Re: [Qemu-devel] [PATCH 2/2] add some virtio-scsi trace events

[Paolo Bonzini <pbonzini@redhat.com>]

Il 29/08/2013 16:18, Laszlo Ersek ha scritto:
> On 08/29/13 15:59, Paolo Bonzini wrote:
>> Il 29/08/2013 15:37, Laszlo Ersek ha scritto:
>>> The events that log a hexdump of the cdb and the sense buffer are disabled
>>> by default, because they require more processing than a simple trace_XXX()
>>> function call.
>>>
>>> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
>>
>> trace_event_get_state doesn't work with the dtrace backend.  Can you
>> prepare v2 without those tracepoints?
> 
> (a) I was just following "docs/tracing.txt"; see the last section in
> there.
> 
> (b) If I kill those two events, this is what you get:
> 
> Incoming request:
> 
>   virtio_scsi_handle_cmd_enter vdev 0x7f1be4054468 vq 0x7f1be4054b60
>   virtio_scsi_pop_req req 0x7f1be5d77650
>   virtio_scsi_handle_cmd_exit vdev 0x7f1be4054468 vq 0x7f1be4054b60
> 
> This gives you the address of the request, so you can look up the
> corresponding completion. However you don't know the actual command
> (cdb) without "virtio_scsi_dump_cmd_req".

Yes, but you can see almost all of the cdb from scsi_req_parsed and
scsi_req_parsed_lba.

>   virtio_scsi_command_complete_enter req 0x7f1be5d77650 status 2 resid 0
>   virtio_scsi_complete_req_enter req 0x7f1be5d77650
>   virtio_scsi_complete_req_exit req 0x7f1be5d77650
>   virtio_scsi_command_complete_exit req 0x7f1be5d77650 status 2 resid 0 sense_len 18
> 
> this will not tell you the virtio-scsi transport response code, or the
> actual sense data.

Same here: scsi_req_build_sense can give the sense data, and we could
add another tracepoint scsi_req_complete for the response code.

> (c) The way I submitted the series, the events in question are disabled
> in "trace-events". Check out the functions themselves: they are
> protected (ie. even the trace_event_get_state() calls are protected)
> with preprocessing directives. I did it this way because I call them in
> several places, and I wanted to keep the #if's centralized.

Tracing was supposed to remove the need for #if... :)

I'll try to salvage the patch.

Paolo