Re: [Qemu-devel] [PATCH v2] virtio-blk: add default serial id

[Dave Young]

On 10/09/2012 04:31 PM, Stefan Hajnoczi wrote:

> On Tue, Oct 09, 2012 at 10:27:26AM +0800, Dave Young wrote:
>> On 10/05/2012 04:14 PM, Stefan Hajnoczi wrote:
>>
>>> On Sun, Sep 23, 2012 at 10:37:09AM +0800, Dave Young wrote:
>>>> For the serial number decreasing issue, I think there's only these two 
>>>> ways to
>>>> select, there's no ideal way to resolve this issue.
>>>> My use case for this is for the kdump kernel to find proper disks,
>>>> after 1st kernel crashing 2nd kernel need find right disk to dump vmcore.
>>>> In this case v1 and v2 aproaches are both find to me.
>>>>
>>>> From my point of view, patch v1 is better though, I think unpluging 100000 
>>>> is
>>>> not a sane use case. It's not likely to happen.
>>>
>>> I'm not sure auto-assigning serial numbers is a good idea.  The guest can 
>>> use
>>> the serial number in /etc/fstab or other places where it expects the serial
>>> number to be persistent.
>>>
>>> Your patch does not provide persistent serial numbers, so a change to the 
>>> QEMU
>>> invocation could result in different serial numbers.  The guest will get
>>> confused or perhaps refuse to boot.
>>
>>
>> Yes, it introduce confusion, but in this way at least the serial number
>> can be persistent across guest reboot. Traditionally ide disks use this
>> way as well, such as QEMU_HARDISK_00001, I think guest should not use
>> this in /etc/fstab.
> 
> If you don't want to set a persistent serial number, use another mechanism to
> identify the disk.  For example, Linux has /dev/disk/by-path/ which identifies
> virtio-blk PCI adapters, IDE, SCSI disks, etc.

>

> Does this work for your use case?


I have tried this before, but after rebooting (kexec/kdump) the by-path
link was not created. It might be udev bug anyway, I'm not sure though.


> 
> Stefan
> 



-- 
Thanks
Dave