[PATCH RFC 4/6] RFC: snapshot: Add support for specifying snapshot disk backing type

[Peter Krempa <pkrempa@xxxxxxxxxx>]

Add support for specifying various types when doing snapshots. This will
later allow to do snapshots on network backed volumes.

RFC: This patch is lacking tests and domain schema touch up.
---
 src/conf/snapshot_conf.c |  9 ++++++++
 src/qemu/qemu_driver.c   | 56 +++++++++++++++++++++++++++++++-----------------
 2 files changed, 45 insertions(+), 20 deletions(-)

diff --git a/src/conf/snapshot_conf.c b/src/conf/snapshot_conf.c
index 5958f13..f6f170e 100644
--- a/src/conf/snapshot_conf.c
+++ b/src/conf/snapshot_conf.c
@@ -108,6 +108,7 @@ virDomainSnapshotDiskDefParseXML(xmlNodePtr node,
 {
     int ret = -1;
     char *snapshot = NULL;
+    char *type = NULL;
     xmlNodePtr cur;

     def->name = virXMLPropString(node, "name");
@@ -129,6 +130,13 @@ virDomainSnapshotDiskDefParseXML(xmlNodePtr node,
     }

     def->type = -1;
+    if ((type = virXMLPropString(node, "type"))) {
+        if ((def->type = virDomainDiskTypeFromString(type)) < 0) {
+            virReportError(VIR_ERR_XML_ERROR,
+                           _("unknown disk snapshot type '%s'"), type);
+            goto cleanup;
+        }
+    }

     for (cur = node->children; cur; cur = cur->next) {
         if (cur->type != XML_ELEMENT_NODE)
@@ -174,6 +182,7 @@ virDomainSnapshotDiskDefParseXML(xmlNodePtr node,
     ret = 0;
 cleanup:
     VIR_FREE(snapshot);
+    VIR_FREE(type);
     if (ret < 0)
         virDomainSnapshotDiskDefClear(def);
     return ret;
diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index b9c270b..e6d4f47 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -12115,33 +12115,48 @@ qemuDomainSnapshotCreateSingleDiskActive(virQEMUDriverPtr driver,
     }

     if (virAsprintf(&device, "drive-%s", disk->info.alias) < 0 ||
-        VIR_STRDUP(source, snap->file) < 0 ||
         (persistDisk && VIR_STRDUP(persistSource, source) < 0))
         goto cleanup;

-    /* create the stub file and set selinux labels; manipulate disk in
-     * place, in a way that can be reverted on failure. */
-    if (!reuse) {
-        fd = qemuOpenFile(driver, vm, source, O_WRONLY | O_TRUNC | O_CREAT,
-                          &need_unlink, NULL);
-        if (fd < 0)
-            goto cleanup;
-        VIR_FORCE_CLOSE(fd);
-    }
-
     /* XXX Here, we know we are about to alter disk->backingChain if
-     * successful, so we nuke the existing chain so that future
-     * commands will recompute it.  Better would be storing the chain
-     * ourselves rather than reprobing, but this requires modifying
-     * domain_conf and our XML to fully track the chain across
-     * libvirtd restarts.  */
+     * successful, so we nuke the existing chain so that future commands will
+     * recompute it.  Better would be storing the chain ourselves rather than
+     * reprobing, but this requires modifying domain_conf and our XML to fully
+     * track the chain across libvirtd restarts.  */
     virStorageFileFreeMetadata(disk->backingChain);
     disk->backingChain = NULL;

-    if (qemuDomainPrepareDiskChainElement(driver, vm, disk, source,
-                                          VIR_DISK_CHAIN_READ_WRITE) < 0) {
-        qemuDomainPrepareDiskChainElement(driver, vm, disk, source,
-                                          VIR_DISK_CHAIN_NO_ACCESS);
+    switch (snap->type) {
+    case VIR_DOMAIN_DISK_TYPE_BLOCK:
+        reuse = true;
+        /* fallthrough */
+    case -1: /* type was not provided in snapshot conf */
+    case VIR_DOMAIN_DISK_TYPE_FILE:
+        if (VIR_STRDUP(source, snap->file) < 0)
+            goto cleanup;
+
+        /* create the stub file and set selinux labels; manipulate disk in
+         * place, in a way that can be reverted on failure. */
+        if (!reuse) {
+            fd = qemuOpenFile(driver, vm, source, O_WRONLY | O_TRUNC | O_CREAT,
+                              &need_unlink, NULL);
+            if (fd < 0)
+                goto cleanup;
+            VIR_FORCE_CLOSE(fd);
+        }
+
+        if (qemuDomainPrepareDiskChainElement(driver, vm, disk, source,
+                                              VIR_DISK_CHAIN_READ_WRITE) < 0) {
+            qemuDomainPrepareDiskChainElement(driver, vm, disk, source,
+                                              VIR_DISK_CHAIN_NO_ACCESS);
+            goto cleanup;
+        }
+        break;
+
+    default:
+        virReportError(VIR_ERR_OPERATION_UNSUPPORTED,
+                       _("snapshots are not supported on '%s' volumes"),
+                       virDomainDiskTypeToString(snap->type));
         goto cleanup;
     }

@@ -12160,6 +12175,7 @@ qemuDomainSnapshotCreateSingleDiskActive(virQEMUDriverPtr driver,
     disk->src = source;
     source = NULL;
     disk->format = format;
+    disk->type = snap->type;
     if (persistDisk) {
         VIR_FREE(persistDisk->src);
         persistDisk->src = persistSource;
-- 
1.8.4.3

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