block: Add 'x-blockdev-del' QMP command

This command is still experimental, hence the name.

This is the companion to 'blockdev-add'. It allows deleting a
BlockBackend with its associated BlockDriverState tree, or a
BlockDriverState that is not attached to any backend.

In either case, the command fails if the reference count is greater
than 1 or the BlockDriverState has any parents.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: 6cfc148c77aca1da942b094d811bfa3fcf7ac7bb.1446475331.git.berto@igalia.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

blockdev.c

@@ -3479,6 +3479,72 @@ fail:
     qmp_output_visitor_cleanup(ov);
 }
 
+void qmp_x_blockdev_del(bool has_id, const char *id,
+                        bool has_node_name, const char *node_name, Error **errp)
+{
+    AioContext *aio_context;
+    BlockBackend *blk;
+    BlockDriverState *bs;
+
+    if (has_id && has_node_name) {
+        error_setg(errp, "Only one of id and node-name must be specified");
+        return;
+    } else if (!has_id && !has_node_name) {
+        error_setg(errp, "No block device specified");
+        return;
+    }
+
+    if (has_id) {
+        blk = blk_by_name(id);
+        if (!blk) {
+            error_setg(errp, "Cannot find block backend %s", id);
+            return;
+        }
+        if (blk_get_refcnt(blk) > 1) {
+            error_setg(errp, "Block backend %s is in use", id);
+            return;
+        }
+        bs = blk_bs(blk);
+        aio_context = blk_get_aio_context(blk);
+    } else {
+        bs = bdrv_find_node(node_name);
+        if (!bs) {
+            error_setg(errp, "Cannot find node %s", node_name);
+            return;
+        }
+        blk = bs->blk;
+        if (blk) {
+            error_setg(errp, "Node %s is in use by %s",
+                       node_name, blk_name(blk));
+            return;
+        }
+        aio_context = bdrv_get_aio_context(bs);
+    }
+
+    aio_context_acquire(aio_context);
+
+    if (bs) {
+        if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_DRIVE_DEL, errp)) {
+            goto out;
+        }
+
+        if (bs->refcnt > 1 || !QLIST_EMPTY(&bs->parents)) {
+            error_setg(errp, "Block device %s is in use",
+                       bdrv_get_device_or_node_name(bs));
+            goto out;
+        }
+    }
+
+    if (blk) {
+        blk_unref(blk);
+    } else {
+        bdrv_unref(bs);
+    }
+
+out:
+    aio_context_release(aio_context);
+}
+
 BlockJobInfoList *qmp_query_block_jobs(Error **errp)
 {
     BlockJobInfoList *head = NULL, **p_next = &head;

qapi/block-core.json

@@ -1895,8 +1895,8 @@
 # level and no BlockBackend will be created.
 #
 # This command is still a work in progress.  It doesn't support all
-# block drivers, it lacks a matching blockdev-del, and more.  Stay
-# away from it unless you want to help with its development.
+# block drivers among other things.  Stay away from it unless you want
+# to help with its development.
 #
 # @options: block device options for the new device
 #
@@ -1904,6 +1904,34 @@
 ##
 { 'command': 'blockdev-add', 'data': { 'options': 'BlockdevOptions' } }
 
+##
+# @x-blockdev-del:
+#
+# Deletes a block device that has been added using blockdev-add.
+# The selected device can be either a block backend or a graph node.
+#
+# In the former case the backend will be destroyed, along with its
+# inserted medium if there's any. The command will fail if the backend
+# or its medium are in use.
+#
+# In the latter case the node will be destroyed. The command will fail
+# if the node is attached to a block backend or is otherwise being
+# used.
+#
+# One of @id or @node-name must be specified, but not both.
+#
+# This command is still a work in progress and is considered
+# experimental. Stay away from it unless you want to help with its
+# development.
+#
+# @id: #optional Name of the block backend device to delete.
+#
+# @node-name: #optional Name of the graph node to delete.
+#
+# Since: 2.5
+##
+{ 'command': 'x-blockdev-del', 'data': { '*id': 'str', '*node-name': 'str' } }
+
 ##
 # @blockdev-open-tray:
 #

qmp-commands.hx

@@ -3946,8 +3946,8 @@ blockdev-add
 Add a block device.
 
 This command is still a work in progress.  It doesn't support all
-block drivers, it lacks a matching blockdev-del, and more.  Stay away
-from it unless you want to help with its development.
+block drivers among other things.  Stay away from it unless you want
+to help with its development.
 
 Arguments:
 
@@ -3990,6 +3990,63 @@ Example (2):
 
 <- { "return": {} }
 
+EQMP
+
+    {
+        .name       = "x-blockdev-del",
+        .args_type  = "id:s?,node-name:s?",
+        .mhandler.cmd_new = qmp_marshal_x_blockdev_del,
+    },
+
+SQMP
+x-blockdev-del
+------------
+Since 2.5
+
+Deletes a block device thas has been added using blockdev-add.
+The selected device can be either a block backend or a graph node.
+
+In the former case the backend will be destroyed, along with its
+inserted medium if there's any. The command will fail if the backend
+or its medium are in use.
+
+In the latter case the node will be destroyed. The command will fail
+if the node is attached to a block backend or is otherwise being
+used.
+
+One of "id" or "node-name" must be specified, but not both.
+
+This command is still a work in progress and is considered
+experimental. Stay away from it unless you want to help with its
+development.
+
+Arguments:
+
+- "id": Name of the block backend device to delete (json-string, optional)
+- "node-name": Name of the graph node to delete (json-string, optional)
+
+Example:
+
+-> { "execute": "blockdev-add",
+     "arguments": {
+         "options": {
+             "driver": "qcow2",
+             "id": "drive0",
+             "file": {
+                 "driver": "file",
+                 "filename": "test.qcow2"
+             }
+         }
+     }
+   }
+
+<- { "return": {} }
+
+-> { "execute": "x-blockdev-del",
+     "arguments": { "id": "drive0" }
+   }
+<- { "return": {} }
+
 EQMP
 
     {