qemu: domain: Reject shared disk access if backing format does not support it

Disk sharing between two VMs may corrupt the images if the format driver
does not support it. Check that the user declared use of a supported
storage format when they want to share the disk.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1511480

src/qemu/qemu_domain.c

@@ -25,6 +25,7 @@
 
 #include "qemu_domain.h"
 #include "qemu_alias.h"
+#include "qemu_block.h"
 #include "qemu_cgroup.h"
 #include "qemu_command.h"
 #include "qemu_process.h"
@@ -3724,6 +3725,29 @@ qemuDomainDeviceDefValidateVideo(const virDomainVideoDef *video)
 }
 
 
+static int
+qemuDomainDeviceDefValidateDisk(const virDomainDiskDef *disk)
+{
+    if (disk->src->shared && !disk->src->readonly) {
+        if (disk->src->format <= VIR_STORAGE_FILE_AUTO) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                           _("shared access for disk '%s' requires use of "
+                             "explicitly specified disk format"), disk->dst);
+            return -1;
+        }
+
+        if (!qemuBlockStorageSourceSupportsConcurrentAccess(disk->src)) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                           _("shared access for disk '%s' requires use of "
+                             "supported storage format"), disk->dst);
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
+
 static int
 qemuDomainDeviceDefValidate(const virDomainDeviceDef *dev,
                             const virDomainDef *def,
@@ -3765,6 +3789,9 @@ qemuDomainDeviceDefValidate(const virDomainDeviceDef *dev,
         break;
 
     case VIR_DOMAIN_DEVICE_DISK:
+        ret = qemuDomainDeviceDefValidateDisk(dev->data.disk);
+        break;
+
     case VIR_DOMAIN_DEVICE_LEASE:
     case VIR_DOMAIN_DEVICE_FS:
     case VIR_DOMAIN_DEVICE_INPUT:

tests/qemuxml2argvdata/qemuxml2argv-disk-drive-shared-qcow.xml

+<domain type='qemu'>
+  <name>QEMUGuest1</name>
+  <uuid>c7a5fdbd-edaf-9455-926a-d65c16db1809</uuid>
+  <memory unit='KiB'>219136</memory>
+  <currentMemory unit='KiB'>219136</currentMemory>
+  <vcpu placement='static'>1</vcpu>
+  <os>
+    <type arch='i686' 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-i686</emulator>
+    <disk type='block' device='disk'>
+      <driver name='qemu' type='qcow2'/>
+      <source dev='/dev/HostVG/QEMUGuest1'/>
+      <target dev='hda' bus='ide'/>
+      <shareable/>
+      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
+    </disk>
+    <controller type='usb' index='0'/>
+    <controller type='ide' index='0'/>
+    <memballoon model='virtio'/>
+  </devices>
+</domain>

tests/qemuxml2argvdata/qemuxml2argv-disk-drive-shared.args

@@ -19,7 +19,7 @@ server,nowait \
 -no-acpi \
 -boot c \
 -usb \
--drive file=/dev/HostVG/QEMUGuest1,format=qcow2,if=none,id=drive-ide0-0-0,\
+-drive file=/dev/HostVG/QEMUGuest1,format=raw,if=none,id=drive-ide0-0-0,\
 serial=XYZXYZXYZYXXYZYZYXYZY,cache=none \
 -device ide-drive,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0 \
 -drive file=/dev/HostVG/QEMUGuest2,format=raw,if=none,id=drive-ide0-1-0,\

tests/qemuxml2argvdata/qemuxml2argv-disk-drive-shared.xml

@@ -15,7 +15,7 @@
   <devices>
     <emulator>/usr/bin/qemu-system-i686</emulator>
     <disk type='block' device='disk'>
-      <driver name='qemu' type='qcow2'/>
+      <driver name='qemu' type='raw'/>
       <source dev='/dev/HostVG/QEMUGuest1'/>
       <target dev='hda' bus='ide'/>
       <shareable/>

tests/qemuxml2argvtest.c

@@ -908,6 +908,7 @@ mymain(void)
             QEMU_CAPS_DRIVE_BOOT);
     DO_TEST("disk-drive-shared",
             QEMU_CAPS_DRIVE_SERIAL);
+    DO_TEST_PARSE_ERROR("disk-drive-shared-qcow", NONE);
     DO_TEST("disk-drive-error-policy-stop",
             QEMU_CAPS_MONITOR_JSON);
     DO_TEST("disk-drive-error-policy-enospace",