Re: [Qemu-devel] [PATCH 1/2] pvpanic: initialization cleanup

[Laszlo Ersek]

On 06/17/13 11:19, Michael S. Tsirkin wrote:
> On Mon, Jun 17, 2013 at 09:56:56AM +0200, Laszlo Ersek wrote:
>> On 06/16/13 22:59, Michael S. Tsirkin wrote:
>>> Avoid use of static variables: PC systems initialize pvpanic device
>>> through pvpanic_init, so we can simply create the fw_cfg file at that
>>> point.  Others don't use fw_cfg at all.  This also makes it possible to
>>> assert if fw_cfg is not there rather than skipping the device silently.
>>>
>>> Signed-off-by: Michael S. Tsirkin <address@hidden>
>>> ---
>>>  hw/misc/pvpanic.c | 23 ++++++++++-------------
>>>  1 file changed, 10 insertions(+), 13 deletions(-)
>>>
>>> diff --git a/hw/misc/pvpanic.c b/hw/misc/pvpanic.c
>>> index 060099b..9ed9897 100644
>>> --- a/hw/misc/pvpanic.c
>>> +++ b/hw/misc/pvpanic.c
>>> @@ -97,25 +97,22 @@ static void pvpanic_isa_realizefn(DeviceState *dev, 
>>> Error **errp)
>>>  {
>>>      ISADevice *d = ISA_DEVICE(dev);
>>>      PVPanicState *s = ISA_PVPANIC_DEVICE(dev);
>>> -    static bool port_configured;
>>> -    FWCfgState *fw_cfg;
>>>  
>>>      isa_register_ioport(d, &s->io, s->ioport);
>>> -
>>> -    if (!port_configured) {
>>> -        fw_cfg = fw_cfg_find();
>>> -        if (fw_cfg) {
>>> -            fw_cfg_add_file(fw_cfg, "etc/pvpanic-port",
>>> -                            g_memdup(&s->ioport, sizeof(s->ioport)),
>>> -                            sizeof(s->ioport));
>>> -            port_configured = true;
>>> -        }
>>> -    }
>>>  }
>>>  
>>>  int pvpanic_init(ISABus *bus)
>>>  {
>>> -    isa_create_simple(bus, TYPE_ISA_PVPANIC_DEVICE);
>>> +    ISADevice *dev = isa_create_simple(bus, TYPE_ISA_PVPANIC_DEVICE);
>>> +    PVPanicState *s = ISA_PVPANIC_DEVICE(dev);
>>> +    FWCfgState *fw_cfg = fw_cfg_find();
>>> +
>>> +    assert(fw_cfg);
>>
>> Won't the assert fire if:
>>
>>   xen_enabled() &&
>>   machine != "pc-0.10" && machine != "pc-0.11" &&
>>   machine != "pc-0.12" && machine != "pc-0.13" &&
>>   machine != "pc-q35-1.4"
>>
>> Because under the above condition "has_pvpanic" remains "true", but
>> fw_cfg is not initialized.
>>
>> (pc_init_pci_no_kvmclock() in "hw/i386/pc_piix.c" sets "has_pvpanic" to
>> "false", and claims to be "reused by xenfv", so the above condition may
>> be constant false.)
> 
> That's what I think - if user wants pvpanic to work, fw cfg is required ATM.

What I have in mind is the following: suppose xen is enabled and qemu is
started with -M pc-i440fx-1.5.

Before the patch, the pvpanic device didn't work, but qemu didn't crash
either. After the patch, the assert() is triggered at startup.

Of course, if starting qemu for xen with "-M pc-i440fx-1.5" is *already*
broken (for other, maybe more serious, reasons), ie. PEBKAC, then the
patch is correct. But I can't evaluate that condition to constant false,
and suppose that it's a possible configuration, under which qemu would
now start with an assertion failure.

Can someone with Xen knowledge chime in? CC'ing Stefano.

Laszlo