Warn user if the vga flag is passed but no vga device is created

A global boolean variable "vga_interface_created"(declared in softmmu/globals.c)
has been used to track the creation of vga interface. If the vga flag is passed
in the command line "default_vga"(declared in softmmu/vl.c) variable is set to 0.
To warn user, the condition checks if vga_interface_created is false
and default_vga is equal to 0. If "-vga none" is passed, this patch will not warn the
user regarding the creation of VGA device.

The warning "A -vga option was passed but this
machine type does not use that option; no VGA device has been created"
is logged if vga flag is passed but no vga device is created.

This patch has been tested for x86_64, i386, sparc, sparc64 and arm boards.

Signed-off-by: Gautam Agrawal <gautamnagrawal@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/581
Message-Id: <20220501122505.29202-1-gautamnagrawal@gmail.com>
[thuth: Fix wrong warning with "-device" in some cases as reported by Paolo]
Signed-off-by: Thomas Huth <thuth@redhat.com>

hw/hppa/machine.c

@@ -265,6 +265,7 @@ static void machine_hppa_init(MachineState *machine)
 
     /* Graphics setup. */
     if (machine->enable_graphics && vga_interface_type != VGA_NONE) {
+        vga_interface_created = true;
         dev = qdev_new("artist");
         s = SYS_BUS_DEVICE(dev);
         sysbus_realize_and_unref(s, &error_fatal);

hw/isa/isa-bus.c

@@ -166,6 +166,7 @@ bool isa_realize_and_unref(ISADevice *dev, ISABus *bus, Error **errp)
 
 ISADevice *isa_vga_init(ISABus *bus)
 {
+    vga_interface_created = true;
     switch (vga_interface_type) {
     case VGA_CIRRUS:
         return isa_create_simple(bus, "isa-cirrus-vga");

hw/mips/fuloong2e.c

@@ -320,6 +320,7 @@ static void mips_fuloong2e_init(MachineState *machine)
 
     /* GPU */
     if (vga_interface_type != VGA_NONE) {
+        vga_interface_created = true;
         pci_dev = pci_new(-1, "ati-vga");
         dev = DEVICE(pci_dev);
         qdev_prop_set_uint32(dev, "vgamem_mb", 16);

hw/pci/pci.c

@@ -2037,6 +2037,7 @@ PCIDevice *pci_nic_init_nofail(NICInfo *nd, PCIBus *rootbus,
 
 PCIDevice *pci_vga_init(PCIBus *bus)
 {
+    vga_interface_created = true;
     switch (vga_interface_type) {
     case VGA_CIRRUS:
         return pci_create_simple(bus, -1, "cirrus-vga");

hw/ppc/spapr.c

@@ -1742,6 +1742,7 @@ static void spapr_rtc_create(SpaprMachineState *spapr)
 /* Returns whether we want to use VGA or not */
 static bool spapr_vga_init(PCIBus *pci_bus, Error **errp)
 {
+    vga_interface_created = true;
     switch (vga_interface_type) {
     case VGA_NONE:
         return false;

hw/sparc/sun4m.c

@@ -920,6 +920,7 @@ static void sun4m_hw_init(MachineState *machine)
             /* sbus irq 5 */
             cg3_init(hwdef->tcx_base, slavio_irq[11], 0x00100000,
                      graphic_width, graphic_height, graphic_depth);
+            vga_interface_created = true;
         } else {
             /* If no display specified, default to TCX */
             if (graphic_depth != 8 && graphic_depth != 24) {
@@ -935,6 +936,7 @@ static void sun4m_hw_init(MachineState *machine)
 
             tcx_init(hwdef->tcx_base, slavio_irq[11], 0x00100000,
                      graphic_width, graphic_height, graphic_depth);
+            vga_interface_created = true;
         }
     }
 

hw/sparc64/sun4u.c

@@ -632,6 +632,7 @@ static void sun4uv_init(MemoryRegion *address_space_mem,
     switch (vga_interface_type) {
     case VGA_STD:
         pci_create_simple(pci_busA, PCI_DEVFN(2, 0), "VGA");
+        vga_interface_created = true;
         break;
     case VGA_NONE:
         break;

hw/xenpv/xen_machine_pv.c

@@ -63,6 +63,7 @@ static void xen_init_pv(MachineState *machine)
     if (vga_interface_type == VGA_XENFB) {
         xen_config_dev_vfb(0, "vnc");
         xen_config_dev_vkbd(0);
+        vga_interface_created = true;
     }
 
     /* configure disks */

include/sysemu/sysemu.h

@@ -34,6 +34,7 @@ typedef enum {
 } VGAInterfaceType;
 
 extern int vga_interface_type;
+extern bool vga_interface_created;
 
 extern int graphic_width;
 extern int graphic_height;

softmmu/globals.c

@@ -40,6 +40,7 @@ int nb_nics;
 NICInfo nd_table[MAX_NICS];
 int autostart = 1;
 int vga_interface_type = VGA_NONE;
+bool vga_interface_created;
 Chardev *parallel_hds[MAX_PARALLEL_PORTS];
 int win2k_install_hack;
 int singlestep;

softmmu/vl.c

@@ -1353,6 +1353,7 @@ static void qemu_disable_default_devices(void)
 
     if (!vga_model && !default_vga) {
         vga_interface_type = VGA_DEVICE;
+        vga_interface_created = true;
     }
     if (!has_defaults || machine_class->no_serial) {
         default_serial = 0;
@@ -2736,6 +2737,12 @@ static void qemu_machine_creation_done(void)
     if (foreach_device_config(DEV_GDB, gdbserver_start) < 0) {
         exit(1);
     }
+    if (!vga_interface_created && !default_vga &&
+        vga_interface_type != VGA_NONE) {
+        warn_report("A -vga option was passed but this machine "
+                    "type does not use that option; "
+                    "No VGA device has been created");
+    }
 }
 
 void qmp_x_exit_preconfig(Error **errp)