busybox-mdev: Support automatic mounting of block devices

Upon inserting a USB stick or similar device, mdev will run
an automounter script that mounts valid partitions on
/media/<device>. The script first checks /etc/fstab entries
so that mounting on UUID or LABEL or using custom mount options
is still possible. If /etc/fstab does not contain particular
mount options, the script will create (and remove) the mountpoint
automatically.
The script also supports full disk partitions (devices without
partition table).

The following environments can be set in /etc/default/mdev:
MDEV_AUTOMOUNT=n (Disables automounting completely)
MDEV_AUTOMOUNT_ROOT=/media (Change the mount root location)

Automatic mounting for a particular device can be disabled by
creating a file "/dev/<device>.nomount". This is helpful in
scripts that create partitions for example, and want to perform
specific actions which require the device to remain unmounted.

A more complex variation (using LABEL based mounts) on this script
has been in use in OpenPLi for many years now, and I've used this
one on many projects already, so it's about time to push this to
mainline.

(From OE-Core rev: 19073fb991b3e2d2304e55f94e30674adf375197)

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-core/busybox/busybox.inc

@@ -270,6 +270,7 @@ do_install () {
                        install -m 644 ${WORKDIR}/mdev.conf ${D}${sysconfdir}/mdev.conf
                        install -d ${D}${sysconfdir}/mdev
                        install -m 0755 ${WORKDIR}/find-touchscreen.sh ${D}${sysconfdir}/mdev
+                       install -m 0755 ${WORKDIR}/mdev-mount.sh ${D}${sysconfdir}/mdev
                fi
 	fi
 

meta/recipes-core/busybox/busybox_1.22.1.bb

@@ -20,6 +20,7 @@ SRC_URI = "http://www.busybox.net/downloads/busybox-${PV}.tar.bz2;name=tarball \
            file://busybox-syslog.default \
            file://mdev \
            file://mdev.conf \
+           file://mdev-mount.sh \
            file://umount.busybox \
            file://defconfig \
            file://busybox-syslog.service.in \

meta/recipes-core/busybox/busybox_git.bb

@@ -24,6 +24,7 @@ SRC_URI = "git://busybox.net/busybox.git \
            file://busybox-syslog.default \
            file://mdev \
            file://mdev.conf \
+           file://mdev-mount.sh \
            file://umount.busybox \
            file://defconfig \
            file://busybox-syslog.service.in \

meta/recipes-core/busybox/files/mdev-mount.sh

@@ -0,0 +1,63 @@
+#!/bin/sh
+MDEV_AUTOMOUNT=y
+MDEV_AUTOMOUNT_ROOT=/run/media
+[ -f /etc/default/mdev ] && . /etc/default/mdev
+if [ "${MDEV_AUTOMOUNT}" = "n" ] ; then
+	exit 0
+fi
+
+case "$ACTION" in
+	add|"")
+		ACTION="add"
+		# check if already mounted
+		if grep -q "^/dev/${MDEV} " /proc/mounts ; then
+			# Already mounted
+			exit 0
+		fi
+		DEVBASE=`expr substr $MDEV 1 3`
+		if [ "${DEVBASE}" == "mmc" ] ; then
+			DEVBASE=`expr substr $MDEV 1 7`
+		fi
+		# check for "please don't mount it" file
+		if [ -f "/dev/nomount.${DEVBASE}" ] ; then
+			# blocked
+			exit 0
+		fi
+		# check for full-disk partition
+		if [ "${DEVBASE}" == "${MDEV}" ] ; then
+			if [ -d /sys/block/${DEVBASE}/${DEVBASE}*1 ] ; then
+				# Partition detected, just quit
+				exit 0
+			fi
+			if [ ! -f /sys/block/${DEVBASE}/size ] ; then
+				# No size at all
+				exit 0
+			fi
+			if [ `cat /sys/block/${DEVBASE}/size` == 0 ] ; then
+				# empty device, bail out
+				exit 0
+			fi
+		fi
+		# first allow fstab to determine the mountpoint
+		if ! mount /dev/$MDEV > /dev/null 2>&1
+		then
+			MOUNTPOINT="${MDEV_AUTOMOUNT_ROOT}/$MDEV"
+			mkdir "$MOUNTPOINT"
+			mount -t auto /dev/$MDEV "$MOUNTPOINT"
+		fi
+		;;
+	remove)
+		MOUNTPOINT=`grep "^/dev/$MDEV\s" /proc/mounts | cut -d' ' -f 2`
+		if [ ! -z "$MOUNTPOINT" ]
+		then
+			umount "$MOUNTPOINT"
+			rmdir "$MOUNTPOINT"
+		else
+			umount /dev/$MDEV
+		fi
+		;;
+	*)
+		# Unexpected keyword
+		exit 1
+		;;
+esac

meta/recipes-core/busybox/files/mdev.conf

@@ -37,3 +37,6 @@ input/mice 0:0 0660
 input/mouse.* 0:0 0660
 
 tun[0-9]* 0:0 0660 =net/
+
+[hs]d[a-z][0-9]? 0:0 660 */etc/mdev/mdev-mount.sh
+mmcblk[0-9].* 0:0 660 */etc/mdev/mdev-mount.sh