qemu: Reject updating unsupported disk information

If one calls update-device with information that is not updatable,
libvirt reports success even though no data were updated.  The example
used in the bug linked below uses updating device with <boot order='2'/>
which, in my opinion, is a valid thing to request from user's
perspective.  Mainly since we properly error out if user wants to update
such data on a network device for example.

And since there are many things that might happen (update-device on disk
basically knows just how to change removable media), check for what's
changing and moreover, since the function might be usable in other
drivers (updating only disk path is a valid possibility) let's abstract
it for any two disks.

We can't possibly check for everything since for many fields our code
does not properly differentiate between default and unspecified values.
Even though this could be changed, I don't feel like it's worth the
complexity so it's not the aim of this patch.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1007228

src/conf/domain_conf.c

@@ -5690,6 +5690,134 @@ virDomainDiskFindByBusAndDst(virDomainDefPtr def,
     return NULL;
 }
 
+
+/*
+ * Makes sure the @disk differs from @orig_disk only by the source
+ * path and nothing else.  Fields that are being checked and the
+ * information whether they are nullable (may not be specified) or is
+ * taken from the virDomainDiskDefFormat() code.
+ */
+bool
+virDomainDiskDiffersSourceOnly(virDomainDiskDefPtr disk,
+                               virDomainDiskDefPtr orig_disk)
+{
+#define CHECK_EQ(field, field_name, nullable)                           \
+    do {                                                                \
+        if (nullable && !disk->field)                                   \
+            break;                                                      \
+        if (disk->field != orig_disk->field) {                          \
+            virReportError(VIR_ERR_OPERATION_UNSUPPORTED,               \
+                           _("cannot modify field '%s' of the disk"),   \
+                           field_name);                                 \
+            return false;                                               \
+        }                                                               \
+    } while (0)
+
+    CHECK_EQ(device, "device", false);
+    CHECK_EQ(cachemode, "cache", true);
+    CHECK_EQ(error_policy, "error_policy", true);
+    CHECK_EQ(rerror_policy, "rerror_policy", true);
+    CHECK_EQ(iomode, "io", true);
+    CHECK_EQ(ioeventfd, "ioeventfd", true);
+    CHECK_EQ(event_idx, "event_idx", true);
+    CHECK_EQ(copy_on_read, "copy_on_read", true);
+    CHECK_EQ(discard, "discard", true);
+    CHECK_EQ(iothread, "iothread", true);
+
+    if (disk->geometry.cylinders &&
+        disk->geometry.heads &&
+        disk->geometry.sectors) {
+        CHECK_EQ(geometry.cylinders, "geometry cylinders", false);
+        CHECK_EQ(geometry.heads, "geometry heads", false);
+        CHECK_EQ(geometry.sectors, "geometry sectors", false);
+        CHECK_EQ(geometry.trans, "BIOS-translation-modus", true);
+    }
+
+    CHECK_EQ(blockio.logical_block_size,
+             "blockio logical_block_size", false);
+    CHECK_EQ(blockio.physical_block_size,
+             "blockio physical_block_size", false);
+
+    if (disk->bus == VIR_DOMAIN_DISK_BUS_USB)
+        CHECK_EQ(removable, "removable", true);
+
+    CHECK_EQ(blkdeviotune.total_bytes_sec,
+             "blkdeviotune total_bytes_sec",
+             true);
+    CHECK_EQ(blkdeviotune.read_bytes_sec,
+             "blkdeviotune read_bytes_sec",
+             true);
+    CHECK_EQ(blkdeviotune.write_bytes_sec,
+             "blkdeviotune write_bytes_sec",
+             true);
+    CHECK_EQ(blkdeviotune.total_iops_sec,
+             "blkdeviotune total_iops_sec",
+             true);
+    CHECK_EQ(blkdeviotune.read_iops_sec,
+             "blkdeviotune read_iops_sec",
+             true);
+    CHECK_EQ(blkdeviotune.write_iops_sec,
+             "blkdeviotune write_iops_sec",
+             true);
+    CHECK_EQ(blkdeviotune.total_bytes_sec_max,
+             "blkdeviotune total_bytes_sec_max",
+             true);
+    CHECK_EQ(blkdeviotune.read_bytes_sec_max,
+             "blkdeviotune read_bytes_sec_max",
+             true);
+    CHECK_EQ(blkdeviotune.write_bytes_sec_max,
+             "blkdeviotune write_bytes_sec_max",
+             true);
+    CHECK_EQ(blkdeviotune.total_iops_sec_max,
+             "blkdeviotune total_iops_sec_max",
+             true);
+    CHECK_EQ(blkdeviotune.read_iops_sec_max,
+             "blkdeviotune read_iops_sec_max",
+             true);
+    CHECK_EQ(blkdeviotune.write_iops_sec_max,
+             "blkdeviotune write_iops_sec_max",
+             true);
+    CHECK_EQ(blkdeviotune.size_iops_sec,
+             "blkdeviotune size_iops_sec",
+             true);
+
+    CHECK_EQ(transient, "transient", true);
+
+    if (disk->serial && STRNEQ(disk->serial, orig_disk->serial)) {
+        virReportError(VIR_ERR_OPERATION_UNSUPPORTED,
+                       _("cannot modify field '%s' of the disk"),
+                       "serial");
+        return false;
+    }
+
+    if (disk->wwn && STRNEQ(disk->wwn, orig_disk->wwn)) {
+        virReportError(VIR_ERR_OPERATION_UNSUPPORTED,
+                       _("cannot modify field '%s' of the disk"),
+                       "wwn");
+        return false;
+    }
+
+    if (disk->vendor && STRNEQ(disk->vendor, orig_disk->vendor)) {
+        virReportError(VIR_ERR_OPERATION_UNSUPPORTED,
+                       _("cannot modify field '%s' of the disk"),
+                       "vendor");
+        return false;
+    }
+
+    if (disk->product && STRNEQ(disk->product, orig_disk->product)) {
+        virReportError(VIR_ERR_OPERATION_UNSUPPORTED,
+                       _("cannot modify field '%s' of the disk"),
+                       "product");
+        return false;
+    }
+
+    CHECK_EQ(info.bootIndex, "boot order", true);
+
+#undef CHECK_EQ
+
+    return true;
+}
+
 int
 virDomainDiskDefAssignAddress(virDomainXMLOptionPtr xmlopt,
                               virDomainDiskDefPtr def)

src/conf/domain_conf.h

@@ -2474,6 +2474,8 @@ int virDomainDeviceFindControllerModel(virDomainDefPtr def,
 virDomainDiskDefPtr virDomainDiskFindByBusAndDst(virDomainDefPtr def,
                                                  int bus,
                                                  char *dst);
+bool virDomainDiskDiffersSourceOnly(virDomainDiskDefPtr disk,
+                                    virDomainDiskDefPtr orig_disk);
 void virDomainControllerDefFree(virDomainControllerDefPtr def);
 void virDomainFSDefFree(virDomainFSDefPtr def);
 void virDomainActualNetDefFree(virDomainActualNetDefPtr def);

src/libvirt_private.syms

@@ -249,6 +249,7 @@ virDomainDiskDefFree;
 virDomainDiskDefNew;
 virDomainDiskDefSourceParse;
 virDomainDiskDeviceTypeToString;
+virDomainDiskDiffersSourceOnly;
 virDomainDiskDiscardTypeToString;
 virDomainDiskErrorPolicyTypeFromString;
 virDomainDiskErrorPolicyTypeToString;

src/qemu/qemu_driver.c

@@ -7920,6 +7920,9 @@ qemuDomainChangeDiskMediaLive(virConnectPtr conn,
             goto end;
         }
 
+        if (!virDomainDiskDiffersSourceOnly(disk, orig_disk))
+            goto end;
+
         /* Add the new disk src into shared disk hash table */
         if (qemuAddSharedDevice(driver, dev, vm->def->name) < 0)
             goto end;