[RFC] migration: Add migrate-set-bitmap-node-mapping

* [RFC] migration: Add migrate-set-bitmap-node-mapping
@ 2020-05-13 14:49 Max Reitz
  2020-05-13 14:51 ` Max Reitz
                   ` (4 more replies)
  0 siblings, 5 replies; 6+ messages in thread
From: Max Reitz @ 2020-05-13 14:49 UTC (permalink / raw)
  To: qemu-block
  Cc: Vladimir Sementsov-Ogievskiy, Juan Quintela, Markus Armbruster,
	qemu-devel, Dr . David Alan Gilbert, Peter Krempa, Max Reitz

This command allows mapping block node names to aliases for the purpose
of block dirty bitmap migration.

This way, management tools can use different node names on the source
and destination and pass the mapping of how bitmaps are to be
transferred to qemu (on the source, the destination, or even both with
arbitrary aliases in the migration stream).

Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
---
Branch: https://github.com/XanClic/qemu.git migration-bitmap-mapping-rfc
Branch: https://git.xanclic.moe/XanClic/qemu.git migration-bitmap-mapping-rfc

Vladimir has proposed something like this in April:
https://lists.nongnu.org/archive/html/qemu-block/2020-04/msg00171.html

Now I’ve been asked by my manager to look at this, so I decided to just
write a patch to see how it’d play out.

This is an RFC, because I’d like to tack on tests to the final version,
but I’m not sure whether I can come up with something before the end of
the week (and I’ll be on PTO for the next two weeks).

Also, I don’t know whether migration/block-dirty-bitmap.c is the best
place to put qmp_migrate_set_bitmap_mapping(), but it appears we already
have some QMP handlers in migration/, so I suppose it isn’t too bad.
---
 qapi/migration.json            | 36 ++++++++++++++++++++
 migration/block-dirty-bitmap.c | 60 ++++++++++++++++++++++++++++++++--
 2 files changed, 94 insertions(+), 2 deletions(-)

diff --git a/qapi/migration.json b/qapi/migration.json
index d5000558c6..94aec8d194 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -1621,3 +1621,39 @@
 ##
 { 'event': 'UNPLUG_PRIMARY',
   'data': { 'device-id': 'str' } }
+
+##
+# @MigrationBlockNodeMapping:
+#
+# Maps a block node name to an alias for migration.
+#
+# @node-name: A block node name.
+#
+# @alias: An alias name for migration (for example the node name on
+#         the opposite site).
+#
+# Since: 5.1
+##
+{ 'struct': 'MigrationBitmapMapping',
+  'data': {
+      'node-name': 'str',
+      'alias': 'str'
+  } }
+
+##
+# @migrate-set-bitmap-node-mapping:
+#
+# Maps block node names to arbitrary aliases for the purpose of dirty
+# bitmap migration.  Such aliases may for example be the corresponding
+# node names on the opposite site.
+#
+# By default, every node name is mapped to itself.
+#
+# @mapping: The mapping; must be one-to-one, but not necessarily
+#           complete.  Any mapping not given will be reset to the
+#           default (i.e. the identity mapping).
+#
+# Since: 5.1
+##
+{ 'command': 'migrate-set-bitmap-node-mapping',
+  'data': { 'mapping': ['MigrationBlockNodeMapping'] } }
diff --git a/migration/block-dirty-bitmap.c b/migration/block-dirty-bitmap.c
index 7eafface61..8b434f7011 100644
--- a/migration/block-dirty-bitmap.c
+++ b/migration/block-dirty-bitmap.c
@@ -73,6 +73,8 @@
 #include "qemu/hbitmap.h"
 #include "qemu/cutils.h"
 #include "qapi/error.h"
+#include "qapi/qapi-commands-migration.h"
+#include "qapi/qmp/qdict.h"
 #include "trace.h"
 
 #define CHUNK_SIZE     (1 << 10)
@@ -121,6 +123,9 @@ typedef struct DirtyBitmapMigState {
     bool bulk_completed;
     bool no_bitmaps;
 
+    QDict *node_in_mapping;
+    QDict *node_out_mapping;
+
     /* for send_bitmap_bits() */
     BlockDriverState *prev_bs;
     BdrvDirtyBitmap *prev_bitmap;
@@ -281,8 +286,13 @@ static int init_dirty_bitmap_migration(void)
     dirty_bitmap_mig_state.no_bitmaps = false;
 
     for (bs = bdrv_next_all_states(NULL); bs; bs = bdrv_next_all_states(bs)) {
+        const QDict *map = dirty_bitmap_mig_state.node_out_mapping;
         const char *name = bdrv_get_device_or_node_name(bs);
 
+        if (map) {
+            name = qdict_get_try_str(map, name) ?: name;
+        }
+
         FOR_EACH_DIRTY_BITMAP(bs, bitmap) {
             if (!bdrv_dirty_bitmap_name(bitmap)) {
                 continue;
@@ -600,6 +610,8 @@ static int dirty_bitmap_load_bits(QEMUFile *f, DirtyBitmapLoadState *s)
 
 static int dirty_bitmap_load_header(QEMUFile *f, DirtyBitmapLoadState *s)
 {
+    const QDict *map = dirty_bitmap_mig_state.node_in_mapping;
+    const char *mapped_node = "(none)";
     Error *local_err = NULL;
     bool nothing;
     s->flags = qemu_get_bitmap_flags(f);
@@ -612,7 +624,13 @@ static int dirty_bitmap_load_header(QEMUFile *f, DirtyBitmapLoadState *s)
             error_report("Unable to read node name string");
             return -EINVAL;
         }
-        s->bs = bdrv_lookup_bs(s->node_name, s->node_name, &local_err);
+
+        mapped_node = s->node_name;
+        if (map) {
+            mapped_node = qdict_get_try_str(map, mapped_node) ?: mapped_node;
+        }
+
+        s->bs = bdrv_lookup_bs(mapped_node, mapped_node, &local_err);
         if (!s->bs) {
             error_report_err(local_err);
             return -EINVAL;
@@ -634,7 +652,7 @@ static int dirty_bitmap_load_header(QEMUFile *f, DirtyBitmapLoadState *s)
         if (!s->bitmap && !(s->flags & DIRTY_BITMAP_MIG_FLAG_START)) {
             error_report("Error: unknown dirty bitmap "
                          "'%s' for block device '%s'",
-                         s->bitmap_name, s->node_name);
+                         s->bitmap_name, mapped_node);
             return -EINVAL;
         }
     } else if (!s->bitmap && !nothing) {
@@ -713,6 +731,44 @@ static bool dirty_bitmap_has_postcopy(void *opaque)
     return true;
 }
 
+void qmp_migrate_set_bitmap_mapping(MigrationBitmapMappingList *mapping,
+                                    Error **errp)
+{
+    QDict *in_mapping = qdict_new();
+    QDict *out_mapping = qdict_new();
+
+    for (; mapping; mapping = mapping->next) {
+        MigrationBitmapMapping *entry = mapping->value;
+
+        if (qdict_haskey(out_mapping, entry->node_name)) {
+            error_setg(errp, "Cannot map node name '%s' twice",
+                       entry->node_name);
+            goto fail;
+        }
+
+        if (qdict_haskey(in_mapping, entry->alias)) {
+            error_setg(errp, "Cannot use alias '%s' twice",
+                       entry->alias);
+            goto fail;
+        }
+
+        qdict_put_str(in_mapping, entry->alias, entry->node_name);
+        qdict_put_str(out_mapping, entry->node_name, entry->alias);
+    }
+
+    qobject_unref(dirty_bitmap_mig_state.node_in_mapping);
+    qobject_unref(dirty_bitmap_mig_state.node_out_mapping);
+
+    dirty_bitmap_mig_state.node_in_mapping = in_mapping;
+    dirty_bitmap_mig_state.node_out_mapping = out_mapping;
+
+    return;
+
+fail:
+    qobject_unref(in_mapping);
+    qobject_unref(out_mapping);
+}
+
 static SaveVMHandlers savevm_dirty_bitmap_handlers = {
     .save_setup = dirty_bitmap_save_setup,
     .save_live_complete_postcopy = dirty_bitmap_save_complete,
-- 
2.26.2



^ permalink raw reply related	[flat|nested] 6+ messages in thread