[libvirt] [PATCH 0/6] Support online block resizing

Osier Yang jyang at redhat.com
Thu Sep 1 13:42:02 UTC 2011

于 2011年09月01日 21:37, Daniel P. Berrange 写道:
> On Thu, Sep 01, 2011 at 02:14:23PM +0100, Daniel P. Berrange wrote:
>> On Wed, Aug 31, 2011 at 09:31:58PM +0800, Osier Yang wrote:
>>> Upstream QEMU introduced online block resizing to resize the
>>> block device when domain is running since commit 6d4a2b3a4795.
>>> It simply reuses existing "bdrv_truncate" method which is used
>>> by "qemu-img" to resize the images. This means it supports to
>>> resize all the format that "qemu-img resize" supports. E.g.
>>> qcow2, raw, qed, qcow, etc. (NB, it doesn't support to shrink
>>> size of qcow2 image, and QEMU reports "An undefined error
>>> has ocurred" in this case).
>>> For block device of virtio bus, the guest can update the device
>>> size automatically, needs kernel support, since kernel-2.6.32-117:
>>>    http://patchwork.usersys.redhat.com/patch/33040/
>>> For block device of SCSI bus, one needs to execute command like
>>> below in the guest (linux) to update the size:
>>>    % echo>  /sys/class/scsi_device/0:0:0:0/device/rescan
>>> For block device of IDE bus, seems there is no way to let guest
>>> update the size after resizing.
>> Your API proprosal looks reasonable, but unfortunately the QEMU
>> command 'block_resize' is either broken, or incomplete since it
>> does not have a way to notify the guest that a block device has
>> been resized, independantly of actually resizing the host file.
>> This is required in order for guest disk resize to work on LVM,
>> SCSI, iSCSI, etc block devices, since QEMU cannot itself do a
>> resize of the block devices. The resize has to be done either
>> by libvirt using host commands, or by the SAN administrator on
>> the remote storage appliance.
>> IMHO, we should not commit to the libvirt API design, until we
>> can get confirmation from QEMU about whether they will fix the
>> block_resize command to work for block devices, or add a new
>> command for just notifying guests of external block device
>> resizes
> See this thread...
> http://lists.nongnu.org/archive/html/qemu-devel/2011-09/msg00068.html
> Daniel

Thanks for clarifying the requirement to QEMU guys, Daniel.


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