[PULL 1/2] qcow2: Release read-only bitmaps when inactivated

[Eric Blake <eblake@redhat.com>]

From: Max Reitz <mreitz@redhat.com>

During migration, we release all bitmaps after storing them on disk, as
long as they are (1) stored on disk, (2) not read-only, and (3)
consistent.

(2) seems arbitrary, though.  The reason we do not release them is
because we do not write them, as there is no need to; and then we just
forget about all bitmaps that we have not written to the file.  However,
read-only persistent bitmaps are still in the file and in sync with
their in-memory representation, so we may as well release them just like
any R/W bitmap that we have updated.

It leads to actual problems, too: After migration, letting the source
continue may result in an error if there were any bitmaps on read-only
nodes (such as backing images), because those have not been released by
bdrv_inactive_all(), but bdrv_invalidate_cache_all() attempts to reload
them (which fails, because they are still present in memory).

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200730120234.49288-2-mreitz@redhat.com>
Tested-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
---
 block/qcow2-bitmap.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c
index 1f38806ca6ea..8c34b2aef7cd 100644
--- a/block/qcow2-bitmap.c
+++ b/block/qcow2-bitmap.c
@@ -1562,11 +1562,22 @@ void qcow2_store_persistent_dirty_bitmaps(BlockDriverState *bs,
         Qcow2Bitmap *bm;

         if (!bdrv_dirty_bitmap_get_persistence(bitmap) ||
-            bdrv_dirty_bitmap_readonly(bitmap) ||
             bdrv_dirty_bitmap_inconsistent(bitmap)) {
             continue;
         }

+        if (bdrv_dirty_bitmap_readonly(bitmap)) {
+            /*
+             * Store the bitmap in the associated Qcow2Bitmap so it
+             * can be released later
+             */
+            bm = find_bitmap_by_name(bm_list, name);
+            if (bm) {
+                bm->dirty_bitmap = bitmap;
+            }
+            continue;
+        }
+
         need_write = true;

         if (check_constraints_on_bitmap(bs, name, granularity, errp) < 0) {
@@ -1618,7 +1629,9 @@ void qcow2_store_persistent_dirty_bitmaps(BlockDriverState *bs,

     /* allocate clusters and store bitmaps */
     QSIMPLEQ_FOREACH(bm, bm_list, entry) {
-        if (bm->dirty_bitmap == NULL) {
+        BdrvDirtyBitmap *bitmap = bm->dirty_bitmap;
+
+        if (bitmap == NULL || bdrv_dirty_bitmap_readonly(bitmap)) {
             continue;
         }

@@ -1641,6 +1654,7 @@ void qcow2_store_persistent_dirty_bitmaps(BlockDriverState *bs,
         g_free(tb);
     }

+success:
     if (release_stored) {
         QSIMPLEQ_FOREACH(bm, bm_list, entry) {
             if (bm->dirty_bitmap == NULL) {
@@ -1651,13 +1665,14 @@ void qcow2_store_persistent_dirty_bitmaps(BlockDriverState *bs,
         }
     }

-success:
     bitmap_list_free(bm_list);
     return;

 fail:
     QSIMPLEQ_FOREACH(bm, bm_list, entry) {
-        if (bm->dirty_bitmap == NULL || bm->table.offset == 0) {
+        if (bm->dirty_bitmap == NULL || bm->table.offset == 0 ||
+            bdrv_dirty_bitmap_readonly(bm->dirty_bitmap))
+        {
             continue;
         }

-- 
2.28.0