[Qemu-devel] [PATCH RFC 1/1] vmstate: draft fix for failed iotests case 68 and 91

[QingFeng Hao <haoqf@linux.vnet.ibm.com>]

I am not very clear about the logic in vmstate.c, but from its context in
vmstate_save_state, it seems size should not be 0, otherwise the followed
for loop will keep working on the same element. So I just add a simple
check to pass that case, not sure if it's right but it can pass iotest
case 68 and 91 now.

The iotest's failed output is:
068 1s ... - output mismatch (see 068.out.bad)
--- /home/haoqf/KVMonz/gitcheck/work/qemu-master/tree/qemu/tests/qemu-iotests/068.out   2017-03-06 05:52:24.817328899 +0100
+++ 068.out.bad 2017-03-07 03:28:44.426714519 +0100
@@ -3,9 +3,13 @@
 === Saving and reloading a VM state to/from a qcow2 image ===

 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=131072
+qemu-system-s390x: migration/vmstate.c:336: vmstate_save_state: Assertion `first_elem || !n_elems' failed.
+./common.config: line 109: 52497 Aborted                 ( if [ -n "${QEMU_NEED_PID}" ]; then
+    echo $BASHPID > "${QEMU_TEST_DIR}/qemu-${_QEMU_HANDLE}.pid";
+fi; exec "$QEMU_PROG" $QEMU_OPTIONS "$@" )
 QEMU X.Y.Z monitor - type 'help' for more information
 (qemu) savevm 0
-(qemu) quit
+qemu-system-s390x: Device 'virtio0' does not have the requested snapshot '0'
 QEMU X.Y.Z monitor - type 'help' for more information
 (qemu) quit
 *** done

091 1s ... [failed, exit status 1] - output mismatch (see 091.out.bad)
    --- tests/qemu-iotests/091.out	2016-08-30 12:35:04.207683276 +0200
    +++ 091.out.bad	2017-03-06 13:08:03.717135426 +0100
    @@ -11,18 +11,23 @@
     
     vm1: qemu-io disk write complete
     vm1: live migration started
    -vm1: live migration completed
    -
    -=== VM 2: Post-migration, write to disk, verify running ===
    -
    -vm2: qemu-io disk write complete
    -vm2: qemu process running successfully
    -vm2: flush io, and quit
    -Check image pattern
    -read 4194304/4194304 bytes at offset 0
    -4 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
    -Running 'qemu-img check -r all $TEST_IMG'
    -No errors were found on the image.
    -80/16384 = 0.49% allocated, 0.00% fragmented, 0.00% compressed clusters
    -Image end offset: 5570560
    -*** done
    +./common.qemu: line 110: write error: Broken pipe
    +./common.qemu: line 110: write error: Broken pipe
    +./common.qemu: line 110: write error: Broken pipe
    +./common.qemu: line 110: write error: Broken pipe
    +./common.qemu: line 110: write error: Broken pipe
    +./common.qemu: line 110: write error: Broken pipe
    +./common.qemu: line 110: write error: Broken pipe
    +./common.qemu: line 110: write error: Broken pipe
    +./common.qemu: line 110: write error: Broken pipe
    +./common.qemu: line 110: write error: Broken pipe
    +./common.qemu: line 110: write error: Broken pipe
    +./common.qemu: line 110: write error: Broken pipe
    +./common.qemu: line 110: write error: Broken pipe
    +./common.qemu: line 110: write error: Broken pipe
    +./common.qemu: line 110: write error: Broken pipe
    +./common.qemu: line 110: write error: Broken pipe
    +./common.qemu: line 110: write error: Broken pipe
    +./common.qemu: line 110: write error: Broken pipe
    +./common.qemu: line 110: write error: Broken pipe
    +Timeout waiting for completed on handle 0

Signed-off-by: QingFeng Hao <haoqf@linux.vnet.ibm.com>
---
 migration/vmstate.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/migration/vmstate.c b/migration/vmstate.c
index 78b3cd4..ff28dde 100644
--- a/migration/vmstate.c
+++ b/migration/vmstate.c
@@ -106,6 +106,10 @@ int vmstate_load_state(QEMUFile *f, const VMStateDescription *vmsd,
             int i, n_elems = vmstate_n_elems(opaque, field);
             int size = vmstate_size(opaque, field);
 
+            if (size == 0) {
+                field++;
+                continue;
+            }
             vmstate_handle_alloc(first_elem, field, opaque);
             if (field->flags & VMS_POINTER) {
                 first_elem = *(void **)first_elem;
@@ -322,6 +326,10 @@ void vmstate_save_state(QEMUFile *f, const VMStateDescription *vmsd,
             int64_t old_offset, written_bytes;
             QJSON *vmdesc_loop = vmdesc;
 
+            if (size == 0) {
+                field++;
+                continue;
+            }
             trace_vmstate_save_state_loop(vmsd->name, field->name, n_elems);
             if (field->flags & VMS_POINTER) {
                 first_elem = *(void **)first_elem;
-- 
2.8.4