qemu: enable using implicit sata controller in q35 machines

q35 machines have an implicit ahci (sata) controller at 00:1F.2 which
has no "id" associated with it. For this reason, we can't refer to it
as "ahci0". Instead, we don't give an id on the commandline, which
qemu interprets as "use the first ahci controller". We then need to
specify the unit with "unit=%d" rather than adding it onto the bus
arg.

src/qemu/qemu_command.c

@@ -4211,9 +4211,26 @@ qemuBuildDriveDevStr(virDomainDefPtr def,
             virBufferAddLit(&opt, "ide-drive");
         }
 
-        virBufferAsprintf(&opt, ",bus=ahci%d.%d",
-                          disk->info.addr.drive.controller,
-                          disk->info.addr.drive.unit);
+        if (qemuDomainMachineIsQ35(def) &&
+            disk->info.addr.drive.controller == 0) {
+            /* Q35 machines have an implicit ahci (sata) controller at
+             * 00:1F.2 which has no "id" associated with it. For this
+             * reason, we can't refer to it as "ahci0". Instead, we
+             * don't give an id, which qemu interprets as "use the
+             * first ahci controller". We then need to specify the
+             * unit with "unit=%d" rather than adding it onto the bus
+             * arg.
+             */
+            virBufferAsprintf(&opt, ",unit=%d", disk->info.addr.drive.unit);
+        } else {
+            /* All other ahci controllers have been created by
+             * libvirt, so they *do* have an id, and we can identify
+             * them that way.
+             */
+            virBufferAsprintf(&opt, ",bus=ahci%d.%d",
+                              disk->info.addr.drive.controller,
+                              disk->info.addr.drive.unit);
+        }
         break;
     case VIR_DOMAIN_DISK_BUS_VIRTIO:
         if (disk->info.type == VIR_DOMAIN_DEVICE_ADDRESS_TYPE_CCW) {

tests/qemuxml2argvdata/qemuxml2argv-q35.args

@@ -3,4 +3,6 @@ LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test \
 -monitor unix:/tmp/test-monitor,server,nowait -no-acpi -boot c \
 -device i82801b11-bridge,id=pci.1,bus=pcie.0,addr=0x2 \
 -device pci-bridge,chassis_nr=2,id=pci.2,bus=pci.1,addr=0x1 \
+-drive file=/dev/HostVG/QEMUGuest1,if=none,id=drive-sata0-0-0 \
+-device ide-drive,unit=0,drive=drive-sata0-0-0,id=sata0-0-0 \
 -vga qxl -global qxl.ram_size=67108864 -global qxl.vram_size=18874368

tests/qemuxml2argvdata/qemuxml2argv-q35.xml

@@ -14,6 +14,11 @@
   <on_crash>destroy</on_crash>
   <devices>
     <emulator>/usr/libexec/qemu-kvm</emulator>
+    <disk type='block' device='disk'>
+      <source dev='/dev/HostVG/QEMUGuest1'/>
+      <target dev='sda' bus='sata'/>
+      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
+    </disk>
     <controller type='pci' index='0' model='pcie-root'/>
     <controller type='pci' index='1' model='dmi-to-pci-bridge'/>
     <controller type='pci' index='2' model='pci-bridge'/>

tests/qemuxml2argvtest.c

@@ -1001,7 +1001,7 @@ mymain(void)
     DO_TEST("q35",
             QEMU_CAPS_DEVICE, QEMU_CAPS_DEVICE_PCI_BRIDGE,
             QEMU_CAPS_DEVICE_DMI_TO_PCI_BRIDGE,
-            QEMU_CAPS_ICH9_AHCI,
+            QEMU_CAPS_DRIVE, QEMU_CAPS_ICH9_AHCI,
             QEMU_CAPS_VGA, QEMU_CAPS_DEVICE_VIDEO_PRIMARY,
             QEMU_CAPS_VGA, QEMU_CAPS_VGA_QXL, QEMU_CAPS_DEVICE_QXL);
 

tests/qemuxml2xmloutdata/qemuxml2xmlout-q35.xml

@@ -14,6 +14,11 @@
   <on_crash>destroy</on_crash>
   <devices>
     <emulator>/usr/libexec/qemu-kvm</emulator>
+    <disk type='block' device='disk'>
+      <source dev='/dev/HostVG/QEMUGuest1'/>
+      <target dev='sda' bus='sata'/>
+      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
+    </disk>
     <controller type='pci' index='0' model='pcie-root'/>
     <controller type='pci' index='1' model='dmi-to-pci-bridge'/>
     <controller type='pci' index='2' model='pci-bridge'/>