Re: [Qemu-devel] [PATCH] Always use 10.0.2.2 as host addr for -net user (slirp)

[Fabrice Bellard <fabrice@bellard.org>]

I am not sure this patch is sufficient: sometimes our_addr is used to 
open socket on the host side and 10.0.2.2 has a meanning only on the VM 
side.

Fabrice.

Ed Swierk wrote:
> A couple of serious problems remain in the slirp redirection code
> after the patch Paul applied on 23 April.
> 
> * If the IP address returned by gethostbyname(gethostname()) is the
> address of one of the host's Ethernet interfaces, bringing down that
> interface or changing its IP address disrupts redir connections
> between the host and VM.
> 
> * If the IP address returned by gethostbyname(gethostname()) is
> outside the 10.0.2.0/24 subnet, and the user has not manually added
> this address to the routing table within the VM (in addition to the
> 10.0.2.0/24 route added by DHCP), TCP connections from the host to the
> VM are never answered, because the response packets are dropped on the
> floor.
> 
> The attached patch solves both of these problems simply by always
> using 10.0.2.2 as our_addr. There seems to be no value in exposing the
> host's "real" address to the VM; thanks to NAT, 10.0.2.2 always works.
> 
> --Ed
> 
> 
> ------------------------------------------------------------------------
> 
> diff -BurN qemu-snapshot-2006-04-27_23.orig/slirp/misc.c qemu-snapshot-2006-04-27_23/slirp/misc.c
> --- qemu-snapshot-2006-04-27_23.orig/slirp/misc.c	2006-04-23 19:41:17.000000000 +0000
> +++ qemu-snapshot-2006-04-27_23/slirp/misc.c	2006-04-27 22:19:40.000000000 +0000
> @@ -87,17 +87,7 @@
>  void
>  getouraddr()
>  {
> -	char buff[256];
> -	struct hostent *he = NULL;
> -	
> -	if (gethostname(buff,256) == 0)
> -            he = gethostbyname(buff);
> -        if (he)
> -            our_addr = *(struct in_addr *)he->h_addr;
> -        /* If the host doesn't have a useful IP address then use the
> -           guest side address.  */
> -        if (our_addr.s_addr == 0 || our_addr.s_addr == loopback_addr.s_addr)
> -            our_addr.s_addr = special_addr.s_addr | htonl(CTL_ALIAS);
> +	our_addr.s_addr = special_addr.s_addr | htonl(CTL_ALIAS);
>  }
>  
>  #if SIZEOF_CHAR_P == 8
> 
> 
> ------------------------------------------------------------------------
> 
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