[Qemu-devel] [RFC v2 3/5] vmstate: add VMS_MUST_EXIST

["Michael S. Tsirkin" <mst@redhat.com>]

Can be used to verify a required field exists or validate
state in some other way.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 include/migration/vmstate.h |  1 +
 vmstate.c                   | 10 +++++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index 3a1587e..eb90cef 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -101,6 +101,7 @@ enum VMStateFlags {
     VMS_MULTIPLY         = 0x200,  /* multiply "size" field by field_size */
     VMS_VARRAY_UINT8     = 0x400,  /* Array with size in uint8_t field*/
     VMS_VARRAY_UINT32    = 0x800,  /* Array with size in uint32_t field*/
+    VMS_MUST_EXIST       = 0x1000, /* Field must exist in input */
 };
 
 typedef struct {
diff --git a/vmstate.c b/vmstate.c
index fe53735..4943b83 100644
--- a/vmstate.c
+++ b/vmstate.c
@@ -13,7 +13,7 @@ static int vmstate_n_elems(void *opaque, VMStateField *field)
 {
     int n_elems = 1;
 
-    if (!(field->flags & ~VMS_NONE)) {
+    if (!(field->flags & ~(VMS_NONE | VMS_MUST_EXIST))) {
         n_elems = 0;
     } else if (field->flags & VMS_ARRAY) {
         n_elems = field->num;
@@ -107,6 +107,9 @@ int vmstate_load_state(QEMUFile *f, const VMStateDescription *vmsd,
             }
         }
         field++;
+    } else if (field->flags & VMS_MUST_EXIST) {
+        fprintf(stderr, "Input validation failed: %s/%s\n", vmsd->name, field->name);
+        return -1;
     }
     ret = vmstate_subsection_load(f, vmsd, opaque);
     if (ret != 0) {
@@ -148,6 +151,11 @@ void vmstate_save_state(QEMUFile *f, const VMStateDescription *vmsd,
                     field->info->put(f, addr, size);
                 }
             }
+        } else {
+            if (field->flags & VMS_MUST_EXIST) {
+                fprintf(stderr, "Input validation failed: %s/%s\n", vmsd->name, field->name);
+                assert(!(field->flags & VMS_MUST_EXIST));
+            }
         }
         field++;
     }
-- 
MST