UBIFS on-media format changed to version 3

UBIFS on-media format changed to version 3

[Artem Bityutskiy]

Hi,

we have found a bug in UBIFS and the fix changes the on-media format.
Namely, the direntry hash function changed. We've always assumed it to
be 29 bits wide, but because of incorrect bitmask it has been only 25
bits wide.

Please, update UBIFS and mkfs.ubifs to version 0.7. We have changed
media format version from 2 to 3 as well. We support compatibility with
older JFFS2 format (version 2) for now, but we would like to drop the
support, unless someone really needs this and asks us not to do this. We
are not in mainline so far, so we probably have luxury of changing
on-flash format so far.

I've CCed people who may be using UBIFS and should be aware of the
change.

We have updated 2.6.21--2.6.25 back-ports as well.

Thanks.

P.S. It is anyway good idea to update as we've fixed a number of bugs.
P.P.S. We are hoping to get merged to 2.6.27 and are working on this.

-- 
Best regards,
Artem Bityutskiy (Битюцкий Артём)

Re: UBIFS on-media format changed to version 3

[Hamish Moffatt]

On Thu, May 29, 2008 at 10:50:42AM +0300, Artem Bityutskiy wrote:
> we have found a bug in UBIFS and the fix changes the on-media format.
> Namely, the direntry hash function changed. We've always assumed it to
> be 29 bits wide, but because of incorrect bitmask it has been only 25
> bits wide.
> 
> Please, update UBIFS and mkfs.ubifs to version 0.7. We have changed
> media format version from 2 to 3 as well. We support compatibility with
> older JFFS2 format (version 2) for now, but we would like to drop the
> support, unless someone really needs this and asks us not to do this. We
> are not in mainline so far, so we probably have luxury of changing
> on-flash format so far.
> 
> I've CCed people who may be using UBIFS and should be aware of the
> change.

Hi Artem,

Thanks for the notification.

What's the impact of the bug? Does it only affect particularly large
volumes or directories with a particularly large number of files or
something else?

As I understand your comments, the new source will currently work with 
existing file systems but you want to drop that ability?

We're just about to deploy devices with 2.6.24 + ubifs from GIT a month
or two back, though we're probably not going to upgrade the kernel on
existing devices in the future anyway.

Hamish
-- 
Hamish Moffatt VK3SB <hamish@debian.org> <hamish@cloud.net.au>

Re: UBIFS on-media format changed to version 3

[Artem Bityutskiy]

Hi,

On Fri, 2008-05-30 at 17:30 +1000, Hamish Moffatt wrote:
> What's the impact of the bug? Does it only affect particularly large
> volumes or directories with a particularly large number of files or
> something else?

Right. It is basically harmless, it's just that the hash function will
collide more often which may result in poorer performance in case of
large directories.

> As I understand your comments, the new source will currently work with 
> existing file systems but you want to drop that ability?

Right. But we may keep the support if you need this of course.

> We're just about to deploy devices with 2.6.24 + ubifs from GIT a month
> or two back, though we're probably not going to upgrade the kernel on
> existing devices in the future anyway.

Oh. We fixed many bugs since that time :-) Of course you may never hit
them, everything depends on the use-case. But I would update the kernel.

Anyway, if you want, we may keep backward compatibility so that new
kernel will work fine with older (version 2) images.

-- 
Best regards,
Artem Bityutskiy (Битюцкий Артём)