Re: [win-pv-devel] XenBus_AddWatch

[hanji unit <hanjiunit@gmail.com>]

Yea, I debugged through Harper's code and it seems like the error
response is coming from XenStore on Dom0. Ive been looking at it, and
OXenStored is running on Dom0. Of all the languages possible, they
decided to write xenstore in OCaml. I am not very good at OCaml and
dont know anyone that is, so I could work with someone to help them
fix this bug if there is interest.

I cannot watch a xenstore node, even when the DomU that I'm watching
from owns the node and allows full access to everyone else that wants
to access the node. Permissions are "bU" where U is the DomID of the
DomU doing the watching.

Is there any requirement for consistency of programming languages and
use of common languages across the different subprojects in Xen?

On Tue, Jan 6, 2015 at 5:34 AM, Paul Durrant <Paul.Durrant@citrix.com> wrote:
>> -----Original Message-----
>> From: win-pv-devel-bounces@lists.xenproject.org [mailto:win-pv-devel-
>> bounces@lists.xenproject.org] On Behalf Of hanji unit
>> Sent: 31 December 2014 15:15
>> To: win-pv-devel@lists.xenproject.org; xen-devel@lists.xen.org
>> Subject: [win-pv-devel] XenBus_AddWatch
>>
>> Hello, I am calling XenBus_AddWatch API from a DomU guest in the
>> win-pvdrivers xenpci driver, and noticed that I am not able to watch
>> xenstore entries that are outside of the DomU's xenstore tree. For
>> example, the following call in
>> XenPci_EvtDeviceD0EntryPostInterruptsEnabled fails with response="EIO"
>> even if the xenstore permissions for Container and Container/DomU in
>> xenstore are both "b0":
>>
>> response = XenBus_AddWatch(xpdd, XN_BASE_GLOBAL,
>> "Container/DomU",
>> MyCallback, xpdd);
>>
>> However, the following call works and it watches a xenstore entry
>> relative to DomUs xenstore tree:
>>
>> response = XenBus_AddWatch(xpdd, XBT_NIL, "DomU", MyCallback, xpdd);
>>
>> Writing to an entry outside the DomUs tree is allowed if permissions are b0:
>>
>> result = XnWriteString(xpdd, XN_BASE_GLOBAL, "Container/DomU", buffer);
>>
>> It seems like DomUs should be allowed to watch xenstore entries
>> outside their trees. Is this a bug or is it by design?
>
> Hi,
>
>   The API you're referring to is part of James Harper's GPLPV drivers I believe, which I'm no expert on. I would imagine the API simply passes error codes back from xenstored though so you should probably check xenstored-access.log, although EIO does sound like an odd code to get back.
>
>   Paul
>
>>
>> Thanks.
>>
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