Merge lp:~smoser/cloud-utils/trunk.lp1630274 into lp:cloud-utils

[Scott Moser]

mount-image-callback: try mounting overlay rather than checking first

The logic to determine if mount would work was flawed in it assumed
that both or neither of the following would succeed:
  modprobe --quiet --use-blacklist fstype
  mount -t fstype would succeed

That logic failed when modprobe could not load the module due to
being in a chroot or some other reason. The change here is to just
do try the mount. In order to avoid confusing output about trying
to mount overlayfs we first try mounting overlay. If that fails
and 'overlay' seems present in /proc/filesystems, then do not bother
trying to mount overlayfs.

=== modified file 'bin/mount-image-callback'
--- bin/mount-image-callback	2016-09-27 21:05:03 +0000
+++ bin/mount-image-callback	2016-10-04 15:12:25 +0000
@@ -4,6 +4,8 @@
 TEMP_D=""
 UMOUNTS=( )
 QEMU_DISCONNECT=""
+CR=$'\n'
+TAB=$'\t'
 
 error() { echo "$@" 1>&2; }
 
@@ -138,23 +140,37 @@
 	fi
 }
 
-has_fs_support() {
-	local fstype="$1" tab='	'
-	grep -q "${tab}${fstype}$" /proc/filesystems
-}
+mount_overlay() {
+	local lower="$1" upper="$2" workdir="$3"
+	local olayopts="lowerdir=$lower,upperdir=$upper"
+	# 3.18+ require 'workdir=' option.
+	case "$(uname -r)" in
+		2*|3.1[01234567]*|3.[0-9].*) :;;
+		*) olayopts="${olayopts},workdir=$workdir"
+			mkdir -p "$workdir" ||
+				{ _ERR="Failed to create workdir '$workdir'"; return 1; }
+			;;
+	esac
 
-find_overlay_fstype() {
-	local fstype
-	set -- overlay overlayfs
-	for fstype in "$@"; do
-		has_fs_support "$m" && _RET="$fstype" && return 0
-	done
-	for modname in "$@"; do
-		if modprobe --quiet --use-blacklist "$modname"; then
-			has_fs_support "$modname" && _RET="$modname" && return 0
-		fi
-	done
-	return 1
+	local cmd="" fstype="" ret="" out="" fsfile="/proc/filesystems"
+	_ERR=""
+	for fstype in overlay overlayfs; do
+		cmd=( mount -t "$fstype" -o "$olayopts" "$lower" "$upper" )
+		debug 2 "attempting '$fstype' mount with: ${cmd[*]}"
+		out=$("${cmd[@]}" 2>&1)
+		ret=$?
+		if [ $ret -eq 0 ]; then
+			debug 1 "mounted '$fstype' via $fstype: ${cmd[*]}"
+			return 0
+		fi
+		_ERR="${_ERR}Failed [$ret]: ${cmd[*]}:${CR}"
+		_ERR="${_ERR}$out${CR}"
+		if [ -r "$fsfile" ] && grep -q "${TAB}${fstype}$" "$fsfile"; then
+			# this failed and we have support in kernel. do not try further.
+			return $ret
+		fi
+	done
+	return $ret
 }
 
 mount_callback_umount() {
@@ -321,7 +337,7 @@
 		fi
 
 		local nptnum=""
-		debug 1 "connected $img_in ($fmt) to $nbd. waiting for device."
+		debug 1 "connected ${readonly:+${readonly} }$img_in ($fmt) to $nbd. waiting for device."
 		i=0
 		while i=$(($i+1)):; do
 			get_partition "$nbd" && nptnum="$_RET" && break
@@ -377,27 +393,14 @@
 	fi
 
 	if $overlay; then
-		find_overlay_fstype || {
-			error "Unable to find a filesystem type for overlay."
-			error "You need support for overlayfs or overlay in your kernel."
+		mount_overlay "$img_mp" "$mp" "${TEMP_D}/workdir" || {
+			[ -n "${_ERR}" ] && error "${_ERR}"
+			error "Unable to mount overlay filesystem.  Maybe no kernel support?"
 			return 1
 		}
-		overlay_fstype="$_RET"
-			
-		local olayopts="lowerdir=$img_mp,upperdir=$mp"
-		workdir="${TEMP_D}/workdir"
-		mkdir "$workdir"
-		# 3.18+ require 'workdir=' option.
-		case "$(uname -r)" in
-			2*|3.1[01234567]*|3.[0-9].*) :;;
-			*) olayopts="${olayopts},workdir=$workdir";;
-		esac
-		mount -t "${overlay_fstype}" -o "$olayopts" "$img_mp" "$mp" || {
-			error "failed mount -t ${overlay_fstype} -o '$olayopts' '$img_mp' '$mp'"
-			return 1;
-		}
 		UMOUNTS[${#UMOUNTS[@]}]="$mp"
 	fi
+
 	local bindmp=""
 	for bindmp in $bmounts; do
 		[ -d "$mp${bindmp}" ] || mkdir "$mp${bindmp}" ||