[Dnsmasq-discuss] dry run mode

[Graeme Peterson]

Hi all. Happy 2019!

A bit of an odd question: Is there any way to run dnsmasq in some kind
of standalone test or dry-run mode without being connected to
actual/virtual networks, where I could define subnets and IP ranges,
somehow issue requests for IPs on subnets, and then use those IPs in my
VM deployment tests that require static IPs, releasing them when done or
when their lease expires?

EXPLANATION
===

I work in a test team on a product that does a lot of virtual network
configuration for various deployed VMs. Some of the testing uses dhcp
for the VMs' interfaces, so far so good. Some tests need to exercise
static IP configuration. I need a way to manage the allocation of static
IPs on all the test VMs in our automation. Hard coding the values is
cumbersome, error prone, and we run out of IPs in most /24 subnets
pretty quickly if we make sure every test deployment has a unique static
IP.

So I got to thinking. I could write some kind of static IP allocator
that would respond to requests on a per-subnet basis, release the IPs
back into a pool of some kind when the test is done with them, maybe
have a timeout to auto-release the IPs in case the release is missed,...


Hang on. Sounds like dhcp. Which brings me to my above question, and
this email.

Thank you,
Graeme___
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[Dnsmasq-discuss] [PATCH] lease: prune lease as soon as expired

[Florent Fourcot]

We detected a performance issue on a dnsmasq running many dhcp sessions
(more than 10 000). At the end of the day, the server was only releasing
old DHCP leases but was consuming a lot of CPU.

It looks like curent dhcp pruning:
 1) it's pruning old sessions (iterate on all current leases). It's
 important to note that it's only pruning session expired since more
 than one second
 2) it's looking for next lease to expire (iterate on all current leases
 again)
 3) it launchs an alarm to catch next expiration found in step 2). This
 value can be zero for leases just expired (but not pruned).

So, for a second, dnsmasq could fall in a "prune loop" by doing:
 * Not pruning anything, since difftime() is not > 0
 * Run alarm again with zero as argument

On a server with very large number of leases and releasing often
sessions, that can waste a very big CPU time.

Signed-off-by: Florent Fourcot 
---
 src/lease.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/lease.c b/src/lease.c
index 97bee21..7299227 100644
--- a/src/lease.c
+++ b/src/lease.c
@@ -563,7 +563,7 @@ void lease_prune(struct dhcp_lease *target, time_t now)
   for (lease = leases, up =  lease; lease = tmp)
 {
   tmp = lease->next;
-  if ((lease->expires != 0 && difftime(now, lease->expires) > 0) || lease 
== target)
+  if ((lease->expires != 0 && difftime(now, lease->expires) >= 0) || lease 
== target)
{
  file_dirty = 1;
  if (lease->hostname)
-- 
2.11.0


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