text: /*
   * fs/kernfs/file.c - kernfs file implementation
   *
   * Copyright (c) 2001-3 Patrick Mochel
   * Copyright (c) 2007 SUSE Linux Products GmbH
   * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
   *
   * This file is released under the GPLv2.
   */
  
  #include <linux/fs.h>
  #include <linux/seq_file.h>
  #include <linux/slab.h>
  #include <linux/poll.h>
  #include <linux/pagemap.h>
  #include <linux/sched/mm.h>
  #include <linux/fsnotify.h>
  
  #include "kernfs-internal.h"
  
  /*
   * There's one kernfs_open_file for each open file and one kernfs_open_node
   * for each kernfs_node with one or more open files.
   *
   * kernfs_node->attr.open points to kernfs_open_node.  attr.open is
   * protected by kernfs_open_node_lock.
   *
   * filp->private_data points to seq_file whose ->private points to
   * kernfs_open_file.  kernfs_open_files are chained at
   * kernfs_open_node->files, which is protected by kernfs_open_file_mutex.
   */
  static DEFINE_SPINLOCK(kernfs_open_node_lock);
  static DEFINE_MUTEX(kernfs_open_file_mutex);
  
  struct kernfs_open_node {
  	atomic_t		refcnt;
  	atomic_t		event;
  	wait_queue_head_t	poll;
  	struct list_head	files; /* goes through kernfs_open_file.list */
  };
  
  /*
   * kernfs_notify() may be called from any context and bounces notifications
   * through a work item.  To minimize space overhead in kernfs_node, the
   * pending queue is implemented as a singly linked list of kernfs_nodes.
   * The list is terminated with the self pointer so that whether a
   * kernfs_node is on the list or not can be determined by testing the next
   * pointer for NULL.
   */
  #define KERNFS_NOTIFY_EOL			((void *)&kernfs_notify_list)
  
  static DEFINE_SPINLOCK(kernfs_notify_lock);
  static struct kernfs_node *kernfs_notify_list = KERNFS_NOTIFY_EOL;
  
  static struct kernfs_open_file *kernfs_of(struct file *file)
  {
  	return ((struct seq_file *)file->private_data)->private;
  }
  
  /*
   * Determine the kernfs_ops for the given kernfs_node.  This function must
   * be called while holding an active reference.
   */
  static const struct kernfs_ops *kernfs_ops(struct kernfs_node *kn)
  {
  	if (kn->flags & KERNFS_LOCKDEP)
  		lockdep_assert_held(kn);
  	return kn->attr.ops;
  }
  
  /*
   * As kernfs_seq_stop() is also called after kernfs_seq_start() or
   * kernfs_seq_next() failure, it needs to distinguish whether it's stopping
   * a seq_file iteration which is fully initialized with an active reference
   * or an aborted kernfs_seq_start() due to get_active failure.  The
   * position pointer is the only context for each seq_file iteration and
   * thus the stop condition should be encoded in it.  As the return value is
   * directly visible to userland, ERR_PTR(-ENODEV) is the only acceptable
   * choice to indicate get_active failure.
   *
   * Unfortunately, this is complicated due to the optional custom seq_file
   * operations which may return ERR_PTR(-ENODEV) too.  kernfs_seq_stop()
   * can't distinguish whether ERR_PTR(-ENODEV) is from get_active failure or
   * custom seq_file operations and thus can't decide whether put_active
   * should be performed or not only on ERR_PTR(-ENODEV).
   *
   * This is worked around by factoring out the custom seq_stop() and
   * put_active part into kernfs_seq_stop_active(), skipping it from
   * kernfs_seq_stop() if ERR_PTR(-ENODEV) while invoking it directly after
   * custom seq_file operations fail with ERR_PTR(-ENODEV) - this ensures
   * that kernfs_seq_stop_active() is skipped only after get_active failure.
   */
  static void kernfs_seq_stop_active(struct seq_file *sf, void *v)
  {
  	struct kernfs_open_file *of = sf->private;
  	const struct kernfs_ops *ops = kernfs_ops(of->kn);
  
  	if (ops->seq_stop)
  		ops->seq_stop(sf, v);
  	kernfs_put_active(of->kn);
  }
  
  static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
  {
  	struct kernfs_open_file *of = sf->private;
  	const struct kernfs_ops *ops;
  
  	/*
  	 * @of->mutex nests outside active ref and is primarily to ensure that
  	 * the ops aren't called concurrently for the same open file.
  	 */
  	mutex_lock(&of->mutex);
  	if (!kernfs_get_active(of->kn))
  		return ERR_PTR(-ENODEV);
  
  	ops = kernfs_ops(of->kn);
  	if (ops->seq_start) {
  		void *next = ops->seq_start(sf, ppos);
  		/* see the comment above kernfs_seq_stop_active() */
  		if (next == ERR_PTR(-ENODEV))
  			kernfs_seq_stop_active(sf, next);
  		return next;
  	} else {
  		/*
  		 * The same behavior and code as single_open().  Returns
  		 * !NULL if pos is at the beginning; otherwise, NULL.
  		 */
  		return NULL + !*ppos;
  	}
  }
  
  static void *kernfs_seq_next(struct seq_file *sf, void *v, loff_t *ppos)
  {
  	struct kernfs_open_file *of = sf->private;
  	const struct kernfs_ops *ops = kernfs_ops(of->kn);
  
  	if (ops->seq_next) {
  		void *next = ops->seq_next(sf, v, ppos);
  		/* see the comment above kernfs_seq_stop_active() */
  		if (next == ERR_PTR(-ENODEV))
  			kernfs_seq_stop_active(sf, next);
  		return next;
  	} else {
  		/*
  		 * The same behavior and code as single_open(), always
  		 * terminate after the initial read.
  		 */
  		++*ppos;
  		return NULL;
  	}
  }
  
  static void kernfs_seq_stop(struct seq_file *sf, void *v)
  {
  	struct kernfs_open_file *of = sf->private;
  
  	if (v != ERR_PTR(-ENODEV))
  		kernfs_seq_stop_active(sf, v);
  	mutex_unlock(&of->mutex);
  }
  
  static int kernfs_seq_show(struct seq_file *sf, void *v)
  {
  	struct kernfs_open_file *of = sf->private;
  
  	of->event = atomic_read(&of->kn->attr.open->event);
  
  	return of->kn->attr.ops->seq_show(sf, v);
  }
  
  static const struct seq_operations kernfs_seq_ops = {
  	.start = kernfs_seq_start,
  	.next = kernfs_seq_next,
  	.stop = kernfs_seq_stop,
  	.show = kernfs_seq_show,
  };
  
  /*
   * As reading a bin file can have side-effects, the exact offset and bytes
   * specified in read(2) call should be passed to the read callback making
   * it difficult to use seq_file.  Implement simplistic custom buffering for
   * bin files.
   */
  static ssize_t kernfs_file_direct_read(struct kernfs_open_file *of,
  				       char __user *user_buf, size_t count,
  				       loff_t *ppos)
  {
  	ssize_t len = min_t(size_t, count, PAGE_SIZE);
  	const struct kernfs_ops *ops;
  	char *buf;
  
  	buf = of->prealloc_buf;
  	if (buf)
  		mutex_lock(&of->prealloc_mutex);
  	else
  		buf = kmalloc(len, GFP_KERNEL);
  	if (!buf)
  		return -ENOMEM;
  
  	/*
  	 * @of->mutex nests outside active ref and is used both to ensure that
  	 * the ops aren't called concurrently for the same open file.
  	 */
  	mutex_lock(&of->mutex);
  	if (!kernfs_get_active(of->kn)) {
  		len = -ENODEV;
  		mutex_unlock(&of->mutex);
  		goto out_free;
  	}
  
  	of->event = atomic_read(&of->kn->attr.open->event);
  	ops = kernfs_ops(of->kn);
  	if (ops->read)
  		len = ops->read(of, buf, len, *ppos);
  	else
  		len = -EINVAL;
  
  	kernfs_put_active(of->kn);
  	mutex_unlock(&of->mutex);
  
  	if (len < 0)
  		goto out_free;
  
  	if (copy_to_user(user_buf, buf, len)) {
  		len = -EFAULT;
  		goto out_free;
  	}
  
  	*ppos += len;
  
   out_free:
  	if (buf == of->prealloc_buf)
  		mutex_unlock(&of->prealloc_mutex);
  	else
  		kfree(buf);
  	return len;
  }
  
  /**
   * kernfs_fop_read - kernfs vfs read callback
   * @file: file pointer
   * @user_buf: data to write
   * @count: number of bytes
   * @ppos: starting offset
   */
  static ssize_t kernfs_fop_read(struct file *file, char __user *user_buf,
  			       size_t count, loff_t *ppos)
  {
  	struct kernfs_open_file *of = kernfs_of(file);
  
  	if (of->kn->flags & KERNFS_HAS_SEQ_SHOW)
  		return seq_read(file, user_buf, count, ppos);
  	else
  		return kernfs_file_direct_read(of, user_buf, count, ppos);
  }
  
  /**
   * kernfs_fop_write - kernfs vfs write callback
   * @file: file pointer
   * @user_buf: data to write
   * @count: number of bytes
   * @ppos: starting offset
   *
   * Copy data in from userland and pass it to the matching kernfs write
   * operation.
   *
   * There is no easy way for us to know if userspace is only doing a partial
   * write, so we don't support them. We expect the entire buffer to come on
   * the first write.  Hint: if you're writing a value, first read the file,
   * modify only the the value you're changing, then write entire buffer
   * back.
   */
  static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf,
  				size_t count, loff_t *ppos)
  {
  	struct kernfs_open_file *of = kernfs_of(file);
  	const struct kernfs_ops *ops;
  	size_t len;
  	char *buf;
  
  	if (of->atomic_write_len) {
  		len = count;
  		if (len > of->atomic_write_len)
  			return -E2BIG;
  	} else {
  		len = min_t(size_t, count, PAGE_SIZE);
  	}
  
  	buf = of->prealloc_buf;
  	if (buf)
  		mutex_lock(&of->prealloc_mutex);
  	else
  		buf = kmalloc(len + 1, GFP_KERNEL);
  	if (!buf)
  		return -ENOMEM;
  
  	if (copy_from_user(buf, user_buf, len)) {
  		len = -EFAULT;
  		goto out_free;
  	}
  	buf[len] = '\0';	/* guarantee string termination */
  
  	/*
  	 * @of->mutex nests outside active ref and is used both to ensure that
  	 * the ops aren't called concurrently for the same open file.
  	 */
  	mutex_lock(&of->mutex);
  	if (!kernfs_get_active(of->kn)) {
  		mutex_unlock(&of->mutex);
  		len = -ENODEV;
  		goto out_free;
  	}
  
  	ops = kernfs_ops(of->kn);
  	if (ops->write)
  		len = ops->write(of, buf, len, *ppos);
  	else
  		len = -EINVAL;
  
  	kernfs_put_active(of->kn);
  	mutex_unlock(&of->mutex);
  
  	if (len > 0)
  		*ppos += len;
  
  out_free:
  	if (buf == of->prealloc_buf)
  		mutex_unlock(&of->prealloc_mutex);
  	else
  		kfree(buf);
  	return len;
  }
  
  static void kernfs_vma_open(struct vm_area_struct *vma)
  {
  	struct file *file = vma->vm_file;
  	struct kernfs_open_file *of = kernfs_of(file);
  
  	if (!of->vm_ops)
  		return;
  
  	if (!kernfs_get_active(of->kn))
  		return;
  
  	if (of->vm_ops->open)
  		of->vm_ops->open(vma);
  
  	kernfs_put_active(of->kn);
  }
  
  static int kernfs_vma_fault(struct vm_fault *vmf)
  {
  	struct file *file = vmf->vma->vm_file;
  	struct kernfs_open_file *of = kernfs_of(file);
  	int ret;
  
  	if (!of->vm_ops)
  		return VM_FAULT_SIGBUS;
  
  	if (!kernfs_get_active(of->kn))
  		return VM_FAULT_SIGBUS;
  
  	ret = VM_FAULT_SIGBUS;
  	if (of->vm_ops->fault)
  		ret = of->vm_ops->fault(vmf);
  
  	kernfs_put_active(of->kn);
  	return ret;
  }
  
  static int kernfs_vma_page_mkwrite(struct vm_fault *vmf)
  {
  	struct file *file = vmf->vma->vm_file;
  	struct kernfs_open_file *of = kernfs_of(file);
  	int ret;
  
  	if (!of->vm_ops)
  		return VM_FAULT_SIGBUS;
  
  	if (!kernfs_get_active(of->kn))
  		return VM_FAULT_SIGBUS;
  
  	ret = 0;
  	if (of->vm_ops->page_mkwrite)
  		ret = of->vm_ops->page_mkwrite(vmf);
  	else
  		file_update_time(file);
  
  	kernfs_put_active(of->kn);
  	return ret;
  }
  
  static int kernfs_vma_access(struct vm_area_struct *vma, unsigned long addr,
  			     void *buf, int len, int write)
  {
  	struct file *file = vma->vm_file;
  	struct kernfs_open_file *of = kernfs_of(file);
  	int ret;
  
  	if (!of->vm_ops)
  		return -EINVAL;
  
  	if (!kernfs_get_active(of->kn))
  		return -EINVAL;
  
  	ret = -EINVAL;
  	if (of->vm_ops->access)
  		ret = of->vm_ops->access(vma, addr, buf, len, write);
  
  	kernfs_put_active(of->kn);
  	return ret;
  }
  
  #ifdef CONFIG_NUMA
  static int kernfs_vma_set_policy(struct vm_area_struct *vma,
  				 struct mempolicy *new)
  {
  	struct file *file = vma->vm_file;
  	struct kernfs_open_file *of = kernfs_of(file);
  	int ret;
  
  	if (!of->vm_ops)
  		return 0;
  
  	if (!kernfs_get_active(of->kn))
  		return -EINVAL;
  
  	ret = 0;
  	if (of->vm_ops->set_policy)
  		ret = of->vm_ops->set_policy(vma, new);
  
  	kernfs_put_active(of->kn);
  	return ret;
  }
  
  static struct mempolicy *kernfs_vma_get_policy(struct vm_area_struct *vma,
  					       unsigned long addr)
  {
  	struct file *file = vma->vm_file;
  	struct kernfs_open_file *of = kernfs_of(file);
  	struct mempolicy *pol;
  
  	if (!of->vm_ops)
  		return vma->vm_policy;
  
  	if (!kernfs_get_active(of->kn))
  		return vma->vm_policy;
  
  	pol = vma->vm_policy;
  	if (of->vm_ops->get_policy)
  		pol = of->vm_ops->get_policy(vma, addr);
  
  	kernfs_put_active(of->kn);
  	return pol;
  }
  
  #endif
  
  static const struct vm_operations_struct kernfs_vm_ops = {
  	.open		= kernfs_vma_open,
  	.fault		= kernfs_vma_fault,
  	.page_mkwrite	= kernfs_vma_page_mkwrite,
  	.access		= kernfs_vma_access,
  #ifdef CONFIG_NUMA
  	.set_policy	= kernfs_vma_set_policy,
  	.get_policy	= kernfs_vma_get_policy,
  #endif
  };
  
  static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma)
  {
  	struct kernfs_open_file *of = kernfs_of(file);
  	const struct kernfs_ops *ops;
  	int rc;
  
  	/*
  	 * mmap path and of->mutex are prone to triggering spurious lockdep
  	 * warnings and we don't want to add spurious locking dependency
  	 * between the two.  Check whether mmap is actually implemented
  	 * without grabbing @of->mutex by testing HAS_MMAP flag.  See the
  	 * comment in kernfs_file_open() for more details.
  	 */
  	if (!(of->kn->flags & KERNFS_HAS_MMAP))
  		return -ENODEV;
  
  	mutex_lock(&of->mutex);
  
  	rc = -ENODEV;
  	if (!kernfs_get_active(of->kn))
  		goto out_unlock;
  
  	ops = kernfs_ops(of->kn);
  	rc = ops->mmap(of, vma);
  	if (rc)
  		goto out_put;
  
  	/*
  	 * PowerPC's pci_mmap of legacy_mem uses shmem_zero_setup()
  	 * to satisfy versions of X which crash if the mmap fails: that
  	 * substitutes a new vm_file, and we don't then want bin_vm_ops.
  	 */
  	if (vma->vm_file != file)
  		goto out_put;
  
  	rc = -EINVAL;
  	if (of->mmapped && of->vm_ops != vma->vm_ops)
  		goto out_put;
  
  	/*
  	 * It is not possible to successfully wrap close.
  	 * So error if someone is trying to use close.
  	 */
  	rc = -EINVAL;
  	if (vma->vm_ops && vma->vm_ops->close)
  		goto out_put;
  
  	rc = 0;
  	of->mmapped = true;
  	of->vm_ops = vma->vm_ops;
  	vma->vm_ops = &kernfs_vm_ops;
  out_put:
  	kernfs_put_active(of->kn);
  out_unlock:
  	mutex_unlock(&of->mutex);
  
  	return rc;
  }
  
  /**
   *	kernfs_get_open_node - get or create kernfs_open_node
   *	@kn: target kernfs_node
   *	@of: kernfs_open_file for this instance of open
   *
   *	If @kn->attr.open exists, increment its reference count; otherwise,
   *	create one.  @of is chained to the files list.
   *
   *	LOCKING:
   *	Kernel thread context (may sleep).
   *
   *	RETURNS:
   *	0 on success, -errno on failure.
   */
  static int kernfs_get_open_node(struct kernfs_node *kn,
  				struct kernfs_open_file *of)
  {
  	struct kernfs_open_node *on, *new_on = NULL;
  
   retry:
  	mutex_lock(&kernfs_open_file_mutex);
  	spin_lock_irq(&kernfs_open_node_lock);
  
  	if (!kn->attr.open && new_on) {
  		kn->attr.open = new_on;
  		new_on = NULL;
  	}
  
  	on = kn->attr.open;
  	if (on) {
  		atomic_inc(&on->refcnt);
  		list_add_tail(&of->list, &on->files);
  	}
  
  	spin_unlock_irq(&kernfs_open_node_lock);
  	mutex_unlock(&kernfs_open_file_mutex);
  
  	if (on) {
  		kfree(new_on);
  		return 0;
  	}
  
  	/* not there, initialize a new one and retry */
  	new_on = kmalloc(sizeof(*new_on), GFP_KERNEL);
  	if (!new_on)
  		return -ENOMEM;
  
  	atomic_set(&new_on->refcnt, 0);
  	atomic_set(&new_on->event, 1);
  	init_waitqueue_head(&new_on->poll);
  	INIT_LIST_HEAD(&new_on->files);
  	goto retry;
  }
  
  /**
   *	kernfs_put_open_node - put kernfs_open_node
   *	@kn: target kernfs_nodet
   *	@of: associated kernfs_open_file
   *
   *	Put @kn->attr.open and unlink @of from the files list.  If
   *	reference count reaches zero, disassociate and free it.
   *
   *	LOCKING:
   *	None.
   */
  static void kernfs_put_open_node(struct kernfs_node *kn,
  				 struct kernfs_open_file *of)
  {
  	struct kernfs_open_node *on = kn->attr.open;
  	unsigned long flags;
  
  	mutex_lock(&kernfs_open_file_mutex);
  	spin_lock_irqsave(&kernfs_open_node_lock, flags);
  
  	if (of)
  		list_del(&of->list);
  
  	if (atomic_dec_and_test(&on->refcnt))
  		kn->attr.open = NULL;
  	else
  		on = NULL;
  
  	spin_unlock_irqrestore(&kernfs_open_node_lock, flags);
  	mutex_unlock(&kernfs_open_file_mutex);
  
  	kfree(on);
  }
  
  static int kernfs_fop_open(struct inode *inode, struct file *file)
  {
  	struct kernfs_node *kn = file->f_path.dentry->d_fsdata;
  	struct kernfs_root *root = kernfs_root(kn);
  	const struct kernfs_ops *ops;
  	struct kernfs_open_file *of;
  	bool has_read, has_write, has_mmap;
  	int error = -EACCES;
  
  	if (!kernfs_get_active(kn))
  		return -ENODEV;
  
  	ops = kernfs_ops(kn);
  
  	has_read = ops->seq_show || ops->read || ops->mmap;
  	has_write = ops->write || ops->mmap;
  	has_mmap = ops->mmap;
  
  	/* see the flag definition for details */
  	if (root->flags & KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK) {
  		if ((file->f_mode & FMODE_WRITE) &&
  		    (!(inode->i_mode & S_IWUGO) || !has_write))
  			goto err_out;
  
  		if ((file->f_mode & FMODE_READ) &&
  		    (!(inode->i_mode & S_IRUGO) || !has_read))
  			goto err_out;
  	}
  
  	/* allocate a kernfs_open_file for the file */
  	error = -ENOMEM;
  	of = kzalloc(sizeof(struct kernfs_open_file), GFP_KERNEL);
  	if (!of)
  		goto err_out;
  
  	/*
  	 * The following is done to give a different lockdep key to
  	 * @of->mutex for files which implement mmap.  This is a rather
  	 * crude way to avoid false positive lockdep warning around
  	 * mm->mmap_sem - mmap nests @of->mutex under mm->mmap_sem and
  	 * reading /sys/block/sda/trace/act_mask grabs sr_mutex, under
  	 * which mm->mmap_sem nests, while holding @of->mutex.  As each
  	 * open file has a separate mutex, it's okay as long as those don't
  	 * happen on the same file.  At this point, we can't easily give
  	 * each file a separate locking class.  Let's differentiate on
  	 * whether the file has mmap or not for now.
  	 *
  	 * Both paths of the branch look the same.  They're supposed to
  	 * look that way and give @of->mutex different static lockdep keys.
  	 */
  	if (has_mmap)
  		mutex_init(&of->mutex);
  	else
  		mutex_init(&of->mutex);
  
  	of->kn = kn;
  	of->file = file;
  
  	/*
  	 * Write path needs to atomic_write_len outside active reference.
  	 * Cache it in open_file.  See kernfs_fop_write() for details.
  	 */
  	of->atomic_write_len = ops->atomic_write_len;
  
  	error = -EINVAL;
  	/*
  	 * ->seq_show is incompatible with ->prealloc,
  	 * as seq_read does its own allocation.
  	 * ->read must be used instead.
  	 */
  	if (ops->prealloc && ops->seq_show)
  		goto err_free;
  	if (ops->prealloc) {
  		int len = of->atomic_write_len ?: PAGE_SIZE;
  		of->prealloc_buf = kmalloc(len + 1, GFP_KERNEL);
  		error = -ENOMEM;
  		if (!of->prealloc_buf)
  			goto err_free;
  		mutex_init(&of->prealloc_mutex);
  	}
  
  	/*
  	 * Always instantiate seq_file even if read access doesn't use
  	 * seq_file or is not requested.  This unifies private data access
  	 * and readable regular files are the vast majority anyway.
  	 */
  	if (ops->seq_show)
  		error = seq_open(file, &kernfs_seq_ops);
  	else
  		error = seq_open(file, NULL);
  	if (error)
  		goto err_free;
  
  	of->seq_file = file->private_data;
  	of->seq_file->private = of;
  
  	/* seq_file clears PWRITE unconditionally, restore it if WRITE */
  	if (file->f_mode & FMODE_WRITE)
  		file->f_mode |= FMODE_PWRITE;
  
  	/* make sure we have open node struct */
  	error = kernfs_get_open_node(kn, of);
  	if (error)
  		goto err_seq_release;
  
  	if (ops->open) {
  		/* nobody has access to @of yet, skip @of->mutex */
  		error = ops->open(of);
  		if (error)
  			goto err_put_node;
  	}
  
  	/* open succeeded, put active references */
  	kernfs_put_active(kn);
  	return 0;
  
  err_put_node:
  	kernfs_put_open_node(kn, of);
  err_seq_release:
  	seq_release(inode, file);
  err_free:
  	kfree(of->prealloc_buf);
  	kfree(of);
  err_out:
  	kernfs_put_active(kn);
  	return error;
  }
  
  /* used from release/drain to ensure that ->release() is called exactly once */
  static void kernfs_release_file(struct kernfs_node *kn,
  				struct kernfs_open_file *of)
  {
  	/*
  	 * @of is guaranteed to have no other file operations in flight and
  	 * we just want to synchronize release and drain paths.
  	 * @kernfs_open_file_mutex is enough.  @of->mutex can't be used
  	 * here because drain path may be called from places which can
  	 * cause circular dependency.
  	 */
  	lockdep_assert_held(&kernfs_open_file_mutex);
  
  	if (!of->released) {
  		/*
  		 * A file is never detached without being released and we
  		 * need to be able to release files which are deactivated
  		 * and being drained.  Don't use kernfs_ops().
  		 */
  		kn->attr.ops->release(of);
  		of->released = true;
  	}
  }
  
  static int kernfs_fop_release(struct inode *inode, struct file *filp)
  {
  	struct kernfs_node *kn = filp->f_path.dentry->d_fsdata;
  	struct kernfs_open_file *of = kernfs_of(filp);
  
  	if (kn->flags & KERNFS_HAS_RELEASE) {
  		mutex_lock(&kernfs_open_file_mutex);
  		kernfs_release_file(kn, of);
  		mutex_unlock(&kernfs_open_file_mutex);
  	}
  
  	kernfs_put_open_node(kn, of);
  	seq_release(inode, filp);
  	kfree(of->prealloc_buf);
  	kfree(of);
  
  	return 0;
  }
  
  void kernfs_drain_open_files(struct kernfs_node *kn)
  {
  	struct kernfs_open_node *on;
  	struct kernfs_open_file *of;
  
  	if (!(kn->flags & (KERNFS_HAS_MMAP | KERNFS_HAS_RELEASE)))
  		return;
  
  	spin_lock_irq(&kernfs_open_node_lock);
  	on = kn->attr.open;
  	if (on)
  		atomic_inc(&on->refcnt);
  	spin_unlock_irq(&kernfs_open_node_lock);
  	if (!on)
  		return;
  
  	mutex_lock(&kernfs_open_file_mutex);
  
  	list_for_each_entry(of, &on->files, list) {
  		struct inode *inode = file_inode(of->file);
  
  		if (kn->flags & KERNFS_HAS_MMAP)
  			unmap_mapping_range(inode->i_mapping, 0, 0, 1);
  
  		if (kn->flags & KERNFS_HAS_RELEASE)
  			kernfs_release_file(kn, of);
  	}
  
  	mutex_unlock(&kernfs_open_file_mutex);
  
  	kernfs_put_open_node(kn, NULL);
  }
  
  /*
   * Kernfs attribute files are pollable.  The idea is that you read
   * the content and then you use 'poll' or 'select' to wait for
   * the content to change.  When the content changes (assuming the
   * manager for the kobject supports notification), poll will
   * return POLLERR|POLLPRI, and select will return the fd whether
   * it is waiting for read, write, or exceptions.
   * Once poll/select indicates that the value has changed, you
   * need to close and re-open the file, or seek to 0 and read again.
   * Reminder: this only works for attributes which actively support
   * it, and it is not possible to test an attribute from userspace
   * to see if it supports poll (Neither 'poll' nor 'select' return
   * an appropriate error code).  When in doubt, set a suitable timeout value.
   */
  static unsigned int kernfs_fop_poll(struct file *filp, poll_table *wait)
  {
  	struct kernfs_open_file *of = kernfs_of(filp);
  	struct kernfs_node *kn = filp->f_path.dentry->d_fsdata;
  	struct kernfs_open_node *on = kn->attr.open;
  
  	if (!kernfs_get_active(kn))
  		goto trigger;
  
  	poll_wait(filp, &on->poll, wait);
  
  	kernfs_put_active(kn);
  
  	if (of->event != atomic_read(&on->event))
  		goto trigger;
  
  	return DEFAULT_POLLMASK;
  
   trigger:
  	return DEFAULT_POLLMASK|POLLERR|POLLPRI;
  }
  
  static void kernfs_notify_workfn(struct work_struct *work)
  {
  	struct kernfs_node *kn;
  	struct kernfs_open_node *on;
  	struct kernfs_super_info *info;
  repeat:
  	/* pop one off the notify_list */
  	spin_lock_irq(&kernfs_notify_lock);
  	kn = kernfs_notify_list;
  	if (kn == KERNFS_NOTIFY_EOL) {
  		spin_unlock_irq(&kernfs_notify_lock);
  		return;
  	}
  	kernfs_notify_list = kn->attr.notify_next;
  	kn->attr.notify_next = NULL;
  	spin_unlock_irq(&kernfs_notify_lock);
  
  	/* kick poll */
  	spin_lock_irq(&kernfs_open_node_lock);
  
  	on = kn->attr.open;
  	if (on) {
  		atomic_inc(&on->event);
  		wake_up_interruptible(&on->poll);
  	}
  
  	spin_unlock_irq(&kernfs_open_node_lock);
  
  	/* kick fsnotify */
  	mutex_lock(&kernfs_mutex);
  
  	list_for_each_entry(info, &kernfs_root(kn)->supers, node) {
  		struct kernfs_node *parent;
  		struct inode *inode;
  
  		/*
  		 * We want fsnotify_modify() on @kn but as the
  		 * modifications aren't originating from userland don't
  		 * have the matching @file available.  Look up the inodes
  		 * and generate the events manually.
  		 */
  		inode = ilookup(info->sb, kn->ino);
  		if (!inode)
  			continue;
  
  		parent = kernfs_get_parent(kn);
  		if (parent) {
  			struct inode *p_inode;
  
  			p_inode = ilookup(info->sb, parent->ino);
  			if (p_inode) {
  				fsnotify(p_inode, FS_MODIFY | FS_EVENT_ON_CHILD,
  					 inode, FSNOTIFY_EVENT_INODE, kn->name, 0);
  				iput(p_inode);
  			}
  
  			kernfs_put(parent);
  		}
  
  		fsnotify(inode, FS_MODIFY, inode, FSNOTIFY_EVENT_INODE,
  			 kn->name, 0);
  		iput(inode);
  	}
  
  	mutex_unlock(&kernfs_mutex);
  	kernfs_put(kn);
  	goto repeat;
  }
  
  /**
   * kernfs_notify - notify a kernfs file
   * @kn: file to notify
   *
   * Notify @kn such that poll(2) on @kn wakes up.  Maybe be called from any
   * context.
   */
  void kernfs_notify(struct kernfs_node *kn)
  {
  	static DECLARE_WORK(kernfs_notify_work, kernfs_notify_workfn);
  	unsigned long flags;
  
  	if (WARN_ON(kernfs_type(kn) != KERNFS_FILE))
  		return;
  
  	spin_lock_irqsave(&kernfs_notify_lock, flags);
  	if (!kn->attr.notify_next) {
  		kernfs_get(kn);
  		kn->attr.notify_next = kernfs_notify_list;
  		kernfs_notify_list = kn;
  		schedule_work(&kernfs_notify_work);
  	}
  	spin_unlock_irqrestore(&kernfs_notify_lock, flags);
  }
  EXPORT_SYMBOL_GPL(kernfs_notify);
  
  const struct file_operations kernfs_file_fops = {
  	.read		= kernfs_fop_read,
  	.write		= kernfs_fop_write,
  	.llseek		= generic_file_llseek,
  	.mmap		= kernfs_fop_mmap,
  	.open		= kernfs_fop_open,
  	.release	= kernfs_fop_release,
  	.poll		= kernfs_fop_poll,
  	.fsync		= noop_fsync,
  };
  
  /**
   * __kernfs_create_file - kernfs internal function to create a file
   * @parent: directory to create the file in
   * @name: name of the file
   * @mode: mode of the file
   * @size: size of the file
   * @ops: kernfs operations for the file
   * @priv: private data for the file
   * @ns: optional namespace tag of the file
   * @key: lockdep key for the file's active_ref, %NULL to disable lockdep
   *
   * Returns the created node on success, ERR_PTR() value on error.
   */
  struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
  					 const char *name,
  					 umode_t mode, loff_t size,
  					 const struct kernfs_ops *ops,
  					 void *priv, const void *ns,
  					 struct lock_class_key *key)
  {
  	struct kernfs_node *kn;
  	unsigned flags;
  	int rc;
  
  	flags = KERNFS_FILE;
  
  	kn = kernfs_new_node(parent, name, (mode & S_IALLUGO) | S_IFREG, flags);
  	if (!kn)
  		return ERR_PTR(-ENOMEM);
  
  	kn->attr.ops = ops;
  	kn->attr.size = size;
  	kn->ns = ns;
  	kn->priv = priv;
  
  #ifdef CONFIG_DEBUG_LOCK_ALLOC
  	if (key) {
  		lockdep_init_map(&kn->dep_map, "s_active", key, 0);
  		kn->flags |= KERNFS_LOCKDEP;
  	}
  #endif
  
  	/*
  	 * kn->attr.ops is accesible only while holding active ref.  We
  	 * need to know whether some ops are implemented outside active
  	 * ref.  Cache their existence in flags.
  	 */
  	if (ops->seq_show)
  		kn->flags |= KERNFS_HAS_SEQ_SHOW;
  	if (ops->mmap)
  		kn->flags |= KERNFS_HAS_MMAP;
  	if (ops->release)
  		kn->flags |= KERNFS_HAS_RELEASE;
  
  	rc = kernfs_add_one(kn);
  	if (rc) {
  		kernfs_put(kn);
  		return ERR_PTR(rc);
  	}
  	return kn;
  }
  