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

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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On Tue, Nov 06, 2018 at 09:14:57AM +0000, Richard W.M. Jones
wrote:
> This link shows how to combine delay and error filters together:
> 
>   https://rwmj.wordpress.com/2018/11/04/nbd-graphical-viewer/
Oops, that's in a forthcoming blog post not this one.  Not enough
caffeine this morning.

Combining the filters is easy however:

  nbdkit --filter=error --filter=delay \
         memory size=$size \
         rdelay=$delay wdelay=$delay \
         error-rate=100% error-file=/tmp/error

Then touching /tmp/error will inject errors, and removing /tmp/error
will stop injecting errors.

The documentation says you should be able to write error-rate=1
instead of error-rate=100%, but in fact that was broken until
recently, and fixed in:

 
https://github.com/libguestfs/nbdkit/commit/ee2d3b4fea6d4b7618262f85f882374c23674b4a

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-p2v converts physical machines to virtual machines.  Boot with a
live CD or over the network (PXE) and turn machines into KVM guests.
http://libguestfs.org/virt-v2v

On Tue, Nov 06, 2018 at 09:43:06AM +0000, Richard W.M. Jones
wrote:
> On Tue, Nov 06, 2018 at 09:14:57AM +0000, Richard W.M. Jones wrote:
> > This link shows how to combine delay and error filters together:
> > 
> >   https://rwmj.wordpress.com/2018/11/04/nbd-graphical-viewer/
> 
> Oops, that's in a forthcoming blog post not this one.  Not enough
> caffeine this morning.
Up now:

https://rwmj.wordpress.com/2018/11/06/nbd-graphical-viewer-raid-5-edition/

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
libguestfs lets you edit virtual machines.  Supports shell scripting,
bindings from many languages.  http://libguestfs.org