Re: [libvirt] [RFC PATCHv2] network: try to eliminate default network conflict during package install

Sometimes libvirt is installed on a host that is already using the network 192.168.122.0/24. If the libvirt-daemon-config-network package is installed, this creates a conflict, since that package has been hard-coded to create a virtual network that also uses 192.168.122.0/24. In the past libvirt has attempted to warn of / remediate this situation by checking for conflicting routes when the network is started, but it turns out that isn't always useful (for example in the case that the *other* interface/network creating the conflict hasn't yet been started at the time libvirtd start its own networks). This patch attempts to catch the problem earlier - at install time. During the %post install script for libvirt-daemon-config-network, we use a case statement to look through the output of "ip route show" for a route that exactly matches 192.168.122.0/24, and if found we search for a similar route that *doesn't* match (e.g. 192.168.123.0/24). When we find an available route, we just replace all occurrences of "122" in the default.xml that is being created with the newly found 192.168 subnet. This could obviously be made more complicated - examine the template defaul.xml

to automatically determine the existing network address and mask rather than hard coding it in the specfile, etc, but this scripting is simpler and gets the job done as long as we continue to use 192.168.122.0/24 in the template. (If anyone with mad bash skillz wants to suggest something to do that, by all means please do). This is intended to at least "further reduce" occurrence of the problems detailed in: https://bugzilla.redhat.com/show_bug.cgi?id=811967 --- Difference from V1: fixed some typos in the commit message as pointed out by Eric.

Also switched from using comparison loops for route matching, to using a case statement as a low cost replacement for grep (again, as suggested by Eric). Unless there is an objection, I will push this patch later this afternoon so that we can try it out. In the off chance that it causes any disasters, we have plenty of time to revert before the next release :-) libvirt.spec.in | 31 ++++++++++++++++++++++++++++++- 1 file changed, 30 insertions(+), 1 deletion(-) diff --git a/libvirt.spec.in b/libvirt.spec.in index a6a58cf..90da0c2 100644 --- a/libvirt.spec.in +++ b/libvirt.spec.in @@ -1728,8 +1728,37 @@ fi %if %{with_network} %post daemon-config-network if test $1 -eq 1 && test ! -f %{_sysconfdir}/libvirt/qemu/networks/default.xml ; then + # see if the network used by default network creates a conflict, + # and try to resolve it + # NB: 192.168.122.0/24 is used in the default.xml template file; + # do not modify any of those values here without also modifying + # them in the template.