commit: Allow users to request only format driver names in backing file format

Introduce a new flag 'backing-mask-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>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Message-ID: <2cb46e37093ce793ea1604abc8bbb90f4c8e434b.1701796348.git.pkrempa@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

diff --git a/block.c b/block.c
index a097772238ddbb634b3563e157b6f42a07662e17..30afdcbba60eab8ffdaeffe5b2a0a168cffd040a 100644 (file)
--- 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_mask_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_mask_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_mask_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_mask_protocol,
+                                            errp);
     }
     return 0;
 }
@@ -5803,7 +5824,8 @@ 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_mask_protocol)
 {
     BlockDriverState *explicit_top = top;
     bool update_inherits_from;
@@ -5869,6 +5891,7 @@ int bdrv_drop_intermediate(BlockDriverState *top, BlockDriverState *base,
 
         if (c->klass->update_filename) {
             ret = c->klass->update_filename(c, base, backing_file_str,
+                                            backing_mask_protocol,
                                             &local_err);
             if (ret < 0) {
                 /*

diff --git a/block/commit.c b/block/commit.c
index 1dd7a65ffb8946855876b1b66d638e0c8476c64a..7c3fdcb0caeb03a000b64ba76d11bed53d34e982 100644 (file)
--- 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_mask_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_mask_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_mask_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_mask_protocol = backing_mask_protocol;
     s->on_error = on_error;
 
     trace_commit_start(bs, base, top, s);

diff --git a/blockdev.c b/blockdev.c
index 3a5e7222eca6b6ff3a9fd5f0d7179cd902fdfc7c..292c8af3f9da98e976e7bc479f2c48e22451c055 100644 (file)
--- a/blockdev.c
+++ b/blockdev.c
@@ -2420,6 +2420,8 @@ 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_mask_protocol,
+                      bool backing_mask_protocol,
                       bool has_speed, int64_t speed,
                       bool has_on_error, BlockdevOnError on_error,
                       const char *filter_node_name,
@@ -2450,6 +2452,9 @@ 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_mask_protocol) {
+        backing_mask_protocol = false;
+    }
 
     /* Important Note:
      *  libvirt relies on the DeviceNotFound error class in order to probe for
@@ -2591,6 +2596,7 @@ 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_mask_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 4ec0b217f059944241461a4863d8eb502c5e4fce..bd7cecd1cf44c13c448aaa5eb6e17572ae240ef4 100644 (file)
--- a/include/block/block-global-state.h
+++ b/include/block/block-global-state.h
@@ -144,7 +144,8 @@ 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_mask_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 151279d481d031522053f1c3aa9f66aec0204e5f..761276127ed2fa8cd9d8166471fd72072cb68c92 100644 (file)
--- 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_mask_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 ef31c58bb3e33f19fd90afc5ddeec4e9add341a7..2162269df68806c1aed7bf4e299c9b2d11e1740a 100644 (file)
--- 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_mask_protocol: Replace potential protocol name with 'raw' in
+ *                         'backing file format' header
  * @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_mask_protocol,
                   const char *filter_node_name, Error **errp);
 /**
  * commit_active_start:

diff --git a/qapi/block-core.json b/qapi/block-core.json
index ca390c570022a82355d50d295120347a9e5ed2b4..726145ec8a580f4272b948ca9df72ead4946a1a5 100644 (file)
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1810,6 +1810,11 @@
 #     Care should be taken when specifying the string, to specify a
 #     valid filename or protocol.  (Since 2.1)
 #
+# @backing-mask-protocol: If true, replace any protocol mentioned in the
+#     'backing file format' with 'raw', rather than storing the protocol
+#     name as the backing format.  Can be used even when no image header
+#     will be updated (default false; since 9.0).
+#
 # @speed: the maximum speed, in bytes per second
 #
 # @on-error: the action to take on an error.  'ignore' means that the
@@ -1856,7 +1861,8 @@
             '*base': { 'type': 'str', 'features': [ 'deprecated' ] },
             '*top-node': 'str',
             '*top': { 'type': 'str', 'features': [ 'deprecated' ] },
-            '*backing-file': 'str', '*speed': 'int',
+            '*backing-file': 'str', '*backing-mask-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 17830a69c1a5909ec10fd9aa71839fa5d7c7fa7a..666880472b89f57b6fa4217619ad0d5e3b01afaf 100644 (file)
--- a/tests/unit/test-bdrv-drain.c
+++ b/tests/unit/test-bdrv-drain.c
@@ -1591,6 +1591,7 @@ static const BlockJobDriver test_simple_job_driver = {
 static int drop_intermediate_poll_update_filename(BdrvChild *child,
                                                   BlockDriverState *new_base,
                                                   const char *filename,
+                                                  bool backing_mask_protocol,
                                                   Error **errp)
 {
     /*
@@ -1702,7 +1703,7 @@ 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);