[Yaffs] Re: yaffs robustness against power failures

[Vitaly Wool]

Hi Charles,

Charles Manning wrote:

>You will end up with a partial write. eg. If you have 500k free and you 
>attempt to write 1MB then 500k will be written and the write call will return 
>500k.
>
>YAFFS keeps enough space in reserve to flush any in-flight internal cache and 
>flush file handles etc.
>
>What definitely will not happen is file structure getting corrupted.
>  
>
thanks! However I meant the following situation: suppose we've got 500k 
free, and we're trying to write a new version of 1M file (i. e. rewrite 
the old one). How will the filesystem handle this? I. e. will it refuse 
the write operation or grant it? If latter, what will happen if a power 
failure happens in the midst of the write (for instance, when 600k is 
written already -- there's not enough space to hold both the old and the 
new versions so how will the incomplete write be reverted?)
OTOH, if there's enough space to hold both the old and the new versions, 
will the power pailure always be handled by the filesystem in such a way 
that retains the integrity of the file being written (i. e. either the 
old or the new version). I hope it will, but still being sure is better 
than thinking 'probably it will' :)

Thanks,
   Vitaly