qmp: Allow to change password on named block driver states.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
Reviewed-by: Fam Zheng <famz@redhat.com>

There was two candidate ways to implement named node manipulation:

1)
{ 'command': 'block_passwd', 'data': {'*device': 'str',
                                      '*node-name': 'str', 'password': 'str'}
}

2)

{ 'command': 'block_passwd', 'data': {'device': 'str',
                                      '*device-is-node': 'bool',
                                      'password': 'str'} }

Luiz proposed 1 and says 2 was an abuse of the QMP interface and proposed to
rewrite the QMP block interface for 2.0.

Luiz does not like in 1 the fact that 2 fields are optional but one of them must
be specified leading to an abuse of the QMP semantic.

Kevin argumented that 2 what a clear abuse of the device field and would not be
practical when reading fast some log file because the user would read "device"
and think that a device is manipulated when it's in fact a node name.
Documentation of 1 make it pretty clear what to do for the user.

Kevin argued that all bs are node including devices ones so 2 does not make
sense.

Kevin also argued that rewriting the QMP block interface would not make disapear
the current one.

Kevin pushed the argument that making the QAPI generator compatible with the
semantic of the operation would need a rewrite that no one has done yet.

A vote has been done on the list to elect the version to use and 1 won.

For reference the complete thread is:
"[Qemu-devel] [PATCH V4 4/7] qmp: Allow to change password on names block driver
states."

Signed-off-by: Benoit Canet <benoit@irqsave.net>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -3309,6 +3309,38 @@ BlockDeviceInfoList *bdrv_named_nodes_list(void)
     return list;
 }
 
+BlockDriverState *bdrv_lookup_bs(const char *device,
+                                 const char *node_name,
+                                 Error **errp)
+{
+    BlockDriverState *bs = NULL;
+
+    if ((!device && !node_name) || (device && node_name)) {
+        error_setg(errp, "Use either device or node-name but not both");
+        return NULL;
+    }
+
+    if (device) {
+        bs = bdrv_find(device);
+
+        if (!bs) {
+            error_set(errp, QERR_DEVICE_NOT_FOUND, device);
+            return NULL;
+        }
+
+        return bs;
+    }
+
+    bs = bdrv_find_node(node_name);
+
+    if (!bs) {
+        error_set(errp, QERR_DEVICE_NOT_FOUND, node_name);
+        return NULL;
+    }
+
+    return bs;
+}
+
 BlockDriverState *bdrv_next(BlockDriverState *bs)
 {
     if (!bs) {

blockdev.c

@@ -1481,14 +1481,19 @@ void qmp_eject(const char *device, bool has_force, bool force, Error **errp)
     eject_device(bs, force, errp);
 }
 
-void qmp_block_passwd(const char *device, const char *password, Error **errp)
+void qmp_block_passwd(bool has_device, const char *device,
+                      bool has_node_name, const char *node_name,
+                      const char *password, Error **errp)
 {
+    Error *local_err = NULL;
     BlockDriverState *bs;
     int err;
 
-    bs = bdrv_find(device);
-    if (!bs) {
-        error_set(errp, QERR_DEVICE_NOT_FOUND, device);
+    bs = bdrv_lookup_bs(has_device ? device : NULL,
+                        has_node_name ? node_name : NULL,
+                        &local_err);
+    if (error_is_set(&local_err)) {
+        error_propagate(errp, local_err);
         return;
     }
 

hmp.c

@@ -871,7 +871,7 @@ void hmp_block_passwd(Monitor *mon, const QDict *qdict)
     const char *password = qdict_get_str(qdict, "password");
     Error *errp = NULL;
 
-    qmp_block_passwd(device, password, &errp);
+    qmp_block_passwd(true, device, false, NULL, password, &errp);
     hmp_handle_error(mon, &errp);
 }
 

include/block/block.h

@@ -380,6 +380,9 @@ const char *bdrv_get_format_name(BlockDriverState *bs);
 BlockDriverState *bdrv_find(const char *name);
 BlockDriverState *bdrv_find_node(const char *node_name);
 BlockDeviceInfoList *bdrv_named_nodes_list(void);
+BlockDriverState *bdrv_lookup_bs(const char *device,
+                                 const char *node_name,
+                                 Error **errp);
 BlockDriverState *bdrv_next(BlockDriverState *bs);
 void bdrv_iterate(void (*it)(void *opaque, BlockDriverState *bs),
                   void *opaque);

qapi-schema.json

@@ -1678,7 +1678,11 @@
 # determine which ones are encrypted, set the passwords with this command, and
 # then start the guest with the @cont command.
 #
-# @device:   the name of the device to set the password on
+# Either @device or @node-name must be set but not both.
+#
+# @device: #optional the name of the block backend device to set the password on
+#
+# @node-name: #optional graph node name to set the password on (Since 2.0)
 #
 # @password: the password to use for the device
 #
@@ -1692,7 +1696,8 @@
 #
 # Since: 0.14.0
 ##
-{ 'command': 'block_passwd', 'data': {'device': 'str', 'password': 'str'} }
+{ 'command': 'block_passwd', 'data': {'*device': 'str',
+                                      '*node-name': 'str', 'password': 'str'} }
 
 ##
 # @balloon:

qmp-commands.hx

@@ -1503,7 +1503,7 @@ EQMP
 
     {
         .name       = "block_passwd",
-        .args_type  = "device:B,password:s",
+        .args_type  = "device:s?,node-name:s?,password:s",
         .mhandler.cmd_new = qmp_marshal_input_block_passwd,
     },
 
@@ -1516,6 +1516,7 @@ Set the password of encrypted block devices.
 Arguments:
 
 - "device": device name (json-string)
+- "node-name": name in the block driver state graph (json-string)
 - "password": password (json-string)
 
 Example: