mnt = mntget(f->f_path.mnt);
  		file_list_unlock();
  		/*
  		 * This can sleep, so we can't hold
  		 * the file_list_lock() spinlock.
  		 */
  		mnt_drop_write(mnt);
  		mntput(mnt);
  		goto retry;
  	}
  	file_list_unlock();
  }

  void __init files_init(unsigned long mempages)
  { 
  	int n; 

  
  	filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
  			SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
  
  	/*
  	 * 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);

  }