Date: Thu, 1 Aug 2013 19:48:05 +0200 From: Pawel Jakub Dawidek <pjd@FreeBSD.org> To: Brooks Davis <brooks@freebsd.org> Cc: Rotate 13 <rabgvzr@gmail.com>, freebsd-geom@freebsd.org Subject: Re: How to disable all GEOM tasting? Message-ID: <20130801174805.GB5771@garage.freebsd.pl> In-Reply-To: <20130730231348.GN13659@lor.one-eyed-alien.net> References: <CADBSp1fcO9Eb7nQXDQPghd0ModKuAtKBiwHfS80h_njn10U8Gg@mail.gmail.com> <20130730214114.GL13659@lor.one-eyed-alien.net> <CADBSp1dH01%2B1i1ydq-nWtivq30vxfjnnnJPnH%2Bqb0XycsbbjcA@mail.gmail.com> <20130730231348.GN13659@lor.one-eyed-alien.net>
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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@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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