[Nut-upsdev] Changes to upscli_connect

[Stuart D Gathman]

On 06/28/2011 02:29 PM, Arjen de Korte wrote:
>
> Citeren Frédéric Bohé <fredericbohe at eaton.com>:
>
>> I am currently working on the nut scanner. For detecting available upsd
>> on the network, I rely on upscli_connect. The problem with this function
>> is that it calls a blocking "connect" function.
>
> The upscli_connnect() call should not block. If it does, that is a 
> problem that needs fixing, rather than adding an timeout. On what kind 
> of system did you test this? If I attempt to connect upsmon to a 
> non-existing server socket, the following is shown (-DDD):
>
>    0.001902     Trying to connect to UPS [myups at localhost]
>    0.002667     UPS [myups at localhost]: connect failed: Connection 
> failure: Network is unreachable
>    0.002690     do_notify: ntype 0x0005 (COMMBAD)
>    0.002704     Communications with UPS myups at localhost lost
>
Your test is with localhost - so any non-existent socket would get 
immediately rejected.  The nut scanner has to deal with hosts on the 
network.  If they send an ICMP reject, then there is no need for a 
timeout.  But it is very common for a host to simply "eat" attempts to 
connect to a port not allowed in their firewall.  So nut scanner needs a 
non-blocking version of upscli_connect.

Instead of a timeout, which is problematic (host may just be slow), I 
suggest an actual non-blocking call so that N connects may be started, 
and then waited on as a group using select() or os equivalent.  The 
upscli_connect_start(...) should return a small integer (e.g. file 
descriptor), so the app can track the pending connect in a data 
structure (along with IP, port, etc), and upscli_connect_wait() will 
return the small integer of a pending connect that finished, and 
upscli_connect_finish(int) will complete the operation.

There may still be a need for an overall timeout (passed to 
upscli_connect_start), since 3 minutes is too long to wait.  Something 
more like 30 seconds would be appropriate for nut scanner.