Re: grub-probe detects ext4 wronly as ext2

[Felix Zielcke]

From: "JavierMartín" <address@hidden>
Sent: Wednesday, July 16, 2008 6:38 PM
To: "The development of GRUB 2" <address@hidden>
Subject: Re: grub-probe detects ext4 wronly as ext2

> Er... of course, the Linux extN implementation is the de-facto
> reference
> implementation. Some incompat features are only used in newer versions
> like ext3 and ext4, while others are added to ext2 too. I was talking
> about the GRUB extN driver, which recently got patched by Bean.

I thought you thought that META_BG is ext4 specific, but even ext2 supports 
it
Anyway I just grepped for META_BG in the e2fsprogs 1.41 source and mke2fs.c 
says that resize_inode and meta_bg are not compatible
resize_inode is by default enabled.
I have it disabled on my ext4, because I just don't need it but I don't 
think this means meta_bg is enabled.
So for me it looks like there's no need to worry about meta_bg
Maybe I'll find something about that

> Uninit_bg is signaled (iIrc) in the superblock by a ROCOMPAT flag,
> GDT_CSUM, and then in the block groups by whatever-it-is (head spinning
> even faster).

Oh well, I gave you a link to ext4.h and I even didn't notice there's really 
no UNINIT flag in the 3 lists of compat,incompat and rocompat
I grepped e2fsprogs source for it
You're right it is uninit_bg "is" the ROCOMPAT flag GDT_CSUM

> AFAIK, uninit_bg should work if the (readonly) GRUB reader respects the
> spec and skips "invalid" block groups/inodes/whatever (those that
> haven't been initialized). As I don't know what the f*** do META_BG and
> FLEX_BG do, I can't tell you whether they truly work or it's just a
> matter of luck: it's Bean who can tell us whether or not he implemented
> support for them -

Yeah, Bean has to tell you. I only looked a few secons at the differences 
between his 2 patches which made my ext4 working
and even if I would have read it longer, I didn't think I would fully 
understand it :)

At [0] there's a mail from me on this list, with 2 quotes from 
Documentation/ext4.txt and what mke2fs(8) says about it and a quote of Bean 
what he found about flex_bg

> I only added the "extents" flag to the supported
> list
> on my patch, but including more is a matter of seconds.

Yeah, I just wanted to make sure that uninit_bg and flex_bg don't get 
forgot, and then I forget this, install the debian package and then end up 
on a unbootable system :)
But even if that happens, it's not a big problem for me now.
Currently I only use ext4 in VMware

[0] http://lists.gnu.org/archive/html/grub-devel/2008-07/msg00157.html