[qemu-xen staging] qcow2: Release read-only bitmaps when inactivated

[patchbot@xxxxxxx]

commit fe16c7ddf82b25e54cb76936a4cdf6bf9327ece5
Author:     Max Reitz <mreitz@xxxxxxxxxx>
AuthorDate: Thu Jul 30 14:02:33 2020 +0200
Commit:     Eric Blake <eblake@xxxxxxxxxx>
CommitDate: Mon Aug 3 08:59:37 2020 -0500

    qcow2: Release read-only bitmaps when inactivated
    
    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@xxxxxxxxxx>
    Message-Id: <20200730120234.49288-2-mreitz@xxxxxxxxxx>
    Tested-by: Peter Krempa <pkrempa@xxxxxxxxxx>
    Reviewed-by: Eric Blake <eblake@xxxxxxxxxx>
    Signed-off-by: Eric Blake <eblake@xxxxxxxxxx>
---
 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 1f38806ca6..8c34b2aef7 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;
         }
 
--
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