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[Qemu-devel] [Bug 1716028] Re: qemu 2.10 locks images with no feature fl

From: ChristianEhrhardt
Subject: [Qemu-devel] [Bug 1716028] Re: qemu 2.10 locks images with no feature flag
Date: Thu, 04 Jan 2018 15:47:24 -0000

Libvirt will make this "easier" to be avoided by
commit 28907b0043fbf71085a798372ab9c816ba043b93
Author: Peter Krempa <address@hidden>
Date:   Wed Nov 15 15:21:14 2017 +0100

    qemu: command: Mark <shared/> disks as such in qemu
    Qemu has now an internal mechanism for locking images to fix specific
    cases of disk corruption. This requires libvirt to mark the image as
    shared so that qemu lifts certain restrictions.
    Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1378242

commit 860a3c4bea1d24773d8a495f213d5de3ac48a462
Author: Peter Krempa <address@hidden>
Date:   Wed Nov 15 15:02:58 2017 +0100

    qemu: caps: Add capability for 'share-rw' disk option
    'share-rw' for the disk device configures qemu to allow concurrent
    access to the backing storage.
    The capability is checked in various supported disk frontend buses since
    it does not make sense to partially backport it.

Once this is complete in bionic by taking the new upstream I'll take a
look at how backportable that is (changes look ok, but might need some
testing in the SRU spirit of things).

** Also affects: qemu (Ubuntu Artful)
   Importance: Undecided
       Status: New

** Also affects: libvirt (Ubuntu Artful)
   Importance: Undecided
       Status: New

** Changed in: libvirt (Ubuntu Artful)
       Status: New => Triaged

** Changed in: libvirt (Ubuntu Artful)
   Importance: Undecided => Low

** Bug watch added: Red Hat Bugzilla #1378242

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  qemu 2.10 locks images with no feature flag

Status in QEMU:
Status in libvirt package in Ubuntu:
Status in qemu package in Ubuntu:
Status in libvirt source package in Artful:
Status in qemu source package in Artful:

Bug description:
  1) % lsb_release -rd
  Description:  Ubuntu Artful Aardvark (development branch)
  Release:      17.10

  2) % apt-cache policy qemu-system-x86
    Installed: 1:2.10~rc3+dfsg-0ubuntu1
    Candidate: 1:2.10+dfsg-0ubuntu1
    Version table:
       1:2.10+dfsg-0ubuntu1 500
          500 http://archive.ubuntu.com//ubuntu devel/main amd64 Packages
   *** 1:2.10~rc3+dfsg-0ubuntu1 100
          100 /var/lib/dpkg/status

  3) qemu locks image files with no way to discover this feature nor how
  to disable it

  4) qemu provides a way to query if it supports image locking, and what
  the default value is, and how to disable the locking via cli

  qemu 2.10 now will lock image files and warn if an image is currently
  locked.  This prevent qemu from running (and possibly corrupting said

  However, qemu does not provide any way to determine if a qemu binary
  actually has this capability.  Normally behavior changing features are
  exposed via some change to the qemu help menu or QMP/QAPI output of

  I believe this slipped through since libvirt already does image
  locking, but direct cli users will be caught by this change.

  In particular, we have a use-case where we simulate multipath disks by
  creating to disks which point to the same file which now breaks
  without adding the 'file.locking=off' to the -drive parameters;  which
  is also completely undocumented and unexposed.

  Some parts of the cli like -device allow querying of settable options
  (qemu-system-x86 -device scsi_hd,?)  but nothing equivalent exists for
  -drive parameters.

  ProblemType: Bug
  DistroRelease: Ubuntu 17.10
  Package: qemu-system-x86 1:2.10~rc3+dfsg-0ubuntu1
  ProcVersionSignature: Ubuntu 4.12.0-11.12-generic 4.12.5
  Uname: Linux 4.12.0-11-generic x86_64
  NonfreeKernelModules: zfs zunicode zavl zcommon znvpair
  ApportVersion: 2.20.6-0ubuntu7
  Architecture: amd64
  Date: Fri Sep  8 12:56:53 2017
   Hint: You are currently not seeing messages from other users and the system.
         Users in groups 'adm', 'systemd-journal' can see all messages.
         Pass -q to turn off this notice.
   -- Logs begin at Mon 2017-01-30 11:56:02 CST, end at Fri 2017-09-08 12:56:46 
CDT. --
   -- No entries --
  MachineType: HP ProLiant DL360 Gen9
   PATH=(custom, no user)
  ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.12.0-11-generic 
root=UUID=45354276-e0c0-4bf6-9083-f130b89411cc ro --- console=ttyS1,115200
  SourcePackage: qemu
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 03/05/2015
  dmi.bios.vendor: HP
  dmi.bios.version: P89
  dmi.chassis.type: 23
  dmi.chassis.vendor: HP
  dmi.product.family: ProLiant
  dmi.product.name: ProLiant DL360 Gen9
  dmi.sys.vendor: HP

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