Charles,

> You should find the power fail stuff very robust (ie. zero 
> problems). If you 
> don't then please shout ***loud***.

the first problem found after a dozen power cycles ;-(

I have a counter file that contains a number 
that needs to be incremented. Increment is done as:
1. Read the number from the counter file (open as O_RDONLY, read, close)
2. Increment the number
3. Write the number to a temporary file
4. Rename temporary file to counter file

Rename() suppose to be atomic per 
http://www.opengroup.org/onlinepubs/007908799/xsh/rename.html:
"If the link named by the new argument exists, it is removed and 
old renamed to new. In this case, a link named new will remain 
visible to other processes throughout the renaming operation and 
will refer either to the file referred to by new or old before 
the operation began."

After a few power cycle tests the counter file disappeared, but 
the temp file is still there. rename() never reported failure.
 
-------------------Code---------------------
ret = rename(FnameBlockTmp,FnameBlock);
    if(ret < 0) terminate(instance,ERR,
			  "writer: failed to rename tmp block file %s",
			  FnameBlockTmp);

------------------Output-------------------
running external script /mnt/flash/run.sh
writer 0 started
instance 0 terminated with status -1
writer: failed to open block file /mnt/flash/blockno0
writing status to </mnt/flash/status0>

# cd /mnt/flash/
# ls
blockno.tmp0  jffs2tester   run.sh        test0         write.sh
init.sh       lost+found    status0       verify.sh

# cat /proc/yaffs
YAFFS built:Apr 20 2005 14:39:45
$Id: yaffs_fs.c,v 1.35 2004/10/20 20:12:43 charles Exp $
$Id: yaffs_guts.c,v 1.37 2004/10/20 20:12:43 charles Exp $

Device yaffs
startBlock......... 1
endBlock........... 8191
chunkGroupBits..... 2
chunkGroupSize..... 4
nErasedBlocks...... 7
nTnodesCreated..... 33400
nFreeTnodes........ 2
nObjectsCreated.... 32800
nFreeObjects....... 83
nFreeChunks........ 187105
nPageWrites........ 6
nPageReads......... 14
nBlockErasures..... 0
nGCCopies.......... 0
garbageCollections. 0
passiveGCs......... 0
nRetriedWrites..... 0
nRetireBlocks...... 0
eccFixed........... 0
eccUnfixed......... 0
tagsEccFixed....... 0
tagsEccUnfixed..... 8
cacheHits.......... 0
nDeletedFiles...... 32706
nUnlinkedFiles..... 32706
nBackgroudDeletions 0
useNANDECC......... 1
#
-------------------------------------------

Sergei