How to disable all GEOM tasting?

[Pawel Jakub Dawidek]

On Tue, Jul 30, 2013 at 06:13:48PM -0500, Brooks Davis wrote:
> On Tue, Jul 30, 2013 at 10:19:54PM +0000, Rotate 13 wrote:
> > On Tue, 30 Jul 2013 16:41:14 -0500, Brooks Davis <brooks at freebsd.org> wrote:
> > 
> > > On Mon, Jul 29, 2013 at 05:14:04PM +0000, Rotate 13 wrote:
> > >> How to disable *all* GEOM tasting of newly-attached devices?  I looked
> > >> through the manuals, searched web, grepped sysctl -ad.  I only find
> > >> sysctl to disable all tasting for graid (kern.geom.raid.enable).
> > >>
> > >> Example, if I have removable drive I want to pop in and access from
> > >> userland with open("/dev/foo0", O_RDONLY); without various GEOM
> > >> modules first trying to understand.
> > >
> > > As far as I know there is no way to do this, but the existence of
> > > partition tables shouldn't have any effect on your ability to open the raw
> > > device as long as you haven't configured something in devd or similar to
> > > open those partitions.
> > 
> > Any pointer to look in sources for where triggers the tasting?  I
> > understand each GEOM has the taste code of its own...  but something
> > must start it all when device is inserted.
> 
> The creation of a geom provider triggers the tasting.  I suppose you
> could create a new driver to matches the device preferentally to umass
> or what ever device it normally attaches it and provides a simple node
> for it.  That sounds like a lot of work and you haven't explained why
> you can't just let the tasting happen and ignore any partions that are
> found.

If you use ZVOLs and snapshots you can easly end up with thousands GEOM
providers, which doesn't scale well. Giving them all for tasting to all
available GEOM classes will take a while too.

In Illumos ZFS /dev/ entries for ZVOLs are lazy created - when someone
looks up the given entry ZFS is noticed and corresponding entry is
created. This was not always the case. Earlier they were creating /dev/
entries for all ZVOLs, but apperently they found it problematic.
I remember this, because it took me a while to bring back non-lazy
creation of /dev/ entries for ZVOLs. GEOM doesn't support anything like
that.

-- 
Pawel Jakub Dawidek                       http://www.wheelsystems.com
FreeBSD committer                         http://www.FreeBSD.org
Am I Evil? Yes, I Am!                     http://mobter.com
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