1 files changed, 1020 insertions, 0 deletions

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
new file mode 100644
index 000000000..c75719312
--- /dev/null
+++ b/fs/kernfs/file.c
@@ -0,0 +1,1020 @@
+// 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"
+
+/*
+ * 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_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->kn->attr.open->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 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.
+         */
+        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 = 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_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 = inode->i_private;
+        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 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_node *kn = kernfs_dentry_node(of->file->f_path.dentry);
+        struct kernfs_open_node *on = kn->attr.open;
+
+        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;
+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 fsnotify */
+        mutex_lock(&kernfs_mutex);
+
+        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);
+        }
+
+        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;
+        struct kernfs_open_node *on;
+
+        if (WARN_ON(kernfs_type(kn) != KERNFS_FILE))
+                return;
+
+        /* kick poll immediately */
+        spin_lock_irqsave(&kernfs_open_node_lock, flags);
+        on = kn->attr.open;
+        if (on) {
+                atomic_inc(&on->event);
+                wake_up_interruptible(&on->poll);
+        }
+        spin_unlock_irqrestore(&kernfs_open_node_lock, flags);
+
+        /* 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 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;
+}