[Qemu-devel] Re: Block device resize detection

[Kevin Wolf]

Am 06.12.2010 12:29, schrieb Alexander Graf:
> On 06.12.2010, at 11:49, Vandeir Eduardo wrote:
>>
>> I have a KVM guest machine, lets name it VMTEST,
>> using an iSCSI LUN as a virtio device. Something like this:
>>
>> <disk type='block' device='disk'>
>>   <driver name='qemu' type='raw' cache='none'/>
>>   <source 
>> dev='/dev/disk/by-path/ip-w.x.y.z:3260-iscsi-iqn.2010-10.br.furb.inf:disk0-lun-4'/>
>>      <target dev='vda' bus='virtio'/>
>> </disk>
>>
>> On iSCSI server, if I resize this LUN, this resize is detected
>> on KVM host, but not on the VMTEST. The device resize is only
>> detected if I restart VMTEST. Is there a way to make VMTEST detect
>> the /dev/vda resize without restarting it?
>>
>> On VMTEST I already tried commands like partprobe /dev/vda, 
>> hdparm -z /dev/vda and blockdev --rereadpt /dev/vda, but none of
>> was capable to detect the block device (/dev/vda) resize.
> 
> The probing of an image is only done at initialization time of the block 
> backend driver, which in your case is the bootup. The only chance you have of 
> reevaluating it would be to hot-add another virtio device with the resized 
> image.
> 
> Alternatively, you could also try to write a patch for reevaluation plumbing, 
> so that the hba emulation layer can trigger reevaluation in the disk layer.

This is basically online disk resizing, which we have discussed in the
past and which I think we want to have for virtio-blk eventually, but
currently it's supported neither in the host qemu nor in the guest kernel.

Kevin