zdev/dracut: fix kdump by only activating required devices

This prevents out-of-memory (OOM) situations in the kdump crashkernel
environment.

Please note that the new dracut module 95zdev-kdump and the new library
zdev-lib.sh need to be packaged into the same (core) (sub)package as
95zdev.

This patch introduces a new dracut module "zdev-kdump", which is used
instead of module "zdev" when building a kdump initrd:

1. Ignore all persistently configured block devices and disable zfcp auto
LUN scanning => minimize the number of SCSI devices enabled during kdump.

2. Do not rely on chzdev's persistent configuration => work with systems
that do not use chzdev for persistent device configuration.

The detection of kdump is based on strict hostonly mode and on $IN_KDUMP.
See also
https://src.fedoraproject.org/rpms/kexec-tools commit
4eedcae5e154 ("dracut-module-setup.sh: don't include multipath-hostonly")
and https://github.com/dracutdevs/dracut commits
35e86ac117ac ("Merge 90-multipath-hostonly and 90-multipath")
a695250ec7db ("Introduce tri-state hostonly mode")
and
https://src.fedoraproject.org/rpms/kexec-tools/blob/rawhide/f/mkdumprd#_17
https://src.fedoraproject.org/rpms/kexec-tools/blob/rawhide/f/dracut-module-setup.sh#_23.
The detection of kdump is also based on kdump_needed() in
https://github.com/openSUSE/kdump/blob/master/dracut/module-setup.sh.

Reviewed-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: Steffen Maier <maier@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

zdev/dracut/95zdev/module-setup.sh

@@ -19,6 +19,12 @@ check() {
     # Ensure that we're running on s390
     [ "$_arch" = "s390" -o "$_arch" = "s390x" ] || return 1
 
+    source "$moddir/zdev-lib.sh"
+
+    # Leave kdump device configuration to module zdev-kdump to
+    # ensure a minimal device footprint
+    is_kdump && return 1
+
     # Ensure that required tools are available
     require_binaries chzdev lszdev /lib/s390-tools/zdev_id || return 1