1 files changed, 40 insertions, 0 deletions

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index f21e73d10724..d1995e2d6c94 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -167,6 +167,18 @@ static int sysfs_kf_bin_mmap(struct kernfs_open_file *of,
 	return battr->mmap(of->file, kobj, battr, vma);
 }
 
+static loff_t sysfs_kf_bin_llseek(struct kernfs_open_file *of, loff_t offset,
+				  int whence)
+{
+	struct bin_attribute *battr = of->kn->priv;
+	struct kobject *kobj = of->kn->parent->priv;
+
+	if (battr->llseek)
+		return battr->llseek(of->file, kobj, battr, offset, whence);
+	else
+		return generic_file_llseek(of->file, offset, whence);
+}
+
 static int sysfs_kf_bin_open(struct kernfs_open_file *of)
 {
 	struct bin_attribute *battr = of->kn->priv;
@@ -249,6 +261,7 @@ static const struct kernfs_ops sysfs_bin_kfops_mmap = {
 	.write		= sysfs_kf_bin_write,
 	.mmap		= sysfs_kf_bin_mmap,
 	.open		= sysfs_kf_bin_open,
+	.llseek		= sysfs_kf_bin_llseek,
 };
 
 int sysfs_add_file_mode_ns(struct kernfs_node *parent,
@@ -772,3 +785,30 @@ int sysfs_emit_at(char *buf, int at, const char *fmt, ...)
 	return len;
 }
 EXPORT_SYMBOL_GPL(sysfs_emit_at);
+
+/**
+ *	sysfs_bin_attr_simple_read - read callback to simply copy from memory.
+ *	@file:	attribute file which is being read.
+ *	@kobj:	object to which the attribute belongs.
+ *	@attr:	attribute descriptor.
+ *	@buf:	destination buffer.
+ *	@off:	offset in bytes from which to read.
+ *	@count:	maximum number of bytes to read.
+ *
+ * Simple ->read() callback for bin_attributes backed by a buffer in memory.
+ * The @private and @size members in struct bin_attribute must be set to the
+ * buffer's location and size before the bin_attribute is created in sysfs.
+ *
+ * Bounds check for @off and @count is done in sysfs_kf_bin_read().
+ * Negative value check for @off is done in vfs_setpos() and default_llseek().
+ *
+ * Returns number of bytes written to @buf.
+ */
+ssize_t sysfs_bin_attr_simple_read(struct file *file, struct kobject *kobj,
+				   struct bin_attribute *attr, char *buf,
+				   loff_t off, size_t count)
+{
+	memcpy(buf, attr->private + off, count);
+	return count;
+}
+EXPORT_SYMBOL_GPL(sysfs_bin_attr_simple_read);