On Fri 2009-03-27 14:48:10, Artem Bityutskiy wrote:UBIFS has exactly the same properties like ext4 - in case
of power cuts:
1. truncate/write/close leads to empty files
2. create/write/rename leads to empty files
UBIFS is used in hand-held and and power-cuts are very
often there, because users just remove battery often.
I realize the "reality is different" argument, and already
concluded that we need a similar changes as Theo has done
for ext4:
http://git.kernel.org/?p=linux/kernel/git/tytso/ext4.git;a=commitdiff;h=bf1b69c0db7f9b9d8f02e94d40b19fca8336b991
http://git.kernel.org/?p=linux/kernel/git/tytso/ext4.git;a=commitdiff;h=f32b730a69bd56c5c9d704d8b75f03e90e290971
http://git.kernel.org/?p=linux/kernel/git/tytso/ext4.git;a=commitdiff;h=8411e347c3306ed36b8ca88611bf5fbf4d27d705
We have a problem that user-space people do not want to
use 'fsync()', even when they are pointed to their code
which is doing create/write/rename/close without fsync().
Well... they really don't want to spin the disk up for the
fsync(). I'm not sure if fsync() is really sensible operation to use
there.
1. truncate/write/close leads to empty files
this is buggy.
2. create/write/rename leads to empty files
..but this should not be. If we want to make that explicit, we should
provide "replace()" operation; where replace is rename that makes sure
that source file is completely on media before commiting the rename.
It is somehow similar to fsync()/rename(), but does not force disk
spin up immediately -- it only inserts "barrier" between data blocks
and rename. (And yes, it should be implemented as fsync()+rename() for
filesystems like xfs. It can be implemented as plain rename for ext3
and ext4 after the fixes...)