/*
   *  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/lglock.h>
  #include <linux/percpu_counter.h>
  #include <linux/percpu.h>
  #include <linux/hardirq.h>
  #include <linux/task_work.h>
  #include <linux/ima.h>
  
  #include <linux/atomic.h>
  
  #include "internal.h"
  
  /* sysctl tunables... */
  struct files_stat_struct files_stat = {
  	.max_files = NR_FILE
  };
  
  /* SLAB cache for file structures */
  static struct kmem_cache *filp_cachep __read_mostly;
  
  static struct percpu_counter nr_files __cacheline_aligned_in_smp;
  
  static 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 long get_nr_files(void)
  {
  	return percpu_counter_read_positive(&nr_files);
  }
  
  /*
   * Return the maximum number of open files in the system
   */
  unsigned long 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_doulongvec_minmax(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 an error pointer if some error happend e.g. we over file
   * structures limit, run out of memory or operation is not permitted.
   *
   * 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 long old_max;
  	struct file *f;
  	int error;
  
  	/*
  	 * 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 (unlikely(!f))
  		return ERR_PTR(-ENOMEM);
  
  	percpu_counter_inc(&nr_files);
  	f->f_cred = get_cred(cred);
  	error = security_file_alloc(f);
  	if (unlikely(error)) {
  		file_free(f);
  		return ERR_PTR(error);
  	}
  
  	atomic_long_set(&f->f_count, 1);
  	rwlock_init(&f->f_owner.lock);
  	spin_lock_init(&f->f_lock);
  	mutex_init(&f->f_pos_lock);
  	eventpoll_init_file(f);
  	/* f->f_version: 0 */
  	return f;
  
  over:
  	/* Ran out of filps - report that */
  	if (get_nr_files() > old_max) {
  		pr_info("VFS: file-max limit %lu reached
  ", get_max_files());
  		old_max = get_nr_files();
  	}
  	return ERR_PTR(-ENFILE);
  }
  
  /**
   * 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 (IS_ERR(file))
  		return file;
  
  	file->f_path = *path;
  	file->f_inode = path->dentry->d_inode;
  	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));
  	}
  	if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
  		i_readcount_inc(path->dentry->d_inode);
  	return file;
  }
  EXPORT_SYMBOL(alloc_file);
  
  /**
   * 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.
   */
  static 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;
  
  	if (special_file(inode->i_mode))
  		return;
  
  	put_write_access(inode);
  	if (file_check_writeable(file) != 0)
  		return;
  	__mnt_drop_write(mnt);
  	file_release_write(file);
  }
  
  /* the real guts of fput() - releasing the last reference to file
   */
  static void __fput(struct file *file)
  {
  	struct dentry *dentry = file->f_path.dentry;
  	struct vfsmount *mnt = file->f_path.mnt;
  	struct inode *inode = file->f_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->fasync)
  			file->f_op->fasync(-1, file, 0);
  	}
  	ima_file_free(file);
  	if (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 &&
  		     !(file->f_mode & FMODE_PATH))) {
  		cdev_put(inode->i_cdev);
  	}
  	fops_put(file->f_op);
  	put_pid(file->f_owner.pid);
  	if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
  		i_readcount_dec(inode);
  	if (file->f_mode & FMODE_WRITE)
  		drop_file_write_access(file);
  	file->f_path.dentry = NULL;
  	file->f_path.mnt = NULL;
  	file->f_inode = NULL;
  	file_free(file);
  	dput(dentry);
  	mntput(mnt);
  }
  
  static LLIST_HEAD(delayed_fput_list);
  static void delayed_fput(struct work_struct *unused)
  {
  	struct llist_node *node = llist_del_all(&delayed_fput_list);
  	struct llist_node *next;
  
  	for (; node; node = next) {
  		next = llist_next(node);
  		__fput(llist_entry(node, struct file, f_u.fu_llist));
  	}
  }
  
  static void ____fput(struct callback_head *work)
  {
  	__fput(container_of(work, struct file, f_u.fu_rcuhead));
  }
  
  /*
   * If kernel thread really needs to have the final fput() it has done
   * to complete, call this.  The only user right now is the boot - we
   * *do* need to make sure our writes to binaries on initramfs has
   * not left us with opened struct file waiting for __fput() - execve()
   * won't work without that.  Please, don't add more callers without
   * very good reasons; in particular, never call that with locks
   * held and never call that from a thread that might need to do
   * some work on any kind of umount.
   */
  void flush_delayed_fput(void)
  {
  	delayed_fput(NULL);
  }
  
  static DECLARE_DELAYED_WORK(delayed_fput_work, delayed_fput);
  
  void fput(struct file *file)
  {
  	if (atomic_long_dec_and_test(&file->f_count)) {
  		struct task_struct *task = current;
  
  		if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
  			init_task_work(&file->f_u.fu_rcuhead, ____fput);
  			if (!task_work_add(task, &file->f_u.fu_rcuhead, true))
  				return;
  			/*
  			 * After this task has run exit_task_work(),
  			 * task_work_add() will fail.  Fall through to delayed
  			 * fput to avoid leaking *file.
  			 */
  		}
  
  		if (llist_add(&file->f_u.fu_llist, &delayed_fput_list))
  			schedule_delayed_work(&delayed_fput_work, 1);
  	}
  }
  
  /*
   * synchronous analog of fput(); for kernel threads that might be needed
   * in some umount() (and thus can't use flush_delayed_fput() without
   * risking deadlocks), need to wait for completion of __fput() and know
   * for this specific struct file it won't involve anything that would
   * need them.  Use only if you really need it - at the very least,
   * don't blindly convert fput() by kernel thread to that.
   */
  void __fput_sync(struct file *file)
  {
  	if (atomic_long_dec_and_test(&file->f_count)) {
  		struct task_struct *task = current;
  		BUG_ON(!(task->flags & PF_KTHREAD));
  		__fput(file);
  	}
  }
  
  EXPORT_SYMBOL(fput);
  
  void put_filp(struct file *file)
  {
  	if (atomic_long_dec_and_test(&file->f_count)) {
  		security_file_free(file);
  		file_free(file);
  	}
  }
  
  void __init files_init(unsigned long mempages)
  { 
  	unsigned long 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 = max_t(unsigned long, n, NR_FILE);
  	files_defer_init();
  	percpu_counter_init(&nr_files, 0);
  }