From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Stefan Reiter <s.reiter@proxmox.com>
Date: Thu, 22 Oct 2020 17:34:18 +0200
Subject: [PATCH] PVE: Migrate dirty bitmap state via savevm

QEMU provides 'savevm' registrations as a mechanism for arbitrary state
to be migrated along with a VM. Use this to send a serialized version of
dirty bitmap state data from proxmox-backup-qemu, and restore it on the
target node.

Also add a flag to query-proxmox-support so qemu-server can determine if
safe migration is possible and makes sense.

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
[FE: split up state_pending for 8.0]
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
 include/migration/misc.h |   3 ++
 migration/meson.build    |   2 +
 migration/migration.c    |   1 +
 migration/pbs-state.c    | 104 +++++++++++++++++++++++++++++++++++++++
 pve-backup.c             |   1 +
 qapi/block-core.json     |   6 +++
 6 files changed, 117 insertions(+)
 create mode 100644 migration/pbs-state.c

diff --git a/include/migration/misc.h b/include/migration/misc.h
index 8b49841016..78f63ca400 100644
--- a/include/migration/misc.h
+++ b/include/migration/misc.h
@@ -77,4 +77,7 @@ bool migration_in_bg_snapshot(void);
 /* migration/block-dirty-bitmap.c */
 void dirty_bitmap_mig_init(void);
 
+/* migration/pbs-state.c */
+void pbs_state_mig_init(void);
+
 #endif
diff --git a/migration/meson.build b/migration/meson.build
index a7824b5266..de6a271b58 100644
--- a/migration/meson.build
+++ b/migration/meson.build
@@ -6,8 +6,10 @@ migration_files = files(
   'vmstate.c',
   'qemu-file.c',
   'yank_functions.c',
+  'pbs-state.c',
 )
 softmmu_ss.add(migration_files)
+softmmu_ss.add(libproxmox_backup_qemu)
 
 softmmu_ss.add(files(
   'block-dirty-bitmap.c',
diff --git a/migration/migration.c b/migration/migration.c
index bda4789193..c8318aa258 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -245,6 +245,7 @@ void migration_object_init(void)
     blk_mig_init();
     ram_mig_init();
     dirty_bitmap_mig_init();
+    pbs_state_mig_init();
 }
 
 void migration_cancel(const Error *error)
diff --git a/migration/pbs-state.c b/migration/pbs-state.c
new file mode 100644
index 0000000000..887e998b9e
--- /dev/null
+++ b/migration/pbs-state.c
@@ -0,0 +1,104 @@
+/*
+ * PBS (dirty-bitmap) state migration
+ */
+
+#include "qemu/osdep.h"
+#include "migration/misc.h"
+#include "qemu-file.h"
+#include "migration/vmstate.h"
+#include "migration/register.h"
+#include "proxmox-backup-qemu.h"
+
+typedef struct PBSState {
+    bool active;
+} PBSState;
+
+/* state is accessed via this static variable directly, 'opaque' is NULL */
+static PBSState pbs_state;
+
+static void pbs_state_pending(void *opaque, uint64_t *must_precopy,
+                              uint64_t *can_postcopy)
+{
+    /* we send everything in save_setup, so nothing is ever pending */
+}
+
+/* receive PBS state via f and deserialize, called on target */
+static int pbs_state_load(QEMUFile *f, void *opaque, int version_id)
+{
+    /* safe cast, we cannot migrate to target with less bits than source */
+    size_t buf_size = (size_t)qemu_get_be64(f);
+
+    uint8_t *buf = (uint8_t *)malloc(buf_size);
+    size_t read = qemu_get_buffer(f, buf, buf_size);
+
+    if (read < buf_size) {
+        fprintf(stderr, "error receiving PBS state: not enough data\n");
+        return -EIO;
+    }
+
+    proxmox_import_state(buf, buf_size);
+
+    free(buf);
+    return 0;
+}
+
+/* serialize PBS state and send to target via f, called on source */
+static int pbs_state_save_setup(QEMUFile *f, void *opaque)
+{
+    size_t buf_size;
+    uint8_t *buf = proxmox_export_state(&buf_size);
+
+    /* LV encoding */
+    qemu_put_be64(f, buf_size);
+    qemu_put_buffer(f, buf, buf_size);
+
+    proxmox_free_state_buf(buf);
+    pbs_state.active = false;
+    return 0;
+}
+
+static bool pbs_state_is_active(void *opaque)
+{
+    /* we need to return active exactly once, else .save_setup is never called,
+     * but if we'd just return true the migration doesn't make progress since
+     * it'd be waiting for us */
+    return pbs_state.active;
+}
+
+static bool pbs_state_is_active_iterate(void *opaque)
+{
+    /* we don't iterate, everything is sent in save_setup */
+    return pbs_state_is_active(opaque);
+}
+
+static bool pbs_state_has_postcopy(void *opaque)
+{
+    /* PBS state can't change during a migration (since that's blocking any
+     * potential backups), so we can copy everything before the VM is stopped */
+    return false;
+}
+
+static void pbs_state_save_cleanup(void *opaque)
+{
+    /* reset active after migration succeeds or fails */
+    pbs_state.active = false;
+}
+
+static SaveVMHandlers savevm_pbs_state_handlers = {
+    .save_setup = pbs_state_save_setup,
+    .has_postcopy = pbs_state_has_postcopy,
+    .state_pending_exact = pbs_state_pending,
+    .state_pending_estimate = pbs_state_pending,
+    .is_active_iterate = pbs_state_is_active_iterate,
+    .load_state = pbs_state_load,
+    .is_active = pbs_state_is_active,
+    .save_cleanup = pbs_state_save_cleanup,
+};
+
+void pbs_state_mig_init(void)
+{
+    pbs_state.active = true;
+    register_savevm_live("pbs-state", 0, 1,
+                         &savevm_pbs_state_handlers,
+                         NULL);
+}
diff --git a/pve-backup.c b/pve-backup.c
index dd72ee0ed6..cb5312fff3 100644
--- a/pve-backup.c
+++ b/pve-backup.c
@@ -1090,6 +1090,7 @@ ProxmoxSupportStatus *qmp_query_proxmox_support(Error **errp)
     ret->pbs_library_version = g_strdup(proxmox_backup_qemu_version());
     ret->pbs_dirty_bitmap = true;
     ret->pbs_dirty_bitmap_savevm = true;
+    ret->pbs_dirty_bitmap_migration = true;
     ret->query_bitmap_info = true;
     ret->pbs_masterkey = true;
     ret->backup_max_workers = true;
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 47118bf83e..809f3c61bc 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -984,6 +984,11 @@
 # @pbs-dirty-bitmap-savevm: True if 'dirty-bitmaps' migration capability can
 #                           safely be set for savevm-async.
 #
+# @pbs-dirty-bitmap-migration: True if safe migration of dirty-bitmaps including
+#                              PBS state is supported. Enabling 'dirty-bitmaps'
+#                              migration cap if this is false/unset may lead
+#                              to crashes on migration!
+#
 # @pbs-masterkey: True if the QMP backup call supports the 'master_keyfile'
 #                 parameter.
 #
@@ -994,6 +999,7 @@
   'data': { 'pbs-dirty-bitmap': 'bool',
             'query-bitmap-info': 'bool',
             'pbs-dirty-bitmap-savevm': 'bool',
+            'pbs-dirty-bitmap-migration': 'bool',
             'pbs-masterkey': 'bool',
             'pbs-library-version': 'str',
             'backup-max-workers': 'bool' } }
