[Qemu-devel] Re: user-net -redir working? [problem located]

[Richard Neill <rn214@hermes.cam.ac.uk>]

> Re: User-net not working:
> 
> > Disabling the Nagle algorithm (i.e., enabling TCP_NODELAY) or typing a
> > lot of garbage just to fill the buffer with enough data can help,
> > also.
> > 
> > And IIRC, netcat has a UDP mode as well. I see no reason for this to
> > happen, but is there any chance it's using UDP by default, and you're
> > only redirecting TCP?
> > 
> > Good luck!
> 
> Thanks for your message.
> 
> I think that -redir really is broken: I've also been unsuccessful in 
> trying to make it work using an FTP server on a Windows guest, and using 
> the SSH server on a knoppix guest. Has anyone here ever had success with 
> it? It also fails on hosts with 2 different versions of Mandrake.
> 
> Anyway, I've taken your suggestion, and run both ends with ethereal. 
> Here's what I did:
> 
> 
> HOST (Linux);
>    qemu -cdrom /dev/cdrom -boot d -user-net -redir tcp:2200::22
> 
> GUEST (Knoppix):
>    Boot up, then start sshd. Verify that I can indeed do ssh
>    root@localhost, and that PermitRootLogin is yes in sshd_config.
> 
>     Then, start ethereal (on the "any" interface)
> 
> 
> HOST:
>    Start ethereal (on the "any" interface")
>    ssh -p 2200 root@localhost
> 
>   At this point, ssh just stalls. It's obviously waiting for something,
>   but not known what. I get no output at all from it.


Can you try "ssh -p 2200 root@<my IP address not localhost>

I've run into this several times dealing with the -redir
function, especially since localhost resolves as 127.0.0.1.
On my Solaris host with a linux guest, the packet arriving
showed up as 127.0.0.1, which ended up with the same
behavior as you're describing.


---------------


Dear Ben,

Good guess! That's an ingenious bit of debugging, and it now works 
perfectly. I suppose that now means 3 things need to be done:

1)Figure out *why* it doesn't work. It's definitely QEMU-specific, since 
if I run 2 separate netcat processes on the host, I have no problem. I'd 
be interested to know why this occurs. In particular, is it a problem 
with the user-net stuff on the host, or a problem with the guest?

2)Fix it...   :-)

3)Document this on the website as a known bug, so Google can find it. 
Currently, anyone using an earlier version will just think that qemu is 
broken. It hasn't worked since at least 0.6.1, although I can't tell you 
about earlier versions.

I suspect that I am not up to the task of (2), so I must defer to the 
experts...

Best wishes,

Richard