[Qemu-devel] [PATCH 0/2] slirp udp fixes

[Qemu-devel] [PATCH 0/2] slirp udp fixes

[Jason Wessel]

2 patches follow to fix some udp problems with slirp

Jason Wessel (2):
      Fix slirp udp source address contamination
      Fix slirp mac address init

 slirp/libslirp.h |    2 ++
 slirp/slirp.c    |    5 +++++
 slirp/udp.c      |    3 ++-
 vl.c             |    3 +++
 4 files changed, 12 insertions(+), 1 deletions(-)

[Qemu-devel] [PATCH 1/2] Fix slirp udp source address contamination

[Jason Wessel]

When using slirp the "special address" translation should only be
used when the source address is the loopback, else the udp packets
show up with the wrong source address and cannot be routed back to the
original source by applications running inside the QEMU instance.

The problem can be observed by using kgdboe from inside QEMU where you
add a port redirection with slirp networking such as "-redir
udp:4445::6443".  Using a second host or connecting gdb to the IP
address address of the host that the QEMU instance is running on
instead of using the loopback address will fail because the source
address will get translated when it goes through the redirection.

With the patch, you can connect to kgdboe via the loopback on port
4445 or from another host.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
---
 slirp/udp.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/slirp/udp.c b/slirp/udp.c
index c48923b..0dd7da6 100644
--- a/slirp/udp.c
+++ b/slirp/udp.c
@@ -318,7 +318,8 @@ int udp_output(struct socket *so, struct mbuf *m,
     struct sockaddr_in saddr, daddr;
 
     saddr = *addr;
-    if ((so->so_faddr.s_addr & htonl(0xffffff00)) == special_addr.s_addr) {
+    if ((so->so_faddr.s_addr & htonl(0xffffff00)) == special_addr.s_addr &&
+        addr->sin_addr.s_addr == htonl(0x7f000001)) {
         saddr.sin_addr.s_addr = so->so_faddr.s_addr;
         if ((so->so_faddr.s_addr & htonl(0x000000ff)) == htonl(0xff))
             saddr.sin_addr.s_addr = alias_addr.s_addr;
-- 
1.5.4

[Qemu-devel] [PATCH 2/2] Fix slirp mac address init

[Jason Wessel]

It is not possible to communicate to a qemu instance via a slirp
redirected udp port until the OS running in qemu has executed a dhcp
request.  This is because the internal qemu dhcp server populates the
slirp mac address.  Until the dhcp request is processed the translated
mac address is zeroed out and the packets bound for the target OS will
not correctly get the mac address of the qemu ethernet adapter.

The solution is to initialize the slirp mac address when the qemu
network adapter client is initialized.  This allows the use
bi-directional udp redirection with a static IP address configured on
the qemu ethernet adapter.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
---
 slirp/libslirp.h |    2 ++
 slirp/slirp.c    |    5 +++++
 vl.c             |    3 +++
 3 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/slirp/libslirp.h b/slirp/libslirp.h
index 7e4cfa9..e862de6 100644
--- a/slirp/libslirp.h
+++ b/slirp/libslirp.h
@@ -7,6 +7,8 @@ extern "C" {
 
 void slirp_init(void);
 
+void slirp_initial_mac(uint8_t *macaddr);
+
 void slirp_select_fill(int *pnfds,
                        fd_set *readfds, fd_set *writefds, fd_set *xfds);
 
diff --git a/slirp/slirp.c b/slirp/slirp.c
index 303f482..8adc027 100644
--- a/slirp/slirp.c
+++ b/slirp/slirp.c
@@ -136,6 +136,11 @@ static void slirp_cleanup(void)
 }
 #endif
 
+void slirp_initial_mac(uint8_t *macaddr)
+{
+    memcpy(client_ethaddr, macaddr, sizeof(client_ethaddr));
+}
+
 void slirp_init(void)
 {
     //    debug_init("/tmp/slirp.log", DEBUG_DEFAULT);
diff --git a/vl.c b/vl.c
index 6aa27c2..2fd1868 100644
--- a/vl.c
+++ b/vl.c
@@ -4792,6 +4792,9 @@ static int net_client_init(const char *str)
                 return -1;
             }
         }
+#ifdef CONFIG_SLIRP
+        slirp_initial_mac(macaddr);
+#endif
         if (get_param_value(buf, sizeof(buf), "model", p)) {
             nd->model = strdup(buf);
         }
-- 
1.5.4

Re: [Qemu-devel] [PATCH 2/2] Fix slirp mac address init

[Aurelien Jarno]

On Wed, Apr 09, 2008 at 11:22:23PM -0500, Jason Wessel wrote:
> It is not possible to communicate to a qemu instance via a slirp
> redirected udp port until the OS running in qemu has executed a dhcp
> request.  This is because the internal qemu dhcp server populates the

Could you please more details? I am unable to reproduce the problem. A
simple netcat listening on a UDP port in the guest, and another netcat
in the host to send data works here.

> slirp mac address.  Until the dhcp request is processed the translated
> mac address is zeroed out and the packets bound for the target OS will
> not correctly get the mac address of the qemu ethernet adapter.
> 
> The solution is to initialize the slirp mac address when the qemu
> network adapter client is initialized.  This allows the use
> bi-directional udp redirection with a static IP address configured on
> the qemu ethernet adapter.
> 
> Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
> ---
>  slirp/libslirp.h |    2 ++
>  slirp/slirp.c    |    5 +++++
>  vl.c             |    3 +++
>  3 files changed, 10 insertions(+), 0 deletions(-)
> 
> diff --git a/slirp/libslirp.h b/slirp/libslirp.h
> index 7e4cfa9..e862de6 100644
> --- a/slirp/libslirp.h
> +++ b/slirp/libslirp.h
> @@ -7,6 +7,8 @@ extern "C" {
>  
>  void slirp_init(void);
>  
> +void slirp_initial_mac(uint8_t *macaddr);
> +
>  void slirp_select_fill(int *pnfds,
>                         fd_set *readfds, fd_set *writefds, fd_set *xfds);
>  
> diff --git a/slirp/slirp.c b/slirp/slirp.c
> index 303f482..8adc027 100644
> --- a/slirp/slirp.c
> +++ b/slirp/slirp.c
> @@ -136,6 +136,11 @@ static void slirp_cleanup(void)
>  }
>  #endif
>  
> +void slirp_initial_mac(uint8_t *macaddr)
> +{
> +    memcpy(client_ethaddr, macaddr, sizeof(client_ethaddr));
> +}
> +
>  void slirp_init(void)
>  {
>      //    debug_init("/tmp/slirp.log", DEBUG_DEFAULT);
> diff --git a/vl.c b/vl.c
> index 6aa27c2..2fd1868 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -4792,6 +4792,9 @@ static int net_client_init(const char *str)
>                  return -1;
>              }
>          }
> +#ifdef CONFIG_SLIRP
> +        slirp_initial_mac(macaddr);
> +#endif
>          if (get_param_value(buf, sizeof(buf), "model", p)) {
>              nd->model = strdup(buf);
>          }
> -- 
> 1.5.4
> 
> 
> 
> 

-- 
  .''`.  Aurelien Jarno	            | GPG: 1024D/F1BCDB73
 : :' :  Debian developer           | Electrical Engineer
 `. `'   aurel32@debian.org         | aurelien@aurel32.net
   `-    people.debian.org/~aurel32 | www.aurel32.net

Re: [Qemu-devel] [PATCH 2/2] Fix slirp mac address init

[Jason Wessel]

I figured most people do not have kgdboe as a built-in, and the qemu
patch is definitely against an edge case.  The problem is better
described by the case where no packets have been transmitted by the qemu
target and you desire to have the first communication occur externally.

The edge case can happen if you do something like use kgdboe before the
kernel is booted up.  The OS will configure the ethernet interface to
listen and wait for the debugger to attach, and in this case the MAC
address is not set in the slirp because no packets have ever been
transmitted yet.

You would have do something like:

qemu-redir udp:4445::6443 -append "console=ttyS0
kgdboe=@10.0.2.15/,@10.0.2.2/ kgdbwait"

Then you would connect gdb with "target remote udp:localhost:4445".  I
will gladly provide you with a kernel that has kgdboe built in and some
exact boot arguments if you would like to see the problem first hand.

Jason.

Aurelien Jarno wrote:
> On Wed, Apr 09, 2008 at 11:22:23PM -0500, Jason Wessel wrote:
>   
>> It is not possible to communicate to a qemu instance via a slirp
>> redirected udp port until the OS running in qemu has executed a dhcp
>> request.  This is because the internal qemu dhcp server populates the
>>     
>
> Could you please more details? I am unable to reproduce the problem. A
> simple netcat listening on a UDP port in the guest, and another netcat
> in the host to send data works here.
>
>   
>> slirp mac address.  Until the dhcp request is processed the translated
>> mac address is zeroed out and the packets bound for the target OS will
>> not correctly get the mac address of the qemu ethernet adapter.
>>
>> The solution is to initialize the slirp mac address when the qemu
>> network adapter client is initialized.  This allows the use
>> bi-directional udp redirection with a static IP address configured on
>> the qemu ethernet adapter.
>>