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Re: [libvirt] [PATCH 1/5] S390: Documentation for CCW address type



On Thu, Feb 07, 2013 at 05:16:04PM +0100, Viktor Mihajlovski wrote:
> On 02/07/2013 04:02 PM, Daniel P. Berrange wrote:
> >
> >Can you explaiin the semantics of the different components
> >in this device address ? WIth PCI addresses there are 4
> >colon-separated numbers a:b:c:d, which we explicitly
> >separate in the XML
> >
> >   <address type="pci" domain="a" bus="b" device="c" function="d"/>
> >
> >Unless there's a compelling reason not to, I think CCW
> >address XML ought to be similar, and use decimal notication
> >for each part, rather than hex, or at least require an
> >explicit 0x for hex. eg
> >
> >   <address type="ccw" xxxx="254" yyyy="0" zzzz="1234" />
> >   <address type="ccw" xxxx="0xfe" yyyy="0" zzzz="1234" />
> >
> >Daniel
> >
> Thanks for taking a look. To be true my initial version
> was following the PCI example with individual attributes.
> The s390 folks I've talked to didn't like it too much,
> finding it unwieldy.

I can understand that, but the livirt XML configuration
schemas aren't intended to be user friendly - if they
were, we wouldn't have used XML at all :-P The XML is
all about getting a clear, canonical representation of
data. Fully normalizing data by splitting up compound
strings into separate attributes is an important part
of good practice for XML design. By using separate
attrbiutes, it allows applications to directly extract
individual pieces of information, without having to then
write further parsers to decode them.

So using separate attributes for each part of the CCW  address
is the right thing from libvirt XML POV.

Applications built on top of libvirt though, should be free to
present them in the encoded format "x.y.z" if they think it is
more user friendly.

> CCW addresses are much more visible (and relevant) to a Linux
> admin on s390 than usually PCI addresses on other systems.
> In fact on that platform they are more ubiquitous than
> say IPv6 addresses which by power of convention are written
> in a compact hex notation.


Daniel
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