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

[Stefan Hajnoczi]

On Sat, Feb 18, 2012 at 9:19 AM,  <address@hidden> wrote:
> From: Zhi Yong Wu <address@hidden>
>
> 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 <address@hidden>
> ---
>  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.

Stefan