Libguestfs - Nov 2018 - Re: [Qemu-devel] How to emulate block I/O timeout on qemu side?

On 11/2/18 3:11 AM, Dongli Zhang wrote:
> Hi,
> 
> Is there any way to emulate I/O timeout on qemu side (not fault injection
in VM
> kernel) without modifying qemu source code?
You may be interested in Rich's work on nbdkit.  If you don't mind the 
overhead of the host connecting through NBD, then you can use nbdkit's 
delay and fault-injection filters for inserting delays or even 
run-time-controllable failures to investigate how the guest reacts to 
those situations
> 
> For instance, I would like to observe/study/debug the I/O timeout handling
of
> nvme, scsi, virtio-blk (not supported) of VM kernel.
> 
> Is there a way to trigger this on purpose on qemu side?
> 
> Thank you very much!
> 
> Dongli Zhang
> 
> 
-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

On 11/06/2018 01:49 AM, Eric Blake wrote:
> On 11/2/18 3:11 AM, Dongli Zhang wrote:
>> Hi,
>>
>> Is there any way to emulate I/O timeout on qemu side (not fault
injection in VM
>> kernel) without modifying qemu source code?
> 
> You may be interested in Rich's work on nbdkit.  If you don't mind
the overhead
> of the host connecting through NBD, then you can use nbdkit's delay and
> fault-injection filters for inserting delays or even run-time-controllable
> failures to investigate how the guest reacts to those situations
Thank you all very much for the suggestions. I will take a look on nbdkit.

So far I am reproducing the issue with NFS (by shutdown the link to NFS where
the image is placed on purpose) but it did not work well.
> 
>>
>> For instance, I would like to observe/study/debug the I/O timeout
handling of
>> nvme, scsi, virtio-blk (not supported) of VM kernel.
>>
>> Is there a way to trigger this on purpose on qemu side?
>>
>> Thank you very much!
>>
>> Dongli Zhang
>>
>>
> 
Dongli Zhang

On Tue, Nov 06, 2018 at 02:17:46PM +0800, Dongli Zhang
wrote:
> On 11/06/2018 01:49 AM, Eric Blake wrote:
> > On 11/2/18 3:11 AM, Dongli Zhang wrote:
> >> Hi,
> >>
> >> Is there any way to emulate I/O timeout on qemu side (not fault
> >> injection in VM kernel) without modifying qemu source code?
> >
> > You may be interested in Rich's work on nbdkit.  If you don't
mind
> > the overhead of the host connecting through NBD, then you can use
> > nbdkit's delay and fault-injection filters for inserting delays or
> > even run-time-controllable failures to investigate how the guest
> > reacts to those situations
> >
> Thank you all very much for the suggestions. I will take a look on nbdkit.
These links should help:

 
https://rwmj.wordpress.com/2018/09/04/nbdkit-for-loopback-pt-2-injecting-errors/
  https://rwmj.wordpress.com/2018/09/06/nbdkit-for-loopback-pt-7-a-slow-disk/

This link shows how to combine delay and error filters together:

  https://rwmj.wordpress.com/2018/11/04/nbd-graphical-viewer/

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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