Re: [Qemu-devel] [Xen-devel] [XEN][RFC PATCH V2 11/17] xc: modify save/restore to support multiple device models

[Julien Grall <julien.grall@citrix.com>]

On 08/23/2012 08:52 PM, Ian Campbell wrote:
> On Thu, 2012-08-23 at 20:13 +0100, Julien Grall wrote:
>    
>> On 08/23/2012 02:27 PM, Ian Campbell wrote:
>>      
>>>        
>>>> @@ -103,6 +103,9 @@ static ssize_t rdexact(xc_interface *xch, struct restore_ctx *ctx,
>>>>    #else
>>>>    #define RDEXACT read_exact
>>>>    #endif
>>>> +
>>>> +#define QEMUSIG_SIZE 21
>>>> +
>>>>    /*
>>>>    ** In the state file (or during transfer), all page-table pages are
>>>>    ** converted into a 'canonical' form where references to actual mfns
>>>> @@ -467,7 +522,7 @@ static int buffer_tail_hvm(xc_interface *xch, struct restore_ctx *ctx,
>>>>                               int vcpuextstate, uint32_t vcpuextstate_size)
>>>>    {
>>>>        uint8_t *tmp;
>>>> -    unsigned char qemusig[21];
>>>> +    unsigned char qemusig[QEMUSIG_SIZE + 1];
>>>>
>>>>          
>>> An extra + 1 here?
>>>
>>>        
>> QEMUSIG_SIZE doesn't take into account the '\0'. So we need to add 1.
>> If an error occurred, without +1, the output log lost the last character.
>>      
> So this is just a bug fix for a pre-existing issue?
>    
Yes.

>>> [...]
>>>
>>>        
>>>> -    qemusig[20] = '\0';
>>>> +    qemusig[QEMUSIG_SIZE] = '\0';
>>>>
>>>>          
>>> This is one bigger than it used to be now.
>>>
>>> Perhaps this is an unrelated bug fix (I haven't check the real length of
>>> the sig), in which case please can you split it out and submit
>>> separately?
>>>
>>>        
>> #define QEMU_SIGNATURE "DeviceModelRecord0002"
>> Just checked, the length seems to be 21. I will send a patch with
>> this change.
>>      
> Perhaps use either sizeof(QEMU_SIGNATURE) or strlen(QEMU_SIGNATURE)
> (depending on which semantics you want)?
>    
Here, QEMU_SIZE needs to be define as strlen (QEMU_SIGNATURE),
but QEMU_SIGNATURE is not defined in libxc. It's defined
in libxl/libxl_internal.h.
By the way, I'm wondering why QEMU save (libxl__domain_save_device_model)
is made in libxl and restore (dump_qemu) in libxc ?