Re: What pulls in the tray of my /dev/sr1 ?

["Thomas Schmitt" <scdbackup@gmx.net>]

Hi,

i stumbled over btrace(8) which lists the SCSI commands by
blktrace, blkparse, and /sys/kernel/debug.

The only traffic is every 2 seconds a 0x4A GET EVENT STATUS
NOTIFICATION command in "Polled" operational mode, and 
notification class request "Media". I did not find out yet
how to get to view the drive's replies.

 11,1    0        2     2.047952134     0  C   R (4a 01 00 00 10 00 00 00 08 00 ..) [0]
 11,1    1        4     2.047580736 19046  G   N [kworker/1:3]
 11,1    1        5     2.047582462 19046  I   R 8 (4a 01 00 00 10 00 00 00 08 00 ..) [kworker/1:3]
 11,1    1        6     2.047582648 19046  D   R 8 (4a 01 00 00 10 00 00 00 08 00 ..) [kworker/1:3]

(I wonder why C with the older timestamp is listed before
 G, I, and D.)

The other drives get the same treatment.
I tested that e.g. xorriso's SCSI commands are reported.

So either the drive really pulls in the tray on its own,
or it is annoyed by a hundred 0x4A commands and finally
wants to give the caller an answer.

https://lwn.net/Articles/423619/ and Michael Biebl's previous
proposal brought me to
  # cat /sys/block/sr1/events_poll_msecs 
  2000
  # echo 0 >/sys/block/sr1/events_poll_msecs
  # cat /sys/block/sr1/events_poll_msecs
  0
This silences the 0x4A commands.

But the drive tray still gets pulled in.
Shortly after, btrace reports

 11,1    1        0     0.000000000     0  m   N cfq20698S  / put_queue

A second experiment pulled in the tray without any
btrace message.


In summary there seems to be really no initiator in
the operating system for the tray movements.
Very astonishing.


Have a nice day :)

Thomas