Re: Minidisk support (was: Installation Question)
On 2009-12-15, Stephen Powell wrote:
> OK, so if all three drivers support minidisks, then what is Debian
> bug report 447755 all about? The issue here is the *format* of the
> minidisk. A DASD device, be it a dedicated device or a minidisk,
> can have one of four formats under Linux for s390: cdl, ldl, CMS
> non-reserved, and CMS reserved. The FBA driver supports two of the
> four formats: CMS non-reserved and CMS reserved. The DIAG driver
> supports three of the four formats: ldl, CMS non-reserved, and
> CMS reserved. The ECKD driver supports all four formats.
I need to make one further clarification. The DIAG driver (dasd_diag_mod)
really doesn't *take the place* of the basic driver for the underlying dasd
type (dasd_fba_mod or dasd_eckd_mod, depending on whether the device is
an FBA device or a CKD device). Rather it works *with* the basic driver
for the underlying dasd type. The basic driver (dasd_fba_mod or
dasd_eckd_mod) makes some initial tests of the device to see if it
qualifies for use by the DIAG driver. For example: Are we running
in a virtual machine under z/VM? Is it a supported
device type? Is it a supported format? Does it have a valid block size?
etc. Once the basic driver is satisfied that the device qualifies,
it hands it off to the DIAG driver. That means two things: (1) the
initial RAM file system must contain both drivers, and both drivers
must be loaded from the initial RAM file system, and (2) the set of
formats supported by the DIAG driver *for a particular device* is the
intersection of sets of the set of formats supported by the DIAG driver
and the set of formats supported by the basic driver for that type of
device. For example, when using the DIAG driver with an FBA device,
one can only use the CMS non-reserved or the CMS reserved format. The
ldl format cannot be used by the DIAG driver for this type of device,
even though the DIAG driver supports the ldl format, because the underlying
basic driver, the FBA driver in this case, does not support the ldl format.
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