probes: reuse existing slot mounts; explicit -t ext4

The image's fstab keeps the factory slots mounted under /factory, and
busybox mount's auto-type iteration against an already-mounted ext4
device provokes a cosmetic kernel 'Can't open blockdev' for each
foreign-type claim (reproduced and pinned on the bench: ext3-typed
mount of an ext4-held device prints it; ext4-typed does not). Probes
now reuse an existing mountpoint from /proc/mounts and mount fresh
targets with an explicit -t ext4.

scripts/ffboot

@@ -48,16 +48,25 @@ BOOTED_ROOT=$(sed -n 's/.*root=\([^ ]*\).*/\1/p' /proc/cmdline)
 #       P_VERSION P_KERNEL(yes|no)
 probe_part () {
   P_PRESENT=no; P_STATE=unreadable; P_TYPE=unknown; P_VERSION=""; P_KERNEL=no
+  P_MOUNTED=""
   [ -b "$1" ] || return 1
   P_PRESENT=yes
   if [ "$1" = "$BOOTED_ROOT" ]; then
     ROOT_DIR=""
   else
-    ROOT_DIR="/tmp/ffboot.probe.$$"
-    mkdir -p "$ROOT_DIR"
-    if ! mount -o ro "$1" "$ROOT_DIR" 2>/dev/null; then
-      rmdir "$ROOT_DIR" 2>/dev/null
-      return 1
+    # Reuse an existing mount (the image keeps the factory slots mounted
+    # under /factory); a fresh mount is explicit -t ext4 - letting mount
+    # iterate types provokes a cosmetic kernel "Can't open blockdev" for
+    # each foreign-type claim against an already-mounted device.
+    ROOT_DIR=$(sed -n "s|^$1 \([^ ]*\).*|\1|p" /proc/mounts | head -n 1)
+    if [ -z "$ROOT_DIR" ]; then
+      ROOT_DIR="/tmp/ffboot.probe.$$"
+      P_MOUNTED=yes
+      mkdir -p "$ROOT_DIR"
+      if ! mount -o ro -t ext4 "$1" "$ROOT_DIR" 2>/dev/null; then
+        rmdir "$ROOT_DIR" 2>/dev/null
+        return 1
+      fi
     fi
   fi
   if [ -f "$ROOT_DIR/etc/forgefirm-version" ]; then
@@ -70,7 +79,7 @@ probe_part () {
     P_STATE=empty
   fi
   [ -f "$ROOT_DIR/boot/zImage" ] && P_KERNEL=yes
-  if [ -n "$ROOT_DIR" ]; then
+  if [ -n "$P_MOUNTED" ]; then
     umount "$ROOT_DIR" 2>/dev/null
     rmdir "$ROOT_DIR" 2>/dev/null
   fi

scripts/install-forgefirm.sh

@@ -76,21 +76,25 @@ archive_dev () {
 # read-only under /tmp (newer factory firmware has no /factory/imgN
 # mounts, and the rootfs is read-only).
 slot_probe () {
-  S_TYPE=unknown; S_VER=""
+  S_TYPE=unknown; S_VER=""; S_MOUNTED=""
   if [ "$1" = "$ACTIVE" ]; then
     RD=""
   else
-    RD="/tmp/ffinstall.probe.$$"
-    mkdir -p "$RD" || return 1
-    mount -o ro "/dev/mmcblk2p$1" "$RD" 2>/dev/null \
-      || { rmdir "$RD" 2>/dev/null; return 1; }
+    RD=$(sed -n "s|^/dev/mmcblk2p$1 \([^ ]*\).*|\1|p" /proc/mounts | head -n 1)
+    if [ -z "$RD" ]; then
+      RD="/tmp/ffinstall.probe.$$"
+      S_MOUNTED=yes
+      mkdir -p "$RD" || return 1
+      mount -o ro -t ext4 "/dev/mmcblk2p$1" "$RD" 2>/dev/null \
+        || { rmdir "$RD" 2>/dev/null; return 1; }
+    fi
   fi
   if [ -f "$RD/etc/forgefirm-version" ]; then
     S_TYPE=forgefirm; S_VER=$(cat "$RD/etc/forgefirm-version")
   elif [ -f "$RD/etc/version" ]; then
     S_TYPE=factory; S_VER=$(cat "$RD/etc/version")
   fi
-  if [ -n "$RD" ]; then
+  if [ -n "$S_MOUNTED" ]; then
     umount "$RD" 2>/dev/null
     rmdir "$RD" 2>/dev/null
   fi
@@ -235,7 +239,7 @@ rm -f "$KEYFILE"
 # --- post-write verify --------------------------------------------------------
 MP="/tmp/ffinstall.verify.$$"
 mkdir -p "$MP"
-mount -o ro "/dev/mmcblk2p$TARGET" "$MP" || die "new rootfs does not mount"
+mount -o ro -t ext4 "/dev/mmcblk2p$TARGET" "$MP" || die "new rootfs does not mount"
 NEWVER=$(cat "$MP/etc/forgefirm-version" 2>/dev/null)
 [ -n "$NEWVER" ] || { umount "$MP"; die "new rootfs has no ForgeFIRM version stamp"; }
 [ -f "$MP/boot/zImage" ] || { umount "$MP"; die "new rootfs has no kernel"; }