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Re: power safe - appand to file

On Wed, 2004-05-26 at 09:53 +0200, Niels Beier (NB) wrote:
> Hi,
> I have two questions regarding the power safe features of JFFS2 (JFFS2 on eCos).
> 1) As I understand it, JFFS2 (being a journaling file system and not a versioning file system) only 
>    protects the integrity of the file system and not the integrity of the file content. We need
>    to be able to append new data to an existing file (a system log file in an embedded device) and it is important
>    that the file is not corrupted if the power is removed during the append operation.
>    Is the append file operation safe (is the old data still available if the de power is removed during
>    the append operation)?

Of course the _old_ data are available. Some of the new data may also be
available. See POSIX.

> 2) We need to be able to update the firmware of an embedded device in a safe manner. 
>    After we have downloaded new firmware using a another name (old firmware filename : firware_old- new
>    firmware filename: firmware_new), how do we then change the name of firware_new to firmware_old (our
>    boot process expects to find a file called firmware_old) in a power safe way (if this is not possible we must
>    change our boot proces)?

Rename is atomic. See POSIX.


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