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Re: [Qemu-devel] [PATCH 4/5] Add generic drive hotplugging


From: Alexander Graf
Subject: Re: [Qemu-devel] [PATCH 4/5] Add generic drive hotplugging
Date: Tue, 24 Aug 2010 23:53:19 +0200

On 24.08.2010, at 20:35, Anthony Liguori wrote:

> On 08/24/2010 08:44 AM, Daniel P. Berrange wrote:
>> 
>>>> Actually this SCSI example I give above is appending a drive to an existing
>>>> bus (scsi0), in slot 1 (scsi-id=1).  To best of my knowledge there is no
>>>> remaining use case that requires use of IF_SCSI, IF_IDE, etc. The IF_NONE
>>>> approach can cope with all, modulo bugs that appear periodically with code
>>>> that mistakenly checks for a particular IF_XXX constant.
>>>> 
>>>> If you wanted to also create a new SCSI bus, before creating the drive on
>>>> it, you'd need to run three commands in total:
>>>> 
>>>>   device_add lsi,id=scsi0,bus=pci.0,addr=0x7
>>>>   drive_add dummy 
>>>> file=/var/lib/libvirt/images/data.img,if=none,id=drive-scsi0-0-1,format=raw
>>>>   device_add 
>>>> scsi-disk,bus=scsi0.0,scsi-id=1,drive=drive-scsi0-0-1,id=scsi0-0-1
>>>> 
>>>>       
>>> Nice - so we can just deprecate if=!none?
>>>     
>> In theory yes, but its not nice to tell users to switch everything over to
>> use if=none, if we're going to deprecate that too in the next release when
>> blockdev appears. Might as well just deprecate entire of drive_add/-drive
>> at once.
>>   
> 
> I think what Alex is really asking is can we have 'blockdev_add 
> var0=val0,var1=val1[,...]' implemented as 'drive_add dummy 
> if=none,var0=val0,var1=val1[,...]'.  I don't know the answer to why that 
> isn't possible or desirable.

Uh, I was really asking for why we need something not drive_add and instead 
have yet another iteration of drive parameter. But oh well.

I guess we deferred a bit from the original thread. What's the preferred way to 
go here? Remove the IF_SCSI case completely or keep two copies of the drive_add 
function around?


Alex




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