Re: [Qemu-devel] [PATCH v2] net: add the support for -netdev socket, listen

[Zhi Yong Wu <zwu.kernel@gmail.com>]

On Sun, Feb 26, 2012 at 10:48 PM, Stefan Hajnoczi <stefanha@gmail.com> wrote:
> On Sat, Feb 18, 2012 at 9:19 AM,  <zwu.kernel@gmail.com> wrote:
>> From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
>>
>> The -net socket,listen option does not work with the newer -netdev
>> syntax:
>> http://lists.gnu.org/archive/html/qemu-devel/2011-11/msg01508.html
>>
>> This patch makes it work now.
>>
>> Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
>> ---
>>  net.c        |   26 +++++++++++++++++++++
>>  net.h        |    2 +
>>  net/socket.c |   72 +++++++++++++++++++++++++++++++++++++++++++++-------------
>>  3 files changed, 84 insertions(+), 16 deletions(-)
>
> I wanted to understand the problem better so I tried out -net
> socket,listen=.  Here is its behavior:
>
> 1. A client can connect to QEMU, this creates a new socket
> VLANClientState on the VLAN.
> 2. If another client connects to QEMU, another VLANClientState is
> created.  That means many socket clients can be added to the same
> "VLAN".
> 3. When a simple TCP client like netcat connects and then disconnects,
> the VLANClientState remains forever.  There seems to be no cleanup.
>
> This patch does not handle the -net socket,listen= case where multiple
> clients connect.
>
> Also, the -netdev socket,listen= semantics cannot match -net
> socket-listen= semantics because there is only one peer at any time.
> Some options:
>
> 1. Do not accept new connections while a client is connected.  Once
> the client disconnects we can accept a new connection.  This maintains
> the 1-1 peer behavior.
> 2. Integrate with vlan-hub so that multiple clients can connect even
> with -netdev.  Connections will create new NetClientStates and
> auto-attach to the hub.  This mimics -net socket,listen= but requires
> a hub to be used.
> 3. Forbid -netdev socket,listen=, only allow -net socket,listen=.
>
> I think #1 would be okay, although it no longer allows multiple
> connections, but I don't have a strong opinion either way.
Now i prefer to support #2. Do you think of it? Should the usage
"-netdev socket,listen" also been supported or forbidden? As you said,
-netdev only has one peer, so their usage will be a bit different.

>
> Stefan



-- 
Regards,

Zhi Yong Wu