Re: [Qemu-devel] [PATCH] add VNC reverse connections

[Eddie Kohler <kohler@cs.ucla.edu>]

Anthony Liguori wrote:
>>> This doesn't feel like an option to me, though; rather a different 
>>> means of connecting.  Among other things, in "-vnc :0", the QEMU VNC 
>>> server opens port 5900.  But the client's listening port for reverse 
>>> connections defaults to 5500.  "-vnc :-400,rev" is clearly insane, 
>>> but it seems strange for an option like ",rev" to change the meaning 
>>> of the port field.
>>>     
>>
>> Yes that is a valid point. It is a little unfortunate we switched to 
>> using
>> display num instead of port num for the current VNC code. Having a syntax
>> which makes people use negative display nums for reverse connections 
>> would
>> suck. So reluctantly I think your original proposal may actually be 
>> better.
> 
> Yet this is the syntax we use for normal connections.  I don't see why 
> the asymmetry is okay for reverse connections.

Because reverse connections feel very different from normal connections, use 
ports instead of "display numbers", etc.?

Here's what the manual would look like for the "rev:" syntax.


interface:d
TCP connections will only be allowed from interface on display d. By convention 
the TCP port is 5900+d. Optionally, interface can be omitted in which case the 
server will bind to all interfaces.
...
rev:[address:]port
Connects to a VNC client listening at address:port. Optionally, address can be 
omitted in which case the server connects to localhost:port.


Here's what the manual would look like for the ",reverse" syntax.


Valid syntax for the display is

interface:d
TCP connections will only be allowed from interface on display d. By convention 
the TCP port is 5900+d. Optionally, interface can be omitted in which case the 
server will bind to all interfaces.
...
reverse
QEMU will connect to a listening VNC client, rather than waiting for a client 
connection.  If the connection has type "interface:d", then "interface" is the 
client address; if omitted, localhost is used. The display number "d" is added 
to 5900 to determine the port, so negative numbers might be necessary to 
connect to default client ports.


Or are you thinking


For reverse connections, the display number "d" is added to 5500 to determine 
the port.


in which case the interface:d definition is incorrect?

I'm not trying to make this look ugly on purpose.  The prefix syntax seems 
friendlier.

Eddie