------- Comment From [email protected] 2016-07-13 11:52 EDT-------
Hmm, just one hour ago the s390-tools maintainer submitted a patch for the 
manpage of cio_ignore  to clarify that the example command "cio_ignore -u -k" 
modifies(!) the current cio_ignore blacklist.
It was not obvious until today, that it really modifies something!

What does it mean:
1. Under z/VM, if somebody had invoked "cio_ignore -u -k" via installation of 
kdump-tools, performs no reboot AND attaches additional CCW devices, they will 
not show up in the channel subsystem (e.g. via lscss) until they are 
unblacklisted (e.g. via cio_ignore -r <busid>)
2. Similar for LPAR, if you define additional CCW devices via dynamic I/O 
configuration change in HCD.
3. If someone performs a "cio_ignore -p" after invoking "cio_ignore -u -k" 
(e.g. via installation of kdump-tools), the change becomes effective and 
visible also for existing unused devices, and all unused CCW devices are 
blacklisted and no more visible.
4. After a reboot, the cio_ignore blacklist is concurrent to what has been 
specified via kernel parameter line. (Which means: Everything is fine again.)

My recommendation:
1. Go ahead with the actual implementation as of today, since it is worth to 
have a kdump when required, even with the above misbehaviour (which can be 
worked around).
2. When a new version of cio_ignore (within s390-tools) is available, you 
should pick up this new s390-tools version and also fix the postinst script in 
kdump-tools package picking by adjusting the cio_ignore parameters.

We will open a new bug to fix the postinst script again, when an updated
version of s390-tools is available.

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https://bugs.launchpad.net/bugs/1570775

Title:
  makekdump should re-exec with cio_ignore on s390x

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