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Date: Tue, 12 Oct 2010 08:27:21 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] qdev: Some ISA devices don't handle second
	instantiation gracefully
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To: Markus Armbruster <armbru@redhat.com>
Cc: qemu-devel@nongnu.org, "H. Peter Anvin" <hpa@linux.intel.com>, Gerd Hoffmann <kraxel@redhat.com>, Alexander Graf <agraf@suse.de>, "Richard W. M. Jones" <rjones@redhat.com>

On 10/12/2010 08:00 AM, Markus Armbruster wrote:
> Markus Armbruster<armbru@redhat.com>  writes:
>
>    
>> When I try -device isa-applesmc -device isa-applesmc, I get
>>
>>      WARNING: Using AppleSMC with invalid key
>>      qemu: hardware error: register_ioport_read: invalid opaque
>>      [...]
>>
>> and a core dump.
>>
>> I know nothing about this device.  Instantiating twice may well make no
>> sense.  But hw_error() is not a nice way to reject a command line
>> option.
>>      
> Actually, ib700 and isa-debugcon fail the same way.
>
> They call register_ioport_write(), which aborts via hw_error() when the
> port is already in use.  This is okay for non-configurable parts of a
> board emulation, but not okay for a qdev device, unless it has no_user
> set.
>    

It's definitely right to fail but I agree, it's better to propagate the 
error.

> Related: when isa_init_irq() finds the requested IRQ already in use, it
> fails with exit(1).  Maybe register_ioport_write()&  friends should do
> that as well.
>
> Or maybe qdev device models should have an "at most one" flag.
>    

I think the proper thing to do is remove all exit(1)s and propagate 
errors instead.

A simple approach would be to make register_ioport_{read,write}() return 
an int, then do a query-replace on the source tree to make all 
invocations of it simply check the return value and exit if it's non-zero.

Regards,

Anthony Liguori