QMP command add_client's schema:
##
# @add_client:
#
# Allow client connections for VNC, Spice and socket based
# character devices to be passed in to QEMU via SCM_RIGHTS.
#
# @protocol: protocol name. Valid names are "vnc", "spice", "@dbus-display" or
# the name of a character device (eg. from -chardev id=XXXX)
#
# @fdname: file descriptor name previously passed via 'getfd' command
#
# @skipauth: whether to skip authentication. Only applies
# to "vnc" and "spice" protocols
#
# @tls: whether to perform TLS. Only applies to the "spice"
# protocol
#
# Returns: nothing on success.
#
# Since: 0.14
#
# Example:
#
# -> { "execute": "add_client", "arguments": { "protocol": "vnc",
# "fdname": "myclient" } }
# <- { "return": {} }
#
##
{ 'command': 'add_client',
'data': { 'protocol': 'str', 'fdname': 'str', '*skipauth': 'bool',
'*tls': 'bool' } }
Spot the design flaw!
It's overloaded @protocol. Two issues.
One, character device IDs "vnc", "spice", "@dbus-display" don't work
here. If we ever add another protocol, we make another device ID not
work. Perhaps this is why Marc-André chose "@dbus-display", which
otherwise looks like a typo :)
That's right, I tried to avoid conflicting with chardev ID namespace. IDs can't start with '@'.
btw, I have a few patches pending to extend add_client for windows sockets.
I also have patches to check if fds are actually sockets, since that command doesn't make much sense with other fds.
Two, introspection can't tell us what protocols are supported.
Hmm, not really a big deal I suppose. You would have both compile-time and run-time config. There are other means to introspect the display protocol, like query-vnc or query-spice. I thought I had something covering dbus as well, but I can't find it, I'll look at it.
Let me know if you plan to touch that command, it will likely conflict with my work. I plan to submit it soon after the release, but I might do it earlier.