🚀 go-pugleaf

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> Alternatively, does it matter?  It's all very well to say that your file
> system is in a user-state server rather than in your kernel, but your users
> are probably just as dependent on every little detail being right.  To make
> user-state servers more than an irrelevant implementation detail, the user
> must be offered a choice of servers AND IT MUST BE EASY TO WRITE A SERVER!
> Or at least, not impossibly hard.  If writing a server is as touchy a job
> as writing the equivalent inside the kernel, the wonderful flexibility will
> get little use. 

I agree.  For my master's project I wrote a distributed file
system for 4.2BSD VAX/UNIX.  All of the important code for
the distributed file system was done in the kernel.
Unfortunately, I was only able to bring the file system up
on four VAXen.  If I had designed the distributed file
system so that a user-level server could have been written
for *any* BSD-like UNIX system, I could have had my project
on all the machines in the College of Engineering -- the
VAXen plus over 30 SUNs!

Also, debugging the kernel had to be done late at night when
nobody in their right mind should have been awake!  If I had
user-level servers to debug, I could have done it during the
day.  Ugh.  Also, crashes of my file system meant a reboot
of the machine, and crashes of a user-level server simply
mean remote file access would be down for a while.

However, the performance of my distributed file system was
extremely good.  I think it had about twice the throughput
of SUN's NFS.

I guess the main reason I designed my distributed file
system in the kernel was to ensure that existing binaries
did not have to be recompiled to take advantage of remote
access.  I don't think this is possible with user-level
servers, is it?  If it is, could you please direct me to
technical information about how this is/was/could be done?
I would be very interested.

[Conceptually it is easy to do, take a look at the MACH papers. -DL]

Anthony Discolo
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Anthony Discolo
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