Re: [Qemu-devel] [PATCH 1/2] pc: make vgabios exit port more useful

[Avi Kivity <avi@redhat.com>]

On 08/24/2011 03:38 PM, Anthony Liguori wrote:
>>
>>>
>>> diff --git a/hw/pc.c b/hw/pc.c
>>> index 1c9d89a..4b07b35 100644
>>> --- a/hw/pc.c
>>> +++ b/hw/pc.c
>>> @@ -549,8 +549,7 @@ static void bochs_bios_write(void *opaque,
>>> uint32_t addr, uint32_t val)
>>> /* LGPL'ed VGA BIOS messages */
>>> case 0x501:
>>> case 0x502:
>>> - fprintf(stderr, "VGA BIOS panic, line %d\n", val);
>>> - exit(1);
>>> + exit((val<< 1) | 1);
>>
>> This code (before the patch) circumvents -no-shutdown.
>
>
> Indeed.  I believe that's a feature though?

Depends on what the user of -no-shutdown expects.

>
>>
>> Shifting val left is surprising. What's wrong with even exit codes?
>
> Hrm, the '| 1' is wrong.  My intention was to make the bottom bit of 
> the exit code mean "if set to 0, this is an exit coming from a guest'.

Too subtle, IMO.  I understand that we want to avoid a full qmp parser 
for one-off unit tests, but using bit fields in the exit code?

Perhaps a python script that launches qemu with qmp and -no-shutdown, 
listens for the guest shutdown event, and prints out the result?  That 
can be easily reused in test scripts.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.