Re: [Qemu-devel] Adding Disk-Level Introspection to QEMU

[Stefan Hajnoczi]

On Tue, Apr 23, 2013 at 7:12 PM, Wolfgang Richter <address@hidden> wrote:
> I'm interested in adding introspection of disk writes to QEMU for various
> applications and research potential.
>
> What I mean by introspection of disk writes is that, when enabled, each
> write
> passing through QEMU to backing storage would also be copied to an
> introspection channel for further analysis.
>
> I currently have an implementation piggy-backing on the tracing subsystem,
> but
> adding binary trace events breaks various assumptions about that subsystem
> (for
> example, the stderr backend would no longer be readable when tracing disk
> writes).
>
> I'd really like to someday have introspection in the QEMU mainline, and thus
> I'm wondering:
>
> (1) Should the tracing subsystem be extended to include binary events?
>
> or
>
> (2) Should a separate "introspection subsystem" be implemented?

The tracing subsystem is geared towards tracepoint instrumentation
rather than binary dumps.

Can you share some specific applications?

Eric's suggestion to use NBD makes sense to me.  The block-backup code
can be extended fairly easier using sync mode=none (do not perform a
background copy of the entire disk) and by disabling the bitmap
(essentially "tap" mode).

Stefan