chreipl-fcp-mpath: test if event subject represents re-IPL target

Now that we know that the system uses s390x IPL and the current re-IPL
target is from FCP, whenever we get a udev event that indicates a path
state changed, we have to figure out whether it affects the path that is
currently set as re-IPL target, or goes to the same volume (so we might
use it as alternative re-IPL path).

Add a new helper `chreipl-fcp-mpath-is-ipl-tgt` for this task.

Based on the information provided in
/sys/firmware/reipl/fcp/{device,wwpn,lun} it figures out whether the
current event subject has the same triplet <Dev-Bus-ID>:<WWPN>:<LUN> (in
T10 SCSI: I_T_L nexus), or whether one of its parts (in case of
dm-multipath) has.

If true, we know for sure, that we deal with an event affecting the
current re-IPL setting, and continue.

When accessing the re-IPL firmware information a lock is taken via the
`flock` utility (from util-linux). This is done so concurrent changes
from the toolset, that are added in a later commit, don't result in
inconsistent reads.

Reviewed-by: Steffen Maier <maier@linux.ibm.com>
Signed-off-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

chreipl-fcp-mpath/.gitignore

@@ -1,3 +1,4 @@
 # build artifacts
 /chreipl-fcp-mpath-common.sh
+/chreipl-fcp-mpath-is-ipl-tgt
 /chreipl-fcp-mpath-is-reipl-zfcp

chreipl-fcp-mpath/Makefile

@@ -44,6 +44,7 @@ clean: chreipl-fcp-mpath-clean
 CHREIPL_FCP_MPATH_COMMON	:=					\
 	chreipl-fcp-mpath-common.sh
 CHREIPL_FCP_MPATH_UDEV_HELPER	:=					\
+	chreipl-fcp-mpath-is-ipl-tgt					\
 	chreipl-fcp-mpath-is-reipl-zfcp
 
 $(CHREIPL_FCP_MPATH_UDEV_HELPER) $(CHREIPL_FCP_MPATH_COMMON): $(MAKEFILE_LIST)

chreipl-fcp-mpath/chreipl-fcp-mpath-common.sh.in

@@ -7,10 +7,15 @@
 # Uses the following system-utilities (and shell-builtins):
 #   GNU coreutils:
 #     - mktemp
+#     - readlink
+#   util-linux:
+#     - flock
 
 # Makes use of udev event environment variables:
 #	SEQNUM
 
+# (1) expand failed globs to an empty string
+shopt -s nullglob
 # (1) don't overwrite existing files using redirects (e.g.: `>`)
 set -o noclobber
 
@@ -42,3 +47,164 @@ then
 else
 	unset tlg
 fi
+
+declare -gr FW_LOCK_FILE='@chreiplzfcpmp-fwlock-file@'
+
+declare -gA TRAP_EXIT_FN=()
+declare -gf trap_exit 1>/dev/null
+function trap_exit() {
+	local fn
+
+	for fn in "${TRAP_EXIT_FN[@]}"; do
+		"${fn}"
+	done
+
+	trap - EXIT
+}
+trap trap_exit EXIT
+
+# Output variables:
+#  firmware_unlock_shared() - call to unlock when finished with critical section
+#
+# XXX: `firmware_lock_*` can't be taken recursively
+function firmware_lock_shared() {
+	declare -g FIRMWARE_LOCK=""
+
+	# Open the file defined in ${FW_LOCK_FILE} for reading, and store the
+	# corresponding file descriptor in ${FIRMWARE_LOCK} (it doesn't matter
+	# whether this is a normal file or directory). This file descriptor
+	# will only be used for locking - not for actual I/O.
+	{ exec {FIRMWARE_LOCK}<"${FW_LOCK_FILE}"; } 2>/dev/null	|| return 1
+
+	declare -gf firmware_unlock_shared 1>/dev/null
+	function firmware_unlock_shared() {
+		if [ -v FIRMWARE_LOCK ]; then
+			# release file and implicitly the lock, if taken
+			exec {FIRMWARE_LOCK}<&-
+			unset FIRMWARE_LOCK
+		fi
+
+		unset "TRAP_EXIT_FN[firmware_unlock_shared]"
+	}
+	TRAP_EXIT_FN+=([firmware_unlock_shared]=firmware_unlock_shared)
+
+	flock --shared --timeout 5 "${FIRMWARE_LOCK}"		|| return 2
+
+	return 0
+}
+
+# Output variables:
+#  IPL_TYPE
+#  IPL_BUSID
+#  IPL_WWPN
+#  IPL_LUN
+function firmware_get_ipl_information() {
+	declare -g IPL_TYPE="" IPL_BUSID="" IPL_WWPN="" IPL_LUN=""
+
+	# Take lock so we don't see any intermediate state from other helpers
+	# running in parallel
+	firmware_lock_shared					|| return 5
+
+	{ read -r IPL_TYPE _ < /sys/firmware/reipl/reipl_type; } 2>/dev/null \
+								|| return 1
+	{ read -r IPL_BUSID _ < /sys/firmware/reipl/fcp/device; } 2>/dev/null \
+								|| return 2
+	{ read -r IPL_WWPN _ < /sys/firmware/reipl/fcp/wwpn; } 2>/dev/null \
+								|| return 3
+	{ read -r IPL_LUN _ < /sys/firmware/reipl/fcp/lun; } 2>/dev/null \
+								|| return 4
+
+	firmware_unlock_shared
+
+	# show read values in debug log if enabled
+	if '@DEBUG@'; then
+		declare -p IPL_TYPE IPL_BUSID IPL_WWPN IPL_LUN 1>&2
+	fi
+
+	return 0
+}
+
+# Input:
+#  1: absolute canonical path to the scsi device in sysfs, e.g.:
+#     /sys/devices/css0/0.0.0014/0.0.1700/host1/rport-1:0-0/target1:0:0/1:0:0:1075789848
+# Output variables:
+#  SDEV_LUN
+function sdev_get_lun() {
+	local sdev="${1}" sdev_lun_str
+	# bash uses `intmax_t` as width for integer variables, and glibc
+	# defines this either as `long int` on 64 bit systems, or
+	# `long long int` on other.
+	local -i sdev_lun=0 fcp_lun=0
+
+	sdev_lun_str="${sdev##*:}"
+	# e.g.: 1075789848
+	[[ "${sdev_lun_str}" == +([[:digit:]]) ]]		|| return 1
+	# "cast" to integer
+	sdev_lun="${sdev_lun_str}"
+
+	# convert the Linux integer LUN format to the hexadecimal 64 bit T10
+	# LUN representation format used by many s390x interfaces
+	(( fcp_lun = (((sdev_lun >> 0) & 0xffff) << 48)
+			| (((sdev_lun >> 16) & 0xffff) << 32)
+			| (((sdev_lun >> 32) & 0xffff) << 16)
+			| (((sdev_lun >> 48) & 0xffff) << 0) ))
+	# the '0x' prefix is part of the length
+	printf -v SDEV_LUN "%#018llx" "${fcp_lun}"
+
+	# show read values in debug log if enabled
+	if '@DEBUG@'; then
+		declare -p SDEV_LUN 1>&2
+	fi
+
+	return 0
+}
+
+# Input:
+#  1: path to the scsi device in sysfs, e.g.:
+#     /sys/devices/css0/0.0.0014/0.0.1700/host1/rport-1:0-0/target1:0:0/1:0:0:1075789848
+#     , or a symlink pointing to the scsi device, e.g.:
+#     /sys/class/block/sds/device
+# Output variables:
+#  SDEV_BUSID
+#  SDEV_WWPN
+#  SDEV_LUN
+function sdev_get_fcp_addressing() {
+	local sdev="${1}" fcp_lun rport rport_wwpn zfcp_dev
+
+	declare -g SDEV_BUSID="" SDEV_WWPN="" SDEV_LUN=""
+
+	sdev="$(readlink -se "${sdev}")"			|| return 1
+
+	# get the LUN for this SDEV
+	#
+	# sets ${SDEV_LUN}
+	sdev_get_lun "${sdev}"					|| return 2
+
+	# get the WWPN of the remote port this SDEV is attached to
+	printf -v rport "%s" "${sdev}"/../../fc_remote_ports/rport-*:*-*
+	# e.g.: /sys/devices/css0/0.0.0016/0.0.1740/host0/rport-0:0-1/fc_remote_ports/rport-0:0-1
+	[ "${rport}" != "" ]					|| return 3
+
+	# XXX: This works even if the rport is currently in a bad
+	#      state, so e.g. when it has just gone down because of a
+	#      cable pull.
+	{ read -r rport_wwpn _ < "${rport}"/port_name; } 2>/dev/null	\
+								|| return 4
+
+	# The Linux kernel doesn't guarantee the same format as in
+	# /sys/firmware/..., so make sure it is the one we expect.
+	[[ "${rport_wwpn}" =~ ^0x[[:xdigit:]]{1,16}$ ]]		|| return 5
+	# the '0x' prefix is part of the length
+	printf -v rport_wwpn "%#018llx" "${rport_wwpn}"
+
+	# get the Device Bus-ID of the device via which this SDEV is attached
+	zfcp_dev="$(readlink -se "${sdev}"/../../../..)"	|| return 6
+	# e.g.: /sys/devices/css0/0.0.0016/0.0.1740
+	zfcp_dev="${zfcp_dev##*/}"
+
+	# shellcheck disable=2034
+	SDEV_BUSID="${zfcp_dev}"
+	# shellcheck disable=2034
+	SDEV_WWPN="${rport_wwpn}"
+	return 0
+}

chreipl-fcp-mpath/chreipl-fcp-mpath-is-ipl-tgt.in

@@ -0,0 +1,56 @@
+#!/bin/bash
+# SPDX-License-Identifier: MIT
+#
+# chreipl-fcp-mpath: use multipath information to change FCP IPL target
+# (C) Copyright IBM Corp. 2021
+#
+# Uses the following system-utilities (and shell-builtins):
+#   Those necessary for sourced library:
+#     - chreipl-fcp-mpath-common.sh
+
+# Find out whether the device in udev event environment variable ${DEVPATH}
+# represents the device we want to re-IPL from. We do this by comparing
+# Device-Bus-ID/Target-WWPN/LUN of the individual SDEVs to the parameters set
+# in `/sys/firmware/reipl/fcp/`.
+#
+# Makes use of udev event environment variables:
+#	DM_UUID
+#	SUBSYSTEM
+#	DEVPATH
+
+# shellcheck disable=SC2034
+declare -gr debug_trace_tag=05iilt
+# shellcheck disable=SC1091
+source '@chreiplzfcpmp-lib@' || exit 127
+
+firmware_get_ipl_information					|| exit 1
+
+if [[ "${DM_UUID}" == mpath-* ]]; then
+	# Assume Multipath Device Mapper Device;
+	# e.g.: DEVPATH = /devices/virtual/block/dm-0
+	declare sdev
+
+	# depends on `nullglob` from `chreipl-fcp-mpath-common.sh`
+	for sdev in /sys/"${DEVPATH}"/slaves/sd*/device; do
+		sdev_get_fcp_addressing "${sdev}"		|| continue
+		[ "${SDEV_LUN}" = "${IPL_LUN}" ]		|| continue
+		[ "${SDEV_WWPN}" = "${IPL_WWPN}" ]		|| continue
+		[ "${SDEV_BUSID}" = "${IPL_BUSID}" ]		|| continue
+
+		exit 0
+	done
+	unset sdev
+
+elif [ "${SUBSYSTEM}" = block ]; then
+	# Assume SCSI Disk;
+	# e.g.: DEVPATH = /devices/css0/0.0.0014/0.0.1700/host0/rport-0:0-0/target0:0:0/0:0:0:1074806808/block/sds
+
+	sdev_get_fcp_addressing /sys/"${DEVPATH}"/device	|| exit 2
+	[ "${SDEV_LUN}" = "${IPL_LUN}" ]			|| exit 3
+	[ "${SDEV_WWPN}" = "${IPL_WWPN}" ]			|| exit 4
+	[ "${SDEV_BUSID}" = "${IPL_BUSID}" ]			|| exit 5
+
+	exit 0
+fi
+
+exit 6

chreipl-fcp-mpath/chreipl-fcp-mpath.mak

@@ -23,6 +23,13 @@ DEBUGOUTDIR	 = $(UDEVRUNDIR)
 INSTALL_EXEC	 = $(INSTALL) -g $(GROUP) -o $(OWNER) --preserve-timestamps
 INSTALL_DATA	 = $(INSTALL_EXEC) --mode=0644
 
+# file used to implement mutual exclusion when accessing firmware IPL info:
+#   - this should be something that is (practically) always available, so we
+#     dont have to worry about fallbacks or error-handling;
+#   - at the same time, it should not be used by anything else with flock(2) to
+#     hold a lock for long periods.
+chreiplzfcpmp-fwlock-file	 = /sys/firmware/reipl
+
 .DELETE_ON_ERROR:
 
 # export build-time definitions to the scripts/built-components
@@ -30,6 +37,7 @@ define chreiplzfcpmp-sed-buildvar-replace =
 tmpout=$$(mktemp -p ./ .make.tmp.XXXXXXXXXXXXXXXX) && {			\
 	$(SED) -E 							\
 		-e 's|@DEBUG@|$(if $(filter 1,$(D)),true,false)|g'	\
+		-e 's|@chreiplzfcpmp-fwlock-file@|$(chreiplzfcpmp-fwlock-file)|g' \
 		-e 's|@chreiplzfcpmp-lib@|$(CHREIPLZFCPMPDIR)/chreipl-fcp-mpath-common.sh|g' \
 		-e 's|@debugoutdir@|$(DEBUGOUTDIR)|g'			\
 		$(1) > $${tmpout}					\

chreipl-fcp-mpath/udev/rules.d/70-chreipl-fcp-mpath.rules

@@ -23,4 +23,34 @@ LABEL="chreipl_fcp_mpath_path_change"
 TEST!="/sys/firmware/ipl", GOTO="chreipl_fcp_mpath_end"
 PROGRAM!="chreipl-fcp-mpath-is-reipl-zfcp", GOTO="chreipl_fcp_mpath_end"
 
+# Consider the following scenarios.
+# Either:
+#
+# (A) We recognized a new SCSI Disk. This might represent:
+#     (a) the path we want to ReIPL from.
+#
+# Or:
+#
+# (B) We recognized a PATH_ event for a multipath device. This might represent:
+#     the path we want to ReIPL from:
+#         (a) went away;
+#         (b) came back online;
+#     an alternative path to the volume we want to ReIPL from:
+#         (c) went away;
+#         (d) came back online.
+
+# Test whether the affected device is, or contains, the current IPL target.
+#
+# This covers scenarios:
+#     (A) (a),
+#     (B) (a)/(b)/(c)/(d)
+PROGRAM!="chreipl-fcp-mpath-is-ipl-tgt",				\
+	ENV{CHREIPL_FCP_MPATH_IS_TGT}="false",				\
+	GOTO="chreipl_fcp_mpath_not_direct_match"
+ENV{CHREIPL_FCP_MPATH_IS_TGT}="true"
+
+# If the even subject is not a direct match (not the sdev that is the current
+# ReIPL target, and not a mpath device that contains the current ReIPL target)
+LABEL="chreipl_fcp_mpath_not_direct_match"
+
 LABEL="chreipl_fcp_mpath_end"