[PATCH 1/2] block: commit: Allow users to request only format driver names in backing file format

[Peter Krempa]

Introduce a new flag 'backing_file_format_no_protocol' for the
block-commit QMP command which instructs the internals to use 'raw'
instead of the protocol driver in case when a image is used without a
dummy 'raw' wrapper.

The flag is designed such that it can be always asserted by management
tools even when there isn't any update to backing files.

The flag will be used by libvirt so that the backing images still
reference the proper format even when libvirt will stop using the dummy
raw driver (raw driver with no other config). Libvirt needs this so that
the images stay compatible with older libvirt versions which didn't
expect that a protocol driver name can appear in the backing file format
field.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
---
 block.c                                | 37 +++++++++++++++++++++-----
 block/commit.c                         |  6 ++++-
 blockdev.c                             |  6 +++++
 include/block/block-global-state.h     |  3 ++-
 include/block/block_int-common.h       |  4 ++-
 include/block/block_int-global-state.h |  3 +++
 qapi/block-core.json                   | 11 +++++++-
 tests/unit/test-bdrv-drain.c           |  3 ++-
 8 files changed, 61 insertions(+), 12 deletions(-)

diff --git a/block.c b/block.c
index bfb0861ec6..986a529941 100644
--- a/block.c
+++ b/block.c
@@ -1309,11 +1309,14 @@ static void bdrv_backing_detach(BdrvChild *c)
 }

 static int bdrv_backing_update_filename(BdrvChild *c, BlockDriverState *base,
-                                        const char *filename, Error **errp)
+                                        const char *filename,
+                                        bool backing_file_format_no_protocol,
+                                        Error **errp)
 {
     BlockDriverState *parent = c->opaque;
     bool read_only = bdrv_is_read_only(parent);
     int ret;
+    const char *format_name;
     GLOBAL_STATE_CODE();

     if (read_only) {
@@ -1323,9 +1326,23 @@ static int bdrv_backing_update_filename(BdrvChild *c, 
BlockDriverState *base,
         }
     }

-    ret = bdrv_change_backing_file(parent, filename,
-                                   base->drv ? base->drv->format_name : "",
-                                   false);
+    if (base->drv) {
+        /*
+         * If the new base image doesn't have a format driver layer, which we
+         * detect by the fact that @base is a protocol driver, we record
+         * 'raw' as the format instead of putting the protocol name as the
+         * backing format
+         */
+        if (backing_file_format_no_protocol && base->drv->protocol_name) {
+            format_name = "raw";
+        } else {
+            format_name = base->drv->format_name;
+        }
+    } else {
+        format_name = "";
+    }
+
+    ret = bdrv_change_backing_file(parent, filename, format_name, false);
     if (ret < 0) {
         error_setg_errno(errp, -ret, "Could not update backing file link");
     }
@@ -1479,10 +1496,14 @@ static void GRAPH_WRLOCK bdrv_child_cb_detach(BdrvChild 
*child)
 }

 static int bdrv_child_cb_update_filename(BdrvChild *c, BlockDriverState *base,
-                                         const char *filename, Error **errp)
+                                         const char *filename,
+                                         bool backing_file_format_no_protocol,
+                                         Error **errp)
 {
     if (c->role & BDRV_CHILD_COW) {
-        return bdrv_backing_update_filename(c, base, filename, errp);
+        return bdrv_backing_update_filename(c, base, filename,
+                                            backing_file_format_no_protocol,
+                                            errp);
     }
     return 0;
 }
@@ -5961,7 +5982,8 @@ void bdrv_unfreeze_backing_chain(BlockDriverState *bs, 
BlockDriverState *base)
  *
  */
 int bdrv_drop_intermediate(BlockDriverState *top, BlockDriverState *base,
-                           const char *backing_file_str)
+                           const char *backing_file_str,
+                           bool backing_file_format_no_protocol)
 {
     BlockDriverState *explicit_top = top;
     bool update_inherits_from;
@@ -6027,6 +6049,7 @@ int bdrv_drop_intermediate(BlockDriverState *top, 
BlockDriverState *base,

         if (c->klass->update_filename) {
             ret = c->klass->update_filename(c, base, backing_file_str,
+                                            backing_file_format_no_protocol,
                                             &local_err);
             if (ret < 0) {
                 /*
diff --git a/block/commit.c b/block/commit.c
index 69cc75be0c..5a584b712e 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -42,6 +42,7 @@ typedef struct CommitBlockJob {
     bool base_read_only;
     bool chain_frozen;
     char *backing_file_str;
+    bool backing_file_format_no_protocol;
 } CommitBlockJob;

 static int commit_prepare(Job *job)
@@ -61,7 +62,8 @@ static int commit_prepare(Job *job)
     /* FIXME: bdrv_drop_intermediate treats total failures and partial failures
      * identically. Further work is needed to disambiguate these cases. */
     return bdrv_drop_intermediate(s->commit_top_bs, s->base_bs,
-                                  s->backing_file_str);
+                                  s->backing_file_str,
+                                  s->backing_file_format_no_protocol);
 }

 static void commit_abort(Job *job)
@@ -254,6 +256,7 @@ void commit_start(const char *job_id, BlockDriverState *bs,
                   BlockDriverState *base, BlockDriverState *top,
                   int creation_flags, int64_t speed,
                   BlockdevOnError on_error, const char *backing_file_str,
+                  bool backing_file_format_no_protocol,
                   const char *filter_node_name, Error **errp)
 {
     CommitBlockJob *s;
@@ -408,6 +411,7 @@ void commit_start(const char *job_id, BlockDriverState *bs,
     blk_set_disable_request_queuing(s->top, true);

     s->backing_file_str = g_strdup(backing_file_str);
+    s->backing_file_format_no_protocol = backing_file_format_no_protocol;
     s->on_error = on_error;

     trace_commit_start(bs, base, top, s);
diff --git a/blockdev.c b/blockdev.c
index 4c1177e8db..038031bb03 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -2555,6 +2555,8 @@ void qmp_block_commit(const char *job_id, const char 
*device,
                       const char *top_node,
                       const char *top,
                       const char *backing_file,
+                      bool has_backing_file_format_no_protocol,
+                      bool backing_file_format_no_protocol,
                       bool has_speed, int64_t speed,
                       bool has_on_error, BlockdevOnError on_error,
                       const char *filter_node_name,
@@ -2585,6 +2587,9 @@ void qmp_block_commit(const char *job_id, const char 
*device,
     if (has_auto_dismiss && !auto_dismiss) {
         job_flags |= JOB_MANUAL_DISMISS;
     }
+    if (!has_backing_file_format_no_protocol) {
+        backing_file_format_no_protocol = false;
+    }

     /* Important Note:
      *  libvirt relies on the DeviceNotFound error class in order to probe for
@@ -2727,6 +2732,7 @@ void qmp_block_commit(const char *job_id, const char 
*device,
         }
         commit_start(job_id, bs, base_bs, top_bs, job_flags,
                      speed, on_error, backing_file,
+                     backing_file_format_no_protocol,
                      filter_node_name, &local_err);
     }
     if (local_err != NULL) {
diff --git a/include/block/block-global-state.h 
b/include/block/block-global-state.h
index 6b21fbc73f..b7aec4cd30 100644
--- a/include/block/block-global-state.h
+++ b/include/block/block-global-state.h
@@ -145,7 +145,8 @@ int GRAPH_RDLOCK bdrv_make_empty(BdrvChild *c, Error 
**errp);

 void bdrv_register(BlockDriver *bdrv);
 int bdrv_drop_intermediate(BlockDriverState *top, BlockDriverState *base,
-                           const char *backing_file_str);
+                           const char *backing_file_str,
+                           bool backing_file_format_no_protocol);

 BlockDriverState * GRAPH_RDLOCK
 bdrv_find_overlay(BlockDriverState *active, BlockDriverState *bs);
diff --git a/include/block/block_int-common.h b/include/block/block_int-common.h
index 4e31d161c5..e08204dec6 100644
--- a/include/block/block_int-common.h
+++ b/include/block/block_int-common.h
@@ -985,7 +985,9 @@ struct BdrvChildClass {
      * can update its reference.
      */
     int (*update_filename)(BdrvChild *child, BlockDriverState *new_base,
-                           const char *filename, Error **errp);
+                           const char *filename,
+                           bool backing_file_format_no_protocol,
+                           Error **errp);

     bool (*change_aio_ctx)(BdrvChild *child, AioContext *ctx,
                            GHashTable *visited, Transaction *tran,
diff --git a/include/block/block_int-global-state.h 
b/include/block/block_int-global-state.h
index ef31c58bb3..4f253ff362 100644
--- a/include/block/block_int-global-state.h
+++ b/include/block/block_int-global-state.h
@@ -82,6 +82,8 @@ void stream_start(const char *job_id, BlockDriverState *bs,
  * @speed: The maximum speed, in bytes per second, or 0 for unlimited.
  * @on_error: The action to take upon error.
  * @backing_file_str: String to use as the backing file in @top's overlay
+ * @backing_file_format_no_protocol: Use format name instead of potental
+ *                                   protocol name as backing image format
  * @filter_node_name: The node name that should be assigned to the filter
  * driver that the commit job inserts into the graph above @top. NULL means
  * that a node name should be autogenerated.
@@ -92,6 +94,7 @@ void commit_start(const char *job_id, BlockDriverState *bs,
                   BlockDriverState *base, BlockDriverState *top,
                   int creation_flags, int64_t speed,
                   BlockdevOnError on_error, const char *backing_file_str,
+                  bool backing_file_format_no_protocol,
                   const char *filter_node_name, Error **errp);
 /**
  * commit_active_start:
diff --git a/qapi/block-core.json b/qapi/block-core.json
index ca390c5700..367e896905 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1810,6 +1810,14 @@
 #     Care should be taken when specifying the string, to specify a
 #     valid filename or protocol.  (Since 2.1)
 #
+# @backing-file-format-no-protocol: If true always use a 'format' driver name
+#     for the 'backing file format' field if updating the image header of the
+#     overlay of 'top'. Otherwise the real name of the driver of the backing
+#     image may be used which may be a protocol driver.
+#
+#     Can be used also when no image header will be updated.
+#     (default: false; since: 8.2)
+#
 # @speed: the maximum speed, in bytes per second
 #
 # @on-error: the action to take on an error.  'ignore' means that the
@@ -1856,7 +1864,8 @@
             '*base': { 'type': 'str', 'features': [ 'deprecated' ] },
             '*top-node': 'str',
             '*top': { 'type': 'str', 'features': [ 'deprecated' ] },
-            '*backing-file': 'str', '*speed': 'int',
+            '*backing-file': 'str', '*backing-file-format-no-protocol': 'bool',
+            '*speed': 'int',
             '*on-error': 'BlockdevOnError',
             '*filter-node-name': 'str',
             '*auto-finalize': 'bool', '*auto-dismiss': 'bool' },
diff --git a/tests/unit/test-bdrv-drain.c b/tests/unit/test-bdrv-drain.c
index 704d1a3f36..422f0c7cd8 100644
--- a/tests/unit/test-bdrv-drain.c
+++ b/tests/unit/test-bdrv-drain.c
@@ -1638,6 +1638,7 @@ static const BlockJobDriver test_simple_job_driver = {
 static int drop_intermediate_poll_update_filename(BdrvChild *child,
                                                   BlockDriverState *new_base,
                                                   const char *filename,
+                                                  bool 
backing_file_format_no_protocol,
                                                   Error **errp)
 {
     /*
@@ -1749,7 +1750,7 @@ static void test_drop_intermediate_poll(void)
     job->should_complete = true;

     g_assert(!job_has_completed);
-    ret = bdrv_drop_intermediate(chain[1], chain[0], NULL);
+    ret = bdrv_drop_intermediate(chain[1], chain[0], NULL, false);
     aio_poll(qemu_get_aio_context(), false);
     g_assert(ret == 0);
     g_assert(job_has_completed);
-- 
2.43.0