block: Add 'base-node' parameter to the 'block-stream' command

The way to specify the node from which to copy data in the
block-stream operation is by using the 'base' parameter. This
parameter however takes a file name, not a node name.

Since we want to be able to perform this operation using only node
names, this patch adds a new 'base-node' parameter.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

blockdev.c

@@ -2932,6 +2932,7 @@ static void block_job_cb(void *opaque, int ret)
 
 void qmp_block_stream(bool has_job_id, const char *job_id, const char *device,
                       bool has_base, const char *base,
+                      bool has_base_node, const char *base_node,
                       bool has_backing_file, const char *backing_file,
                       bool has_speed, int64_t speed,
                       bool has_on_error, BlockdevOnError on_error,
@@ -2955,6 +2956,12 @@ void qmp_block_stream(bool has_job_id, const char *job_id, const char *device,
     aio_context = bdrv_get_aio_context(bs);
     aio_context_acquire(aio_context);
 
+    if (has_base && has_base_node) {
+        error_setg(errp, "'base' and 'base-node' cannot be specified "
+                   "at the same time");
+        goto out;
+    }
+
     if (has_base) {
         base_bs = bdrv_find_backing_image(bs, base);
         if (base_bs == NULL) {
@@ -2965,6 +2972,20 @@ void qmp_block_stream(bool has_job_id, const char *job_id, const char *device,
         base_name = base;
     }
 
+    if (has_base_node) {
+        base_bs = bdrv_lookup_bs(NULL, base_node, errp);
+        if (!base_bs) {
+            goto out;
+        }
+        if (bs == base_bs || !bdrv_chain_contains(bs, base_bs)) {
+            error_setg(errp, "Node '%s' is not a backing image of '%s'",
+                       base_node, device);
+            goto out;
+        }
+        assert(bdrv_get_aio_context(base_bs) == aio_context);
+        base_name = base_bs->filename;
+    }
+
     /* Check for op blockers in the whole chain between bs and base */
     for (iter = bs; iter && iter != base_bs; iter = backing_bs(iter)) {
         if (bdrv_op_is_blocked(iter, BLOCK_OP_TYPE_STREAM, errp)) {

docs/qmp-commands.txt

@@ -750,8 +750,11 @@ Arguments:
 - "job-id": Identifier for the newly-created block job. If omitted,
             the device name will be used. (json-string, optional)
 - "device": The device name or node-name of a root node (json-string)
-- "base": The file name of the backing image above which copying starts
+- "base": The file name of the backing image above which copying starts.
-          (json-string, optional)
+          It cannot be set if 'base-node' is also set (json-string, optional)
+- "base-node": the node name of the backing image above which copying starts.
+               It cannot be set if 'base' is also set.
+               (json-string, optional) (Since 2.8)
 - "backing-file": The backing file string to write into the active layer. This
                   filename is not validated.
 

hmp.c

@@ -1571,7 +1571,7 @@ void hmp_block_stream(Monitor *mon, const QDict *qdict)
     int64_t speed = qdict_get_try_int(qdict, "speed", 0);
 
     qmp_block_stream(false, NULL, device, base != NULL, base, false, NULL,
-                     qdict_haskey(qdict, "speed"), speed,
+                     false, NULL, qdict_haskey(qdict, "speed"), speed,
                      true, BLOCKDEV_ON_ERROR_REPORT, &error);
 
     hmp_handle_error(mon, &error);

qapi/block-core.json

@@ -1484,7 +1484,11 @@
 #
 # @device: the device or node name of the top image
 #
-# @base:   #optional the common backing file name
+# @base:   #optional the common backing file name.
+#                    It cannot be set if @base-node is also set.
+#
+# @base-node: #optional the node name of the backing file.
+#                       It cannot be set if @base is also set. (Since 2.8)
 #
 # @backing-file: #optional The backing file string to write into the top
 #                          image. This filename is not validated.
@@ -1511,7 +1515,7 @@
 ##
 { 'command': 'block-stream',
   'data': { '*job-id': 'str', 'device': 'str', '*base': 'str',
-            '*backing-file': 'str', '*speed': 'int',
+            '*base-node': 'str', '*backing-file': 'str', '*speed': 'int',
             '*on-error': 'BlockdevOnError' } }
 
 ##