State of read-only filesystems in NAND / MTD bad blocks handling when reading

[Thilo Fromm]

Hello Ricard,

>>> With a root file system in ubifs, you can boot directly with a root
>>> filesystem in UBI, with a kernel command line such as
>>>
>>> ubi.mtd=2 root=ubi0:rootfs rootfstype=ubifs
>>>
>>> I don't know how far back that was possible, you were using 2.6.27 were
>>> you not (in my case I'm using 2.6.35)?
>>
>> This would work for me (since I'm on 2.6.37) but I deeply eschew the
>> complexity this approach would bring to our system. Don't get me wrong
>> - I really like UBIFS; we use it for application partitions. I just
>> don't think it's the right thing to use for a RO rootfs. I want
>> simple.
>
>
> If you are using ubifs already on your system then you have all the required
> parts at hand. From a use point of view ubifs as a rootfs is simple; create
> a volume for your rootfs, write your data, specify appropriate parameters on
> the command line. So in that sense it is simple, even if a lot goes on
> 'under the hood'.

The 'under the hood' complexity is what's troubles me. Actually it
worries me a lot more than use case complexity. Use case complexity
can be wrapped for a specific purpose and then isn't complex anymore.

> In a comparison I did a while ago, switching from jffs2 to ubifs cut about 9
> seconds off the boot time for our system (which was in the range of one
> minute to start with) and gave us 3 MB more of free RAM after boot. It did
> consume a couple of MB more of flash (the jffs2 file system was 18 MB, the
> ubifs one 22 MB).

I totally get this; small r/w "configuration" partitions is the only
use case we ever choose JFFS2 for.

> So yes, it may be overly complex, but in practice I feel there are
> significant advantages: faster boot and consistent use of UBI/ubifs
> throughout the whole system in this case.

I don't trust UBIFS enough to have my *whole* root fs depend on it. If
you like, take a look at
<https://github.com/DFE/HidaV/wiki/File-system-layout> to get an
overview of what we're aiming for.

Regards,
Thilo

-- 
Dipl.-Ing (FH) Thilo Fromm, MSc., Embedded Systems Architect
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