[pve-devel] [PATCH qemu 2/4] PVE: Migrate dirty bitmap state via savevm

[Stefan Reiter <s.reiter@proxmox.com>]

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>
---

Depends on the updated proxmox-backup-qemu library of course.

The new query-proxmox-support property is also used to detect the fix from patch
2, so these must be applied together.

 include/migration/misc.h |  3 ++
 migration/Makefile.objs  |  1 +
 migration/pbs-state.c    | 92 ++++++++++++++++++++++++++++++++++++++++
 pve-backup.c             |  1 +
 qapi/block-core.json     |  9 +++-
 softmmu/vl.c             |  1 +
 6 files changed, 106 insertions(+), 1 deletion(-)
 create mode 100644 migration/pbs-state.c

diff --git a/include/migration/misc.h b/include/migration/misc.h
index 34e7d75713..f83816dd3c 100644
--- a/include/migration/misc.h
+++ b/include/migration/misc.h
@@ -75,4 +75,7 @@ bool migration_in_incoming_postcopy(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/Makefile.objs b/migration/Makefile.objs
index 0fc619e380..20b3792599 100644
--- a/migration/Makefile.objs
+++ b/migration/Makefile.objs
@@ -9,6 +9,7 @@ common-obj-y += qjson.o
 common-obj-y += block-dirty-bitmap.o
 common-obj-y += multifd.o
 common-obj-y += multifd-zlib.o
+common-obj-y += pbs-state.o
 common-obj-$(CONFIG_ZSTD) += multifd-zstd.o
 
 common-obj-$(CONFIG_RDMA) += rdma.o
diff --git a/migration/pbs-state.c b/migration/pbs-state.c
new file mode 100644
index 0000000000..165895b488
--- /dev/null
+++ b/migration/pbs-state.c
@@ -0,0 +1,92 @@
+/*
+ * 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"
+
+static void pbs_state_save_pending(QEMUFile *f, void *opaque,
+                                      uint64_t max_size,
+                                      uint64_t *res_precopy_only,
+                                      uint64_t *res_compatible,
+                                      uint64_t *res_postcopy_only)
+{
+    /* we send everything in save_setup, so nothing is ever pending */
+    *res_precopy_only = 0;
+    *res_compatible = 0;
+    *res_postcopy_only = 0;
+}
+
+/* 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);
+    return 0;
+}
+
+static bool pbs_state_is_active(void *opaque)
+{
+    /* always active, i.e. we do our job for every migration, since there's no
+     * harm done if we just copy an empty buffer */
+    return true;
+}
+
+static bool pbs_state_is_active_iterate(void *opaque)
+{
+    /* we don't iterate, everything is sent in save_setup */
+    return false;
+}
+
+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 SaveVMHandlers savevm_pbs_state_handlers = {
+    .save_setup = pbs_state_save_setup,
+    .has_postcopy = pbs_state_has_postcopy,
+    .save_live_pending = pbs_state_save_pending,
+    .is_active_iterate = pbs_state_is_active_iterate,
+    .load_state = pbs_state_load,
+    .is_active = pbs_state_is_active,
+};
+
+void pbs_state_mig_init(void)
+{
+    register_savevm_live("pbs-state", 0, 1,
+                         &savevm_pbs_state_handlers,
+                         NULL);
+}
diff --git a/pve-backup.c b/pve-backup.c
index 53cf23ed5a..1954d22069 100644
--- a/pve-backup.c
+++ b/pve-backup.c
@@ -1080,5 +1080,6 @@ ProxmoxSupportStatus *qmp_query_proxmox_support(Error **errp)
     ProxmoxSupportStatus *ret = g_malloc0(sizeof(*ret));
     ret->pbs_dirty_bitmap = true;
     ret->query_bitmap_info = true;
+    ret->pbs_dirty_bitmap_migration = true;
     return ret;
 }
diff --git a/qapi/block-core.json b/qapi/block-core.json
index b31ad8d989..00c9e12fcc 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -890,9 +890,16 @@
 #
 # @query-bitmap-info: True if the 'query-pbs-bitmap-info' QMP call is supported.
 #
+# @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!
+#
 ##
 { 'struct': 'ProxmoxSupportStatus',
-  'data': { 'pbs-dirty-bitmap': 'bool', 'query-bitmap-info': 'bool' } }
+  'data': { 'pbs-dirty-bitmap': 'bool',
+            'query-bitmap-info': 'bool',
+            'pbs-dirty-bitmap-migration': 'bool' } }
 
 ##
 # @query-proxmox-support:
diff --git a/softmmu/vl.c b/softmmu/vl.c
index 16aa2186b0..88b13871fd 100644
--- a/softmmu/vl.c
+++ b/softmmu/vl.c
@@ -4288,6 +4288,7 @@ void qemu_init(int argc, char **argv, char **envp)
     blk_mig_init();
     ram_mig_init();
     dirty_bitmap_mig_init();
+    pbs_state_mig_init();
 
     qemu_opts_foreach(qemu_find_opts("mon"),
                       mon_init_func, NULL, &error_fatal);
-- 
2.20.1