qemu: process: Move handling of non-backing files into qemuDomainDetermineDiskChain

Until now we would skip loading of the backing chain for files which
don't support backing chains only when starting up the VM. Move the
check from qemuProcessPrepareHostStorage with some adaptations so that's
always applied.

src/qemu/qemu_domain.c

@@ -6372,6 +6372,23 @@ qemuDomainDetermineDiskChain(virQEMUDriverPtr driver,
     if (force_probe)
         virStorageSourceBackingStoreClear(src);
 
+    /* There is no need to check the backing chain for disks without backing
+     * support */
+    if (virStorageSourceIsLocalStorage(src) &&
+        src->format > VIR_STORAGE_FILE_NONE &&
+        src->format < VIR_STORAGE_FILE_BACKING) {
+
+        if (!virFileExists(src->path)) {
+            if (report_broken)
+                virStorageFileReportBrokenChain(errno, src, disk->src);
+
+            goto cleanup;
+        }
+
+        ret = 0;
+        goto cleanup;
+    }
+
     /* skip to the end of the chain if there is any */
     while (virStorageSourceHasBacking(src)) {
         if (report_broken &&

src/qemu/qemu_process.c

@@ -5555,20 +5555,10 @@ qemuProcessPrepareHostStorage(virQEMUDriverPtr driver,
     for (i = vm->def->ndisks; i > 0; i--) {
         size_t idx = i - 1;
         virDomainDiskDefPtr disk = vm->def->disks[idx];
-        virStorageFileFormat format = virDomainDiskGetFormat(disk);
 
         if (virStorageSourceIsEmpty(disk->src))
             continue;
 
-        /* There is no need to check the backing chain for disks
-         * without backing support, the fact that the file exists is
-         * more than enough */
-        if (virStorageSourceIsLocalStorage(disk->src) &&
-            format > VIR_STORAGE_FILE_NONE &&
-            format < VIR_STORAGE_FILE_BACKING &&
-            virFileExists(virDomainDiskGetSource(disk)))
-            continue;
-
         if (qemuDomainDetermineDiskChain(driver, vm, disk, true, true) >= 0)
             continue;