UBIFS sync question

[Artem Bityutskiy]

On Tue, 2008-09-30 at 15:28 -0700, Bruce_Leonard at selinc.com wrote:
> Artem,
> 
> We've run into a side effect that we think is probably a design choice in 
> UBIFS, but we want to make sure before we start trying to troubleshoot a 
> "bug".  What we do is open an existing  file in a UBIFS formated UBI 
> volume on a NAND flash, add a few lines to it, close the file, then 
> WITHOUT un-mounting the file system, reboot the box (simulating a power 
> outage).  When the box reboots and we look at the file, it's zero length 
> and has no contents.  I suspect it's because UBIFS does less frequent 
> syncs than say ext2 for performance reasons, and we're just losing the 
> contents of the file because there's no sync before the reboot.
> 
> Is this correct or do we need to start digging for something broken?

Well, you should sync the file, see
http://www.linux-mtd.infradead.org/doc/ubifs.html#L_writeback

However, if you open a file, and just add few lines to it, then it
should not become empty after reboot. You should just loose whole or
part of new data.

I think you actually truncate the file, then re-write it, instead of
appending. This often happens in case of shell scripts - shell commands
like truncating files.

-- 
Best regards,
Artem Bityutskiy (Битюцкий Артём)