net: Deprecate the "name" parameter of -net

In early times, network backends were specified by a "vlan" and "name"
tuple. With the introduction of netdevs, the "name" was replaced by an
"id" (which is supposed to be unique), but the "name" parameter stayed
as an alias which could be used instead of "id". Unfortunately, we miss
the duplication check for "name":

 $ qemu-system-x86_64 -net user,name=n1 -net user,name=n1

... starts without an error, while "id" correctly complains:

 $ qemu-system-x86_64 -net user,id=n1 -net user,id=n1
 qemu-system-x86_64: -net user,id=n1: Duplicate ID 'n1' for net

Instead of trying to fix the code for the legacy "name" parameter, let's
rather get rid of this old interface and deprecate the "name" parameter
now - this will also be less confusing for the users in the long run.
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NThomas Huth <thuth@redhat.com>

net/net.c

@@ -984,6 +984,10 @@ static int net_client_init1(const void *object, bool is_netdev, Error **errp)
         /* missing optional values have been initialized to "all bits zero" */
         name = net->has_id ? net->id : net->name;
 
+        if (net->has_name) {
+            warn_report("The 'name' parameter is deprecated, use 'id' instead");
+        }
+
         /* Map the old options to the new flat type */
         switch (opts->type) {
         case NET_LEGACY_OPTIONS_TYPE_NONE:

qemu-deprecated.texi

@@ -83,6 +83,11 @@ The 'file' driver for drives is no longer appropriate for character or host
 devices and will only accept regular files (S_IFREG). The correct driver
 for these file types is 'host_cdrom' or 'host_device' as appropriate.
 
+@subsection -net ...,name=@var{name} (since 3.1)
+
+The @option{name} parameter of the @option{-net} option is a synonym
+for the @option{id} parameter, which should now be used instead.
+
 @section QEMU Machine Protocol (QMP) commands
 
 @subsection block-dirty-bitmap-add "autoload" parameter (since 2.12.0)