On Wed, May 14, 2014 at 12:15:47AM +0200, Samuel Thibault wrote: > Edgar E. Iglesias, le Thu 08 May 2014 06:59:22 +0000, a écrit : > > On Thu, May 08, 2014 at 08:50:33AM +0200, Samuel Thibault wrote: > > > Edgar E. Iglesias, le Thu 08 May 2014 06:10:18 +0000, a écrit : > > > > The search part looks OK to me but when adding to the arp table, don't > > > > you at least want to avoid adding mappings for 0.0.0.0/32? > > > > > > I don't see the gain, actually. It would mean burning some CPU all the > > > time just to save a small potential memory loss and CPU burning in the > > > rare case when the guest behaves oddly. > > > > > > > to avoid for ex garps to pollute the cache with invalid entries? > > > > > > Only one entry will be created and updated by garps. The guest already > > > has a lot of ways to pollute the cache :) > > > > I was under the impression that entries for 0.0.0.0 are strictly > > invalid (not about performance). I might be wrong though. > > I'd tend to think that, but what should be done? I don't think we want > an assert failure :) >
Right, I didn't mean that the assert should stay. > At best I could think of using the patch below, which avoids registering > anything for 0.0.0.0, and use a broadcast to answer a guest which > would have used 0.0.0.0 as a source for whatever reason. I don't find > anything else reasonable. What would be preferred? Specs are not super clear on this but rfc1700 says that 0.0.0.0 is a source only address. http://www.rfc-editor.org/rfc/rfc1700.txt Page 3 http://tools.ietf.org/html/draft-iana-special-ipv4-04 Page 1 What I was trying to suggest was a mix between your two versions. Removing the assert in table_search and avoid adding 0.0.0.0/32 to the cache in table_add. We might need to complement with something that drops datagrams destined to 0.0.0.0 in upper layers so we dont keep trying, not sure. Does something like that make sense? Cheers, Edgar > > Samuel > > diff --git a/slirp/arp_table.c b/slirp/arp_table.c > index ecdb0ba..d160cfc 100644 > --- a/slirp/arp_table.c > +++ b/slirp/arp_table.c > @@ -37,12 +37,7 @@ void arp_table_add(Slirp *slirp, uint32_t ip_addr, uint8_t > ethaddr[ETH_ALEN]) > ethaddr[0], ethaddr[1], ethaddr[2], > ethaddr[3], ethaddr[4], ethaddr[5])); > > - /* Check 0.0.0.0/8 invalid source-only addresses */ > - if ((ip_addr & htonl(~(0xfU << 28))) == 0) { > - return; > - } > - > - if (ip_addr == 0xffffffff || ip_addr == broadcast_addr) { > + if (ip_addr == 0 || ip_addr == 0xffffffff || ip_addr == broadcast_addr) { > /* Do not register broadcast addresses */ > return; > } > @@ -73,11 +68,8 @@ bool arp_table_search(Slirp *slirp, uint32_t ip_addr, > DEBUG_CALL("arp_table_search"); > DEBUG_ARG("ip = 0x%x", ip_addr); > > - /* Check 0.0.0.0/8 invalid source-only addresses */ > - assert((ip_addr & htonl(~(0xfU << 28))) != 0); > - > /* If broadcast address */ > - if (ip_addr == 0xffffffff || ip_addr == broadcast_addr) { > + if (ip_addr == 0 || ip_addr == 0xffffffff || ip_addr == broadcast_addr) { > /* return Ethernet broadcast address */ > memset(out_ethaddr, 0xff, ETH_ALEN); > return 1;
