[libvirt] RFC: Introduce API to return configuration/state paths of the network driver

[Daniel P. Berrange]

On Thu, Jul 25, 2013 at 07:01:05PM +0800, Osier Yang wrote:
> On 25/07/13 18:53, Daniel P. Berrange wrote:
> >On Thu, Jul 25, 2013 at 06:43:00PM +0800, Osier Yang wrote:
> >>On 25/07/13 17:35, Daniel P. Berrange wrote:
> >>>On Thu, Jul 25, 2013 at 02:02:36PM +0530, Nehal J. Wani wrote:
> >>>>Currently, there is no API which returns configuration/state paths of the
> >>>>network driver.
> >>>>Although it is a private implementation of the network driver, I don't see
> >>>>any harm in
> >>>>making the locations public because although the locations might change,
> >>>>there will always
> >>>>be a location for these files. There is a need for this API to implement
> >>>>method 2 of the
> >>>>"API to query ip addresses of a given domain", refer:
> >>>>http://www.mail-archive.com/libvir-list@redhat.com/msg79793.html . It is
> >>>>required to parse
> >>>>the leases file generated by dnsmasq. So, this API will be used by the qemu
> >>>>driver, but it
> >>>>can also be made public, so that, if a user wants to know get some
> >>>>information from a
> >>>>configuration file, he can get the location from libvirt and analyze it on
> >>>>his own. Right now,
> >>>>there is an alternate way to get the info: by using
> >>>>networkDnsmasqLeaseFileNameDefault,
> >>>>defined in /src/network/bridge_driver.c Since this function is static, it
> >>>>is part of the private
> >>>>implementation and not visible outside. To make it public, the following
> >>>>hack is possible:
> >>>NACK,
> >>>
> >>>As I explained on IRC, the hypervisor drivers have no business accessing
> >>>the dnsmasq lease files from the bridge driver. This is considered to be
> >>>a private implementation detail.
> >>>
> >>>At a conceptual level, what you're after here is a list of all the IP,
> >>>mac address mappings of the virtual network. This information is useful
> >>>even outside the context of the hypervisor driver method you're working
> >>>on. So we should create formal APIs for exposing this, something like:
> >>>
> >>>    virNetworkGetDHCPLeases(virNetworkPtr network,
> >>>                            virNetworkDHCPLeasePtr *leases,
> >>>                            unsigned int nleases);
> >>i'm wondering if it should be more than just the lease file path, e.g.
> >>also the $net.conf, $net-radvd.conf, etc, though they are useless
> >>now, but may be useful in future, i.e. to have a more general api
> >>than this one.  and in that case, it should return an array of typed
> >>parameter instead.
> >We've already discussed this in the context of the virDomain API for
> >getting IP addresses & decided that virTypedParameter was not appropriate
> >there & we'd use a struct. The same arguments apply here IMHO.
> >
> the api to get the ip addresses is more complicate than this, and we
> finally chose the struct is because of the multiple level information
> is hard to constuct with typed parameter, but for this api, it's different,
> as it just needs to return the file paths.

No, file paths will absolutely never be exposed outside of the bridge
driver. The API I suggest above are about exposing the IP address + MAC
address of current leases. ie the actual data the user needs, *not* the
file path containing the data which is a private impl detail.


Daniel
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