qemu: snapshot: error out early when reverting snapshot for VM with non-file disk

Before this patch the code would start the revert process by destroying
the VM and preparing to revert where it would fail with following error:

    error: unsupported configuration: source for disk 'sdb' is not a regular file; refusing to generate external snapshot name

and leaving user with offline VM even if it was running.

Make the check before we start the revert process to not destroy VMs.

Resolves: https://issues.redhat.com/browse/RHEL-30971
Resolves: https://issues.redhat.com/browse/RHEL-79928
Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>

diff --git a/src/qemu/qemu_snapshot.c b/src/qemu/qemu_snapshot.c
index 0d940d3d3809ea823afbf432171fd3e65e5b2615..9556bd121664bc9ac3f81f43a710c7b28e70387d 100644 (file)
--- a/src/qemu/qemu_snapshot.c
+++ b/src/qemu/qemu_snapshot.c
@@ -2203,6 +2203,8 @@ qemuSnapshotRevertValidate(virDomainObj *vm,
                            virDomainSnapshotDef *snapdef,
                            unsigned int flags)
 {
+    size_t i;
+
     if (!vm->persistent &&
         snapdef->state != VIR_DOMAIN_SNAPSHOT_RUNNING &&
         snapdef->state != VIR_DOMAIN_SNAPSHOT_PAUSED &&
@@ -2230,6 +2232,22 @@ qemuSnapshotRevertValidate(virDomainObj *vm,
         }
     }
 
+    /* Reverting to external snapshot creates overlay files for every disk and
+     * it would fail for non-file based disks.
+     * See qemuSnapshotRevertExternalPrepare for more details. */
+    if (virDomainSnapshotIsExternal(snap)) {
+        for (i = 0; i < snap->def->dom->ndisks; i++) {
+            virDomainDiskDef *disk = snap->def->dom->disks[i];
+
+            if (disk->src->type != VIR_STORAGE_TYPE_FILE) {
+                virReportError(VIR_ERR_OPERATION_UNSUPPORTED,
+                               _("source disk for '%1$s' is not a regular file, reverting to snapshot is not supported"),
+                               disk->dst);
+                return -1;
+            }
+        }
+    }
+
     return 0;
 }
 
@@ -2381,6 +2399,9 @@ qemuSnapshotRevertExternalPrepare(virDomainObj *vm,
     if (virDomainMomentDefPostParse(&tmpsnapdef->parent) < 0)
         return -1;
 
+    /* Force default location to be external in order to create overlay files
+     * for every disk. In qemuSnapshotRevertValidate we make sure that each
+     * disk is regular file otherwise this would fail. */
     if (virDomainSnapshotAlignDisks(tmpsnapdef, domdef,
                                     VIR_DOMAIN_SNAPSHOT_LOCATION_EXTERNAL,
                                     false, true) < 0) {