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Date: Fri, 20 Feb 2015 18:03:54 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: [ANNOUNCEMENT] TEST RELEASE: Cygwin 1.7.35-0.3
Message-ID: <20150220170354.GE26084@calimero.vinschen.de>
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References: <announce DOT 20150218105937 DOT GA28211 AT calimero DOT vinschen DOT de> <87d255htw7 DOT fsf AT Rainer DOT invalid> <20150220095617 DOT GO26084 AT calimero DOT vinschen DOT de> <54E75BB9 DOT 90807 AT coverity DOT com> <20150220162442 DOT GA26084 AT calimero DOT vinschen DOT de> <54E763CD DOT 9000307 AT coverity DOT com>
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On Feb 20 11:41, Tom Honermann wrote:
> On 02/20/2015 11:24 AM, Corinna Vinschen wrote:
> >On Feb 20 11:07, Tom Honermann wrote:
> >>On 02/20/2015 04:56 AM, Corinna Vinschen wrote:
> >>>>Lastly, running cygserver to cache the LDAP data has another side-eff=
ect
> >>>>when using VPN.  Since the cygserver is usually started before you've
> >>>>dialed into the VPN, your username and some groups will get reported =
as
> >>>>"DOM+User(12345)".  You have to restart cygserver after the VPN is up=
 to
> >>>>correct that.
> >>>
> >>>Yep.  We should contemplate to allow sending a signal to cygserver to
> >>>invalidate its cache.
> >>
> >>Perhaps cygserver could subscribe to network event notifications and
> >>automatically invalidate its cache?
> >>
> >>https://msdn.microsoft.com/en-us/library/windows/desktop/aa366334%28v=
=3Dvs.85%29.aspx
> >
> >How do you know if and when an interface change requires a cache
> >invalidation?
>=20
> I doubt there is a perfect algorithm, but perhaps a heuristic would work
> fairly well.  For non-mobile systems, interface changes are presumably
> rather rare and invalidation on the addition of any new interface might be
> acceptable.  For mobile systems migrating between networks, the situation=
 is
> tougher
> [...]

Maybe it is actually simpler than that.  Invalidating the cache as a
whole probably never makes sense.  In fact there are two reasons for
invalidation:

- The pw_name, pw_shell, pw_home, pw_gecos settings for a user changed.

- The interface to the DC was broken and there are entries of the type
  Achim mentioned, "DOM+User(RID)".

The first case can only be fixed by invalidating the cache on a regular
basis.  If we didn't fetch the info for a user for, say, 5 minutes, drop
the entry from the cache and renew the information by asking the DC
again.

As for the second case, the DOM+User(RID) entries are undesired and
wrong anyway.  So maybe the caching code could do what you said in the
first place.  Invalidate the cache on every network change.  But then,
only invalidate the entries of the aforementioned type.

Care to hack a bit?


Corinna

--=20
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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