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From: "dawidek.net" <pawel@dawidek.net>
Subject: Re: How to disable all GEOM tasting?
Date: Thu, 1 Aug 2013 12:33:18 +0200
To: Luca Ferrari <fluca1978@infinito.it>
Cc: Rotate 13 <rabgvzr@gmail.com>, "lev@freebsd.org" <lev@freebsd.org>,
 Brooks Davis <brooks@freebsd.org>,
 "freebsd-geom@freebsd.org" <freebsd-geom@freebsd.org>
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Dnia 1 sie 2013 o godz. 11:16 Luca Ferrari <fluca1978@infinito.it> napisa=C5=
=82(a):

> On Thu, Aug 1, 2013 at 10:21 AM, Lev Serebryakov <lev@freebsd.org> wrote:
>> Hello, Luca.
>> You wrote 1 =D0=B0=D0=B2=D0=B3=D1=83=D1=81=D1=82=D0=B0 2013 =D0=B3., 11:3=
1:21:
>>=20
>> LF> However, I don't get the whole point in disabling tasting: it is
>> LF> required for proper system functioning.
>>   Presence of a lot (and "a lot" could mean THOUSANDS -- think about regu=
lar ZVOLs
>> snapshots on iSCSI-used NAS) of "foreign" "block devices".
>=20
> Uhm...but in such case the class should have a g_taste set to NULL to
> avoid tasting on itself. What I was saying is that disabling taste
> system wide (i.e., in the geom subsystem) cannot work.
> Am I wrong?

The biggest problem with disabling tasting is that the corresponding entries=
 won't be created in /dev/. There is the DEV GEOM class, which create those e=
ntries from its taste method.

I do see a value in being able to temporairly disable tasting in some emerge=
ncy situations, but there is no way to do that now.

Taste methods are called from three different places:
1. When new provider is created all GEOM classes are noticed.
2. When new GEOM class is loaded it gets all existing providers for tasting.=

3. When the last consumer that had provider open for writing closes its acce=
ss, GEOM notices all the classes again, as writes might have changed provide=
r's metadata and classes may be able to find something interesting now.

--=20
Pawe=C5=82 Jakub Dawidek=