Re: [PATCH v3] vga: don't abort when adding a duplicate isa-vga device

[Philippe Mathieu-Daudé]

On 8/17/21 9:36 AM, Mark Cave-Ayland wrote:
> On 17/08/2021 08:25, Thomas Huth wrote:
> 
>> On 16/08/2021 15.55, Jose R. Ziviani wrote:
>>> If users try to add an isa-vga device that was already registered,
>>> still in command line, qemu will crash:
>>>
>>> $ qemu-system-mips64el -M pica61 -device isa-vga
>>> RAMBlock "vga.vram" already registered, abort!
>>> Aborted (core dumped)
>>>
>>> That particular board registers the device automaticaly, so it's
>>> not obvious that a VGA device already exists. This patch changes
>>> this behavior by displaying a message and exiting without crashing.
>>>
>>> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/44
>>> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>>> Signed-off-by: Jose R. Ziviani <jziviani@suse.de>
>>> ---
>>> v2 to v3: Improved error message
>>> v1 to v2: Use error_setg instead of error_report
>>>
>>>   hw/display/vga-isa.c | 10 ++++++++++
>>>   1 file changed, 10 insertions(+)
>>>
>>> diff --git a/hw/display/vga-isa.c b/hw/display/vga-isa.c
>>> index 90851e730b..30d55b41c3 100644
>>> --- a/hw/display/vga-isa.c
>>> +++ b/hw/display/vga-isa.c
>>> @@ -33,6 +33,7 @@
>>>   #include "hw/loader.h"
>>>   #include "hw/qdev-properties.h"
>>>   #include "qom/object.h"
>>> +#include "qapi/error.h"
>>>   #define TYPE_ISA_VGA "isa-vga"
>>>   OBJECT_DECLARE_SIMPLE_TYPE(ISAVGAState, ISA_VGA)
>>> @@ -61,6 +62,15 @@ static void vga_isa_realizefn(DeviceState *dev,
>>> Error **errp)
>>>       MemoryRegion *vga_io_memory;
>>>       const MemoryRegionPortio *vga_ports, *vbe_ports;
>>> +    /*
>>> +     * make sure this device is not being added twice, if so
>>> +     * exit without crashing qemu
>>> +     */
>>> +    if (qemu_ram_block_by_name("vga.vram")) {
>>> +        error_setg(errp, "'isa-vga' device already registered");
>>> +        return;
>>> +    }
>>> +
>>>       s->global_vmstate = true;
>>>       vga_common_init(s, OBJECT(dev));
>>>       s->legacy_address_space = isa_address_space(isadev);
>>>
>>
>> Reviewed-by: Thomas Huth <thuth@redhat.com>
> 
> Instead of checking for the presence of the vga.vram block, would it be
> better to use the standard object_resolve_path_type() method to check
> for the presence of the existing isa-vga device instead? See
> https://lists.gnu.org/archive/html/qemu-devel/2021-07/msg00717.html for
> how this was done for virgl.

I remembered there was a nicer way but couldn't find it.
If this patch were for 6.1, it was good enough. Now it
will be merged in 6.2, I prefer Mark's suggestion.
Jose, do you mind a v4?