Coda File System

Re: blocking on open()

From: Stephen J. Turnbull <>
Date: Sat, 25 Sep 2004 14:54:34 +0900
>>>>> "Troy" == Troy Benjegerdes <> writes:

    >> Say what?  In terms of the file contents, disconnected
    >> operation is just a set of additional restrictions on cache
    >> semantics, no?  I would be surprised if a general facility like
    >> cachefs will satisfy them out of the box.  It's possible, but
    >> requires proof.  There's a pretty good chance that proof itself
    >> will be on the order of difficulty of generalizing venus.

    Troy> The additional restrictions on cache semantics is keeping
    Troy> track of what has changed that the server hasn't seen, and
    Troy> resolving conflicts with the server.

And ensuring file integrity for disconnected operation.  In other
words, venus needs to know everything that cachefs knows about what's

Furthermore, I can imagine applications that really want to assume
that the whole file is available before they get to work, even though
the data in Coda may be read-only for that application.  Currently we
don't need an API for that.  With your scheme, we do, to account for
situations where we go disconnected while a file is open for read.

    Troy> The hard part that requires proof is dealing with writes.

Writes are the hard part, yes, but they are not the only thing that
requires proof.

    Troy> I can't think of very many situations I would actually
    Troy> *want* to be able to write without requireing the whole file
    Troy> be present,

Any "blind" append.  Files bigger than cache (think handhelds).  A
database application might want to do it.  Journaling file systems
already do it fairly generally in a certain sense.

    Troy> but there are a ton of situations where I want
    Troy> to be able to read without waiting for the whole thing.

Sure.  You're impatient to read.  Other users/applications will be
impatient to write.

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Received on 2004-09-25 01:56:19