glabel for ufs: size check is overzealous?

Pawel Jakub Dawidek pjd at FreeBSD.org
Wed Apr 22 07:59:52 UTC 2009


On Tue, Apr 21, 2009 at 04:29:05PM +0300, Andriy Gapon wrote:
> 
> glabel insists that for UFS2 the following must hold true:
> pp->mediasize / fs->fs_fsize == fs->fs_size
> 
> But in reality it doesn't have to be this way, there can be valid reasons to make
> filesystem smaller than available raw media size.
> 
> I understand that this is a good sanity check, but maybe there are other ways to
> extra-check that we see a proper superblock, without imposing the limitation in
> question.

This check is there is case you have few GEOM providers that start at
the same disk offset, but have different sizes.

For example ad0s1, ad0s1a, mirror/foo, mirror/foo.journal all might
start exactly at the same offset and glabel would have hard time to
figure out on top of which to place glabel provider.

Having file system smaller than provider size is perfectly valid, but
this is about choosing lesser evil, that's all. It is just much more
common to have file system using entire provider size.

-- 
Pawel Jakub Dawidek                       http://www.wheel.pl
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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