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

From: Mark Cave-Ayland
Subject: Re: [PATCH v3] vga: don't abort when adding a duplicate isa-vga device
Date: Tue, 17 Aug 2021 08:36:08 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0

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"
@@ -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.



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