Re: [PATCH 1/2] qxl: remove assert in qxl_pre_save.

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 7/23/21 8:55 AM, Gerd Hoffmann wrote:
> On Fri, Jul 23, 2021 at 08:47:09AM +0200, Philippe Mathieu-Daudé wrote:
>> On 7/23/21 8:32 AM, Gerd Hoffmann wrote:
>>> On Thu, Jul 22, 2021 at 03:44:54PM +0100, Dr. David Alan Gilbert wrote:
>>>> * Gerd Hoffmann (kraxel@redhat.com) wrote:
>>>>> Since commit 551dbd0846d2 ("migration: check pre_save return in
>>>>> vmstate_save_state") the pre_save hook can fail.  So lets finally
>>>>> use that to drop the guest-triggerable assert in qxl_pre_save().
>>>>>
>>>>> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
>>>>> ---
>>>>>  hw/display/qxl.c | 4 +++-
>>>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/hw/display/qxl.c b/hw/display/qxl.c
>>>>> index 84f99088e0a0..3867b94fe236 100644
>>>>> --- a/hw/display/qxl.c
>>>>> +++ b/hw/display/qxl.c
>>>>> @@ -2283,7 +2283,9 @@ static int qxl_pre_save(void *opaque)
>>>>>      } else {
>>>>>          d->last_release_offset = (uint8_t *)d->last_release - ram_start;
>>>>>      }
>>>>> -    assert(d->last_release_offset < d->vga.vram_size);
>>>>> +    if (d->last_release_offset < d->vga.vram_size) {
>>>>> +        return 1;
>>>>
>>>> It would be great if there was an error_report or something there
>>>> so that we get some idea of what happened.
>>>
>>> Hmm.  Strictly speaking qemu_log_mask(LOG_GUEST_ERROR, "..."); would be
>>> the correct approach here, but I guess that wouldn't help much for
>>> trouble-shooting as the message would only show up with "-d
>>> guest_errors".  So better make that error_report("...") ?
>>
>> It depends who is interested in such errors.
> 
> Migration fails and you want know why.
> 
> Reason migration fails is the guest violates qxl specs (which doesn't
> cause actual problems unless you want migrate the guest).

Then I agree error_report() is better ("Report an error to the current
monitor if we have one, else stderr").