Flash File Systems or Translation Layers?

[Benno Rice]

marty fouts wrote:
> On 5/17/06, Benno Rice <benno at freebsd.org> wrote:
>> gnn at freebsd.org wrote:
>> > Howdy,
>> >
>> > So, a few of us have talked off list of the need for a flash file
>> > system or translation layer for FreeBSD in order to better target the
>> > kind of boards we want to support.  The one lead I had was to a poorly
>> > written, binary only solution with nasty licensing.   That is, it was
>> > a dead end.  Does anyone know of anything that exists now that we
>> > might coopt or have the knowledge to do this right/well?
>>
>> I thought about doing a port of jffs2.  Probably a rewrite actually, so
>> we can have a non-GPL version.  It's waiting on me getting to the point
>> where I need it though. =)
>>
> 
> You probably don't want jffs2, because it has, um, interesting,
> performance characteristics. I also vaguely recall reading that the
> authors had stopped development on jffs3.

It depends on what we're doing with it.  If all we're doing is booting 
off it and then switching to something else, it's not really an issue 
IMO so long as it can keep up with the boot process.  It's also 
supported by things like U-Boot which is helpful.

> Also, jffs requires MTD, and it's debatable whether a rewrite of MTD
> would be a good thing or not.  See discussions on the yaffs mailing
> list and, IIRC, one of the NetBSD mailing lists on this recently.
> 
> It's not clear to me that "flash" is a good dividing point for making
> a file system. It seems a lot more likely that NOR and NAND flash are
> enough different that they would require their own file systems, or,
> at the least, their own address translation layers.

That may be the case, but I'm not so much interested in the "perfect" 
solution, I'm just after one that works and that requires the least 
amount of dinking with the bootloader that ships with the hardware I'm 
working on.  In my current case (Gumstix Connex 400xm-bt, Intel XScale 
PXA255) the board has U-Boot and the shipped Linux image uses jffs2.  I 
think the U-Boot on the board supports FAT and jffs2, so one of those is 
my preference.

-- 
Benno Rice
benno at FreeBSD.org