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Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from devic
From: |
Ryan Harper |
Subject: |
Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal |
Date: |
Mon, 8 Nov 2010 12:41:04 -0600 |
User-agent: |
Mutt/1.5.6+20040907i |
* Daniel P. Berrange <address@hidden> [2010-11-08 11:05]:
> On Mon, Nov 08, 2010 at 06:56:02PM +0200, Michael S. Tsirkin wrote:
> > On Mon, Nov 08, 2010 at 08:02:50AM -0600, Ryan Harper wrote:
> > > * Markus Armbruster <address@hidden> [2010-11-08 06:04]:
> > > > "Michael S. Tsirkin" <address@hidden> writes:
> > > > >> Here's how the various objects are connected to each other:
> > > > >>
> > > > >> contains
> > > > >> drivelist -----------> DriveInfo
> > > > >> |
> > > > >> | .bdrv
> > > > >> | .id == .bdrv->device_name
> > > > >> |
> > > > >> contains V
> > > > >> bdrv_states -----------> BlockDriverState
> > > > >> | ^
> > > > >> .peer | |
> > > > >> | | host part
> > > > >> -----------------------------|---|-----------------------------------
> > > > >> | | guest part
> > > > >> | | property "drive"
> > > > >> v |
> > > > >> DeviceState
> > > > >>
> > > > >> To disconnect host from guest part, you need to cut both pointers.
> > > > >> To
> > > > >> delete the host part, you need to delete both objects,
> > > > >> BlockDriverState
> > > > >> and DriveInfo.
> > > > >
> > > > >
> > > > > If we remove DriveInfo, how can management later detect that guest
> > > > > part
> > > > > was deleted?
> > > >
> > > > Directly: check whether the qdev is gone.
> > > >
> > > > I don't know how to check that indirectly, via DriveInfo.
> > > >
> > > > > If you want symmetry with netdev, it's possible to keep a
> > > > > shell of BlockDriverState/DriveInfo around (solving dangling pointer
> > > > > problems).
> > > >
> > > > netdev_del deletes the host network part:
> > > >
> > > > (qemu) info network
> > > > Devices not on any VLAN:
> > > > net.0: net=10.0.2.0, restricted=n peer=nic.0
> > > > nic.0: model=virtio-net-pci,macaddr=52:54:00:12:34:56 peer=net.0
> > > > (qemu) netdev_del net.0
> > > > (qemu) info network
> > > > Devices not on any VLAN:
> > > > nic.0: model=virtio-net-pci,macaddr=52:54:00:12:34:56 peer=net.0
> > > >
> > > > It leaves around the VLAN object. Since qdev property points to that,
> > > > it doesn't dangle.
> > > >
> > > > In my opinion, drive_del should make the drive vanish from "info block",
> > >
> > > Yeah; that's the right thing to do here. Let me respin the patch with
> > > the name change and the additional work to fix up the pointers and
> > > ensure that we don't see the drive in info block.
> >
> > Daniel, I'd like your input here: can you live with
> > device diappearing from info block and parsing
> > qdev tree info to figure out whether device is really gone?
>
> We don't use info block for anything. Having to parse the full qdev tree
> to determine if a single device is gone seems rather tedious. It would
> be better if query-qdev took an optional argument, which is the name
> of the device to root the tree at. Then checking whether a device
> named 'foo' is gone just means running 'query-qdev foo' and seeing if
> that returns an error about the device not existing, then we know it
> has gone. No need to parse anything. Being able to query the qdev data
> for a single device, or sub-tree of devices seems useful in its own
> right.
Since I'm not looking forward to parsing info block (easy) nor parsing
all of qdev tree (much harder) I really like the query approach.
That makes it easy to put a query in the netdev_del/drive_del commands
to skip invoking them if the guest has already responded.
>
> Regards,
> Daniel
> --
> |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :|
> |: http://libvirt.org -o- http://virt-manager.org -o- http://deltacloud.org :|
> |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :|
> |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|
--
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
address@hidden
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal, (continued)
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal, Markus Armbruster, 2010/11/05
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal, Ryan Harper, 2010/11/05
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal, Markus Armbruster, 2010/11/06
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal, Ryan Harper, 2010/11/07
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal, Markus Armbruster, 2010/11/08
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal, Michael S. Tsirkin, 2010/11/08
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal, Markus Armbruster, 2010/11/08
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal, Ryan Harper, 2010/11/08
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal, Michael S. Tsirkin, 2010/11/08
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal, Daniel P. Berrange, 2010/11/08
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal,
Ryan Harper <=
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal, Ryan Harper, 2010/11/08
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal, Daniel P. Berrange, 2010/11/08
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal, Michael S. Tsirkin, 2010/11/08
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal, Michael S. Tsirkin, 2010/11/05
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal, Ryan Harper, 2010/11/05
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal, Markus Armbruster, 2010/11/05
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal, Michael S. Tsirkin, 2010/11/08