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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0
 /*
  * fs/sysfs/file.c - sysfs regular (text) file implementation
  *
  * Copyright (c) 2001-3 Patrick Mochel
  * Copyright (c) 2007 SUSE Linux Products GmbH
  * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
  *
  * Please see Documentation/filesystems/sysfs.rst for more information.
  */
 
 #include <linux/module.h>
 #include <linux/kobject.h>
 #include <linux/slab.h>
 #include <linux/list.h>
 #include <linux/mutex.h>
 #include <linux/seq_file.h>
 #include <linux/mm.h>
 
 #include "sysfs.h"
 
 /*
  * Determine ktype->sysfs_ops for the given kernfs_node.  This function
  * must be called while holding an active reference.
  */
 static const struct sysfs_ops *sysfs_file_ops(struct kernfs_node *kn)
 {
     struct kobject *kobj = kn->parent->priv;
 
     if (kn->flags & KERNFS_LOCKDEP)
         lockdep_assert_held(kn);
     return kobj->ktype ? kobj->ktype->sysfs_ops : NULL;
 }
 
 /*
  * Reads on sysfs are handled through seq_file, which takes care of hairy
  * details like buffering and seeking.  The following function pipes
  * sysfs_ops->show() result through seq_file.
  */
 static int sysfs_kf_seq_show(struct seq_file *sf, void *v)
 {
     struct kernfs_open_file *of = sf->private;
     struct kobject *kobj = of->kn->parent->priv;
     const struct sysfs_ops *ops = sysfs_file_ops(of->kn);
     ssize_t count;
     char *buf;
 
     if (WARN_ON_ONCE(!ops->show))
         return -EINVAL;
 
     /* acquire buffer and ensure that it's >= PAGE_SIZE and clear */
     count = seq_get_buf(sf, &buf);
     if (count < PAGE_SIZE) {
         seq_commit(sf, -1);
         return 0;
     }
     memset(buf, 0, PAGE_SIZE);
 
     count = ops->show(kobj, of->kn->priv, buf);
     if (count < 0)
         return count;
 
     /*
      * The code works fine with PAGE_SIZE return but it's likely to
      * indicate truncated result or overflow in normal use cases.
      */
     if (count >= (ssize_t)PAGE_SIZE) {
         printk("fill_read_buffer: %pS returned bad count\n",
                 ops->show);
         /* Try to struggle along */
         count = PAGE_SIZE - 1;
     }
     seq_commit(sf, count);
     return 0;
 }
 
 static ssize_t sysfs_kf_bin_read(struct kernfs_open_file *of, char *buf,
                  size_t count, loff_t pos)
 {
     struct bin_attribute *battr = of->kn->priv;
     struct kobject *kobj = of->kn->parent->priv;
     loff_t size = file_inode(of->file)->i_size;
 
     if (!count)
         return 0;
 
     if (size) {
         if (pos >= size)
             return 0;
         if (pos + count > size)
             count = size - pos;
     }
 
     if (!battr->read)
         return -EIO;
 
     return battr->read(of->file, kobj, battr, buf, pos, count);
 }
 
 /* kernfs read callback for regular sysfs files with pre-alloc */
 static ssize_t sysfs_kf_read(struct kernfs_open_file *of, char *buf,
                  size_t count, loff_t pos)
 {
     const struct sysfs_ops *ops = sysfs_file_ops(of->kn);
     struct kobject *kobj = of->kn->parent->priv;
     ssize_t len;
 
     /*
      * If buf != of->prealloc_buf, we don't know how
      * large it is, so cannot safely pass it to ->show
      */
     if (WARN_ON_ONCE(buf != of->prealloc_buf))
         return 0;
     len = ops->show(kobj, of->kn->priv, buf);
     if (len < 0)
         return len;
     if (pos) {
         if (len <= pos)
             return 0;
         len -= pos;
         memmove(buf, buf + pos, len);
     }
     return min_t(ssize_t, count, len);
 }
 
 /* kernfs write callback for regular sysfs files */
 static ssize_t sysfs_kf_write(struct kernfs_open_file *of, char *buf,
                   size_t count, loff_t pos)
 {
     const struct sysfs_ops *ops = sysfs_file_ops(of->kn);
     struct kobject *kobj = of->kn->parent->priv;
 
     if (!count)
         return 0;
 
     return ops->store(kobj, of->kn->priv, buf, count);
 }
 
 /* kernfs write callback for bin sysfs files */
 static ssize_t sysfs_kf_bin_write(struct kernfs_open_file *of, char *buf,
                   size_t count, loff_t pos)
 {
     struct bin_attribute *battr = of->kn->priv;
     struct kobject *kobj = of->kn->parent->priv;
     loff_t size = file_inode(of->file)->i_size;
 
     if (size) {
         if (size <= pos)
             return -EFBIG;
         count = min_t(ssize_t, count, size - pos);
     }
     if (!count)
         return 0;
 
     if (!battr->write)
         return -EIO;
 
     return battr->write(of->file, kobj, battr, buf, pos, count);
 }
 
 static int sysfs_kf_bin_mmap(struct kernfs_open_file *of,
                  struct vm_area_struct *vma)
 {
     struct bin_attribute *battr = of->kn->priv;
     struct kobject *kobj = of->kn->parent->priv;
 
     return battr->mmap(of->file, kobj, battr, vma);
 }
 
 static int sysfs_kf_bin_open(struct kernfs_open_file *of)
 {
     struct bin_attribute *battr = of->kn->priv;
 
     if (battr->f_mapping)
         of->file->f_mapping = battr->f_mapping();
 
     return 0;
 }
 
 void sysfs_notify(struct kobject *kobj, const char *dir, const char *attr)
 {
     struct kernfs_node *kn = kobj->sd, *tmp;
 
     if (kn && dir)
         kn = kernfs_find_and_get(kn, dir);
     else
         kernfs_get(kn);
 
     if (kn && attr) {
         tmp = kernfs_find_and_get(kn, attr);
         kernfs_put(kn);
         kn = tmp;
     }
 
     if (kn) {
         kernfs_notify(kn);
         kernfs_put(kn);
     }
 }
 EXPORT_SYMBOL_GPL(sysfs_notify);
 
 static const struct kernfs_ops sysfs_file_kfops_empty = {
 };
 
 static const struct kernfs_ops sysfs_file_kfops_ro = {
     .seq_show   = sysfs_kf_seq_show,
 };
 
 static const struct kernfs_ops sysfs_file_kfops_wo = {
     .write      = sysfs_kf_write,
 };
 
 static const struct kernfs_ops sysfs_file_kfops_rw = {
     .seq_show   = sysfs_kf_seq_show,
     .write      = sysfs_kf_write,
 };
 
 static const struct kernfs_ops sysfs_prealloc_kfops_ro = {
     .read       = sysfs_kf_read,
     .prealloc   = true,
 };
 
 static const struct kernfs_ops sysfs_prealloc_kfops_wo = {
     .write      = sysfs_kf_write,
     .prealloc   = true,
 };
 
 static const struct kernfs_ops sysfs_prealloc_kfops_rw = {
     .read       = sysfs_kf_read,
     .write      = sysfs_kf_write,
     .prealloc   = true,
 };
 
 static const struct kernfs_ops sysfs_bin_kfops_ro = {
     .read       = sysfs_kf_bin_read,
 };
 
 static const struct kernfs_ops sysfs_bin_kfops_wo = {
     .write      = sysfs_kf_bin_write,
 };
 
 static const struct kernfs_ops sysfs_bin_kfops_rw = {
     .read       = sysfs_kf_bin_read,
     .write      = sysfs_kf_bin_write,
 };
 
 static const struct kernfs_ops sysfs_bin_kfops_mmap = {
     .read       = sysfs_kf_bin_read,
     .write      = sysfs_kf_bin_write,
     .mmap       = sysfs_kf_bin_mmap,
     .open       = sysfs_kf_bin_open,
 };
 
 int sysfs_add_file_mode_ns(struct kernfs_node *parent,
         const struct attribute *attr, umode_t mode, kuid_t uid,
         kgid_t gid, const void *ns)
 {
     struct kobject *kobj = parent->priv;
     const struct sysfs_ops *sysfs_ops = kobj->ktype->sysfs_ops;
     struct lock_class_key *key = NULL;
     const struct kernfs_ops *ops = NULL;
     struct kernfs_node *kn;
 
     /* every kobject with an attribute needs a ktype assigned */
     if (WARN(!sysfs_ops, KERN_ERR
             "missing sysfs attribute operations for kobject: %s\n",
             kobject_name(kobj)))
         return -EINVAL;
 
     if (mode & SYSFS_PREALLOC) {
         if (sysfs_ops->show && sysfs_ops->store)
             ops = &sysfs_prealloc_kfops_rw;
         else if (sysfs_ops->show)
             ops = &sysfs_prealloc_kfops_ro;
         else if (sysfs_ops->store)
             ops = &sysfs_prealloc_kfops_wo;
     } else {
         if (sysfs_ops->show && sysfs_ops->store)
             ops = &sysfs_file_kfops_rw;
         else if (sysfs_ops->show)
             ops = &sysfs_file_kfops_ro;
         else if (sysfs_ops->store)
             ops = &sysfs_file_kfops_wo;
     }
 
     if (!ops)
         ops = &sysfs_file_kfops_empty;
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
     if (!attr->ignore_lockdep)
         key = attr->key ?: (struct lock_class_key *)&attr->skey;
 #endif
 
     kn = __kernfs_create_file(parent, attr->name, mode & 0777, uid, gid,
                   PAGE_SIZE, ops, (void *)attr, ns, key);
     if (IS_ERR(kn)) {
         if (PTR_ERR(kn) == -EEXIST)
             sysfs_warn_dup(parent, attr->name);
         return PTR_ERR(kn);
     }
     return 0;
 }
 
 int sysfs_add_bin_file_mode_ns(struct kernfs_node *parent,
         const struct bin_attribute *battr, umode_t mode,
         kuid_t uid, kgid_t gid, const void *ns)
 {
     const struct attribute *attr = &battr->attr;
     struct lock_class_key *key = NULL;
     const struct kernfs_ops *ops;
     struct kernfs_node *kn;
 
     if (battr->mmap)
         ops = &sysfs_bin_kfops_mmap;
     else if (battr->read && battr->write)
         ops = &sysfs_bin_kfops_rw;
     else if (battr->read)
         ops = &sysfs_bin_kfops_ro;
     else if (battr->write)
         ops = &sysfs_bin_kfops_wo;
     else
         ops = &sysfs_file_kfops_empty;
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
     if (!attr->ignore_lockdep)
         key = attr->key ?: (struct lock_class_key *)&attr->skey;
 #endif
 
     kn = __kernfs_create_file(parent, attr->name, mode & 0777, uid, gid,
                   battr->size, ops, (void *)attr, ns, key);
     if (IS_ERR(kn)) {
         if (PTR_ERR(kn) == -EEXIST)
             sysfs_warn_dup(parent, attr->name);
         return PTR_ERR(kn);
     }
     return 0;
 }
 
 /**
  * sysfs_create_file_ns - create an attribute file for an object with custom ns
  * @kobj: object we're creating for
  * @attr: attribute descriptor
  * @ns: namespace the new file should belong to
  */
 int sysfs_create_file_ns(struct kobject *kobj, const struct attribute *attr,
              const void *ns)
 {
     kuid_t uid;
     kgid_t gid;
 
     if (WARN_ON(!kobj || !kobj->sd || !attr))
         return -EINVAL;
 
     kobject_get_ownership(kobj, &uid, &gid);
     return sysfs_add_file_mode_ns(kobj->sd, attr, attr->mode, uid, gid, ns);
 }
 EXPORT_SYMBOL_GPL(sysfs_create_file_ns);
 
 int sysfs_create_files(struct kobject *kobj, const struct attribute * const *ptr)
 {
     int err = 0;
     int i;
 
     for (i = 0; ptr[i] && !err; i++)
         err = sysfs_create_file(kobj, ptr[i]);
     if (err)
         while (--i >= 0)
             sysfs_remove_file(kobj, ptr[i]);
     return err;
 }
 EXPORT_SYMBOL_GPL(sysfs_create_files);
 
 /**
  * sysfs_add_file_to_group - add an attribute file to a pre-existing group.
  * @kobj: object we're acting for.
  * @attr: attribute descriptor.
  * @group: group name.
  */
 int sysfs_add_file_to_group(struct kobject *kobj,
         const struct attribute *attr, const char *group)
 {
     struct kernfs_node *parent;
     kuid_t uid;
     kgid_t gid;
     int error;
 
     if (group) {
         parent = kernfs_find_and_get(kobj->sd, group);
     } else {
         parent = kobj->sd;
         kernfs_get(parent);
     }
 
     if (!parent)
         return -ENOENT;
 
     kobject_get_ownership(kobj, &uid, &gid);
     error = sysfs_add_file_mode_ns(parent, attr, attr->mode, uid, gid,
                        NULL);
     kernfs_put(parent);
 
     return error;
 }
 EXPORT_SYMBOL_GPL(sysfs_add_file_to_group);
 
 /**
  * sysfs_chmod_file - update the modified mode value on an object attribute.
  * @kobj: object we're acting for.
  * @attr: attribute descriptor.
  * @mode: file permissions.
  *
  */
 int sysfs_chmod_file(struct kobject *kobj, const struct attribute *attr,
              umode_t mode)
 {
     struct kernfs_node *kn;
     struct iattr newattrs;
     int rc;
 
     kn = kernfs_find_and_get(kobj->sd, attr->name);
     if (!kn)
         return -ENOENT;
 
     newattrs.ia_mode = (mode & S_IALLUGO) | (kn->mode & ~S_IALLUGO);
     newattrs.ia_valid = ATTR_MODE;
 
     rc = kernfs_setattr(kn, &newattrs);
 
     kernfs_put(kn);
     return rc;
 }
 EXPORT_SYMBOL_GPL(sysfs_chmod_file);
 
 /**
  * sysfs_break_active_protection - break "active" protection
  * @kobj: The kernel object @attr is associated with.
  * @attr: The attribute to break the "active" protection for.
  *
  * With sysfs, just like kernfs, deletion of an attribute is postponed until
  * all active .show() and .store() callbacks have finished unless this function
  * is called. Hence this function is useful in methods that implement self
  * deletion.
  */
 struct kernfs_node *sysfs_break_active_protection(struct kobject *kobj,
                           const struct attribute *attr)
 {
     struct kernfs_node *kn;
 
     kobject_get(kobj);
     kn = kernfs_find_and_get(kobj->sd, attr->name);
     if (kn)
         kernfs_break_active_protection(kn);
     return kn;
 }
 EXPORT_SYMBOL_GPL(sysfs_break_active_protection);
 
 /**
  * sysfs_unbreak_active_protection - restore "active" protection
  * @kn: Pointer returned by sysfs_break_active_protection().
  *
  * Undo the effects of sysfs_break_active_protection(). Since this function
  * calls kernfs_put() on the kernfs node that corresponds to the 'attr'
  * argument passed to sysfs_break_active_protection() that attribute may have
  * been removed between the sysfs_break_active_protection() and
  * sysfs_unbreak_active_protection() calls, it is not safe to access @kn after
  * this function has returned.
  */
 void sysfs_unbreak_active_protection(struct kernfs_node *kn)
 {
     struct kobject *kobj = kn->parent->priv;
 
     kernfs_unbreak_active_protection(kn);
     kernfs_put(kn);
     kobject_put(kobj);
 }
 EXPORT_SYMBOL_GPL(sysfs_unbreak_active_protection);
 
 /**
  * sysfs_remove_file_ns - remove an object attribute with a custom ns tag
  * @kobj: object we're acting for
  * @attr: attribute descriptor
  * @ns: namespace tag of the file to remove
  *
  * Hash the attribute name and namespace tag and kill the victim.
  */
 void sysfs_remove_file_ns(struct kobject *kobj, const struct attribute *attr,
               const void *ns)
 {
     struct kernfs_node *parent = kobj->sd;
 
     kernfs_remove_by_name_ns(parent, attr->name, ns);
 }
 EXPORT_SYMBOL_GPL(sysfs_remove_file_ns);
 
 /**
  * sysfs_remove_file_self - remove an object attribute from its own method
  * @kobj: object we're acting for
  * @attr: attribute descriptor
  *
  * See kernfs_remove_self() for details.
  */
 bool sysfs_remove_file_self(struct kobject *kobj, const struct attribute *attr)
 {
     struct kernfs_node *parent = kobj->sd;
     struct kernfs_node *kn;
     bool ret;
 
     kn = kernfs_find_and_get(parent, attr->name);
     if (WARN_ON_ONCE(!kn))
         return false;
 
     ret = kernfs_remove_self(kn);
 
     kernfs_put(kn);
     return ret;
 }
 EXPORT_SYMBOL_GPL(sysfs_remove_file_self);
 
 void sysfs_remove_files(struct kobject *kobj, const struct attribute * const *ptr)
 {
     int i;
 
     for (i = 0; ptr[i]; i++)
         sysfs_remove_file(kobj, ptr[i]);
 }
 EXPORT_SYMBOL_GPL(sysfs_remove_files);
 
 /**
  * sysfs_remove_file_from_group - remove an attribute file from a group.
  * @kobj: object we're acting for.
  * @attr: attribute descriptor.
  * @group: group name.
  */
 void sysfs_remove_file_from_group(struct kobject *kobj,
         const struct attribute *attr, const char *group)
 {
     struct kernfs_node *parent;
 
     if (group) {
         parent = kernfs_find_and_get(kobj->sd, group);
     } else {
         parent = kobj->sd;
         kernfs_get(parent);
     }
 
     if (parent) {
         kernfs_remove_by_name(parent, attr->name);
         kernfs_put(parent);
     }
 }
 EXPORT_SYMBOL_GPL(sysfs_remove_file_from_group);
 
 /**
  *  sysfs_create_bin_file - create binary file for object.
  *  @kobj:  object.
  *  @attr:  attribute descriptor.
  */
 int sysfs_create_bin_file(struct kobject *kobj,
               const struct bin_attribute *attr)
 {
     kuid_t uid;
     kgid_t gid;
 
     if (WARN_ON(!kobj || !kobj->sd || !attr))
         return -EINVAL;
 
     kobject_get_ownership(kobj, &uid, &gid);
     return sysfs_add_bin_file_mode_ns(kobj->sd, attr, attr->attr.mode, uid,
                        gid, NULL);
 }
 EXPORT_SYMBOL_GPL(sysfs_create_bin_file);
 
 /**
  *  sysfs_remove_bin_file - remove binary file for object.
  *  @kobj:  object.
  *  @attr:  attribute descriptor.
  */
 void sysfs_remove_bin_file(struct kobject *kobj,
                const struct bin_attribute *attr)
 {
     kernfs_remove_by_name(kobj->sd, attr->attr.name);
 }
 EXPORT_SYMBOL_GPL(sysfs_remove_bin_file);
 
 static int internal_change_owner(struct kernfs_node *kn, kuid_t kuid,
                  kgid_t kgid)
 {
     struct iattr newattrs = {
         .ia_valid = ATTR_UID | ATTR_GID,
         .ia_uid = kuid,
         .ia_gid = kgid,
     };
     return kernfs_setattr(kn, &newattrs);
 }
 
 /**
  *  sysfs_link_change_owner - change owner of a sysfs file.
  *  @kobj:  object of the kernfs_node the symlink is located in.
  *  @targ:  object of the kernfs_node the symlink points to.
  *  @name:  name of the link.
  *  @kuid:  new owner's kuid
  *  @kgid:  new owner's kgid
  *
  * This function looks up the sysfs symlink entry @name under @kobj and changes
  * the ownership to @kuid/@kgid. The symlink is looked up in the namespace of
  * @targ.
  *
  * Returns 0 on success or error code on failure.
  */
 int sysfs_link_change_owner(struct kobject *kobj, struct kobject *targ,
                 const char *name, kuid_t kuid, kgid_t kgid)
 {
     struct kernfs_node *kn = NULL;
     int error;
 
     if (!name || !kobj->state_in_sysfs || !targ->state_in_sysfs)
         return -EINVAL;
 
     error = -ENOENT;
     kn = kernfs_find_and_get_ns(kobj->sd, name, targ->sd->ns);
     if (!kn)
         goto out;
 
     error = -EINVAL;
     if (kernfs_type(kn) != KERNFS_LINK)
         goto out;
     if (kn->symlink.target_kn->priv != targ)
         goto out;
 
     error = internal_change_owner(kn, kuid, kgid);
 
 out:
     kernfs_put(kn);
     return error;
 }
 
 /**
  *  sysfs_file_change_owner - change owner of a sysfs file.
  *  @kobj:  object.
  *  @name:  name of the file to change.
  *  @kuid:  new owner's kuid
  *  @kgid:  new owner's kgid
  *
  * This function looks up the sysfs entry @name under @kobj and changes the
  * ownership to @kuid/@kgid.
  *
  * Returns 0 on success or error code on failure.
  */
 int sysfs_file_change_owner(struct kobject *kobj, const char *name, kuid_t kuid,
                 kgid_t kgid)
 {
     struct kernfs_node *kn;
     int error;
 
     if (!name)
         return -EINVAL;
 
     if (!kobj->state_in_sysfs)
         return -EINVAL;
 
     kn = kernfs_find_and_get(kobj->sd, name);
     if (!kn)
         return -ENOENT;
 
     error = internal_change_owner(kn, kuid, kgid);
 
     kernfs_put(kn);
 
     return error;
 }
 EXPORT_SYMBOL_GPL(sysfs_file_change_owner);
 
 /**
  *  sysfs_change_owner - change owner of the given object.
  *  @kobj:  object.
  *  @kuid:  new owner's kuid
  *  @kgid:  new owner's kgid
  *
  * Change the owner of the default directory, files, groups, and attributes of
  * @kobj to @kuid/@kgid. Note that sysfs_change_owner mirrors how the sysfs
  * entries for a kobject are added by driver core. In summary,
  * sysfs_change_owner() takes care of the default directory entry for @kobj,
  * the default attributes associated with the ktype of @kobj and the default
  * attributes associated with the ktype of @kobj.
  * Additional properties not added by driver core have to be changed by the
  * driver or subsystem which created them. This is similar to how
  * driver/subsystem specific entries are removed.
  *
  * Returns 0 on success or error code on failure.
  */
 int sysfs_change_owner(struct kobject *kobj, kuid_t kuid, kgid_t kgid)
 {
     int error;
     const struct kobj_type *ktype;
 
     if (!kobj->state_in_sysfs)
         return -EINVAL;
 
     /* Change the owner of the kobject itself. */
     error = internal_change_owner(kobj->sd, kuid, kgid);
     if (error)
         return error;
 
     ktype = get_ktype(kobj);
     if (ktype) {
         /*
          * Change owner of the default groups associated with the
          * ktype of @kobj.
          */
         error = sysfs_groups_change_owner(kobj, ktype->default_groups,
                           kuid, kgid);
         if (error)
             return error;
     }
 
     return 0;
 }
 EXPORT_SYMBOL_GPL(sysfs_change_owner);
 
 /**
  *  sysfs_emit - scnprintf equivalent, aware of PAGE_SIZE buffer.
  *  @buf:   start of PAGE_SIZE buffer.
  *  @fmt:   format
  *  @...:   optional arguments to @format
  *
  *
  * Returns number of characters written to @buf.
  */
 int sysfs_emit(char *buf, const char *fmt, ...)
 {
     va_list args;
     int len;
 
     if (WARN(!buf || offset_in_page(buf),
          "invalid sysfs_emit: buf:%p\n", buf))
         return 0;
 
     va_start(args, fmt);
     len = vscnprintf(buf, PAGE_SIZE, fmt, args);
     va_end(args);
 
     return len;
 }
 EXPORT_SYMBOL_GPL(sysfs_emit);
 
 /**
  *  sysfs_emit_at - scnprintf equivalent, aware of PAGE_SIZE buffer.
  *  @buf:   start of PAGE_SIZE buffer.
  *  @at:    offset in @buf to start write in bytes
  *      @at must be >= 0 && < PAGE_SIZE
  *  @fmt:   format
  *  @...:   optional arguments to @fmt
  *
  *
  * Returns number of characters written starting at &@buf[@at].
  */
 int sysfs_emit_at(char *buf, int at, const char *fmt, ...)
 {
     va_list args;
     int len;
 
     if (WARN(!buf || offset_in_page(buf) || at < 0 || at >= PAGE_SIZE,
          "invalid sysfs_emit_at: buf:%p at:%d\n", buf, at))
         return 0;
 
     va_start(args, fmt);
     len = vscnprintf(buf + at, PAGE_SIZE - at, fmt, args);
     va_end(args);
 
     return len;
 }
 EXPORT_SYMBOL_GPL(sysfs_emit_at);

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