[9fans] plan9ports venti with arenas on fat filesystem

[Adrian Tritschler <ajft@ajft.org>]

I've been playing/experimenting with a p9p venti with arenas in 512M
files on linux ext3 file systems with no problems, today I decided to
set up a second venti on an external USB drive so I could have a backup
of it.  It seems that I can't create arenas on files on the USB fat32 disk.

% cd /mnt/venti
% venti/fmtarenas arenas6 ./arenas6
fmtarenas ./arenas6: 1 arenas, 536,076,288 bytes storage, 524,288 bytes
for index map
2007/1012 10:25:17 err 4: write ./arenas6 offset 0xc0000 count 49152 buf
8074000 returned 16384: Success
2007/1012 10:25:17 err 4: can't write arena set: write ./arenas6 offset
0xc0000 count 49152 buf 8074000 returned 16384: Success
can't write back arena partition header for ./arenas6: can't write arena
set: write ./arenas6 offset 0xc0000 count 49152 buf 8074000 returned
16384: Success

Copying the file to the ext3 system, performing the venti/fmtarenas then
copying it back works.

% rsync -P arenas[67] $HOME/tmp
arenas6
   536870912 100%    4.96MB/s    0:01:43 (xfer#1, to-check=1/2)
arenas7
   536870912 100%    4.61MB/s    0:01:51 (xfer#2, to-check=0/2)

sent 1073873034 bytes  received 64 bytes  5006401.39 bytes/sec
total size is 1073741824  speedup is 1.00

% cd $HOME/tmp
% venti/fmtarenas arenas6 ./arenas6
fmtarenas ./arenas6: 1 arenas, 536,076,288 bytes storage, 524,288 bytes
for index map
% venti/fmtarenas arenas7 ./arenas7
fmtarenas ./arenas7: 1 arenas, 536,076,288 bytes storage, 524,288 bytes
for index map

Then back on the USB fat32 system all *seems* to work:

% cd /mnt/venti
% rsync -P  $HOME/tmp/arenas6 .
 :
% venti/fmtindex venti.conf
fmtindex: 8 arenas, 23,800 index buckets, 4,288,479,232 bytes storage
% venti/venti -d -h tcp!localhost!1090 -a tcp!localhost!17036
2007/1012 10:40:42 venti: conf...httpd
tcp!localhost!1090...init...icache 0 bytes = 1,000 entries; 4 scache
sync...announce tcp!localhost!17036...serving.

As soon as venti/wrarena starts to write to it, many errors occur, all
seem to be of the form:

2007/1012 10:43:15 err 4: write ./isect1 offset 0x73c000 count 65536 buf
810c000 returned 16384: Success
venti/venti: part ./isect1 addr 0x10c000: icachewritesect writepart:
write ./isect1 offset 0x73c000 count 65536 buf 810c000 returned 16384:
Success

Is the correct answer, "just don't do that", am I doing something wrong,
or this a bug that anyone is interested in fixing?

	Adrian