jffs2: -ENOSPC when truncating file?!

[David Woodhouse]

On Sun, 2008-02-24 at 07:57 +0100, Jörn Engel wrote:
> Could a naïve implementation of this get exploited by doing a large
> number of truncates that just shave single bytes off various files?

Yeah, which is why _my_ naïve implementation would do it for
truncate-to-zero instead of just _any_ truncate (which could even be
truncate-to-larger).

A more complex version might allow _any_ transaction to eat into the
ALLOC_DELETION pool if it is ultimately going to reduce the amount of
space taken on the file system -- even overwriting 'real' data with
zeroes which compress better. That's going to be hard to calculate in
the general case though.

If allowing only truncate-to-zero isn't good enough, perhaps we could
allow truncation to use the ALLOC_DELETION pool when it's going to
obsolete at least one full data node. That's not so hard to check.

-- 
dwmw2