qemu: Format rom.enabled attribute for PCI devices

The attribute can be used to disable ROM loading completely
for a device.

This might be needed because, even when the guest is configured
such that the PCI ROM will not be loaded in the PCI BAR, some
hypervisors (eg. QEMU) might still make it available to the
guest in a form (eg. fw_cfg) that some firmwares (eg. SeaBIOS)
will consume, thus not achieving the desired result.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1425058

Signed-off-by: Andrea Bolognani <abologna@redhat.com>

src/qemu/qemu_command.c

@@ -442,13 +442,20 @@ static int
 qemuBuildRomStr(virBufferPtr buf,
                 virDomainDeviceInfoPtr info)
 {
-    if (info->rombar || info->romfile) {
+    if (info->romenabled || info->rombar || info->romfile) {
         if (info->type != VIR_DOMAIN_DEVICE_ADDRESS_TYPE_PCI) {
             virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
-                           "%s", _("rombar and romfile are supported only for PCI devices"));
+                           "%s", _("ROM tuning is only supported for PCI devices"));
             return -1;
         }
 
+        /* Passing an empty romfile= tells QEMU to disable ROM entirely for
+         * this device, and makes other settings irrelevant */
+        if (info->romenabled == VIR_TRISTATE_BOOL_NO) {
+            virBufferAddLit(buf, ",romfile=");
+            return 0;
+        }
+
         switch (info->rombar) {
         case VIR_TRISTATE_SWITCH_OFF:
             virBufferAddLit(buf, ",rombar=0");
@@ -464,6 +471,7 @@ qemuBuildRomStr(virBufferPtr buf,
            virQEMUBuildBufferEscapeComma(buf, info->romfile);
         }
     }
+
     return 0;
 }
 

tests/qemuxml2argvdata/pci-rom-disabled.args

@@ -0,0 +1,26 @@
+LC_ALL=C \
+PATH=/bin \
+HOME=/home/test \
+USER=test \
+LOGNAME=test \
+QEMU_AUDIO_DRV=none \
+/usr/bin/qemu-system-x86_64 \
+-name guest \
+-S \
+-machine pc,accel=tcg,usb=off,dump-guest-core=off \
+-m 214 \
+-smp 1,sockets=1,cores=1,threads=1 \
+-uuid c7a5fdbd-edaf-9466-926a-d65c16db1809 \
+-display none \
+-no-user-config \
+-nodefaults \
+-chardev socket,id=charmonitor,path=/tmp/lib/domain--1-guest/monitor.sock,\
+server,nowait \
+-mon chardev=charmonitor,id=monitor,mode=control \
+-rtc base=utc \
+-no-shutdown \
+-no-acpi \
+-boot c \
+-netdev user,id=hostnet0 \
+-device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:24:a5:9f,bus=pci.0,\
+addr=0x3,romfile=

tests/qemuxml2argvdata/pci-rom-disabled.xml

@@ -0,0 +1,20 @@
+<domain type='qemu'>
+  <name>guest</name>
+  <uuid>c7a5fdbd-edaf-9466-926a-d65c16db1809</uuid>
+  <memory unit='KiB'>219100</memory>
+  <vcpu placement='static'>1</vcpu>
+  <os>
+    <type arch='x86_64' machine='pc'>hvm</type>
+  </os>
+  <devices>
+    <emulator>/usr/bin/qemu-system-x86_64</emulator>
+    <controller type='pci' model='pci-root'/>
+    <controller type='usb' model='none'/>
+    <interface type='user'>
+      <mac address='52:54:00:24:a5:9f'/>
+      <model type='virtio'/>
+      <rom enabled='no'/>
+    </interface>
+    <memballoon model='none'/>
+  </devices>
+</domain>

tests/qemuxml2argvtest.c

@@ -1554,6 +1554,7 @@ mymain(void)
     DO_TEST_PARSE_ERROR("hostdev-mdev-invalid-target-address",
             QEMU_CAPS_DEVICE_VFIO_PCI);
     DO_TEST("pci-rom", NONE);
+    DO_TEST("pci-rom-disabled", NONE);
 
     DO_TEST_FULL("restore-v2", "exec:cat", 7, 0, 0, GIC_NONE, NONE);
     DO_TEST_FULL("restore-v2-fd", "stdio", 7, 0, 0, GIC_NONE, NONE);

tests/qemuxml2xmloutdata/pci-rom-disabled.xml

@@ -0,0 +1,29 @@
+<domain type='qemu'>
+  <name>guest</name>
+  <uuid>c7a5fdbd-edaf-9466-926a-d65c16db1809</uuid>
+  <memory unit='KiB'>219100</memory>
+  <currentMemory unit='KiB'>219100</currentMemory>
+  <vcpu placement='static'>1</vcpu>
+  <os>
+    <type arch='x86_64' machine='pc'>hvm</type>
+    <boot dev='hd'/>
+  </os>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-x86_64</emulator>
+    <controller type='pci' index='0' model='pci-root'/>
+    <controller type='usb' index='0' model='none'/>
+    <interface type='user'>
+      <mac address='52:54:00:24:a5:9f'/>
+      <model type='virtio'/>
+      <rom enabled='no'/>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
+    </interface>
+    <input type='mouse' bus='ps2'/>
+    <input type='keyboard' bus='ps2'/>
+    <memballoon model='none'/>
+  </devices>
+</domain>

tests/qemuxml2xmltest.c

@@ -474,6 +474,7 @@ mymain(void)
     DO_TEST("hostdev-vfio", NONE);
     DO_TEST("hostdev-mdev-precreated", NONE);
     DO_TEST("pci-rom", NONE);
+    DO_TEST("pci-rom-disabled", NONE);
     DO_TEST("pci-serial-dev-chardev", NONE);
 
     DO_TEST("encrypted-disk", NONE);