[Qemu-devel] [Bug 1070762] [NEW] savevm fails with inserted CD, "Device '%s' is writable but does not support snapshots."

[Oliver Francke]

Public bug reported:

Hi,

yesterday unfortunately a customer reported a failed snapshot of his VM.
Going through the logfile I discovered:

"Device 'ide1-cd0' is writable but does not support snapshots"

this is with qemu-1.2.0 and 1.0.1 at least...

Why writeable?
Even if I specify "-drive ...,readonly=on,snapshot=off" to qemu the 
monitor-command sees the CD-ROM-device as being writeable?!

Somewhere I saw a "hint" for blockdev.c:
=== snip ===

--- /tmp/blockdev.c     2012-10-24 11:37:10.000000000 +0200
+++ blockdev.c  2012-10-24 11:37:17.000000000 +0200
@@ -551,6 +551,7 @@
     case IF_XEN:
     case IF_NONE:
         dinfo->media_cd = media == MEDIA_CDROM;
+       dinfo->bdrv->read_only = 1;
         break;
     case IF_SD:
     case IF_FLOPPY:

=== snap ===

after installing with this small patch applied it works, so insert CD, savevm 
<somename> succeeds.
This should be fixed at all correct places, and the tags 
"readonly=on,snapshot=off" should do it, too. Or even just work after 
specifying a drive being a CD-rom should do the trick ;-)

Another "bad habit" is, that the ISO/DVD-file has to be writeable to be
changed?

Thnx for attention and regards,

Oliver.

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1070762

Title:
  savevm fails with inserted CD, "Device '%s' is writable but does not
  support  snapshots."

Status in QEMU:
  New

Bug description:
  Hi,

  yesterday unfortunately a customer reported a failed snapshot of his
  VM. Going through the logfile I discovered:

  "Device 'ide1-cd0' is writable but does not support snapshots"

  this is with qemu-1.2.0 and 1.0.1 at least...

  Why writeable?
  Even if I specify "-drive ...,readonly=on,snapshot=off" to qemu the 
monitor-command sees the CD-ROM-device as being writeable?!

  Somewhere I saw a "hint" for blockdev.c:
  === snip ===

  --- /tmp/blockdev.c   2012-10-24 11:37:10.000000000 +0200
  +++ blockdev.c        2012-10-24 11:37:17.000000000 +0200
  @@ -551,6 +551,7 @@
       case IF_XEN:
       case IF_NONE:
           dinfo->media_cd = media == MEDIA_CDROM;
  +     dinfo->bdrv->read_only = 1;
           break;
       case IF_SD:
       case IF_FLOPPY:

  === snap ===

  after installing with this small patch applied it works, so insert CD, savevm 
<somename> succeeds.
  This should be fixed at all correct places, and the tags 
"readonly=on,snapshot=off" should do it, too. Or even just work after 
specifying a drive being a CD-rom should do the trick ;-)

  Another "bad habit" is, that the ISO/DVD-file has to be writeable to
  be changed?

  Thnx for attention and regards,

  Oliver.

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