[Dnsmasq-discuss] Execute external commands on DHCP lease allocation / deallocation

[Fabio Muzzi]

Hello Simon,

Monday, April 24, 2006, 10:03:47 PM, you wrote:


SK> This has been asked for before, and I've always said "no", it would be
SK> better to use Dbus for IPC. However, as far as I can see nobody uses
SK> DBus for that, so maybe I'm wrong.

If  you  think  it's better, try using Dbus. I doesn't matter *how*, but I
need this feature, and I have seen that I'm not the only one, it's quite a
common need for people running capitive portals.


SK> Just as an experiment, I tried to implement an external script. It's not
SK> quite as easy as it looks: you need to call "new lease" for every lease
SK> in the database when dnsmasq starts up, and that can be a lot of leases.
SK> If you just fork processes and run them asynchronously, then starting
SK> dnsmasq when it has a few hundred leases generates a flood of hundreds
SK> of child processes running the script. That would swamp a small machine,
SK> and it makes the script much more difficult to write, if it has to lock
SK> against concurrent execution.

Agreed.  Actually,  on  startup  you could also ignore the leases that are
already  stored  in  the lease file. I mean, if the gateway reboots, every
client will have to re-autenticate, but this is not a great issue, because
the gateway MUST NOT reboot in normal operation. Or did I miss something?


SK> My  second attempt serialises script execution: it waits for the first
SK> child  process  to  die  before  lauching another one.

This  is  a nice solution. It's up to the user to write a script that runs
fast  and  does  not  make  the  startup  process too slow. You can't make
miracles after all.

SK> That  works  much  better,  but  it  needs  more work to use the lease
SK> records  to  keep information about script execution. (You can't throw
SK> away a lease record when it expires until you've run the script.)

Well,  you  can  execute  the "expire" call to the script exactly when you
delete the old record from the lease file, or am I wrong?

SK> The old problem of userid still exists.

Yes,  and  for  the  first test I will run as root. Then I'll see if I can
find a better way.

Thanks  a lot for your help, I'll try the patched version tomorrow morning
and report back as soon as I can.


-- 

  Fabio "Kurgan" Muzzi