sysfs: error handling in sysfs, fill_read_buffer()

if a driver returns an error in fill_read_buffer(), the buffer will be
marked as filled. Subsequent reads will return eof. But there is
no data because of an error, not because it has been read.
Not marking the buffer filled is the obvious fix.
Signed-off-by: Oliver Neukum <oliver@neukum.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

fs/sysfs/file.c

@@ -83,7 +83,8 @@ remove_from_collection(struct sysfs_buffer *buffer, struct inode *node)
  *	Allocate @buffer->page, if it hasn't been already, then call the
  *	kobject's show() method to fill the buffer with this attribute's 
  *	data. 
- *	This is called only once, on the file's first read. 
+ *	This is called only once, on the file's first read unless an error
+ *	is returned.
  */
 static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer)
 {
@@ -101,12 +102,13 @@ static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer
 
 	buffer->event = atomic_read(&sd->s_event);
 	count = ops->show(kobj,attr,buffer->page);
-	buffer->needs_read_fill = 0;
 	BUG_ON(count > (ssize_t)PAGE_SIZE);
-	if (count >= 0)
+	if (count >= 0) {
+		buffer->needs_read_fill = 0;
 		buffer->count = count;
-	else
+	} else {
 		ret = count;
+	}
 	return ret;
 }