Re: [Qemu-devel] [RFC PATCH qemu] slirp: Update forwarding IP address if guest receiver non-default IP

[Alexey Kardashevskiy]

On 08/02/18 15:29, Alexey Kardashevskiy wrote:
> On 01/02/18 20:36, Alexey Kardashevskiy wrote:
>> If we run QEMU with -netdev user,id=USER0,hostfwd=tcp::2222-:22, it starts
>> a DHCP server and starts allocating client IPs from 10.0.2.15 so
>> this is what the guest normally receives. Since QEMU automatically adds
>> the DHCP starting address into the forwarding table, everything works.
>> This is the table before guest started:
>>
>> (qemu) info usernet
>> VLAN -1 (USER0):
>>   Protocol[State]    FD  Source Address  Port   Dest. Address  Port RecvQ 
>> SendQ
>>   TCP[HOST_FORWARD]  11               *  2222       10.0.2.15    22     0    
>>  0
>>
>> However if the guest happens to have DHCP lease (for example, 10.0.2.16),
>> the forwarding stops working. The guest can still reach the outer world
>> (which is expected).
>>
>> This updates the forwarding table when QEMU confirms the requested IP
>> to the guest.
>>
>> Signed-off-by: Alexey Kardashevskiy <address@hidden>
>> ---
>>
>> Does this look any useful?

Ping, anyone?

> 
> 
> It does not seem like it does very much but .... :)
> 
> 
>>
>> Sure I can remove /var/lib/dhcp/dhclient.enp0s1.leases in the guest or
>> start QEMU with the DHCP start address equal to what the guest wants to
>> reserve but it is quite confusing why such a simple config just does not
>> work.
>>
>> Found this with the brand new Ubuntu 17.10 which runs dhcp and something
>> called "netplan" and the guest ends up with 2 IPs from 10.0.2.x network.
>> After disabling netplan, the lease remains and it is not 10.0.2.15 but
>> rather .16 or .17.
>>
>> Comments? Thanks.
>>
>> ---
>>  slirp/libslirp.h |  2 ++
>>  slirp/bootp.c    |  2 ++
>>  slirp/slirp.c    | 27 +++++++++++++++++++++++++++
>>  3 files changed, 31 insertions(+)
>>
>> diff --git a/slirp/libslirp.h b/slirp/libslirp.h
>> index 540b3e5..6779081 100644
>> --- a/slirp/libslirp.h
>> +++ b/slirp/libslirp.h
>> @@ -33,6 +33,8 @@ int slirp_add_hostfwd(Slirp *slirp, int is_udp,
>>                        struct in_addr guest_addr, int guest_port);
>>  int slirp_remove_hostfwd(Slirp *slirp, int is_udp,
>>                           struct in_addr host_addr, int host_port);
>> +void slirp_update_hostfwd(Slirp *slirp, struct in_addr old_guest_addr,
>> +                          struct in_addr new_guest_addr);
>>  int slirp_add_exec(Slirp *slirp, int do_pty, const void *args,
>>                     struct in_addr *guest_addr, int guest_port);
>>  
>> diff --git a/slirp/bootp.c b/slirp/bootp.c
>> index 5dd1a41..5876004 100644
>> --- a/slirp/bootp.c
>> +++ b/slirp/bootp.c
>> @@ -225,6 +225,8 @@ static void bootp_reply(Slirp *slirp, const struct 
>> bootp_t *bp)
>>      /* Update ARP table for this IP address */
>>      arp_table_add(slirp, daddr.sin_addr.s_addr, client_ethaddr);
>>  
>> +    slirp_update_hostfwd(slirp, slirp->vdhcp_startaddr, daddr.sin_addr);
>> +
>>      saddr.sin_addr = slirp->vhost_addr;
>>      saddr.sin_port = htons(BOOTP_SERVER);
>>  
>> diff --git a/slirp/slirp.c b/slirp/slirp.c
>> index 1cb6b07..a9d8a16 100644
>> --- a/slirp/slirp.c
>> +++ b/slirp/slirp.c
>> @@ -1061,6 +1061,33 @@ int slirp_add_hostfwd(Slirp *slirp, int is_udp, 
>> struct in_addr host_addr,
>>      return 0;
>>  }
>>  
>> +static void slirp_do_update_hostfwd(Slirp *slirp, struct socket *head,
>> +                                    struct in_addr old_guest_addr,
>> +                                    struct in_addr new_guest_addr)
>> +{
>> +    struct socket *so;
>> +    char oldaddr[17], newaddr[17];
>> +
>> +    for (so = head->so_next; so != head; so = so->so_next) {
>> +        if ((so->so_state & SS_HOSTFWD) &&
>> +            so->lhost.sin.sin_addr.s_addr == old_guest_addr.s_addr) {
>> +            strncpy(oldaddr, inet_ntoa(old_guest_addr), sizeof(oldaddr) - 
>> 1);
>> +            strncpy(newaddr, inet_ntoa(new_guest_addr), sizeof(newaddr) - 
>> 1);
>> +            DEBUG_ARGS((dfd, "Updating forwarding from %s:%d to %s:%d\n",
>> +                       oldaddr, ntohs(so->lhost.sin.sin_port),
>> +                       newaddr, ntohs(so->lhost.sin.sin_port)));
>> +            so->lhost.sin.sin_addr = new_guest_addr;
>> +        }
>> +    }
>> +}
>> +
>> +void slirp_update_hostfwd(Slirp *slirp, struct in_addr old_guest_addr,
>> +                          struct in_addr new_guest_addr)
>> +{
>> +    slirp_do_update_hostfwd(slirp, &slirp->udb, old_guest_addr, 
>> new_guest_addr);
>> +    slirp_do_update_hostfwd(slirp, &slirp->tcb, old_guest_addr, 
>> new_guest_addr);
>> +}
>> +
>>  int slirp_add_exec(Slirp *slirp, int do_pty, const void *args,
>>                     struct in_addr *guest_addr, int guest_port)
>>  {
>>
> 
> 


-- 
Alexey