Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1078 insertions, 0 deletions

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
new file mode 100644
index 000000000..9ab6c92e0
--- /dev/null
+++ b/fs/kernfs/file.c
@@ -0,0 +1,1078 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * 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>
+ */
+
+#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 <linux/uio.h>
+
+#include "kernfs-internal.h"
+
+struct kernfs_open_node {
+	struct rcu_head		rcu_head;
+	atomic_t		event;
+	wait_queue_head_t	poll;
+	struct list_head	files; /* goes through kernfs_open_file.list */
+	unsigned int		nr_mmapped;
+	unsigned int		nr_to_release;
+};
+
+/*
+ * 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 inline struct mutex *kernfs_open_file_mutex_ptr(struct kernfs_node *kn)
+{
+	int idx = hash_ptr(kn, NR_KERNFS_LOCK_BITS);
+
+	return &kernfs_locks->open_file_mutex[idx];
+}
+
+static inline struct mutex *kernfs_open_file_mutex_lock(struct kernfs_node *kn)
+{
+	struct mutex *lock;
+
+	lock = kernfs_open_file_mutex_ptr(kn);
+
+	mutex_lock(lock);
+
+	return lock;
+}
+
+/**
+ * of_on - Return the kernfs_open_node of the specified kernfs_open_file
+ * @of: taret kernfs_open_file
+ */
+static struct kernfs_open_node *of_on(struct kernfs_open_file *of)
+{
+	return rcu_dereference_protected(of->kn->attr.open,
+					 !list_empty(&of->list));
+}
+
+/**
+ * kernfs_deref_open_node_locked - Get kernfs_open_node corresponding to @kn
+ *
+ * @kn: target kernfs_node.
+ *
+ * Fetch and return ->attr.open of @kn when caller holds the
+ * kernfs_open_file_mutex_ptr(kn).
+ *
+ * Update of ->attr.open happens under kernfs_open_file_mutex_ptr(kn). So when
+ * the caller guarantees that this mutex is being held, other updaters can't
+ * change ->attr.open and this means that we can safely deref ->attr.open
+ * outside RCU read-side critical section.
+ *
+ * The caller needs to make sure that kernfs_open_file_mutex is held.
+ */
+static struct kernfs_open_node *
+kernfs_deref_open_node_locked(struct kernfs_node *kn)
+{
+	return rcu_dereference_protected(kn->attr.open,
+				lockdep_is_held(kernfs_open_file_mutex_ptr(kn)));
+}
+
+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;
+	}
+	return single_start(sf, 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_on(of)->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_read_iter(struct kiocb *iocb, struct iov_iter *iter)
+{
+	struct kernfs_open_file *of = kernfs_of(iocb->ki_filp);
+	ssize_t len = min_t(size_t, iov_iter_count(iter), 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_on(of)->event);
+
+	ops = kernfs_ops(of->kn);
+	if (ops->read)
+		len = ops->read(of, buf, len, iocb->ki_pos);
+	else
+		len = -EINVAL;
+
+	kernfs_put_active(of->kn);
+	mutex_unlock(&of->mutex);
+
+	if (len < 0)
+		goto out_free;
+
+	if (copy_to_iter(buf, len, iter) != len) {
+		len = -EFAULT;
+		goto out_free;
+	}
+
+	iocb->ki_pos += len;
+
+ out_free:
+	if (buf == of->prealloc_buf)
+		mutex_unlock(&of->prealloc_mutex);
+	else
+		kfree(buf);
+	return len;
+}
+
+static ssize_t kernfs_fop_read_iter(struct kiocb *iocb, struct iov_iter *iter)
+{
+	if (kernfs_of(iocb->ki_filp)->kn->flags & KERNFS_HAS_SEQ_SHOW)
+		return seq_read_iter(iocb, iter);
+	return kernfs_file_read_iter(iocb, iter);
+}
+
+/*
+ * 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 value you're changing, then write entire buffer
+ * back.
+ */
+static ssize_t kernfs_fop_write_iter(struct kiocb *iocb, struct iov_iter *iter)
+{
+	struct kernfs_open_file *of = kernfs_of(iocb->ki_filp);
+	ssize_t len = iov_iter_count(iter);
+	const struct kernfs_ops *ops;
+	char *buf;
+
+	if (of->atomic_write_len) {
+		if (len > of->atomic_write_len)
+			return -E2BIG;
+	} else {
+		len = min_t(size_t, len, 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_iter(buf, len, iter) != 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, iocb->ki_pos);
+	else
+		len = -EINVAL;
+
+	kernfs_put_active(of->kn);
+	mutex_unlock(&of->mutex);
+
+	if (len > 0)
+		iocb->ki_pos += 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 vm_fault_t kernfs_vma_fault(struct vm_fault *vmf)
+{
+	struct file *file = vmf->vma->vm_file;
+	struct kernfs_open_file *of = kernfs_of(file);
+	vm_fault_t 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 vm_fault_t kernfs_vma_page_mkwrite(struct vm_fault *vmf)
+{
+	struct file *file = vmf->vma->vm_file;
+	struct kernfs_open_file *of = kernfs_of(file);
+	vm_fault_t 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.
+	 */
+	if (vma->vm_ops && vma->vm_ops->close)
+		goto out_put;
+
+	rc = 0;
+	of->mmapped = true;
+	of_on(of)->nr_mmapped++;
+	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;
+	struct mutex *mutex;
+
+	mutex = kernfs_open_file_mutex_lock(kn);
+	on = kernfs_deref_open_node_locked(kn);
+
+	if (!on) {
+		/* not there, initialize a new one */
+		on = kzalloc(sizeof(*on), GFP_KERNEL);
+		if (!on) {
+			mutex_unlock(mutex);
+			return -ENOMEM;
+		}
+		atomic_set(&on->event, 1);
+		init_waitqueue_head(&on->poll);
+		INIT_LIST_HEAD(&on->files);
+		rcu_assign_pointer(kn->attr.open, on);
+	}
+
+	list_add_tail(&of->list, &on->files);
+	if (kn->flags & KERNFS_HAS_RELEASE)
+		on->nr_to_release++;
+
+	mutex_unlock(mutex);
+	return 0;
+}
+
+/**
+ *	kernfs_unlink_open_file - Unlink @of from @kn.
+ *
+ *	@kn: target kernfs_node
+ *	@of: associated kernfs_open_file
+ *	@open_failed: ->open() failed, cancel ->release()
+ *
+ *	Unlink @of from list of @kn's associated open files. If list of
+ *	associated open files becomes empty, disassociate and free
+ *	kernfs_open_node.
+ *
+ *	LOCKING:
+ *	None.
+ */
+static void kernfs_unlink_open_file(struct kernfs_node *kn,
+				    struct kernfs_open_file *of,
+				    bool open_failed)
+{
+	struct kernfs_open_node *on;
+	struct mutex *mutex;
+
+	mutex = kernfs_open_file_mutex_lock(kn);
+
+	on = kernfs_deref_open_node_locked(kn);
+	if (!on) {
+		mutex_unlock(mutex);
+		return;
+	}
+
+	if (of) {
+		if (kn->flags & KERNFS_HAS_RELEASE) {
+			WARN_ON_ONCE(of->released == open_failed);
+			if (open_failed)
+				on->nr_to_release--;
+		}
+		if (of->mmapped)
+			on->nr_mmapped--;
+		list_del(&of->list);
+	}
+
+	if (list_empty(&on->files)) {
+		rcu_assign_pointer(kn->attr.open, NULL);
+		kfree_rcu(on, rcu_head);
+	}
+
+	mutex_unlock(mutex);
+}
+
+static int kernfs_fop_open(struct inode *inode, struct file *file)
+{
+	struct kernfs_node *kn = inode->i_private;
+	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_lock - mmap nests @of->mutex under mm->mmap_lock and
+	 * reading /sys/block/sda/trace/act_mask grabs sr_mutex, under
+	 * which mm->mmap_lock 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_iter() 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_unlink_open_file(kn, of, true);
+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_ptr(kn) 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_ptr(kn));
+
+	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;
+		of_on(of)->nr_to_release--;
+	}
+}
+
+static int kernfs_fop_release(struct inode *inode, struct file *filp)
+{
+	struct kernfs_node *kn = inode->i_private;
+	struct kernfs_open_file *of = kernfs_of(filp);
+
+	if (kn->flags & KERNFS_HAS_RELEASE) {
+		struct mutex *mutex;
+
+		mutex = kernfs_open_file_mutex_lock(kn);
+		kernfs_release_file(kn, of);
+		mutex_unlock(mutex);
+	}
+
+	kernfs_unlink_open_file(kn, of, false);
+	seq_release(inode, filp);
+	kfree(of->prealloc_buf);
+	kfree(of);
+
+	return 0;
+}
+
+bool kernfs_should_drain_open_files(struct kernfs_node *kn)
+{
+	struct kernfs_open_node *on;
+	bool ret;
+
+	/*
+	 * @kn being deactivated guarantees that @kn->attr.open can't change
+	 * beneath us making the lockless test below safe.
+	 */
+	WARN_ON_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS);
+
+	rcu_read_lock();
+	on = rcu_dereference(kn->attr.open);
+	ret = on && (on->nr_mmapped || on->nr_to_release);
+	rcu_read_unlock();
+
+	return ret;
+}
+
+void kernfs_drain_open_files(struct kernfs_node *kn)
+{
+	struct kernfs_open_node *on;
+	struct kernfs_open_file *of;
+	struct mutex *mutex;
+
+	mutex = kernfs_open_file_mutex_lock(kn);
+	on = kernfs_deref_open_node_locked(kn);
+	if (!on) {
+		mutex_unlock(mutex);
+		return;
+	}
+
+	list_for_each_entry(of, &on->files, list) {
+		struct inode *inode = file_inode(of->file);
+
+		if (of->mmapped) {
+			unmap_mapping_range(inode->i_mapping, 0, 0, 1);
+			of->mmapped = false;
+			on->nr_mmapped--;
+		}
+
+		if (kn->flags & KERNFS_HAS_RELEASE)
+			kernfs_release_file(kn, of);
+	}
+
+	WARN_ON_ONCE(on->nr_mmapped || on->nr_to_release);
+	mutex_unlock(mutex);
+}
+
+/*
+ * 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 EPOLLERR|EPOLLPRI, 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.
+ */
+__poll_t kernfs_generic_poll(struct kernfs_open_file *of, poll_table *wait)
+{
+	struct kernfs_open_node *on = of_on(of);
+
+	poll_wait(of->file, &on->poll, wait);
+
+	if (of->event != atomic_read(&on->event))
+		return DEFAULT_POLLMASK|EPOLLERR|EPOLLPRI;
+
+	return DEFAULT_POLLMASK;
+}
+
+static __poll_t kernfs_fop_poll(struct file *filp, poll_table *wait)
+{
+	struct kernfs_open_file *of = kernfs_of(filp);
+	struct kernfs_node *kn = kernfs_dentry_node(filp->f_path.dentry);
+	__poll_t ret;
+
+	if (!kernfs_get_active(kn))
+		return DEFAULT_POLLMASK|EPOLLERR|EPOLLPRI;
+
+	if (kn->attr.ops->poll)
+		ret = kn->attr.ops->poll(of, wait);
+	else
+		ret = kernfs_generic_poll(of, wait);
+
+	kernfs_put_active(kn);
+	return ret;
+}
+
+static void kernfs_notify_workfn(struct work_struct *work)
+{
+	struct kernfs_node *kn;
+	struct kernfs_super_info *info;
+	struct kernfs_root *root;
+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);
+
+	root = kernfs_root(kn);
+	/* kick fsnotify */
+	down_write(&root->kernfs_rwsem);
+
+	list_for_each_entry(info, &kernfs_root(kn)->supers, node) {
+		struct kernfs_node *parent;
+		struct inode *p_inode = NULL;
+		struct inode *inode;
+		struct qstr name;
+
+		/*
+		 * 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, kernfs_ino(kn));
+		if (!inode)
+			continue;
+
+		name = (struct qstr)QSTR_INIT(kn->name, strlen(kn->name));
+		parent = kernfs_get_parent(kn);
+		if (parent) {
+			p_inode = ilookup(info->sb, kernfs_ino(parent));
+			if (p_inode) {
+				fsnotify(FS_MODIFY | FS_EVENT_ON_CHILD,
+					 inode, FSNOTIFY_EVENT_INODE,
+					 p_inode, &name, inode, 0);
+				iput(p_inode);
+			}
+
+			kernfs_put(parent);
+		}
+
+		if (!p_inode)
+			fsnotify_inode(inode, FS_MODIFY);
+
+		iput(inode);
+	}
+
+	up_write(&root->kernfs_rwsem);
+	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;
+	struct kernfs_open_node *on;
+
+	if (WARN_ON(kernfs_type(kn) != KERNFS_FILE))
+		return;
+
+	/* kick poll immediately */
+	rcu_read_lock();
+	on = rcu_dereference(kn->attr.open);
+	if (on) {
+		atomic_inc(&on->event);
+		wake_up_interruptible(&on->poll);
+	}
+	rcu_read_unlock();
+
+	/* schedule work to kick fsnotify */
+	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_iter	= kernfs_fop_read_iter,
+	.write_iter	= kernfs_fop_write_iter,
+	.llseek		= generic_file_llseek,
+	.mmap		= kernfs_fop_mmap,
+	.open		= kernfs_fop_open,
+	.release	= kernfs_fop_release,
+	.poll		= kernfs_fop_poll,
+	.fsync		= noop_fsync,
+	.splice_read	= generic_file_splice_read,
+	.splice_write	= iter_file_splice_write,
+};
+
+/**
+ * __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
+ * @uid: uid of the file
+ * @gid: gid 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, kuid_t uid, kgid_t gid,
+					 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,
+			     uid, gid, 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, "kn->active", key, 0);
+		kn->flags |= KERNFS_LOCKDEP;
+	}
+#endif
+
+	/*
+	 * kn->attr.ops is accessible 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;
+}