[Qemu-devel] [PATCH v8 03/26] block: Add BDS.backing_overridden

[Max Reitz <mreitz@redhat.com>]

If the backing file is overridden, this most probably does change the
guest-visible data of a BDS. Therefore, we will need to consider this in
bdrv_refresh_filename().

Adding a new field to the BDS is not nice, but it is very simple and
exactly keeps track of whether the backing file has been overridden.

This commit adds a FIXME which will be remedied by a follow-up commit.
Until then, the respective piece of code will not result in any behavior
that is worse than what we currently have.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
---
 include/block/block_int.h |  1 +
 block.c                   | 13 +++++++++++++
 block/mirror.c            |  4 ++++
 blockdev.c                | 16 ++++++++++++++++
 4 files changed, 34 insertions(+)

diff --git a/include/block/block_int.h b/include/block/block_int.h
index 29cafa4236..b5c124fcbd 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -619,6 +619,7 @@ struct BlockDriverState {
     char backing_file[PATH_MAX]; /* if non zero, the image is a diff of
                                     this file image */
     char backing_format[16]; /* if non-zero and backing_file exists */
+    bool backing_overridden; /* backing file has been specified by the user */
 
     QDict *full_open_options;
     char exact_filename[PATH_MAX];
diff --git a/block.c b/block.c
index b84aba2d95..66e37219b9 100644
--- a/block.c
+++ b/block.c
@@ -2268,6 +2268,11 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options,
     reference = qdict_get_try_str(parent_options, bdref_key);
     if (reference || qdict_haskey(options, "file.filename")) {
         backing_filename[0] = '\0';
+
+        /* FIXME: Should also be set to true if @options contains other runtime
+         *        options which control the data that is read from the backing
+         *        BDS */
+        bs->backing_overridden = true;
     } else if (bs->backing_file[0] == '\0' && qdict_size(options) == 0) {
         QDECREF(options);
         goto free_exit;
@@ -2469,6 +2474,9 @@ static BlockDriverState *bdrv_append_temp_snapshot(BlockDriverState *bs,
         goto out;
     }
 
+    bs_snapshot->backing_overridden = true;
+    bdrv_refresh_filename(bs_snapshot);
+
 out:
     QDECREF(snapshot_options);
     g_free(tmp_filename);
@@ -2599,6 +2607,7 @@ static BlockDriverState *bdrv_open_inherit(const char *filename,
     backing = qdict_get_try_str(options, "backing");
     if (backing && *backing == '\0') {
         flags |= BDRV_O_NO_BACKING;
+        bs->backing_overridden = true;
         qdict_del(options, "backing");
     }
 
@@ -5031,6 +5040,10 @@ void bdrv_refresh_filename(BlockDriverState *bs)
      * refresh those first */
     QLIST_FOREACH(child, &bs->children, next) {
         bdrv_refresh_filename(child->bs);
+
+        if (child->role == &child_backing && child->bs->backing_overridden) {
+            bs->backing_overridden = true;
+        }
     }
 
     if (drv->bdrv_refresh_filename) {
diff --git a/block/mirror.c b/block/mirror.c
index 5a627ba589..aa68531352 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -530,6 +530,10 @@ static void mirror_exit(BlockJob *job, void *opaque)
             error_report_err(local_err);
             data->ret = -EPERM;
         }
+
+        /* The target image's file already has been created with the backing
+         * file we just set, so there is no need to set backing_overridden or
+         * call bdrv_refresh_filename(). */
     }
 
     if (s->to_replace) {
diff --git a/blockdev.c b/blockdev.c
index 8e977eef11..bbe264c3c0 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1795,6 +1795,8 @@ static void external_snapshot_commit(BlkActionState *common)
 {
     ExternalSnapshotState *state =
                              DO_UPCAST(ExternalSnapshotState, common, common);
+    TransactionAction *action = common->action;
+    bool image_was_existing = false;
     AioContext *aio_context;
 
     aio_context = bdrv_get_aio_context(state->old_bs);
@@ -1808,6 +1810,20 @@ static void external_snapshot_commit(BlkActionState *common)
                     NULL);
     }
 
+    if (action->type == TRANSACTION_ACTION_KIND_BLOCKDEV_SNAPSHOT_SYNC) {
+        BlockdevSnapshotSync *s = action->u.blockdev_snapshot_sync.data;
+        if (s->has_mode && s->mode == NEW_IMAGE_MODE_EXISTING) {
+            image_was_existing = true;
+        }
+    } else {
+        image_was_existing = true;
+    }
+
+    if (image_was_existing) {
+        state->new_bs->backing_overridden = true;
+        bdrv_refresh_filename(state->new_bs);
+    }
+
     aio_context_release(aio_context);
 }
 
-- 
2.14.3