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Date:   Tue, 10 Apr 2018 10:55:40 +0200
From:   Cornelia Huck <cohuck@redhat.com>
To:     Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
Cc:     linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org,
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Subject: Re: [PATCH 4/4] vfio: ccw: add traceponits for interesting error
 paths
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On Tue, 10 Apr 2018 10:16:39 +0800
Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com> wrote:

>   Does the following effect make sense?
> 
> # tracer: nop
> #
> #                              _-----=> irqs-off
> #                             / _----=> need-resched
> #                            | / _---=> hardirq/softirq
> #                            || / _--=> preempt-depth
> #                            ||| /     delay
> #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
> #              | |       |   ||||       |         |
>  qemu-system-s39-4252  [006] ....   231.457214: vfio_ccw_cp_prefetch: schid=0.0.013f errno=0
>  qemu-system-s39-4252  [006] ....   231.457222: vfio_ccw_fsm_io_helper: schid=0.0.013f errno=0
>  qemu-system-s39-4252  [006] ....   231.457223: vfio_ccw_io_fctl: schid=0.0.013f fctl=4 errno=0
>   ... ...

I would likely find this useful for following a code path and making
sure the right things are called.

We certainly want error conditions traced as well (although the code
has been working too well for me to trigger that easily :)