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Re: [Qemu-devel] CD-ROM bug round-up

From: Markus Armbruster
Subject: Re: [Qemu-devel] CD-ROM bug round-up
Date: Thu, 31 Mar 2011 11:56:53 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux)

Stefan Hajnoczi <address@hidden> writes:

> Several of us have been investigating CD-ROM bugs.  Let's update each
> other, make sure we're not duplicating effort, and see if we can help
> each other make progress.
> = Stefan =
> Guests do not notice media change when using Linux host CD-ROM
> pass-through for two reasons:
> 1. QEMU is caching the device size for removable media and never updating it.
> 2. On Linux hosts the /dev/cdrom file descriptor needs to be reopened
> to refresh the underlying device size.
> Patches have been posted to qemu-devel.
> Libvirt does not recognize eject failure due to locked tray.  This
> causes libvirt to get out-of-sync and believe the medium was
> successfully changed.  A libvirt fix is in progress:
> https://bugzilla.redhat.com/show_bug.cgi?id=689101
> = Anthony =
> Using 'change' or scripted commands without a delay between closing
> the BlockDriverState and opening the new CD-ROM.  The guest does not
> have a chance to poll the drive and determine a medium present ->
> medium not present transition followed by a medium not present ->
> medium present transition.
> A fix for this does not exist yet and might be tricky since we need to
> delay or wait for the guest to poll once before opening the new
> = Amit =
> Found that 2.6.38 and later guest kernels fail to report media change.
>  The new in-kernel media change polling framework issues ATAPI
> commands which are not implemented in hw/ide/core.c.
> = Juan =
> ATA HSM violation errors after live migration while CD-ROM read
> operations.  This is probably a hw/ide/* or DMA migration bug.

Note Amit's bug also triggers ATA HSM errors.  Might be related.

> = Markus =
> ?

I've wrestled with a few issues:

* udev choked on unimplemented GPCMD_READ_DISC_INFO.  udev maintainer
  fixed the bad error recovery.

* Lika Amit and Juan, I ran into the ATA HSM errors after media change.

* anaconda sometimes fails to recognize an install disk after the media
  check or a media change.  Could be related to media change bugs /
  unimplemented commands.

* Need to wrap this up:

  Subject: [RFC PATCH] block: Fix eject -f for locked devices
  Date: Fri, 18 Feb 2011 16:16:07 +0100
  Message-ID: <address@hidden>

A common theme seems to be the incomplete emulation.  I figure we should
make an effort to implement the mandatory parts of the relevant specs.
Guest software can't be expected to handle missing mandatory features

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