[PATCH v3 05/11] qapi: add x-blockdev-replace command

[Vladimir Sementsov-Ogievskiy <vsementsov@xxxxxxxxxxxxx>]

Add a command that can replace bs in following BdrvChild structures:

 - qdev blk root child
 - block-export blk root child
 - any child BlockDriverState selected by child-name

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@xxxxxxxxxxxxx>
---
 qapi/block-core.json   | 62 ++++++++++++++++++++++++++++++++++++++++
 blockdev.c             | 65 ++++++++++++++++++++++++++++++++++++++++++
 stubs/blk-by-qdev-id.c |  9 ++++++
 stubs/meson.build      |  1 +
 4 files changed, 137 insertions(+)
 create mode 100644 stubs/blk-by-qdev-id.c

diff --git a/qapi/block-core.json b/qapi/block-core.json
index 9a5a3641d0..f760dc21f5 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -5574,3 +5574,65 @@
 { 'command': 'blockdev-snapshot-delete-internal-sync',
   'data': { 'device': 'str', '*id': 'str', '*name': 'str'},
   'returns': 'SnapshotInfo' }
+
+##
+# @BlockParentType:
+#
+# Since 7.0
+##
+{ 'enum': 'BlockParentType',
+  'data': ['qdev', 'driver', 'export'] }
+
+##
+# @BdrvChildRefQdev:
+#
+# Since 7.0
+##
+{ 'struct': 'BdrvChildRefQdev',
+  'data': { 'qdev-id': 'str' } }
+
+##
+# @BdrvChildRefExport:
+#
+# Since 7.0
+##
+{ 'struct': 'BdrvChildRefExport',
+  'data': { 'export-id': 'str' } }
+
+##
+# @BdrvChildRefDriver:
+#
+# Since 7.0
+##
+{ 'struct': 'BdrvChildRefDriver',
+  'data': { 'node-name': 'str', 'child': 'str' } }
+
+##
+# @BlockdevReplace:
+#
+# Since 7.0
+##
+{ 'union': 'BlockdevReplace',
+  'base': {
+      'parent-type': 'BlockParentType',
+      'new-child': 'str'
+  },
+  'discriminator': 'parent-type',
+  'data': {
+      'qdev': 'BdrvChildRefQdev',
+      'export': 'BdrvChildRefExport',
+      'driver': 'BdrvChildRefDriver'
+  } }
+
+##
+# @x-blockdev-replace:
+#
+# Replace a block-node associated with device (selected by
+# @qdev-id) or with block-export (selected by @export-id) or
+# any child of block-node (selected by @node-name and @child)
+# with @new-child block-node.
+#
+# Since 7.0
+##
+{ 'command': 'x-blockdev-replace', 'boxed': true,
+  'data': 'BlockdevReplace' }
diff --git a/blockdev.c b/blockdev.c
index d20963be2a..9fd1783be2 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -2229,6 +2229,71 @@ static void blockdev_add_abort(BlkActionState *common)
     bdrv_unref(s->bs);
 }
 
+static int blockdev_replace(BlockdevReplace *repl, Transaction *tran,
+                            Error **errp)
+{
+    BdrvChild *child = NULL;
+    BlockDriverState *new_child_bs;
+
+    if (repl->parent_type == BLOCK_PARENT_TYPE_DRIVER) {
+        BlockDriverState *parent_bs;
+
+        parent_bs = bdrv_find_node(repl->u.driver.node_name);
+        if (!parent_bs) {
+            error_setg(errp, "Block driver node with node-name '%s' not "
+                       "found", repl->u.driver.node_name);
+            return -EINVAL;
+        }
+
+        child = bdrv_find_child(parent_bs, repl->u.driver.child);
+        if (!child) {
+            error_setg(errp, "Block driver node '%s' doesn't have child "
+                       "named '%s'", repl->u.driver.node_name,
+                       repl->u.driver.child);
+            return -EINVAL;
+        }
+    } else {
+        /* Other types are similar, they work through blk */
+        BlockBackend *blk;
+        bool is_qdev = repl->parent_type == BLOCK_PARENT_TYPE_QDEV;
+        const char *id =
+            is_qdev ? repl->u.qdev.qdev_id : repl->u.export.export_id;
+
+        assert(is_qdev || repl->parent_type == BLOCK_PARENT_TYPE_EXPORT);
+
+        blk = is_qdev ? blk_by_qdev_id(id, errp) : blk_by_export_id(id, errp);
+        if (!blk) {
+            return -EINVAL;
+        }
+
+        child = blk_root(blk);
+        if (!child) {
+            error_setg(errp, "%s '%s' is empty, nothing to replace",
+                       is_qdev ? "Device" : "Export", id);
+            return -EINVAL;
+        }
+    }
+
+    assert(child);
+    assert(child->bs);
+
+    new_child_bs = bdrv_find_node(repl->new_child);
+    if (!new_child_bs) {
+        error_setg(errp, "Node '%s' not found", repl->new_child);
+        return -EINVAL;
+    }
+
+    return bdrv_replace_child_bs(child, new_child_bs, tran, errp);
+}
+
+void qmp_x_blockdev_replace(BlockdevReplace *repl, Error **errp)
+{
+    Transaction *tran = tran_new();
+    int ret = blockdev_replace(repl, tran, errp);
+
+    tran_finalize(tran, ret);
+}
+
 static const BlkActionOps actions[] = {
     [TRANSACTION_ACTION_KIND_BLOCKDEV_SNAPSHOT] = {
         .instance_size = sizeof(ExternalSnapshotState),
diff --git a/stubs/blk-by-qdev-id.c b/stubs/blk-by-qdev-id.c
new file mode 100644
index 0000000000..0e751ce4f7
--- /dev/null
+++ b/stubs/blk-by-qdev-id.c
@@ -0,0 +1,9 @@
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "sysemu/block-backend.h"
+
+BlockBackend *blk_by_qdev_id(const char *id, Error **errp)
+{
+    error_setg(errp, "blk '%s' not found", id);
+    return NULL;
+}
diff --git a/stubs/meson.build b/stubs/meson.build
index d359cbe1ad..90358823fc 100644
--- a/stubs/meson.build
+++ b/stubs/meson.build
@@ -1,6 +1,7 @@
 stub_ss.add(files('bdrv-next-monitor-owned.c'))
 stub_ss.add(files('blk-commit-all.c'))
 stub_ss.add(files('blk-exp-close-all.c'))
+stub_ss.add(files('blk-by-qdev-id.c'))
 stub_ss.add(files('blockdev-close-all-bdrv-states.c'))
 stub_ss.add(files('change-state-handler.c'))
 stub_ss.add(files('cmos.c'))
-- 
2.31.1