Messages in this thread | | | Date | Sun, 29 Mar 2009 14:26:00 +0200 | From | Pavel Machek <> | Subject | replace() system call needed (was Re: EXT4-ish "fixes" in UBIFS) |
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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...)
Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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