From b2904cb87b55f5481f2c234796649fd82790eb23 Mon Sep 17 00:00:00 2001
From: Peter Krempa <pkrempa@redhat.com>
Date: Tue, 13 Aug 2019 12:23:00 +0200
Subject: [PATCH] qemu: snapshot: Skip overlay file creation/interogation if
 unsupported
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With blockdev we'll be able to support protocols which are not supported
by the storage backends in libvirt. This means that we have to be able
to skip the creation and relative storage path reading if it's not
supported. This will make it impossible to use relative backing for
network protocols but that would be almost insane anyways.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
---
 src/qemu/qemu_driver.c | 53 ++++++++++++++++++++++++------------------
 1 file changed, 31 insertions(+), 22 deletions(-)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 9480df2b39..a332db333a 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -15316,6 +15316,8 @@ qemuDomainSnapshotDiskPrepareOne(virQEMUDriverPtr driver,
 {
     char *backingStoreStr;
     virDomainDiskDefPtr persistdisk;
+    bool supportsCreate;
+    bool supportsBacking;
 
     dd->disk = disk;
 
@@ -15343,31 +15345,38 @@ qemuDomainSnapshotDiskPrepareOne(virQEMUDriverPtr driver,
             return -1;
     }
 
-    if (qemuDomainStorageFileInit(driver, vm, dd->src, NULL) < 0)
-        return -1;
-
-    dd->initialized = true;
+    supportsCreate = virStorageFileSupportsCreate(dd->src);
+    supportsBacking = virStorageFileSupportsBackingChainTraversal(dd->src);
 
-    /* relative backing store paths need to be updated so that relative
-     * block commit still works */
-    if (reuse) {
-        if (virStorageFileGetBackingStoreStr(dd->src, &backingStoreStr) < 0)
+    if (supportsCreate || supportsBacking) {
+        if (qemuDomainStorageFileInit(driver, vm, dd->src, NULL) < 0)
             return -1;
-        if (backingStoreStr != NULL) {
-            if (virStorageIsRelative(backingStoreStr))
-                VIR_STEAL_PTR(dd->relPath, backingStoreStr);
-            else
-                VIR_FREE(backingStoreStr);
-        }
-    } else {
-        /* pre-create the image file so that we can label it before handing it to qemu */
-        if (dd->src->type != VIR_STORAGE_TYPE_BLOCK) {
-            if (virStorageFileCreate(dd->src) < 0) {
-                virReportSystemError(errno, _("failed to create image file '%s'"),
-                                     NULLSTR(dd->src->path));
-                return -1;
+
+        dd->initialized = true;
+
+        /* relative backing store paths need to be updated so that relative
+         * block commit still works */
+        if (reuse) {
+            if (supportsBacking) {
+                if (virStorageFileGetBackingStoreStr(dd->src, &backingStoreStr) < 0)
+                    return -1;
+                if (backingStoreStr != NULL) {
+                    if (virStorageIsRelative(backingStoreStr))
+                        VIR_STEAL_PTR(dd->relPath, backingStoreStr);
+                    else
+                        VIR_FREE(backingStoreStr);
+                }
+            }
+        } else {
+            /* pre-create the image file so that we can label it before handing it to qemu */
+            if (supportsCreate && dd->src->type != VIR_STORAGE_TYPE_BLOCK) {
+                if (virStorageFileCreate(dd->src) < 0) {
+                    virReportSystemError(errno, _("failed to create image file '%s'"),
+                                         NULLSTR(dd->src->path));
+                    return -1;
+                }
+                dd->created = true;
             }
-            dd->created = true;
         }
     }
 
-- 
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