Re: [libvirt] [PATCH 1/2] networkUpdateState: Create virMacMap module more frequently
On 03/28/2017 02:22 AM, Laine Stump wrote:
On 03/22/2017 10:43 AM, Michal Privoznik wrote:
>
> Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com>
> ---
> src/network/bridge_driver.c | 21 +++++++++------------
> 1 file changed, 9 insertions(+), 12 deletions(-)
>
> diff --git a/src/network/bridge_driver.c b/src/network/bridge_driver.c
> index a753cd78b..0ea8e2348 100644
> --- a/src/network/bridge_driver.c
> +++ b/src/network/bridge_driver.c
> @@ -470,6 +470,7 @@ networkUpdateState(virNetworkObjPtr obj,
> {
> virNetworkDriverStatePtr driver = opaque;
> dnsmasqCapsPtr dnsmasq_caps = networkGetDnsmasqCaps(driver);
> + char *macMapFile = NULL;
> int ret = -1;
>
> virObjectLock(obj);
> @@ -486,6 +487,13 @@ networkUpdateState(virNetworkObjPtr obj,
> /* If bridge doesn't exist, then mark it inactive */
> if (!(obj->def->bridge &&
virNetDevExists(obj->def->bridge) == 1))
> obj->active = 0;
> +
> + if (!(macMapFile = networkMacMgrFileName(driver, obj->def->bridge)))
> + goto cleanup;
> +
> + if (!(obj->macmap = virMacMapNew(macMapFile)))
> + goto cleanup;
> +
> break;
... but from what I can understand, the only differences are:
1) the macMapFile used to be regenerated right after reading the
radvdpidfile (which in most cases doesn't exist because I think most of
the time that same duty is handled by dnsmasq instead), and now it is
regenerated *just before* reading radvdpidfile.
I don't think this is any problem. It's just an ordering issue. Those
two features are orthogonal.
2) it used to be regenerated for any network with a def->bridge (so it
would also happen for "unmanaged" bridge networks, where libvirt just
points to an already-existing bridge), and it is now regenerated only
for networks where libvirt creates and destroys the bridge (and might
have a dnsmasq instance running.
Ah. Is that right? I agree that the code is a bit unclear, but the
following should be true:
1) when a network is being freshly started up, the virMacMap module is
created and stored in the network object if and only if dnsmasq is
spawned (because only then it's us who assigns IP addresses).
2) when an interface is allocated/freed from a network that has the
module, the $br.macs file is updated accordingly. The file is created on
the first interface allocation, and unlinked on network undef.
3) when the daemon restarts, networkUpdateState() is called for every
running network. And if the $br.macs file exists for given network, the
module is created (we are reconstructing the network objects after all)
and the file is parsed to restore the previous state. Note, that the
dnsmasq is not spawned again - it kept running while libvirtd was
restarting.
Now, there are two problems that I see:
a) if there is no interface added in the 2nd step and the libvirt daemon
is restarted, in the 3rd step the file does not exist and thus the code
thinks no virMacMap module was used for the network so it does not
create one. This is obviously a bug.
b) if you want to have the module for your network, you need to shut it
down (and thus cut off your domains from the connectivity) and start
over again. It's very annoying. When implementing this, my reasoning was
that it's better to give no results than partial results, it's better to
not have no $br.macs file than have a file containing just newly
allocated interfaces. Well, I was wrong. I think people don't want to
destroy their network unless really necessary. More so if the network
continues running even when the daemon is killed.
Therefore, what I am suggesting here is to rework step 3) so that the
module is created more frequently. It would solve both problems I'm
describing.
Michal