Add "-media" autofs map, to access data on removable media, such as CD

drives or flash keys.  It can be enabled by uncommenting a single entry
in default /etc/auto_master.  It can also be easily modified to use
fuse-based filesystems instead of in-kernel ones.

There is still one deficiency - the mountpoints are permanent, they
don't disappear when user removes the media.  Fixing it needs some
autofs changes.

Differential Revision:	https://reviews.freebsd.org/D1210
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation

etc/auto_master

@@ -3,3 +3,6 @@
 # Automounter master map, see auto_master(5) for details.
 #
 /net		-hosts		-nobrowse,nosuid
+# When using the -media special map, make sure to edit devd.conf(5)
+# to move the call to "automount -c" out of the comments section.
+#/media		-media		-nosuid

etc/autofs/Makefile

@@ -1,6 +1,6 @@
 # $FreeBSD$
 
-FILES=		include_ldap special_hosts special_null
+FILES=		include_ldap special_hosts special_media special_null
 
 NO_OBJ=
 FILESDIR=	/etc/autofs

etc/autofs/special_media

@@ -0,0 +1,93 @@
+#!/bin/sh
+#
+# $FreeBSD$
+#
+
+# Print newline-separated list of devices available for mounting.
+# If there is a filesystem label - use it, otherwise use device name.
+print_available() {
+	local _fstype _fstype_and_label _label _p
+
+	for _p in ${providers}; do
+		_fstype_and_label="$(fstyp -l "/dev/${_p}" 2> /dev/null)"
+		if [ $? -ne 0 ]; then
+			# Ignore devices for which we were unable
+			# to determine filesystem type.
+			continue
+		fi
+
+		_fstype="${_fstype_and_label%% *}"
+		if [ "${_fstype}" != "${_fstype_and_label}" ]; then
+			_label="${_fstype_and_label#* }"
+			echo "${_label}"
+			continue
+		fi
+
+		echo "${_p}"
+	done
+}
+
+# Print a single map entry.
+print_one() {
+	local _fstype _fstype_and_label _label _key _p
+
+	_key="$1"
+
+	_fstype="$(fstyp "/dev/${_key}" 2> /dev/null)"
+	if [ $? -eq 0 ]; then
+		echo "-fstype=${_fstype},nosuid	:/dev/${_key}" 
+		return
+	fi
+
+	for _p in ${providers}; do
+		_fstype_and_label="$(fstyp -l "/dev/${_p}" 2> /dev/null)"
+		if [ $? -ne 0 ]; then
+			# Ignore devices for which we were unable
+			# to determine filesystem type.
+			continue
+		fi
+
+		_fstype="${_fstype_and_label%% *}"
+		if [ "${_fstype}" = "${_fstype_and_label}" ]; then
+			# No label, try another device.
+			continue
+		fi
+
+		_label="${_fstype_and_label#* }"
+		if [ "${_label}" != "${_key}" ]; then
+			# Labels don't match, try another device.
+			continue
+		fi
+
+		echo "-fstype=${_fstype},nosuid	:/dev/${_p}" 
+	done
+
+	# No matching device - don't print anything, autofs will handle it.
+}
+
+# Obtain a list of (geom-provider-name, access-count) pairs, turning this:
+#
+# z0xfffff80005085d00 [shape=hexagon,label="ada0\nr2w2e3\nerr#0\nsector=512\nstripe=0"];
+#
+# Into this:
+#
+# ada0 r2w2e3
+#
+# XXX: It would be easier to use kern.geom.conftxt instead, but it lacks
+#      access counts.
+pairs=$(sysctl kern.geom.confdot | sed -n 's/^.*hexagon,label="\([^\]*\)\\n\([^\]*\).*/\1 \2/p')
+
+# Obtain a list of GEOM providers that are not already open - not mounted,
+# and without other GEOM class, such as gpart, attached.  In other words,
+# grep for "r0w0e0".  Skip providers with names containing slashes; we're
+# not interested in geom_label(4) creations.
+providers=$(echo "$pairs" | awk '$2 == "r0w0e0" && $1 !~ /\// { print $1 }')
+
+if [ $# -eq 0 ]; then
+	print_available
+	exit 0
+fi
+
+print_one "$1"
+exit 0
+

etc/devd.conf

@@ -318,4 +318,16 @@ notify 0 {
 	action			"/usr/local/etc/rc.d/postgresql restart";
 };
 
+# Discard autofs caches, useful for the -media special map.  The one
+# second delay is for GEOM to finish tasting.
+#
+# XXX: We should probably have a devctl(4) event that fires after GEOM
+#      tasting.
+#
+notify 100 {
+	match "system" "DEVFS";
+	match "cdev" "(da|mmcsd)[0-9]+";
+	action "sleep 1 && /usr/sbin/automount -c";
+};
+
 */

usr.sbin/autofs/auto_master.5

@@ -27,7 +27,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd November 21, 2014
+.Dd November 22, 2014
 .Dt AUTO_MASTER 5
 .Os
 .Sh NAME
@@ -213,14 +213,17 @@ Supported special maps are:
 .Pp
 .Bl -tag -width "-hosts" -compact
 .It Li -hosts
-This map queries the remote NFS server and maps exported volumes.
-It is traditionally mounted on
+Query the remote NFS server and map exported shares.
+This map is traditionally mounted on
 .Pa /net .
-It enables access to files on a remote NFS server by accessing
+Access to files on a remote NFS server is provided through the
 .Pa /net/nfs-server-ip/share-name/
-directory, without the need for any further configuration.
+directory without any additional configuration.
+.It Li -media
+Query devices that are not yet mounted, but contain valid filesystems.
+Generally used to access files on removable media.
 .It Li -null
-This map prevents the
+Prevent
 .Xr automountd 8
 from mounting anything on the mountpoint.
 .El