Date: Sat, 10 Apr 2010 17:43:17 +0200 From: Ivan Voras <ivoras@freebsd.org> To: freebsd-geom@freebsd.org Subject: Re: Read/write GMIRROR metadata Message-ID: <hpq6am$ogf$1@dough.gmane.org> In-Reply-To: <BLU0-SMTP401B53789F38FEAF59BA60AD150@phx.gbl> References: <BLU0-SMTP401B53789F38FEAF59BA60AD150@phx.gbl>
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Alfredo Elvira wrote:
> Hello,
>=20
> i=C2=B4m developing a patch for geom mirror module to acelerate synchro=
nizing
> between providers, using bitmaps to write in the provider only modified=
> data since the last rebuilding.
>=20
> I have a trouble in the first access to the new provider attached,
> before mirror creation, when i execute gmirror label ....
>=20
> When the first clean disk is attached, the system runs the
> g_mirror_taste function for two times. The first one, there are not
> valid metadata for mirror class and g_mirror_read_metadata function
> returns error 22. But the second one, valid metadata are read. I don=C2=
=B4t
Usually, the first time your code gets to taste the device before it's=20
labeled, e.g. when it first appears in the system, etc. Then, when=20
something opens the device for writing and then closes is ("spoils it"), =
all GEOM classes are given the opportunity to taste the device again to=20
see if they can use it.
> understand "who" and "when" have been written these metadata, because i=
n
> debugging mode, i=C2=B4ve set breakpoints in functions that write data =
in
> provider (g_mirror_write_metadata and g_write_data) and "aparently"
> these are not called.
Metadata in the "label" step is done in userland, by the gmirror utility =
(or more specifically, /lib/geom/geom_mirror.so).
The usual situation is like this: you need to keep the userland and the=20
kernel code in sync, and this also goes for metadata structures. After=20
the userland does "label", it usually (except for "clean") does not=20
touch the metadata - from there on it's all kernel.
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