Xen devel - Jul 2008 - What''s XenBus and what''s its relation with XenStore

Hello, I''m a new comer to understanding Xen internals.

I want to know what is XenBus.
I wonder where can I find materials explaining the internal of XenBus.
Does it relate to XenStore?
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Tom Creck, le Thu 10 Jul 2008 01:14:26 -0700, a écrit :
> Hello, I''m a new comer to understanding Xen internals.
> 
> I want to know what is XenBus.
> I wonder where can I find materials explaining the internal of XenBus.
> Does it relate to XenStore?
It''s the protocol domains use to talk with XenStore. See the
interface.pdf doc.

Samuel

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On Thursday 10 July 2008, Tom Creck wrote:
> Hello, I''m a new comer to understanding Xen internals.
>
> I want to know what is XenBus.
> I wonder where can I find materials explaining the internal of XenBus.
> Does it relate to XenStore?
Xenstore is a "registry"-like hierarchical store of domain
configuration data.
It''s used to do various stuff, including negotiating connections to
device
drivers at start-up time, asking a domain to adjust its memory footprint or 
shutdown, etc.  It''s not a static store of information - domains can
watch
for changes to it and respond accordingly.

Xenbus is a Linux interface to Xenstore.  This looks like a kind of
"bus" to
Linux, which can be "scanned" to reveal what virtual devices are
available.
It provides an API for paravirtualised drivers to receive notification and 
information from Xenstore and to write data back to it.

Cheers,
Mark

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On Fri, Jul 11, 2008 at 8:39 PM, Mark Williamson
<mark.williamson@cl.cam.ac.uk> wrote:
> On Thursday 10 July 2008, Tom Creck wrote:
>> Hello, I''m a new comer to understanding Xen internals.
>>
>> I want to know what is XenBus.
>> I wonder where can I find materials explaining the internal of XenBus.
>> Does it relate to XenStore?
>
> Xenstore is a "registry"-like hierarchical store of domain
configuration data.
> It''s used to do various stuff, including negotiating connections
to device
> drivers at start-up time, asking a domain to adjust its memory footprint or
> shutdown, etc.  It''s not a static store of information - domains
can watch
> for changes to it and respond accordingly.
>
> Xenbus is a Linux interface to Xenstore.  This looks like a kind of
"bus" to
> Linux, which can be "scanned" to reveal what virtual devices are
available.
> It provides an API for paravirtualised drivers to receive notification and
> information from Xenstore and to write data back to it.
Can we say that (XEN bus + Xenstore) is an alternative way to ( XEND +
xm ) to find the information regarding the virtulised XEN environment.

>
> Cheers,
> Mark
>
> --
> Push Me Pull You - Distributed SCM tool
(http://www.cl.cam.ac.uk/~maw48/pmpu/)
>
> _______________________________________________
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>
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> > Xenstore is a "registry"-like hierarchical store of domain
configuration
> > data. It''s used to do various stuff, including negotiating
connections to
> > device drivers at start-up time, asking a domain to adjust its memory
> > footprint or shutdown, etc.  It''s not a static store of
information -
> > domains can watch for changes to it and respond accordingly.
> >
> > Xenbus is a Linux interface to Xenstore.  This looks like a kind of
"bus"
> > to Linux, which can be "scanned" to reveal what virtual
devices are
> > available. It provides an API for paravirtualised drivers to receive
> > notification and information from Xenstore and to write data back to
it.
>
> Can we say that (XEN bus + Xenstore) is an alternative way to ( XEND +
> xm ) to find the information regarding the virtulised XEN environment.
That''s part of it.

Xenstore is the way Xend configures domains and communicates with them once 
they''re running.  It''s a central place for co-ordinating
operations involving
domains, getting information from them and asking them to do things.

The tools, the backend drivers in dom0 and the domUs themselves use Xenstore 
to share configuration information.

If you want to access this information, you could indeed get it out of 
Xenstore instead of using xm / xend.

There are some command-line tools (xenstore-*) which can be useful for 
exploring Xenstore yourself.  There''s also a PyQt app called xsview,
which
might be useful (although I wouldn''t particularly recommend editing
Xenstore
using it unless you''re sure know what you''re doing - or if
you''re using a
test system, that is).

Cheers,
Mark

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