This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


Re: [Xen-devel] LTTng-Xen Buffer shared between the hypervisor and a dom

To: Mathieu Desnoyers <compudj@xxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] LTTng-Xen Buffer shared between the hypervisor and a dom0 process
From: Keir Fraser <keir@xxxxxxxxxxxxx>
Date: Sat, 10 Mar 2007 17:18:25 +0000
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
Delivery-date: Sat, 10 Mar 2007 09:17:47 -0800
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <20070310030230.GC9323@Krystal>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AcdjOBxzWzawA88rEduDAAAX8io7RQ==
Thread-topic: [Xen-devel] LTTng-Xen Buffer shared between the hypervisor and a dom0 process
User-agent: Microsoft-Entourage/
On 10/3/07 03:02, "Mathieu Desnoyers" <compudj@xxxxxxxxxxxxxxxxxx> wrote:

> I see your idea : the other way around would be to have lttctl-xen
> return an error if the buffers are actually mapped. It would however
> require some changes to the buffer scheme, as I support multiple
> start/stop tracing while keeping the same buffers and the same lttd-xen
> daemon. I would have to create a new ltt sub-hypercall to finalize the
> buffers, which would make lttd-xen write them to disk and exit.
> Controlling tracing from within a guest kernel or within the hypervisor
> would start to be a tricky business, as you would have to explicitely
> keep track of lttd-xen presence before freeing the buffers.

Are the buffer pages only ever shared with domain0? In that case we don't
need to worry about Xen holding a reference on the pages that would stop the
domain from ever being destroyed (since dom0 is never destroyed).

In which case I think you can just take an extra count_info reference in
Xen, which you drop on 'lttctl-xen -r'. You'll need an extra page flag so
that the IS_XEN_HEAP_FRAME case in free_domheap_pages() actually frees the
page rather than leaving that job for later.

 -- Keir

Xen-devel mailing list