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-kdump/module-setup.sh

@@ -0,0 +1,99 @@
+#!/bin/bash
+#
+# Copyright IBM Corp. 2023
+#
+# s390-tools is free software; you can redistribute it and/or modify
+# it under the terms of the MIT license. See LICENSE for details.
+#
+#
+# 95zdev-kdump/module_setup.sh
+#   This module installs configuration files (udev rules and modprobe.conf
+#   files) required to enable the kdump target on s390.
+#
+
+# called by dracut
+check() {
+    local _arch=${DRACUT_ARCH:-$(uname -m)}
+
+    # Ensure that we're running on s390
+    [ "$_arch" = "s390" -o "$_arch" = "s390x" ] || return 1
+
+    source "$moddir/../95zdev/zdev-lib.sh"
+
+    # Ensure this module is only included when building kdump initrd
+    is_kdump || return 1
+
+    # Ensure that required tools are available
+    require_binaries chzdev || return 1
+
+    return 0
+}
+
+# called by dracut
+depends() {
+    return 0
+}
+
+# called by dracut
+installkernel() {
+    # Add modules for all device types supported by chzdev (required for
+    # auto-configuration)
+    instmods ctcm lcs qeth qeth_l2 qeth_l3 dasd_mod dasd_eckd_mod dasd_fba_mod \
+             dasd_diag_mod zfcp
+}
+
+# called by dracut
+install() {
+    local _tempfile
+
+    # Obtain kdump target device configuration
+
+    _tempfile=$(mktemp --tmpdir dracut-zdev.XXXXXX)
+
+    # work with systems that are not based on chzdev persistent config
+    local _configuration="--active"
+    # disable zfcp auto LUN scan to prevent OOM situations on systems with
+    # many zFCP LUNs
+    inst_dir /etc/modprobe.d
+    chzdev zfcp --type "allow_lun_scan=0" --persistent \
+           --base "/etc=$initdir/etc" --yes --quiet --no-root-update \
+           --force >/dev/null
+    # drop /etc/zfcp.conf from dracut module 95zfcp
+    echo "rd.zfcp.conf=0" > "$initdir/etc/cmdline.d/00-no-zfcp-conf.conf"
+    # => only activate individual zfcp paths found as required below
+
+    function check_zdev() {
+        local _dev=$1
+        local _devsysfs _bdevpath
+        _devsysfs=$(
+            cd -P /sys/dev/block/"$_dev" && echo "$PWD"
+                 )
+        _bdevpath=/dev/${_devsysfs##*/}
+        # do not export device type information potentially unknown on import
+        chzdev --export - "$_configuration" --by-node "$_bdevpath" --quiet \
+               2>/dev/null >> "$_tempfile"
+    }
+    for_each_host_dev_and_slaves_all check_zdev
+    sed -i -e 's/^\[active /\[persistent /' "$_tempfile"
+
+    # Apply via --import to prevent other devices from being configured
+    chzdev --import "$_tempfile" --persistent --base "/etc=$initdir/etc" \
+           --yes --quiet --no-root-update --force >/dev/null
+
+    rm -f "$_tempfile"
+
+    # these are purely generated udev rules so we have to glob expand
+    # within $initdir and strip the $initdir prefix for mark_hostonly
+    local -a _array
+    local _nullglob=$(shopt -p nullglob)
+    shopt -u nullglob
+    readarray -t _array < \
+	      <(ls -1 $initdir/etc/udev/rules.d/41-*.rules 2> /dev/null)
+    [[ ${#_array[@]} -gt 0 ]] && mark_hostonly "${_array[@]#$initdir}"
+    readarray -t _array < \
+	      <(ls -1 $initdir/etc/modprobe.d/s390x-*.conf 2> /dev/null)
+    [[ ${#_array[@]} -gt 0 ]] && mark_hostonly "${_array[@]#$initdir}"
+    $_nullglob
+
+    return 0
+}

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
 

zdev/dracut/95zdev/zdev-lib.sh

@@ -0,0 +1,24 @@
+#
+# Copyright IBM Corp. 2023
+#
+# s390-tools is free software; you can redistribute it and/or modify
+# it under the terms of the MIT license. See LICENSE for details.
+#
+#
+# 95zdev/zdev-lib.sh
+#   Common shell library functionality for 95zdev and 95zdev-kdump.
+#
+
+is_kdump() {
+    # https://src.fedoraproject.org/rpms/kexec-tools/c/4eedcae5e1540690a3761857fe2e692774c44960
+    # https://src.fedoraproject.org/rpms/kexec-tools/blob/rawhide/f/mkdumprd
+    # https://src.fedoraproject.org/rpms/kexec-tools/blob/rawhide/f/dracut-module-setup.sh
+    if [[ $hostonly && "$hostonly_mode" == "strict" && -n "$IN_KDUMP" ]]; then
+        return 0
+    fi
+    # https://github.com/openSUSE/kdump/blob/master/dracut/module-setup.sh
+    if [[ " $dracutmodules $add_dracutmodules $force_add_dracutmodules " == *\ kdump\ * ]]; then
+        return 0
+    fi
+    return 1
+}

zdev/dracut/Makefile

@@ -2,6 +2,7 @@
 include ../../common.mak
 
 ZDEVDIR := 95zdev
+ZDEVKDUMPDIR := 95zdev-kdump
 
 # HAVE_DRACUT
 #
@@ -19,5 +20,9 @@ install:
 	$(INSTALL) -m 755 -d $(DESTDIR)$(DRACUTMODDIR)/$(ZDEVDIR)
 	$(INSTALL) -m 755 $(ZDEVDIR)/module-setup.sh \
 		$(ZDEVDIR)/parse-zdev.sh \
+		$(ZDEVDIR)/zdev-lib.sh \
 		$(DESTDIR)$(DRACUTMODDIR)/$(ZDEVDIR)/
+	$(INSTALL) -m 755 -d $(DESTDIR)$(DRACUTMODDIR)/$(ZDEVKDUMPDIR)
+	$(INSTALL) -m 755 $(ZDEVKDUMPDIR)/module-setup.sh \
+		$(DESTDIR)$(DRACUTMODDIR)/$(ZDEVKDUMPDIR)/
 endif