[9fans] Plan 9 file server w/ indexed dirs and logging

[G. David Butler gdb@dbSystems.com]

From: "G. David Butler" <gdb@dbSystems.com>
>
>so if you have a spare PC to use as a Plan9 file server
>and want to have a go at it...  This fileserver has indexed
>directories and logging.  [It also supports mirrored disks,
>sort of.  It works but needs more attention.]  The logging comes
>in two versions (compile flag) of full discrete transactions
>and fileserver protection.  The one below only provides
>fileserver protection.  The other one guarantees the results
>of each successful 9P message.  Both are fully compatible with
>the current Plan9 9P protocol.
>
>Get ftp://ftp.dbSystems.com/pub/PLAN9/9pcfs.xor
>
[snip]

I had a problem recognizing the end of the log during certain
crashs.  You see [take a deep breath], the log is circular and
so you have to find the last checkpoint and you have to make
sure you don't overwrite the last checkpoint and there are two
log writing processes using a log buffer and the changes in the
buffer cache can't be written till you know the changes in the
log buffer have been written...  You get the idea, it's hard.

There is now a new kernel that does a better job of using the log
after a crash.  Sorry.

>One other thing, I would recommend a small log so the search for
>the end doesn't take too long.  Something like pw0.0.0.0.1 (Yeah
>I fixed the partition syntax like the man page...)

Small is at least 1000 pages or about 5Mb.  If it is much smaller
you will start to see the message "sync: forced checkpoint" under
load and your I/O will slow down...

David Butler
gdb@dbSystems.com