Re: [Ext2-devel] [PATCH 2/2] ext2/3: Support 2^32-1blocks(e2fsprogs)

From: Theodore Ts'o
Date: Sat Mar 18 2006 - 07:23:31 EST

On Sat, Mar 18, 2006 at 03:11:02AM -0700, Andreas Dilger wrote:
> > As I said in my previous mail, You should specify -F option to
> > create ext2/3 which has more than 2**31-1 blocks.
> > It is because of the compatibility.
> Oh, using -F for this is highly dangerous. That would allow mke2fs to
> run on e.g. a mounted filesystem or something. Instead use an option
> like "-E 16tb" or something.

Agreed that we shouldn't use -F, but what's the compatibility reason?
Supporting 2**31-1 blocks required bugfixes in the kernel and in
e2fsprogs, yes, but if it's not a filesystem format change, but rather
a "kernel had bugs which have now been fixed" statement, that's not
the sort of thing where I'd think forcing the system administrator to
add a magic command-line flag would be necessary or desirable.

I could see printing a warning message saying that older kernels might
have problems with this, and I could also imagine including with the
kernel patch enabling some sort of flag that could be queried, perhaps
via /sys/fs/ext3/32bit-nr-blocks so that if it isn't present, mke2fs
could give a more emphatic warning that the current kernel wouldn't be
able to deal with filesystems being created.

- Ted
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