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[Qemu-devel] [PATCH 3/5] migration/vmstate: fix array of ptr with nullpt
From: |
Halil Pasic |
Subject: |
[Qemu-devel] [PATCH 3/5] migration/vmstate: fix array of ptr with nullptrs |
Date: |
Thu, 16 Feb 2017 13:11:38 +0100 |
Make VMS_ARRAY_OF_POINTER cope with null pointers. Previously the
reward for trying to migrate an array with some null pointers in it was
an illegal memory access, that is a swift and painless death of the
process. Let's make vmstate cope with this scenario.
The general approach is, when we encounter a null pointer (element),
instead of following the pointer to save/load the data behind it, we
save/load a placeholder. This way we can detect if we expected a null
pointer at the load side but not null data was saved instead.
Signed-off-by: Halil Pasic <address@hidden>
Reviewed-by: Guenther Hutzl <address@hidden>
---
We will need this to load/save some on demand created state in the
(s390x) channel subsystem (see ChannelSubSys.css in hw/s390x/css.c for
an example).
---
include/migration/vmstate.h | 4 ++++
migration/vmstate.c | 33 +++++++++++++++++++++++++++++++--
2 files changed, 35 insertions(+), 2 deletions(-)
diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index 63e7b02..f2dbf84 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -253,6 +253,10 @@ extern const VMStateInfo vmstate_info_uint16;
extern const VMStateInfo vmstate_info_uint32;
extern const VMStateInfo vmstate_info_uint64;
+/** Put this in the stream when migrating a null pointer.*/
+#define VMS_NULLPTR_MARKER (0x30U) /* '0' */
+extern const VMStateInfo vmstate_info_nullptr;
+
extern const VMStateInfo vmstate_info_float64;
extern const VMStateInfo vmstate_info_cpudouble;
diff --git a/migration/vmstate.c b/migration/vmstate.c
index 836a7a4..cb81cef 100644
--- a/migration/vmstate.c
+++ b/migration/vmstate.c
@@ -117,7 +117,11 @@ int vmstate_load_state(QEMUFile *f, const
VMStateDescription *vmsd,
if (field->flags & VMS_ARRAY_OF_POINTER) {
curr_elem = *(void **)curr_elem;
}
- if (field->flags & VMS_STRUCT) {
+ if (!curr_elem) {
+ /* if null pointer check placeholder and do not follow */
+ assert(field->flags & VMS_ARRAY_OF_POINTER);
+ vmstate_info_nullptr.get(f, curr_elem, size, NULL);
+ } else if (field->flags & VMS_STRUCT) {
ret = vmstate_load_state(f, field->vmsd, curr_elem,
field->vmsd->version_id);
} else {
@@ -332,7 +336,11 @@ void vmstate_save_state(QEMUFile *f, const
VMStateDescription *vmsd,
assert(curr_elem);
curr_elem = *(void **)curr_elem;
}
- if (field->flags & VMS_STRUCT) {
+ if (!curr_elem) {
+ /* if null pointer write placeholder and do not follow */
+ assert(field->flags & VMS_ARRAY_OF_POINTER);
+ vmstate_info_nullptr.put(f, curr_elem, size, NULL, NULL);
+ } else if (field->flags & VMS_STRUCT) {
vmstate_save_state(f, field->vmsd, curr_elem, vmdesc_loop);
} else {
field->info->put(f, curr_elem, size, field, vmdesc_loop);
@@ -747,6 +755,27 @@ const VMStateInfo vmstate_info_uint64 = {
.put = put_uint64,
};
+static int get_nullptr(QEMUFile *f, void *pv, size_t size, VMStateField *field)
+
+{
+ return qemu_get_byte(f) == VMS_NULLPTR_MARKER ? 0 : -EINVAL;
+}
+
+static int put_nullptr(QEMUFile *f, void *pv, size_t size,
+ VMStateField *field, QJSON *vmdesc)
+
+{
+ assert(pv == NULL);
+ qemu_put_byte(f, VMS_NULLPTR_MARKER);
+ return 0;
+}
+
+const VMStateInfo vmstate_info_nullptr = {
+ .name = "uint64",
+ .get = get_nullptr,
+ .put = put_nullptr,
+};
+
/* 64 bit unsigned int. See that the received value is the same than the one
in the field */
--
2.8.4
[Qemu-devel] [PATCH 2/5] migration/vmstate: split up vmstate_base_addr, Halil Pasic, 2017/02/16
[Qemu-devel] [PATCH 4/5] tests/test-vmstate.c: test array of ptr with null, Halil Pasic, 2017/02/16