sorry for the late response. I missed the email and found it today.
I understand your concerns and agree with that.
The reason for all this was to get the information on every gateway change.
I need the node ip of the gateway node at the time when the gateway is selected
or deselected. At moment I have modified the batmand to call a script in both
cases to setup /etc/resolv.conf which is important to always have a valid dns
server. the main publich dns servers often are not accessible from different
I can understand your need and agree that your idea with the return value
makes the hole thing very flexible. But i am not sure if it makes sense to
call the policy routing script even more than once because system calls like
that can be quite expensive. And another problem i see comes with the return
values itself. Currently the policy-routing feature is not aware of the
return value of the called script. One reason for this is that the
policy-routing-script is essentially operating in a loop waiting to be feeded
with new commands via a pipe. Therefore the script itself does not terminate
after being feeded and does not return anything. Another problem is that the
C-function execv() (which is currently used) does not really support return
values except in case of an error. As you suggested, the function system()
could be used instead, but the manpage suggests to not use this function with
Regarding the cost (in terms of processing-time) i did some small experiences
on a netgear wgt634u and a linksys WRT with openwrt which showed that
configuring a route via a bash script (using the ip command) or by using
system() to execute the ip command is up to 50 times more expensive than
doing it directly (using netlink sockets).
In my test adding and removing 100 route entries using netlink sockets took
about 200ms while using the ip command it takes about 6-10 seconds.
Even just calling a script with system() which does nothing else than return 0
takes about 50ms per call.
Therefore I am not sure if using the policy routing script in a large network
and with slow devices is a good idea at all. And if the threat must be
blocked during the execution of the script to wait for the return value it
would be even worse.
What about introducing the possibility to define that the routing information
which is forwarded to the policy routing script is only informative and is
still applied by the daemon itself?
On Donnerstag 18 September 2008, Stephan Enderlein (Freifunk Dresden) wrote:
> Hi Axel,
> thanks for your comments. At moment I have no much time to spend for
> batman development. We got a son two month ago and I'm currently enjoy
> him much.
> But I have a good idea concerning the routing script.
> The problem is that I like batman-exp to setup all routes as defined by
> parameters, but also want batman-exp to call the script.
> Batman may call the script twice. One call before and one after setting
> the routes. All should depend on the return code of the first call of the
> If the script returns "0", then batman should not set routes and also
> there is no need to call the script a second time.
> If the first call of the script returns "1", then batman should set the
> routes as defined by parameters and after it should call the script a
> second time (like pre/post scripts).
> This allows me to get the routing information without need to setup all
> routings per hand.
> Bye setting a environment variable you can distingnuish if the script is
> called as pre or post script.
> This leads to the next solution/patch:
> You should also add information about the gateway
> selection/changes/deselection to this script. Together with the
> modification above you can let batmand set the routes and update your
> resolv.conf to find the correct router that knows how to resolve dns
> At moment you have to get the dns ip from dhcp or you should enter this
> as a fix value. But a fix value for this is bad if you build a firmware
> with a simple user interface. Many people don't know how dns works and
> what ip they should enter. If you have different ISP some dns server are
> At moment I have added my own patch where I call
> each time the gateway tunnel is created or deleted. this is working
> > Hi
> > On Montag 15 September 2008, freifunk(a)ddmesh.de wrote:
> >> Hi,
> >> > Just applied your latest patches as well. Thanks for looking over the
> >> > code.
> >> > Virgin eyes stumble easier over nasty stuff. :-)
> >> When you find some problems in batman, can you also apply those patches
> >> to
> >> the batman-experimental branch? At moment it is running without problems
> >> for freifunk dresden. But if the network is growing perhaps some issues
> >> may
> >> cause problems.
> > Over the time a reasonable part of the code structure of bmx and batman
> > has
> > forked pretty much. Therefore I am not sure if it would be easy to simply
> > apply existing batman patches to the bmx branch. But be sure, whenever I
> > am
> > getting aware of critical bugs identified in the batman code which also
> > apply
> > to the bmx code, I'll fix them too. But for many current and older series
> > of
> > patches its simply not necessary. For example looking at the main recent
> > bug-fixes
> > Regarding the debug thread:
> > I have removed the debug thread completely about 2 weeks ago (due to
> > ongoing
> > problems with this thing) and integrated its functionality into the main
> > thread. I could not see any benefit of having this threaded except
> > constant
> > syncronization problems. Unfortunately I could not commit it yet because
> > of
> > unfinished testing. But I'll do it this week.
> > The gw-kernel module: There are no gw-tunnel module problems with bmx
> > simply
> > because there is no support for this feature. Most existing bmx-mesh
> > networks
> > I am aware of are using the one-way-tunnel mode. It does not implement
> > the black hole detection but still allows you to dynamically change the
> > preferred
> > gw. Compared to the two-way-tunnel it has less overhead, avoids tunneling
> > from the gw to the client node (no need to optimize something which does
> > not
> > exist) and allows internet access with only one level of network address
> > translation.
> > Packet aggregation:
> > Have been implemented and activated by default in bmx about a year ago
> > and seem to work quite reliable since then.
> > Problem with timing issues have been solved individually
> > And very important. BMX has continued to rely on the concept of a rolling
> > metric based on the number of received OGMs via the best path. Many
> > patches
> > in the batman-0.3 brach were due to changing this concept to a dedicated
> > metric field carried with each OGM.
> > By the way, I think a number of bugs in bmx and batman have been
> > identified
> > due to your hints. Thanks for that. If you want to intensify your work on
> > the
> > code and want commit patches directly just let us know.
> >> Bye
> >> Stephan
> >> ---------------------------------------
> >> Dipl.Informatiker(FH) Stephan Enderlein
> >> Freifunk Dresden
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> Dipl.Informatiker(FH) Stephan Enderlein
> Freifunk Dresden
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