On Tue, Oct 20, 2015 at 4:53 AM, Joachim Backes <joachim.backes@rhrk.uni-kl.de> wrote:
2. sudo mount /dev/sr0 /mnt
then the CD will be inserted, but immeditaly after it inserted, an error message appears:
mount: no medium found on /dev/sr0

https://github.com/torvalds/linux/blob/master/drivers/cdrom/cdrom.c

When you try to mount the drive, "open_for_data" is called.  If the tray is open, the kernel will try to close it.  It will then check to see if there is a disc in the drive.  What happens at that point varies from drive to drive.  Most drive, I believe, and certainly the ones I have access to, will not respond to the status request until they finish checking for media.  On those drives, a single mount command will succeed.  If your drive responds to the status request before it finishes scanning for media, then the mount command will fail.  It's not a kernel bug, it's your drive.

You can work around that by calling "eject -t <device>" before mounting the drive.  You might also need a delay after calling that command, since your drive seems to respond before it finishes scanning for media.