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Date: Wed, 16 Aug 2017 11:23:49 +0200
From: Cornelia Huck <cohuck@redhat.com>
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Subject: Re: [Qemu-devel] Crash when deleting the diag288 watchdog
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To: Thomas Huth <thuth@redhat.com>
Cc: QEMU Developers <qemu-devel@nongnu.org>, Christian Borntraeger <borntraeger@de.ibm.com>, David Hildenbrand <david@redhat.com>, Sascha Silbe <silbe@linux.vnet.ibm.com>

On Wed, 16 Aug 2017 07:05:37 +0200
Thomas Huth <thuth@redhat.com> wrote:

>  Hi,
> 
> I recently noticed that QEMU abort()s if you try to remove the diag288
> watchdog. For example:
> 
> $ qemu-system-s390x -nographic -nodefaults -S -monitor stdio
> QEMU 2.9.92 monitor - type 'help' for more information
> (qemu) device_add diag288,id=x
> (qemu) device_del x
> **
> ERROR:/home/thuth/devel/qemu/qdev-monitor.c:872:qdev_unplug: assertion
> failed: (hotplug_ctrl)
> Aborted (core dumped)
> 
> This is ugly, can we fix this somehow? For example, should the diag288
> device be hot-pluggable at all, or can it only be used via the
> "-watchdog" parameter instead? In the latter case, we could simply mark
> the device with "user_creatable = false", I guess?

I don't think the diag288 watchdog should be hotpluggable. IIUC, it is
simply present on z/VM (and I don't think it's different on LPAR, but I
could not find docs for that). So yes, user_creatable = false sounds
like the right thing to do.

Related: We currently only handle diag288 via kvm if I did not miss
something. It probably makes sense to wire it up for tcg as well.