[Bug 231060] Re: packages dnsmasq and libvirt-bin conflict with each other

[Emmet Hikory]

@Simon, Thanks for the guidance.  Of the options:

1) This seems least invasive in the short-term

2) There's a few potential issues here.

a) Install order, because defaults need to be adjusted, and services may
need to restart.  Some of this can be handled by triggers, but it
requires cooperation (perhaps having some way that dnsmasq-base requires
users to drop some file that dns-base can use to restart all users when
new ones are installed, or similar awkwardnesses).

b) Removal independence: similar to install issues, the packages need to
be able to coordinate uninstallation.

c) This interferes with use cases where a user wants to use dnsmasq to
provide nameservice inside libvirt and to do dhcp/tftp on a local
network simultaneously or similar cases: using a single demon makes
having multiple configurations difficult.

3) The big item that struck me looking at this was that dnsmasq exits if
unable to bind to every interface in wildcard mode: having this instead
check error conditoins from bind failures and either internally drop the
interface/address from the list of interfaces on which to listen or poll
on the interface being available depending on the nature of the bind
failue would significantly ease the difficulties of running multiple
instances, especially one wildcard instance and one or more bound
instances.  It also eases the race condition identified in comment #11.

Another option would be to extend the D-Bus interface to permit D-Bus to
be used to remove addresses or interfaces from the wildcard set to
reserve them for use by a non-wildcard dnsmasq, preferably in
combination with a D-Bus query on startup to automatically enter non-
wildcard mode if there is already a wildcard server active and
specifically exclude any addresses or interfaces already claimed by
another instance.

This seems a lot of longer-term work though.

4) sounds kinda cool, but needing a lot more investigation and code than
any of the other options.

    So, my plan is as follows:

1) Add a dpkg trigger subscription to dnsmasq that calls the initscript
with force-reload if new configuration snippets are installed

2) Add a configuration snipped to libvirt that switches to bind-
interface by default, and excludes virbr0


    This compeltely ignores the race condition between startng virbr0 adn starting dnsmasq, and it doesn't help for any sort of complex configuration (of either libvirt or dnsmasq), but it seems the least impact path to enable simultaneous operation without crippling either tool or needing extensive coding.

** Changed in: libvirt (Ubuntu)
     Assignee: (unassigned) => Emmet Hikory (persia)

** Changed in: dnsmasq (Ubuntu)
     Assignee: (unassigned) => Emmet Hikory (persia)

** Changed in: dnsmasq (Ubuntu)
       Status: Triaged => In Progress

** Changed in: libvirt (Ubuntu)
       Status: Triaged => In Progress

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packages dnsmasq and libvirt-bin conflict with each other
https://bugs.launchpad.net/bugs/231060
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