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Re: [Xen-devel] Re: hvmloader/xenbus.c: How to modify or add a key-value pair in xenstore

2011/8/16 Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
(please do not top post)

On Tue, 2011-08-16 at 16:32 +0100, Bei Guan wrote:
> Many thanks to all of you.
> I see there are some functions in mini-os/xenbus/xenbus.c, such as
> xenbus_write() and xenbus_rm(). All of them seem to change the keys
> and values in xenstore. I have tried these functions and found that
> they have no effect on the keys and values in xenstore.

Tried in the context of mini-os or tried by ripping them out and into
I tried in the context of mini-os.
I use the test function in mini-os/xenbus/xenbus.c, such as do_write_test("device/vif/0/flibble", "flobble"). Also I comment out the do_rm_test("device/vif/0/flibble").
When the mini-os starts to run, I use the xenstore-ls to see the keys and values, but I cannot find the key /local/domain/<domId>/device/vif/0/flibble and its value.


>  So, do these functions can really work?

mini-os's frontend drivers presumably use them so I'd expect so.
Yes, I saw the frontend drivers use these functions. But, it seems all the keys are created by dom0 or other tools instead of mini-os itself. 
When I change the key name in the front driver that is going to be create by method xenbus_printf(), such as change from
    err = xenbus_printf(xbt, nodename, "ring-ref","%u", dev->ring_ref);
    err = xenbus_printf(xbt, nodename, "ring-ref-0","%u", dev->ring_ref);
I cannot find the ring-ref-0 in xenstore, when mini-os is running.


>  What special things need I to do to make them work?

Which specific path are you trying to write?
I am not sure if the domain can operate any keys and values in /local/domain/<Id of this domain>/, such as change "name" to another one, add a new key-value /local/domain/<Id of this domain>/new-key = new-value.

Bei Gua

> Thanks,
> Bei Guan
> 2011/8/16 Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
>         On Mon, 2011-08-15 at 16:20 +0100, Bei Guan wrote:
>         > Maybe the VM doesn't have the permission to write its own
>         key in
>         > Xenstore.
>         It is quite common for keys in xenstore to be ro for the guest
>         (only the
>         backend or toolstack domain can write to them).
>         Ian.

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