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Date: Fri, 5 Oct 2012 10:14:59 +0200
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20121005081458.GC1399@stefanha-thinkpad.redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v2] virtio-blk: add default serial id
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To: Dave Young <dyoung@redhat.com>
Cc: Eric Blake <eblake@redhat.com>, qemu-devel@nongnu.org

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.

I'd prefer if we don't expose a temporary serial number at all in order to
avoid issues like this.

Stefan