[Qemu-devel] Re: [PATCH 0/8] Basic device state visualization

[Avi Kivity]

On 05/14/2010 04:20 PM, Jan Kiszka wrote:
> While recently fixing the SCSI reset issues, I once again had the need
> for displaying the state of involved devices. So far the common approach
> is to attach gdb to qemu (or even inject some printf). But that time I
> hacked up a 30-minute patch to dump the vmstate of any (fully converted)
> qdev device.
>    

Wonderful! may even motivate some more qmp conversions.

> This series now lays the ground for more sophisticated visulization. It
> adds the monitor command 'device_show<qdev-path>', freezes the vmstate
> of the addressed device, sticks it into a QMP dict, and either transmit
> this via QMP or pretty-prints it on a monitor console. Some example:
>
> (qemu) device_show /i440FX-pcihost/pci.0/piix3-usb-uhci
> dev: piix3-usb-uhci, id ""
>    dev.
>      version_id:         00000002
>      config:             a0 7d d1 00 00 00 00 00 - b0 7e d1 00 00 00 00 00
>                          ...
>      irq_state:          00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00
>    num_ports_vmstate:    02
>    ports[00].
>        ctrl:             0083
>    ports[01].
>        ctrl:             0080
>    cmd:                  00c1
>    status:               0000
>    intr:                 0000
>    frnum:                0077
>    fl_base_addr:         0fffc000
>    sof_timing:           40
>    status2:              00
>    frame_timer:          0000000000cb2bd0
>
> Basically, this is the level of support I recently saw in a
> demonstration of some commercial simulator as well. We are just lacking
> support for the yet unconverted devices. And I think we can even do
> better on the long term, e.g. by annotating state variables that contain
> flags, or by pretty-printing buffers like the PCI config space, or...
>
>    

Will be interesting to pass these annotations via qmp as well.

> Let's give this a start, I bet it will be helpful while adding complex
> device models like AHCI or EHCI. Looking forward to feedback!
>    

I'd like to see qmp command documentation for this.

--
Do not meddle in the internals of kernels, for they are subtle and quick to 
panic.