Subject: PATCH to update proxy arp feature on shaper device

Author: Roberto Arcomano, berto@fatamorgana.com,
        http://www.fatamorgana.com/bertolinux

Date: 9/9/2001

Description: Shaper device is seen by the kernel like a 
             different device (i.e. shaper0) than the 
	     physical one (i.e. eth0)  to which is attached:
	     so kernel always issues an "ARP REPLY" 
	     (if proxy arp is active on shaper physical 
	     interface): this prevent us from use proxy arp on 
	     a shaper device cause, during turning on client
	     machine, we would receive an "IP conflit" message.
	     
Solution: Patch consists in 4 files:
	  a-) "include/linux/netdevice.h", where we add a new
	      net feature, NETIF_F_SHAPER which will help
	      us to understand if a device is a shaper one.
	      
	  b-) "drivers/net/shaper.c", in "shaper_probe" function
	      we set NETIF_F_SHAPER flag for a new shaper
	      device.
	  
	  c-) "include/linux/if_shaper.h" where we add the macro
	      IS_SHAPERDEVICE, used to know if the device is a 
	      shaper one (it checks NETIF_F_SHAPER flag in 
	      features field, under "netdevice" struct).
	
	  d-) "net/ipv4/arp.c" where finally we modify proxy arp;
	      We use shflag to determine if we are managing a
	      shaper device (with IS_SHAPERDEVICE macro): in 
	      this case we check 
	      "rt->u.dst.dev->priv->dev" (physical device) 
	      instead of 
	      "rt->u.dst.dev" (shaper device)
	      while if the device is a non shaper one, we check 
	      rt->u.dst.dev (anded with !shflag)
	      
TODO:	I used "features" field in netdevice struct: maybe it could
        be choosen another place where to put the shaper flag.	      
	      
Tests: I tested new feature using 3 PCs like that:

           CLIENT1  ------------- LINUX ------------- CLIENT2 
     	                   shaper0      ppp0
	                    [eth0]
	   
       LINUX host has proxy arp and shaper enabled, with CLIENT1
       reachable via shaper0.
       With classic proxy arp, when I turn on CLIENT machine I 
       receive an "IP conflit" from OS, while using patched version 
       there are no problems.
       Proxy arp still does its work cause, if I give CLIENT2 IP
       address to CLIENT1 machine, I receive (from CLIENT1 OS) a
       IP busy message.

       Also tests on commercial server have been done with good
       results.

       Kernel version tested is 2.4.9
       

Final notes: It should be very simple to port patch to older
             kernel version (2.0.xx, 2.1.xx, 2.2.xx, 2.3.xx)