block/qcow2-bitmap: Allow resizes with persistent bitmaps

Since we now load all bitmaps into memory anyway, we can just truncate
them in-memory and then flush them back to disk. Just in case, we will
still check and enforce that this shortcut is valid -- i.e. that any
bitmap described on-disk is indeed in-memory and can be modified.

If there are any inconsistent bitmaps, we refuse to allow the truncate
as we do not actually load these bitmaps into memory, and it isn't safe
or reasonable to attempt to truncate corrupted data.

Signed-off-by: John Snow <jsnow@redhat.com>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-id: 20190311185147.52309-4-vsementsov@virtuozzo.com
  [vsementsov: drop bitmap flushing, fix block comments style]
Signed-off-by: John Snow <jsnow@redhat.com>

1 files changed, 46 insertions, 0 deletions

diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c
index 92cef1c..e53a160 100644
--- a/block/qcow2-bitmap.c
+++ b/block/qcow2-bitmap.c
@@ -1175,6 +1175,52 @@ int qcow2_reopen_bitmaps_rw(BlockDriverState *bs, Error **errp)
     return qcow2_reopen_bitmaps_rw_hint(bs, NULL, errp);
 }
 
+/* Checks to see if it's safe to resize bitmaps */
+int qcow2_truncate_bitmaps_check(BlockDriverState *bs, Error **errp)
+{
+    BDRVQcow2State *s = bs->opaque;
+    Qcow2BitmapList *bm_list;
+    Qcow2Bitmap *bm;
+    int ret = 0;
+
+    if (s->nb_bitmaps == 0) {
+        return 0;
+    }
+
+    bm_list = bitmap_list_load(bs, s->bitmap_directory_offset,
+                               s->bitmap_directory_size, errp);
+    if (bm_list == NULL) {
+        return -EINVAL;
+    }
+
+    QSIMPLEQ_FOREACH(bm, bm_list, entry) {
+        BdrvDirtyBitmap *bitmap = bdrv_find_dirty_bitmap(bs, bm->name);
+        if (bitmap == NULL) {
+            /*
+             * We rely on all bitmaps being in-memory to be able to resize them,
+             * Otherwise, we'd need to resize them on disk explicitly
+             */
+            error_setg(errp, "Cannot resize qcow2 with persistent bitmaps that "
+                       "were not loaded into memory");
+            ret = -ENOTSUP;
+            goto out;
+        }
+
+        /*
+         * The checks against readonly and busy are redundant, but certainly
+         * do no harm. checks against inconsistent are crucial:
+         */
+        if (bdrv_dirty_bitmap_check(bitmap, BDRV_BITMAP_DEFAULT, errp)) {
+            ret = -ENOTSUP;
+            goto out;
+        }
+    }
+
+out:
+    bitmap_list_free(bm_list);
+    return ret;
+}
+
 /* store_bitmap_data()
  * Store bitmap to image, filling bitmap table accordingly.
  */