[3299] in Release_7.7_team
Re: Athena Disconnected Operation White Paper Draft 2.
daemon@ATHENA.MIT.EDU (Larry Stone)
Sat May 25 01:26:30 2002
Date: Sat, 25 May 2002 1:26:28 EDT
From: Larry Stone <lcs@MIT.EDU>
Reply-To: <lcs@MIT.EDU>
To: Bill Cattey <wdc@MIT.EDU>
Cc: source-developers@MIT.EDU, release-team@MIT.EDU
In-Reply-To: Your message of 24 May 2002 18:06:20 -0400
Message-ID: <CMM.0.90.4.1022304388.lcs@defiant.mit.edu>
Some disjointed thoughts:
1. Files:
The problems of handling the user's home directory, and that of
handling lockers, could be merged into one concern: extending the
locker model to support disconnected operation. I think this would
be helpful because the user could have other read/write lockers they'd
want to be able to modify while disconnected.
Lockers are a good model because they define a chunk of (usually)
network-accessible resource which can be handled by itself. Instead of
thinking of which subtrees of /afs to mirror or cache locall, you can
use the granularity of lockers.
We can take advantage of the locker conventions to cache only the files
useful on the local system, e.g. the arch/@sys subdirectory, and common
subdirectories like share, man.. "etc". (Of course, sometimes the
arch/@sys subdir has symlinks to other architectures so those would have
to be followed and their targets pulled in as well.)
The read-only locker could be handled specially; its local cache is also
read-only. Even if the user modifies it, those changes get wiped out
when it is resynchronized.
Read-write lockers are a bigger problem. There is the technical
challenge of doing frequent "recursive diffs". The locally cached
version of the locker is a local filesystem, which has different
semantics and protections from AFS. It is vulnerable to local roots.
For that matter, ACLs in the original may prevent the local cache from
being a complete copy -- if the local user has no ACLs on a subdirectory,
she shouldn't get it copied into the local cache (and be able to see it
as root).
2. DNS
We could modify named to check whether the machine is off the net, at
which point it responds immediately with the canned "local map". This
could implement some useful workarounds, e.g. establish localhost as an
MX host for "outgoing.mit.edu", so that mailers would still be able to
send to outgoing to relay their mail but in fact it would be queued
locally.
For that matter, we could leave named alone and simply write a separate
local-named, and the state change script would shut down one and start
the other.
3. Licensing
Third-party software is a significant part of the Athena environment,
and at least some of it has network licensing. FrameMaker comes to
mind (doesn't anyone else like Frame?) but no doubt there are others.
-- Larry
(PS, how about "Disco Athena" as a name for the project, if there is one?
Or maybe not. Put that white leisure suit away, Bill!)
