qemu: Validate backing store of 'mirror' for block copy

Since 4e797f1a we parse backingStore of mirror which will later be used
with blockdev. Add some validation for the user passed mirror at the
current point to make sure it's not used improperly.

Validate that it's not used without blockdev and also that it's not
passed when not requesting a shallow copy. Also add a chain terminator
for a deep copy since we know the resulting mirror will not have chain.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/qemu/qemu_driver.c

@@ -17560,6 +17560,63 @@ qemuDomainBlockCopyValidateMirror(virStorageSourcePtr mirror,
 }
 
 
+/**
+ * qemuDomainBlockCopyCommonValidateUserMirrorBackingStore:
+ * @mirror: target of the block copy
+ * @flags: block copy API flags
+ * @blockdev: true if blockdev is used for the VM
+ *
+ * Validates whether backingStore of @mirror makes sense according to @flags.
+ * This makes sure that:
+ * 1) mirror has a terminator if it isn't supposed to have backing chain
+ * 2) if shallow copy is requested there is a chain or prepopulated image
+ * 3) user specified chain is present only when blockdev is used
+ * 4) if deep copy is requested, there's no chain
+ */
+static int
+qemuDomainBlockCopyCommonValidateUserMirrorBackingStore(virStorageSourcePtr mirror,
+                                                        unsigned int flags,
+                                                        bool blockdev)
+{
+    /* note that if original disk does not have backing chain, shallow is cleared */
+    bool shallow = flags & VIR_DOMAIN_BLOCK_COPY_SHALLOW;
+    bool reuse = flags & VIR_DOMAIN_BLOCK_COPY_REUSE_EXT;
+
+    if (!mirror->backingStore) {
+        /* deep copy won't need backing store so we can terminate it */
+        if (!shallow &&
+            !(mirror->backingStore = virStorageSourceNew()))
+            return -1;
+
+        return 0;
+    }
+
+    /* validate user provided backing store */
+    if (virStorageSourceHasBacking(mirror)) {
+        if (!blockdev) {
+            virReportError(VIR_ERR_INVALID_ARG, "%s",
+                           _("backingStore of mirror target is not supported by this qemu"));
+            return -1;
+        }
+
+        if (!shallow) {
+            virReportError(VIR_ERR_INVALID_ARG, "%s",
+                           _("backingStore of mirror without VIR_DOMAIN_BLOCK_COPY_SHALLOW doesn't make sense"));
+            return -1;
+        }
+    } else {
+        /* shallow copy without reuse requires some kind of backing data */
+        if (!reuse && shallow) {
+            virReportError(VIR_ERR_INVALID_ARG, "%s",
+                           _("VIR_DOMAIN_BLOCK_COPY_SHALLOW implies backing chain for mirror"));
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
+
 /* bandwidth in bytes/s.  Caller must lock vm beforehand, and not
  * access mirror afterwards.  */
 static int
@@ -17574,7 +17631,7 @@ qemuDomainBlockCopyCommon(virDomainObjPtr vm,
                           bool keepParentLabel)
 {
     virQEMUDriverPtr driver = conn->privateData;
-    qemuDomainObjPrivatePtr priv;
+    qemuDomainObjPrivatePtr priv = vm->privateData;
     VIR_AUTOFREE(char *) device = NULL;
     virDomainDiskDefPtr disk = NULL;
     int ret = -1;
@@ -17584,14 +17641,13 @@ qemuDomainBlockCopyCommon(virDomainObjPtr vm,
     bool reuse = !!(flags & VIR_DOMAIN_BLOCK_COPY_REUSE_EXT);
     qemuBlockJobDataPtr job = NULL;
     VIR_AUTOUNREF(virStorageSourcePtr) mirror = mirrorsrc;
+    bool blockdev = virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_BLOCKDEV);
 
     /* Preliminaries: find the disk we are editing, sanity checks */
     virCheckFlags(VIR_DOMAIN_BLOCK_COPY_SHALLOW |
                   VIR_DOMAIN_BLOCK_COPY_REUSE_EXT |
                   VIR_DOMAIN_BLOCK_COPY_TRANSIENT_JOB, -1);
 
-    priv = vm->privateData;
-
     if (virStorageSourceIsRelative(mirror)) {
         virReportError(VIR_ERR_INVALID_ARG, "%s",
                        _("absolute path must be used as block copy target"));
@@ -17640,6 +17696,10 @@ qemuDomainBlockCopyCommon(virDomainObjPtr vm,
     if (!virStorageSourceHasBacking(disk->src))
         flags &= ~VIR_DOMAIN_BLOCK_COPY_SHALLOW;
 
+    if (qemuDomainBlockCopyCommonValidateUserMirrorBackingStore(mirror, flags,
+                                                                blockdev) < 0)
+        goto endjob;
+
     /* unless the user provides a pre-created file, shallow copy into a raw
      * file is not possible */
     if ((flags & VIR_DOMAIN_BLOCK_COPY_SHALLOW) && !reuse &&
@@ -17705,11 +17765,11 @@ qemuDomainBlockCopyCommon(virDomainObjPtr vm,
                                          keepParentLabel) < 0)
         goto endjob;
 
-    /* If reusing an external image that includes a backing file, the pivot may
-     * result in qemu needing to open the entire backing chain, so we need to
-     * label the full backing chain of the mirror instead of just the top image */
+    /* If reusing an external image that includes a backing file but the user
+     * did not enumerate the chain in the XML we need to detect the chain */
     if (flags & VIR_DOMAIN_BLOCK_COPY_REUSE_EXT &&
         mirror->format >= VIR_STORAGE_FILE_BACKING &&
+        mirror->backingStore == NULL &&
         qemuDomainDetermineDiskChain(driver, vm, disk, mirror, true) < 0)
         goto endjob;