RFS data loss for open files and ways to work around it

[Sebastian Huber]

On 09/05/16 07:32, Mohammed Saeed Khoory wrote:
> Hi,
>
> I'm using RFS on a RAMDisk for a LEON3-based system. My program tends to keep files open while writing to them periodically. I've noticed that if the system was reset, the files that were open lose all of the data that was written since they were last open. The files still exist in the filesystem, just with a size of 0. Interestingly however, the free space blocks used by those writes are not reclaimed and is gone, and the only way to get it back from what I can tell is to reformat. An fsck-style tool would probably work too but that doesn't exist.

Even if you flush your data to disk, then this file systems seems to be 
not reset-safe. JFFS2 could be an option for such scenarios.

>
> The way I work around this is that instead of keeping files open, I open the file, write a little, then close instantly. The changes are then preserved in the filesystem if a reset occurs. However, this method is rather awkward, and I was wondering if there's a better way of doing it. I've tried using fflush() and sync(), but that didn't help. Is there a proper way to "synchronize" the writes to the filesystem?

The sync() implementation is not really useful in RTEMS. However, 
fsync() should work. I guess for standard C FILE files you need a

fflush(file);
fsync(fileno(file));

-- 
Sebastian Huber, embedded brains GmbH

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