cowloop technology

Thomas E. Zander riggs at
Wed Jan 11 00:18:51 PST 2006

Am Tue, dem 10. Jan 2006, um 22:48 +0100 Uhr schrubte Peter Schuller
zum Thema [Re: cowloop technology]:

> I have seen semi-negative references to GEOM before, but I have been
> unable to find what exactly it is people have a problem with. Out of
> curiousity, is there anything in particular that is controversial
> about it?

Well, it blocks raw device write if the reference count of this device
is not zero, i.e. you can't change the partition table of a disk in
multi-user mode if you have mounted filesystems on that disk.
It's a bit uncomfortable sometimes but I wouldn't go as far as to speak
of a particular problem. It reminds me that it's better to avoid some
things in multi-user mode :-)

Another thing is - in combination with FreeBSD's devfs - that block
device polling isn't implemented in form of GEOM events yet. However
the only situation where we hit that one is inserting a ZIP disk into a
SCSI ZIP drive. The disk has been formatted on windaz thus containing a
large daXs1 partition. Because the ZIP drive doesn't report media
change, the 's1' device isn't created in devfs and you have to manually
'true > /dev/daXs1' in order to have devfs create the node.
(By the way this wouldn't affect DFly anyways because there is MAKEDEV
and static device nodes. This isn't going to change in the near future,
is it?)

On the other hand, the new GEOM modules like GDBE and GELI are indeed
very much appreciated and they work pretty well, so for my personal
daily usage, GEOM is a clear win.


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