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Blame SOURCES/kvm-dirty-bitmaps-clean-up-bitmaps-loading-and-migration.patch

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From ae232c169a5ae37d3989919775332979d4e3b7d5 Mon Sep 17 00:00:00 2001
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From: John Snow <jsnow@redhat.com>
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Date: Tue, 20 Nov 2018 18:18:26 +0000
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Subject: [PATCH 32/35] dirty-bitmaps: clean-up bitmaps loading and migration
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 logic
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RH-Author: John Snow <jsnow@redhat.com>
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Message-id: <20181120181828.15132-23-jsnow@redhat.com>
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Patchwork-id: 83074
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O-Subject: [RHEL8/rhel qemu-kvm PATCH 22/24] dirty-bitmaps: clean-up bitmaps loading and migration logic
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Bugzilla: 1518989
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RH-Acked-by: Laurent Vivier <lvivier@redhat.com>
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RH-Acked-by: Max Reitz <mreitz@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
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This patch aims to bring the following behavior:
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1. We don't load bitmaps, when started in inactive mode. It's the case
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of incoming migration. In this case we wait for bitmaps migration
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through migration channel (if 'dirty-bitmaps' capability is enabled) or
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for invalidation (to load bitmaps from the image).
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2. We don't remove persistent bitmaps on inactivation. Instead, we only
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remove bitmaps after storing. This is the only way to restore bitmaps,
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if we decided to resume source after [failed] migration with
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'dirty-bitmaps' capability enabled (which means, that bitmaps were not
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stored).
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3. We load bitmaps on open and any invalidation, it's ok for all cases:
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  - normal open
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  - migration target invalidation with dirty-bitmaps capability
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    (bitmaps are migrating through migration channel, the are not
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     stored, so they should have IN_USE flag set and will be skipped
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     when loading. However, it would fail if bitmaps are read-only[1])
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  - migration target invalidation without dirty-bitmaps capability
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    (normal load of the bitmaps, if migrated with shared storage)
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  - source invalidation with dirty-bitmaps capability
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    (skip because IN_USE)
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  - source invalidation without dirty-bitmaps capability
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    (bitmaps were dropped, reload them)
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[1]: to accurately handle this, migration of read-only bitmaps is
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     explicitly forbidden in this patch.
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New mechanism for not storing bitmaps when migrate with dirty-bitmaps
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capability is introduced: migration filed in BdrvDirtyBitmap.
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Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
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Signed-off-by: John Snow <jsnow@redhat.com>
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(cherry picked from commit 9c98f145dfb994e1e9d68a4d606ee5693891280d)
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Signed-off-by: John Snow <jsnow@redhat.com>
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Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
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---
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 block.c                        | 11 ++++---
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 block/dirty-bitmap.c           | 36 +++++++++--------------
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 block/qcow2-bitmap.c           | 16 +++++++++++
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 block/qcow2.c                  | 65 ++++++++++++++++++++++++++++++++++++++++--
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 include/block/dirty-bitmap.h   |  2 +-
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 migration/block-dirty-bitmap.c | 10 +++++--
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 6 files changed, 109 insertions(+), 31 deletions(-)
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diff --git a/block.c b/block.c
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index fbd569c..18ae591 100644
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--- a/block.c
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+++ b/block.c
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@@ -4316,6 +4316,7 @@ static void coroutine_fn bdrv_co_invalidate_cache(BlockDriverState *bs,
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     uint64_t perm, shared_perm;
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     Error *local_err = NULL;
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     int ret;
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+    BdrvDirtyBitmap *bm;
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     if (!bs->drv)  {
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         return;
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@@ -4365,6 +4366,12 @@ static void coroutine_fn bdrv_co_invalidate_cache(BlockDriverState *bs,
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         }
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     }
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+    for (bm = bdrv_dirty_bitmap_next(bs, NULL); bm;
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+         bm = bdrv_dirty_bitmap_next(bs, bm))
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+    {
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+        bdrv_dirty_bitmap_set_migration(bm, false);
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+    }
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+
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     ret = refresh_total_sectors(bs, bs->total_sectors);
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     if (ret < 0) {
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         bs->open_flags |= BDRV_O_INACTIVE;
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@@ -4479,10 +4486,6 @@ static int bdrv_inactivate_recurse(BlockDriverState *bs,
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         }
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     }
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-    /* At this point persistent bitmaps should be already stored by the format
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-     * driver */
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-    bdrv_release_persistent_dirty_bitmaps(bs);
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-
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     return 0;
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 }
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diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
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index 9b9ebd7..89fd1d7 100644
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--- a/block/dirty-bitmap.c
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+++ b/block/dirty-bitmap.c
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@@ -55,6 +55,10 @@ struct BdrvDirtyBitmap {
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                                    and this bitmap must remain unchanged while
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                                    this flag is set. */
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     bool persistent;            /* bitmap must be saved to owner disk image */
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+    bool migration;             /* Bitmap is selected for migration, it should
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+                                   not be stored on the next inactivation
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+                                   (persistent flag doesn't matter until next
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+                                   invalidation).*/
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     QLIST_ENTRY(BdrvDirtyBitmap) list;
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 };
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@@ -390,26 +394,6 @@ void bdrv_release_named_dirty_bitmaps(BlockDriverState *bs)
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 }
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 /**
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- * Release all persistent dirty bitmaps attached to a BDS (for use in
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- * bdrv_inactivate_recurse()).
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- * There must not be any frozen bitmaps attached.
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- * This function does not remove persistent bitmaps from the storage.
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- * Called with BQL taken.
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- */
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-void bdrv_release_persistent_dirty_bitmaps(BlockDriverState *bs)
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-{
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-    BdrvDirtyBitmap *bm, *next;
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-
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-    bdrv_dirty_bitmaps_lock(bs);
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-    QLIST_FOREACH_SAFE(bm, &bs->dirty_bitmaps, list, next) {
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-        if (bdrv_dirty_bitmap_get_persistance(bm)) {
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-            bdrv_release_dirty_bitmap_locked(bm);
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-        }
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-    }
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-    bdrv_dirty_bitmaps_unlock(bs);
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-}
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-
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-/**
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  * Remove persistent dirty bitmap from the storage if it exists.
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  * Absence of bitmap is not an error, because we have the following scenario:
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  * BdrvDirtyBitmap can have .persistent = true but not yet saved and have no
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@@ -761,16 +745,24 @@ void bdrv_dirty_bitmap_set_persistance(BdrvDirtyBitmap *bitmap, bool persistent)
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     qemu_mutex_unlock(bitmap->mutex);
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 }
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+/* Called with BQL taken. */
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+void bdrv_dirty_bitmap_set_migration(BdrvDirtyBitmap *bitmap, bool migration)
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+{
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+    qemu_mutex_lock(bitmap->mutex);
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+    bitmap->migration = migration;
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+    qemu_mutex_unlock(bitmap->mutex);
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+}
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+
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 bool bdrv_dirty_bitmap_get_persistance(BdrvDirtyBitmap *bitmap)
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 {
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-    return bitmap->persistent;
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+    return bitmap->persistent && !bitmap->migration;
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 }
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 bool bdrv_has_changed_persistent_bitmaps(BlockDriverState *bs)
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 {
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     BdrvDirtyBitmap *bm;
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     QLIST_FOREACH(bm, &bs->dirty_bitmaps, list) {
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-        if (bm->persistent && !bm->readonly) {
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+        if (bm->persistent && !bm->readonly && !bm->migration) {
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             return true;
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         }
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     }
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diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c
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index 14050eb..a36773c 100644
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--- a/block/qcow2-bitmap.c
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+++ b/block/qcow2-bitmap.c
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@@ -1418,6 +1418,22 @@ void qcow2_store_persistent_dirty_bitmaps(BlockDriverState *bs, Error **errp)
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         g_free(tb);
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     }
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+    QSIMPLEQ_FOREACH(bm, bm_list, entry) {
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+        /* For safety, we remove bitmap after storing.
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+         * We may be here in two cases:
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+         * 1. bdrv_close. It's ok to drop bitmap.
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+         * 2. inactivation. It means migration without 'dirty-bitmaps'
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+         *    capability, so bitmaps are not marked with
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+         *    BdrvDirtyBitmap.migration flags. It's not bad to drop them too,
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+         *    and reload on invalidation.
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+         */
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+        if (bm->dirty_bitmap == NULL) {
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+            continue;
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+        }
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+
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+        bdrv_release_dirty_bitmap(bs, bm->dirty_bitmap);
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+    }
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+
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     bitmap_list_free(bm_list);
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     return;
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diff --git a/block/qcow2.c b/block/qcow2.c
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index d260cd6..36d1152 100644
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--- a/block/qcow2.c
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+++ b/block/qcow2.c
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@@ -1487,8 +1487,69 @@ static int coroutine_fn qcow2_do_open(BlockDriverState *bs, QDict *options,
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         s->autoclear_features &= QCOW2_AUTOCLEAR_MASK;
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     }
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-    if (qcow2_load_dirty_bitmaps(bs, &local_err)) {
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-        update_header = false;
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+    /* == Handle persistent dirty bitmaps ==
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+     *
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+     * We want load dirty bitmaps in three cases:
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+     *
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+     * 1. Normal open of the disk in active mode, not related to invalidation
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+     *    after migration.
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+     *
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+     * 2. Invalidation of the target vm after pre-copy phase of migration, if
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+     *    bitmaps are _not_ migrating through migration channel, i.e.
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+     *    'dirty-bitmaps' capability is disabled.
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+     *
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+     * 3. Invalidation of source vm after failed or canceled migration.
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+     *    This is a very interesting case. There are two possible types of
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+     *    bitmaps:
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+     *
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+     *    A. Stored on inactivation and removed. They should be loaded from the
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+     *       image.
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+     *
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+     *    B. Not stored: not-persistent bitmaps and bitmaps, migrated through
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+     *       the migration channel (with dirty-bitmaps capability).
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+     *
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+     *    On the other hand, there are two possible sub-cases:
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+     *
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+     *    3.1 disk was changed by somebody else while were inactive. In this
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+     *        case all in-RAM dirty bitmaps (both persistent and not) are
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+     *        definitely invalid. And we don't have any method to determine
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+     *        this.
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+     *
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+     *        Simple and safe thing is to just drop all the bitmaps of type B on
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+     *        inactivation. But in this case we lose bitmaps in valid 4.2 case.
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+     *
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+     *        On the other hand, resuming source vm, if disk was already changed
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+     *        is a bad thing anyway: not only bitmaps, the whole vm state is
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+     *        out of sync with disk.
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+     *
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+     *        This means, that user or management tool, who for some reason
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+     *        decided to resume source vm, after disk was already changed by
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+     *        target vm, should at least drop all dirty bitmaps by hand.
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+     *
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+     *        So, we can ignore this case for now, but TODO: "generation"
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+     *        extension for qcow2, to determine, that image was changed after
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+     *        last inactivation. And if it is changed, we will drop (or at least
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+     *        mark as 'invalid' all the bitmaps of type B, both persistent
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+     *        and not).
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+     *
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+     *    3.2 disk was _not_ changed while were inactive. Bitmaps may be saved
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+     *        to disk ('dirty-bitmaps' capability disabled), or not saved
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+     *        ('dirty-bitmaps' capability enabled), but we don't need to care
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+     *        of: let's load bitmaps as always: stored bitmaps will be loaded,
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+     *        and not stored has flag IN_USE=1 in the image and will be skipped
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+     *        on loading.
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+     *
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+     * One remaining possible case when we don't want load bitmaps:
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+     *
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+     * 4. Open disk in inactive mode in target vm (bitmaps are migrating or
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+     *    will be loaded on invalidation, no needs try loading them before)
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+     */
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+
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+    if (!(bdrv_get_flags(bs) & BDRV_O_INACTIVE)) {
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+        /* It's case 1, 2 or 3.2. Or 3.1 which is BUG in management layer. */
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+        bool header_updated = qcow2_load_dirty_bitmaps(bs, &local_err);
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+
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+        update_header = update_header && !header_updated;
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     }
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     if (local_err != NULL) {
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         error_propagate(errp, local_err);
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diff --git a/include/block/dirty-bitmap.h b/include/block/dirty-bitmap.h
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index 1463943..8f38a3d 100644
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--- a/include/block/dirty-bitmap.h
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+++ b/include/block/dirty-bitmap.h
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@@ -26,7 +26,6 @@ BdrvDirtyBitmap *bdrv_find_dirty_bitmap(BlockDriverState *bs,
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                                         const char *name);
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 void bdrv_release_dirty_bitmap(BlockDriverState *bs, BdrvDirtyBitmap *bitmap);
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 void bdrv_release_named_dirty_bitmaps(BlockDriverState *bs);
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-void bdrv_release_persistent_dirty_bitmaps(BlockDriverState *bs);
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 void bdrv_remove_persistent_dirty_bitmap(BlockDriverState *bs,
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                                          const char *name,
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                                          Error **errp);
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@@ -72,6 +71,7 @@ void bdrv_dirty_bitmap_set_persistance(BdrvDirtyBitmap *bitmap,
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 void bdrv_dirty_bitmap_set_qmp_locked(BdrvDirtyBitmap *bitmap, bool qmp_locked);
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 void bdrv_merge_dirty_bitmap(BdrvDirtyBitmap *dest, const BdrvDirtyBitmap *src,
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                              HBitmap **backup, Error **errp);
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+void bdrv_dirty_bitmap_set_migration(BdrvDirtyBitmap *bitmap, bool migration);
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 /* Functions that require manual locking.  */
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 void bdrv_dirty_bitmap_lock(BdrvDirtyBitmap *bitmap);
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diff --git a/migration/block-dirty-bitmap.c b/migration/block-dirty-bitmap.c
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index 47251af..ffe7aca 100644
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--- a/migration/block-dirty-bitmap.c
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+++ b/migration/block-dirty-bitmap.c
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@@ -307,6 +307,12 @@ static int init_dirty_bitmap_migration(void)
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                 goto fail;
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             }
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+            if (bdrv_dirty_bitmap_readonly(bitmap)) {
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+                error_report("Can't migrate read-only dirty bitmap: '%s",
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+                             bdrv_dirty_bitmap_name(bitmap));
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+                goto fail;
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+            }
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+
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             bdrv_ref(bs);
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             bdrv_dirty_bitmap_set_qmp_locked(bitmap, true);
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@@ -329,9 +335,9 @@ static int init_dirty_bitmap_migration(void)
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         }
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     }
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-    /* unset persistance here, to not roll back it */
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+    /* unset migration flags here, to not roll back it */
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     QSIMPLEQ_FOREACH(dbms, &dirty_bitmap_mig_state.dbms_list, entry) {
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-        bdrv_dirty_bitmap_set_persistance(dbms->bitmap, false);
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+        bdrv_dirty_bitmap_set_migration(dbms->bitmap, true);
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     }
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     if (QSIMPLEQ_EMPTY(&dirty_bitmap_mig_state.dbms_list)) {
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-- 
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1.8.3.1
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