[libvirt] [PATCH] qemu: fix use a nonexist address in qemuDomainAttachDeviceConfig

[Peter Krempa]

On 12/16/14 13:32, Luyao Huang wrote:
> 
> On 12/16/2014 08:00 PM, Peter Krempa wrote:
>> On 12/15/14 10:10, Luyao Huang wrote:
>>> We free them before, then use it. This make we always do
>> We clear the pointer, not free.
>>
>>> virDomainDefAddImplicitControllers when attach a disk.
>>>
>>> Signed-off-by: Luyao Huang <lhuang at redhat.com>
>>> ---
>>>   src/qemu/qemu_driver.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
>>> index df3ba6d..a9afa5d 100644
>>> --- a/src/qemu/qemu_driver.c
>>> +++ b/src/qemu/qemu_driver.c
>>> @@ -7223,10 +7223,10 @@ qemuDomainAttachDeviceConfig(virQEMUCapsPtr
>>> qemuCaps,
>>>           if (virDomainDiskInsert(vmdef, disk))
>>>               return -1;
>>>           /* vmdef has the pointer. Generic codes for vmdef will do
>>> all jobs */
>>> -        dev->data.disk = NULL;
>> The comment even explains why the line is there. From that point on, the
>> pointer is owned by 'vmdef' and thus the original needs to be cleared so
>> that it isn't freed (and doulbe freed) later on.
> Oh, i see. Thanks for your review and i found seems i don't check if gdb
> is real go to virDomainDefAddImplicitControllers, just check the
> pointer's value is optimized out.
> 
> (gdb)
> 7204            dev->data.disk = NULL;
> (gdb)
> 7205            if (disk->bus != VIR_DOMAIN_DISK_BUS_VIRTIO)
> (gdb) p disk
> $3 = <optimized out>

"optimized out" means that GDB can't access the variable as it is stored
in a register or for other reason caused by the code optimizer.

It does not mean that the variable is cleared or whatever, just that GDB
can't print it.

Peter

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