块设备节点上的ctime和mtime是什么意思

Question

我有一个大容量存储设备，有时它的时间戳会更新：

$ stat /dev/sda
  File: ‘/dev/sda’
  Size: 0           Blocks: 0          IO Block: 4096   block special file
Device: 6h/6d   Inode: 21920486    Links: 1     Device type: 8,0
Access: (0660/brw-rw----)  Uid: (    0/    root)   Gid: (    6/    disk)
Access: 2017-01-30 14:46:01.843548633 +0200
Modify: 2017-01-30 14:46:01.843548633 +0200
Change: 2017-01-30 14:46:01.843548633 +0200
 Birth: -

$ stat /dev/sda
  File: ‘/dev/sda’
  Size: 0           Blocks: 0          IO Block: 4096   block special file
Device: 6h/6d   Inode: 21920486    Links: 1     Device type: 8,0
Access: (0660/brw-rw----)  Uid: (    0/    root)   Gid: (    6/    disk)
Access: 2017-01-30 14:47:33.412878263 +0200
Modify: 2017-01-30 14:47:33.412878263 +0200
Change: 2017-01-30 14:47:33.412878263 +0200
 Birth: -

更新这些的内核和/或 SD 驱动程序的逻辑是什么？我只是不知道在哪里查看内核源代码。