[Qemu-devel] [PATCH v2 06/16] savevm: Make use of DeviceState

[Alex Williamson <alex.williamson@redhat.com>]

For callers that pass a device we can traverse up the qdev tree and
make use of the BusInfo.get_dev_path information for creating unique
savevm id strings.  This avoids needing to rely on the instance number,
which can cause problems with device initialization order and hotplug.

For compatibility, we also store away the old id string and instance
so we can accept migrations from VMs as we add new get_dev_path
implementations.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---

 savevm.c |   84 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 files changed, 79 insertions(+), 5 deletions(-)

diff --git a/savevm.c b/savevm.c
index 0052406..e4f50b1 100644
--- a/savevm.c
+++ b/savevm.c
@@ -72,6 +72,7 @@
 
 #include "qemu-common.h"
 #include "hw/hw.h"
+#include "hw/qdev.h"
 #include "net.h"
 #include "monitor.h"
 #include "sysemu.h"
@@ -988,6 +989,11 @@ const VMStateInfo vmstate_info_unused_buffer = {
     .put  = put_unused_buffer,
 };
 
+typedef struct CompatEntry {
+    char idstr[256];
+    int instance_id;
+} CompatEntry;
+
 typedef struct SaveStateEntry {
     QTAILQ_ENTRY(SaveStateEntry) entry;
     char idstr[256];
@@ -1001,6 +1007,7 @@ typedef struct SaveStateEntry {
     LoadStateHandler *load_state;
     const VMStateDescription *vmsd;
     void *opaque;
+    CompatEntry *compat;
 } SaveStateEntry;
 
 
@@ -1022,6 +1029,23 @@ static int calculate_new_instance_id(const char *idstr)
     return instance_id;
 }
 
+static int calculate_compat_instance_id(const char *idstr)
+{
+    SaveStateEntry *se;
+    int instance_id = 0;
+
+    QTAILQ_FOREACH(se, &savevm_handlers, entry) {
+        if (!se->compat)
+            continue;
+
+        if (strcmp(idstr, se->compat->idstr) == 0
+            && instance_id <= se->compat->instance_id) {
+            instance_id = se->compat->instance_id + 1;
+        }
+    }
+    return instance_id;
+}
+
 /* TODO: Individual devices generally have very little idea about the rest
    of the system, so instance_id should be removed/replaced.
    Meanwhile pass -1 as instance_id if you do not already have a clearly
@@ -1039,7 +1063,6 @@ int register_savevm_live(DeviceState *dev,
     SaveStateEntry *se;
 
     se = qemu_mallocz(sizeof(SaveStateEntry));
-    pstrcpy(se->idstr, sizeof(se->idstr), idstr);
     se->version_id = version_id;
     se->section_id = global_section_id++;
     se->set_params = set_params;
@@ -1049,11 +1072,28 @@ int register_savevm_live(DeviceState *dev,
     se->opaque = opaque;
     se->vmsd = NULL;
 
+    if (dev && dev->parent_bus && dev->parent_bus->info->get_dev_path) {
+        char *id = dev->parent_bus->info->get_dev_path(dev);
+        if (id) {
+            pstrcpy(se->idstr, sizeof(se->idstr), id);
+            pstrcat(se->idstr, sizeof(se->idstr), "/");
+            qemu_free(id);
+
+            se->compat = qemu_mallocz(sizeof(CompatEntry));
+            pstrcpy(se->compat->idstr, sizeof(se->compat->idstr), idstr);
+            se->compat->instance_id = instance_id == -1 ?
+                         calculate_compat_instance_id(idstr) : instance_id;
+            instance_id = -1;
+        }
+    }
+    pstrcat(se->idstr, sizeof(se->idstr), idstr);
+
     if (instance_id == -1) {
-        se->instance_id = calculate_new_instance_id(idstr);
+        se->instance_id = calculate_new_instance_id(se->idstr);
     } else {
         se->instance_id = instance_id;
     }
+    assert(!se->compat || se->instance_id == 0);
     /* add at the end of list */
     QTAILQ_INSERT_TAIL(&savevm_handlers, se, entry);
     return 0;
@@ -1074,9 +1114,20 @@ int register_savevm(DeviceState *dev,
 void unregister_savevm(DeviceState *dev, const char *idstr, void *opaque)
 {
     SaveStateEntry *se, *new_se;
+    char id[256] = "";
+
+    if (dev && dev->parent_bus && dev->parent_bus->info->get_dev_path) {
+        char *path = dev->parent_bus->info->get_dev_path(dev);
+        if (path) {
+            pstrcpy(id, sizeof(id), path);
+            pstrcat(id, sizeof(id), "/");
+            qemu_free(path);
+        }
+    }
+    pstrcat(id, sizeof(id), idstr);
 
     QTAILQ_FOREACH_SAFE(se, &savevm_handlers, entry, new_se) {
-        if (strcmp(se->idstr, idstr) == 0 && se->opaque == opaque) {
+        if (strcmp(se->idstr, id) == 0 && se->opaque == opaque) {
             QTAILQ_REMOVE(&savevm_handlers, se, entry);
             qemu_free(se);
         }
@@ -1094,7 +1145,6 @@ int vmstate_register_with_alias_id(DeviceState *dev, int instance_id,
     assert(alias_id == -1 || required_for_version >= vmsd->minimum_version_id);
 
     se = qemu_mallocz(sizeof(SaveStateEntry));
-    pstrcpy(se->idstr, sizeof(se->idstr), vmsd->name);
     se->version_id = vmsd->version_id;
     se->section_id = global_section_id++;
     se->save_live_state = NULL;
@@ -1104,11 +1154,28 @@ int vmstate_register_with_alias_id(DeviceState *dev, int instance_id,
     se->vmsd = vmsd;
     se->alias_id = alias_id;
 
+    if (dev && dev->parent_bus && dev->parent_bus->info->get_dev_path) {
+        char *id = dev->parent_bus->info->get_dev_path(dev);
+        if (id) {
+            pstrcpy(se->idstr, sizeof(se->idstr), id);
+            pstrcat(se->idstr, sizeof(se->idstr), "/");
+            qemu_free(id);
+
+            se->compat = qemu_mallocz(sizeof(CompatEntry));
+            pstrcpy(se->compat->idstr, sizeof(se->compat->idstr), vmsd->name);
+            se->compat->instance_id = instance_id == -1 ?
+                         calculate_compat_instance_id(vmsd->name) : instance_id;
+            instance_id = -1;
+        }
+    }
+    pstrcat(se->idstr, sizeof(se->idstr), vmsd->name);
+
     if (instance_id == -1) {
-        se->instance_id = calculate_new_instance_id(vmsd->name);
+        se->instance_id = calculate_new_instance_id(se->idstr);
     } else {
         se->instance_id = instance_id;
     }
+    assert(!se->compat || se->instance_id == 0);
     /* add at the end of list */
     QTAILQ_INSERT_TAIL(&savevm_handlers, se, entry);
     return 0;
@@ -1454,6 +1521,13 @@ static SaveStateEntry *find_se(const char *idstr, int instance_id)
             (instance_id == se->instance_id ||
              instance_id == se->alias_id))
             return se;
+        /* Migrating from an older version? */
+        if (strstr(se->idstr, idstr) && se->compat) {
+            if (!strcmp(se->compat->idstr, idstr) &&
+                (instance_id == se->compat->instance_id ||
+                 instance_id == se->alias_id))
+                return se;
+        }
     }
     return NULL;
 }