Re: grub-probe detects ext4 wronly as ext2

[Felix Zielcke]

From: "JavierMartín" <address@hidden>
Sent: Wednesday, July 16, 2008 9:07 PM
To: "The development of GRUB 2" <address@hidden>
Subject: Re: grub-probe detects ext4 wronly as ext2

> OK, so this is what I get from your 3 posts, and my proposals for the
> driver future:
>         * meta_bg is a deprecated feature and is incompatible with
> resize_inode, which is used by default in ext4 and can be used by all
> other extN filesystems. We cannot safely ignore it since it signals an
> incompatible change in one of the fs descriptors, so the reading code
> might not be able to locate (meta)data on disk. I advocate _rejecting_
> volumes with it (given that it's no longer being generated by any
> "standard" tool) until someone writes a patch to support it.

resize_inode is not just enabled for ext4 but for every extN by mke2fs.conf
Either check your own /etc/mke2fs.conf or see [0] which is the newest and so 
has all the ext4 features in it :)
I can't remember ever seeing that meta_bg but I do remember that 
resize_inode wasn't just added now in the newest e2fsprogs
The release-notes unfortunatly don't say when it was added or at least I 
didn't found that with searching for resize_inode

>         * flex_bg seemingly allows certain metadata structures to be
> located at
> places other than their default positions. However, given that it is
> only used on volumes quite filled with bad blocks, I think we can (at
> least temporarily) _ignore_ it, but truly supporting it would be a Good
> Thing (tm)

For me currently it works but that's why I added that others should test 
that.
At least on this list only I and Bean tested this and I think Bean just 
tested this with my 30 MB image I gave him,
where grub-fstest failed to read the Linux Kernel

I don't know what this comment on mke2fs(8) about flex_bg means
(use with -G option to group meta-data in order to create a large virtual 
block group).

Oh, I now saw in that mail I forgot to copy the text from that -G option and 
the raw sourcecode of the manpage I linked there isn't really easy to read

-G " number-of-groups"
Specify the number of block goups that will be packed together to
create one large virtual block group on an ext4 filesystem.
This improves meta-data locality and performance on meta-data heavy 
workloads.
The number of goups must be a power of 2 and may only be
specified if the flex_bg filesystem feature is enabled.

But because this grouping needs flex_bg enabled, and flex_bg is INCOMPAT, 
there's maybe a reason grub needs to support it.
Maybe I'll try it out if grub fails to boot with that -G option used

>         * uninit_bg might already be supported (we should check, though,
> with
> bigger partitions) and is not an incompat flag, so my patch does not
> affect its handling.

I've one 8 GB ext4 where ~ 3 GB are used and another 8 GB ext4 where just 
~700 MB are used
Both have uninit_bg and flex_bg and grub works with them
But because I don't use them much, proberbly grub doestn't even reach the 
uninitialized blockgroups/inode tables

[0] 
http://git.kernel.org/?p=fs/ext2/e2fsprogs.git;a=blob;f=misc/mke2fs.conf;hb=HEAD