Re: [Qemu-devel] Looking for an easy way to exchange data bidirectional between host and guest (including some suggestion)

[Henrik Nordstrom]

On Wed, 8 Jun 2005, Jim C. Brown wrote:

> Next to impossible to do portably. I am not sure how user-net port redirection
> even enters the picture - once the FTP daemon is set up, the guest sees
> the FTP server on the host (admittedly on a nonstandard port, but is that
> such a big deal?).

With the user-net port redirection the wrapper can automate the task, 
dynamically assigning a port to the FTP server and map this on port 21 of 
the router.

> > FTP unfortunately doesn't fit in the user-net pipe framework due to it's
> > (ftp) broken design (data channel mess).
>
> Can you explain what you mean here?

The user-net pipe support when seeing a new TCP connection to the piped 
port (as used for the SMB server) forks a child process and connects the 
TCP connection via a pipe to this child process sort of as if it was 
started by inetd.

Problem is that FTP uses more than one TCP connection (the main control 
channel, plus one data channel per transfer) and this isn't supported by 
the slirp pipe support. For this kind of protocols you have to use port 
mapping or forwarding.

The real FTP server only works because it is running on a real TCP/IP, 
allowing it to open additional ports which is bidirectionally reachable 
for the client (direction depending on which PORT/PASV mode is used)

Regards
Henrik