Add zpool_layout command

The zpool_layout command is designed to automatically scan the
udev /dev/disk/by-path directory and generate a /etc/zfs/zdev.conf
file.  It does this by enumerating the disks attached to the
specified buses/ports and sequentially mapping them to short
<channel><rank> names in /dev/disk/zpool/.  This tool should only
be run after all the available disks have been discovered.  And
the resulting config file does not need to be regenerated unless
your backend configuration changes.

cmd/Makefile.am

@@ -1 +1 @@
-SUBDIRS = zfs zpool zpool_id zdb zinject ztest
+SUBDIRS = zfs zpool zpool_id zpool_layout zdb zinject ztest

cmd/zpool_layout/Makefile.am

@@ -0,0 +1 @@
+dist_bin_SCRIPTS = zpool_layout

cmd/zpool_layout/zpool_layout

@@ -0,0 +1,120 @@
+#!/bin/bash
+#
+# Set BUSES and PORTS to match the topology of your system.  As each
+# port is enumerated it will be assigned the next channel name.  The
+# current script enumerates each port on a bus before moving on to
+# enumerate the next bus.
+#
+CONFIG=${CONFIG:-/etc/zfs/zdev.conf}
+BUSES=( 01 02 03 )
+PORTS=( 4 0 )
+CHANNELS=( A B C D E F G H I J K L M N O P Q R S T U V W X Y Z )
+TRIGGER=
+
+usage() {
+	cat << EOF
+Usage: zpool_layout [-th] [-c file] [-b buses] [-p ports] [-n channels]
+  -c    Alternate config file [default=/etc/zfs/zdev.conf]
+  -b    Enumerate buses [default="01 02 03"]
+  -p    Enumerate ports [default="4 0"]
+  -n    Channel names [default="A..Z"]
+  -t    Trigger and wait for udev to settle [default=no]
+  -h    Show this message
+EOF
+	exit 0
+}
+
+while getopts 'c:b:p:n:th' OPTION; do
+	case ${OPTION} in
+	c)
+		CONFIG=${OPTARG}
+		;;
+	b)
+		BUSES=(${OPTARG})
+		;;
+	p)
+		PORTS=(${OPTARG})
+		;;
+	n)
+		CHANNELS=(${OPTARG})
+		;;
+	t)
+		TRIGGER=1
+		;;
+	h)
+		usage
+		;;
+	esac
+done
+
+# Save stdout as fd #8, then redirect stdout to the config file.
+exec 8>&1
+exec >${CONFIG}
+pushd /dev/disk/by-path >/dev/null
+
+# Generate comment header.
+echo "#"
+echo "# Custom /dev/disk/by-path to /dev/disk/zpool mapping, "
+echo "# based of the following physical cable layout."
+echo "#"
+
+# Generate host port layout table for comment header.
+echo "# ------------------ Host Port Layout ---------------------"
+echo -n "#          "
+for (( i=0; i<${#BUSES[*]}; i++ )); do
+	printf "%-8d" ${BUSES[$i]}
+done
+echo
+
+for (( i=0, k=0; i<${#PORTS[*]}; i++ )); do
+	printf "# Port %-2d  " ${PORTS[$i]}
+
+	for (( j=0; j<${#BUSES[*]}; j++, k++ )); do
+		let k=$j*${#PORTS[*]}+$i
+		printf "%-8s" ${CHANNELS[$k]}
+	done
+	echo
+done
+echo "#"
+
+# Generate channel/disk layout table for comment header.
+echo "# ----------------- Channel/Disk Layout -------------------"
+echo "# Channel  Disks"
+for (( i=0, k=0; i<${#BUSES[*]}; i++ )); do
+	for (( j=0; j<${#PORTS[*]}; j++, k++ )); do
+		printf "# %-9s" ${CHANNELS[$k]}
+		ls *:${BUSES[$i]}:*:${PORTS[$j]}* 2>/dev/null | \
+			cut -f7 -d'-' | sort -n | tr '\n' ','
+		echo
+	done
+done
+echo "#"
+
+# Generate mapping from <channel><rank> to by-path name.
+TMP_FILE=`mktemp`
+AWK=${AWK:-/bin/awk}
+
+for (( i=0, k=0; i<${#BUSES[*]}; i++ )); do
+	for (( j=0; j<${#PORTS[*]}; j++, k++ )); do
+		ls *:${BUSES[$i]}:*:${PORTS[$j]}* 2>/dev/null | \
+			sort -n -k7 -t'-'>${TMP_FILE}
+
+		echo
+		echo -n "# Channel ${CHANNELS[$k]}, "
+		echo "Bus ${BUSES[$i]}, Port ${PORTS[$j]}"
+		${AWK} -F '-' -v ch="${CHANNELS[$k]}" \
+			'{print ch$7 "\t" $0 }' ${TMP_FILE}
+	done
+done
+
+# Restore stdout from fd #8 and close fd #8.
+exec 1>&8 8>&-
+rm -f ${TMP_FILE}
+popd >/dev/null
+
+if [ ${TRIGGER} ]; then
+	udevadm trigger
+	udevadm settle
+fi
+
+exit 0

configure.ac

@@ -74,6 +74,7 @@ AC_CONFIG_FILES([
 	cmd/zinject/Makefile
 	cmd/zpool/Makefile
 	cmd/zpool_id/Makefile
+	cmd/zpool_layout/Makefile
 	cmd/ztest/Makefile
 	module/Makefile
 	module/avl/Makefile