[libvirt] [PATCH] Don't validate disk type in virsh attach-disk

Jim Meyering jim at meyering.net
Mon Mar 2 16:29:58 UTC 2009

Cole Robinson wrote:
> Jim Meyering wrote:
>> Cole Robinson wrote:
>>> virsh attempts to validate the requested disk type, rather than just let
>>> the underlying driver do it. This was erroneously denying floppy device
>>> attaches. Patch attached.
>> Hi Cole,
>> Your patch would do the job.
>> Before:
>>   $ virsh -c test:///default attach-disk 1 s t --type floppy --mode readonly
>>   error: No support floppy in command 'attach-disk'
>> with the patch:
>>   $ virsh -c test:///default attach-disk 1 s t --type floppy --mode readonly
>>   error: this function is not supported by the hypervisor: virDomainAttachDevice
>> But consider what happens with e.g., "--type bogus".
>> Before, it'd mention the invalid type, "bogus".
>> With the patch, it doesn't (at least not using the test driver).
>> So maybe it'd be better to keep the up-front type check.
> The idea here is that virsh isn't the one to decide. It could very well
> be that driver foo doesn't support cdrom devices, so even though virsh
> lets it through, it's still not valid. Only AttachDevice can give us the
> full picture.

Sure, I understand that, but if the result of dropping the
harmless (once fixed) up-front check is a diagnostic
that is less helpful, why drop it?

Especially with a 6 or 7-parameter command, it's important
to point out which part is causing trouble, whenever possible.

The alternative is to give better diagnostics from each and every driver.

> Sounds like we should just implement AttachDevice for the test driver:
> it could parse the device xml and unconditionally insert it into the

Changing how the test driver handles this case
won't give a better diagnostic for all the other drivers.

> guest config. This would certainly be useful in testing the above virsh
> commands (and for testing device attaches in virt-manager, among others

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