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 such device automaticaly, so it's
not obvious that a VGA device already exists. This patch changes
this behavior by displaying a message and ignoring that device,
starting qemu normally.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/44
Signed-off-by: Jose R. Ziviani <jziviani@suse.de>
---
 hw/display/vga-isa.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/hw/display/vga-isa.c b/hw/display/vga-isa.c
index 90851e730b..69db502dde 100644
--- a/hw/display/vga-isa.c
+++ b/hw/display/vga-isa.c
@@ -61,6 +61,15 @@ static void vga_isa_realizefn(DeviceState *dev, Error **errp)
     MemoryRegion *vga_io_memory;
     const MemoryRegionPortio *vga_ports, *vbe_ports;
 
+    /*
+     * some machines register VGA by default, so instead of aborting
+     * it, show a message and ignore this device.
+     */
+    if (qemu_ram_block_by_name("vga.vram")) {
+        error_report("vga.vram is already registered, ignoring this device");
+        return;
+    }
+
     s->global_vmstate = true;
     vga_common_init(s, OBJECT(dev));
     s->legacy_address_space = isa_address_space(isadev);
-- 
2.32.0

On 14/08/2021 01.36, 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 such device automaticaly, so it's
> not obvious that a VGA device already exists. This patch changes
> this behavior by displaying a message and ignoring that device,
> starting qemu normally.
> 
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/44
> Signed-off-by: Jose R. Ziviani <jziviani@suse.de>
> ---
>   hw/display/vga-isa.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/hw/display/vga-isa.c b/hw/display/vga-isa.c
> index 90851e730b..69db502dde 100644
> --- a/hw/display/vga-isa.c
> +++ b/hw/display/vga-isa.c
> @@ -61,6 +61,15 @@ static void vga_isa_realizefn(DeviceState *dev, Error **errp)
>       MemoryRegion *vga_io_memory;
>       const MemoryRegionPortio *vga_ports, *vbe_ports;
>   
> +    /*
> +     * some machines register VGA by default, so instead of aborting
> +     * it, show a message and ignore this device.
> +     */
> +    if (qemu_ram_block_by_name("vga.vram")) {
> +        error_report("vga.vram is already registered, ignoring this device");
> +        return;
> +    }

I think we should not ignore the error, but rather turn this into a proper 
error (instead of aborting).

So if you replace error_report(...) with error_setg(errp, ...), the patch 
should be fine.

  Thomas

  Hi,

> > +    if (qemu_ram_block_by_name("vga.vram")) {
> > +        error_report("vga.vram is already registered, ignoring this device");
> > +        return;
> > +    }
> 
> I think we should not ignore the error, but rather turn this into a proper
> error (instead of aborting).

Yes.  Silently fixing up things automatically tends to be worse long-term.

take care,
  Gerd

Hello Thomas and Gerd,

Thank you for reviewing it. Sending a v2 soon.

Thank you very much!

On 16/08/2021 02:05, Gerd Hoffmann wrote:
>    Hi,
>
>>> +    if (qemu_ram_block_by_name("vga.vram")) {
>>> +        error_report("vga.vram is already registered, ignoring this device");
>>> +        return;
>>> +    }
>> I think we should not ignore the error, but rather turn this into a proper
>> error (instead of aborting).
> Yes.  Silently fixing up things automatically tends to be worse long-term.
>
> take care,
>    Gerd
>

Thomas Huth <thuth@redhat.com> writes:

> On 14/08/2021 01.36, 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 such device automaticaly, so it's
>> not obvious that a VGA device already exists. This patch changes
>> this behavior by displaying a message and ignoring that device,
>> starting qemu normally.
>> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/44
>> Signed-off-by: Jose R. Ziviani <jziviani@suse.de>
>> ---
>>   hw/display/vga-isa.c | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>> diff --git a/hw/display/vga-isa.c b/hw/display/vga-isa.c
>> index 90851e730b..69db502dde 100644
>> --- a/hw/display/vga-isa.c
>> +++ b/hw/display/vga-isa.c
>> @@ -61,6 +61,15 @@ static void vga_isa_realizefn(DeviceState *dev, Error **errp)
>>       MemoryRegion *vga_io_memory;
>>       const MemoryRegionPortio *vga_ports, *vbe_ports;
>> +    /*
>> +     * some machines register VGA by default, so instead of aborting
>> +     * it, show a message and ignore this device.
>> +     */
>> +    if (qemu_ram_block_by_name("vga.vram")) {
>> +        error_report("vga.vram is already registered, ignoring this device");
>> +        return;
>> +    }
>
> I think we should not ignore the error, but rather turn this into a
> proper error (instead of aborting).
>
> So if you replace error_report(...) with error_setg(errp, ...), the
> patch should be fine.

Agreed.

error_report() in a function with an Error **errp parameter is almost
always wrong.