block/qapi: include child references in block device info

In combination with using a throttle filter to enforce IO limits for
a guest device, knowing the 'file' child of a block device can be
useful. If the throttle filter is only intended for guest IO, block
jobs should not also be limited by the throttle filter, so the
block operations need to be done with the 'file' child of the top
throttle node as the target. In combination with mirroring, the name
of that child is not fixed.

Another scenario is when unplugging a guest device after mirroring
below a top throttle node, where the mirror target is added explicitly
via blockdev-add. After mirroring, the target becomes the new 'file'
child of the throttle node. For unplugging, both the top throttle node
and the mirror target need to be deleted, because only implicitly
added child nodes are deleted automatically, and the current 'file'
child of the throttle node was explicitly added (as the mirror
target).

In other scenarios, it could be useful to follow the backing chain.

Note that iotests 191 and 273 use _filter_img_info, so the 'children'
information is filtered out there.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Message-ID: <20250702123204.325470-2-f.ebner@proxmox.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

diff --git a/block/qapi.c b/block/qapi.c
index 2c50a6bf3b8a1e0e0bc088fd842caf934ad1d9fb..e08a1e970f533c36b34df8e09f9cb3253d935b53 100644 (file)
--- a/block/qapi.c
+++ b/block/qapi.c
@@ -51,6 +51,8 @@ BlockDeviceInfo *bdrv_block_device_info(BlockBackend *blk,
     ImageInfo *backing_info;
     BlockDriverState *backing;
     BlockDeviceInfo *info;
+    BlockdevChildList **children_list_tail;
+    BdrvChild *child;
 
     if (!bs->drv) {
         error_setg(errp, "Block device %s is ejected", bs->node_name);
@@ -77,6 +79,14 @@ BlockDeviceInfo *bdrv_block_device_info(BlockBackend *blk,
         info->node_name = g_strdup(bs->node_name);
     }
 
+    children_list_tail = &info->children;
+    QLIST_FOREACH(child, &bs->children, next) {
+        BlockdevChild *child_ref = g_new0(BlockdevChild, 1);
+        child_ref->child = g_strdup(child->name);
+        child_ref->node_name = g_strdup(child->bs->node_name);
+        QAPI_LIST_APPEND(children_list_tail, child_ref);
+    }
+
     backing = bdrv_cow_bs(bs);
     if (backing) {
         info->backing_file = g_strdup(backing->filename);

diff --git a/qapi/block-core.json b/qapi/block-core.json
index 1df6644f0de286f629d70360ad91b9715f794644..3e720af5adfed87c0c66a8c0a495f08fcdb51685 100644 (file)
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -461,6 +461,19 @@
             'direct': 'bool',
             'no-flush': 'bool' } }
 
+##
+# @BlockdevChild:
+#
+# @child: The name of the child, for example 'file' or 'backing'.
+#
+# @node-name: The name of the child's block driver node.
+#
+# Since: 10.1
+##
+{ 'struct': 'BlockdevChild',
+  'data': { 'child': 'str',
+            'node-name': 'str' } }
+
 ##
 # @BlockDeviceInfo:
 #
@@ -486,6 +499,8 @@
 # @backing_file_depth: number of files in the backing file chain
 #     (since: 1.2)
 #
+# @children: Information about child block nodes. (since: 10.1)
+#
 # @active: true if the backend is active; typical cases for inactive backends
 #     are on the migration source instance after migration completes and on the
 #     destination before it completes.  (since: 10.0)
@@ -560,6 +575,7 @@
 { 'struct': 'BlockDeviceInfo',
   'data': { 'file': 'str', '*node-name': 'str', 'ro': 'bool', 'drv': 'str',
             '*backing_file': 'str', 'backing_file_depth': 'int',
+            'children': ['BlockdevChild'],
             'active': 'bool', 'encrypted': 'bool',
             'detect_zeroes': 'BlockdevDetectZeroesOptions',
             'bps': 'int', 'bps_rd': 'int', 'bps_wr': 'int',

diff --git a/tests/qemu-iotests/184.out b/tests/qemu-iotests/184.out
index 52692b6b3b9bd162405c4e49f4ce5a24d937d79d..ef99bb2e9ab4765144b261a09da34f0b43618cb8 100644 (file)
--- a/tests/qemu-iotests/184.out
+++ b/tests/qemu-iotests/184.out
@@ -41,6 +41,12 @@ Testing:
             },
             "iops_wr": 0,
             "ro": false,
+            "children": [
+                {
+                    "node-name": "disk0",
+                    "child": "file"
+                }
+            ],
             "node-name": "throttle0",
             "backing_file_depth": 1,
             "drv": "throttle",
@@ -69,6 +75,8 @@ Testing:
             },
             "iops_wr": 0,
             "ro": false,
+            "children": [
+            ],
             "node-name": "disk0",
             "backing_file_depth": 0,
             "drv": "null-co",