2 files changed, 168 insertions, 1 deletions

diff --git a/old-school/grok-block b/old-school/grok-block
index 62b063f..3f61c4a 100755
--- a/old-school/grok-block
+++ b/old-school/grok-block
@@ -172,7 +172,9 @@ then
   # Recognize and mount the Samizdat 
   if ! mountpoint -q /cdrom; then
     mkdir -p /cdrom
-    (retry_mount -t iso9660 -r "$DEVNAME" /cdrom && bootdone samizdat-cdrom) &
+    . mdadm-dup.sh
+    mount_cdrom "$DEVNAME" && bootdone samizdat-cdrom
+#   (retry_mount -t iso9660 -r "$DEVNAME" /cdrom && bootdone samizdat-cdrom) &
   fi
 else
   grok_block &
diff --git a/old-school/mdadm-dup.sh b/old-school/mdadm-dup.sh
new file mode 100644
index 0000000..27a39ca
--- /dev/null
+++ b/old-school/mdadm-dup.sh
@@ -0,0 +1,165 @@
+dm_snapshot()
+{
+    # TODO: eliminate duplication; this function exists elsewhere in a less generalized form
+    local ro_file rw_file cutoff_size
+    ro_file=$1
+    rw_file=$2
+    cutoff_size=$3
+
+    local ro_dev rw_dev size new_dev_name persist chunksize
+
+    if [ -b "$ro_file" ];
+    then ro_dev=$ro_file
+    else ro_dev=$(LoSetup -r -f --show "$ro_file") || return
+    fi
+
+    if [ -b "$rw_file" ];
+    then rw_dev=$rw_file
+    else rw_dev=$(LoSetup -f --show "$rw_file") || return
+    fi
+
+    if [ "$cutoff_size" -a "$cutoff_size" -gt 0 ]; then
+        size=$cutoff_size
+    else
+        size=$(blockdev --getsz "$ro_dev") || return
+    fi
+
+    new_dev_name=${ro_dev##*/}
+    persist=p
+    chunksize=16
+    dmsetup create "$new_dev_name" --table "0 $size snapshot $ro_dev $rw_dev $persist $chunksize" || return
+    wait_for_dm_device /dev/mapper/"$new_dev_name"; 
+    echo /dev/mapper/"$new_dev_name"
+}
+
+dm_snapshot_teardown()
+{
+    local dev="$1"
+    case "$dev" in
+        /dev/dm-*)
+            dmsetup table "$dev" | (
+                read _ _ snapshot ro_dev rw_dev _ _
+                [ "$snapshot" = snapshot ]      || exit 1
+                dmsetup remove "$dev"           || exit 1
+                # errors ignored because the loop dev can be automatically removed upon disuse already
+                losetup -d /dev/block/"$rw_dev" || true
+                eject /dev/block/"$ro_dev"      || exit 1
+            ) || return
+            ;;
+        *) return 1 ;;
+    esac
+}
+
+wait_for_dm_device()
+{
+    # TODO: improve
+    while ! [ -e "$1" ]; do
+        sleep 1
+    done
+}
+
+mount_cdrom()
+{
+    local cdrom_dev="$1"
+
+    local sectors md_dev=/dev/md0 cdrom_rw_file=/"${cdrom_dev##*/}".rw
+
+    sectors=$(get_cdrom_sizelimit "$cdrom_dev") || return
+
+    # TODO: do we even need this backing file? We do need to trick mdadm into
+    # thinking that this is a RW device, but previously we got away with just
+    # creating a loopback device.
+    dd if=/dev/zero of="$cdrom_rw_file" bs=1K count=32 || return
+    cdrom_rw_dev=$(dm_snapshot "$cdrom_dev" "$cdrom_rw_file" "$sectors") || return
+    mdadm_dup "$cdrom_rw_dev" "$md_dev" "$sectors" || return
+    mount -t iso9660 -r $md_dev /cdrom
+}
+
+get_cdrom_sizelimit()
+{
+    # returns 512-byte sectors
+    local dev="$1" sectors
+    sectors=$(blockdev --getsz "$dev") || return
+
+    # Check if we can read the last 8 sectors. With a TAO CDROM, we can't --
+    # these sectors are faux, and not part of the ISO fs. If mdadm is allowed to
+    # read them, it will mark the device failed.
+    if dd count=2 if="$dev" bs=2048 skip=$((sectors/4 - 2)) of=/dev/null 2>/dev/null; then
+        echo $sectors
+    else
+        echo $((sectors - 8))
+    fi
+}
+
+mdadm_dup()
+{
+    local input_dev="$1" md_name="$2" sectors="$3"
+
+    mdadm --build $md_name ${sectors:+--size=$((sectors / 2))} \
+          --level=1 --raid-devices=1 --force --write-mostly "$input_dev" || return
+}
+
+
+mdadm_subdevices()
+{
+    local md_dev="$1"
+    mdadm -D "$md_dev" -Y | sed -ne 's/MD_DEVICE_.*_DEV=//p'
+}
+
+Mdadm()
+{
+    mdadm "$@"
+    # r=$?
+    # mdadm -D "$1"
+    # sleep 2
+    # return $r
+}
+
+mdadm_copy_eject() # NOT INITRD; uses non-busybox "losetup"
+{
+    local md_dev="$1" output_file="$2"
+
+    [ -b "$md_dev" ]                                  || return
+    [ ! -e "$output_file" ]                           || return
+
+    local output_dev sectors
+
+    old_subdev=$(mdadm_subdevices "$md_dev"|head -n1) || return
+    [ -b "$old_subdev" ]                              || return
+    sectors=$(blockdev --getsz "$md_dev")             || return
+
+    truncate -s $((sectors * 512)) "$output_file"     || return
+    output_dev=$(losetup -f --show "$output_file")    || return
+
+    Mdadm "$md_dev" --add "$output_dev"               || return
+    Mdadm "$md_dev" --grow -n2                        || return
+
+    mdadm_wait_remove "$md_dev" "$old_subdev"         || return
+
+    Mdadm "$md_dev" --grow -n1 --force                || return
+    dm_snapshot_teardown "$old_subdev"
+}
+
+mdadm_wait_remove()
+{
+    # We should perhaps use mdadm --monitor's RebuildFinished event.
+
+    local dev="$1" disk="$2" tries
+    if ! mdadm --wait "$dev"; then
+        tries=1000
+        while ! mdadm --detail --test "$dev"; do
+            [ $tries -gt 0 ] || return 1
+            sleep 1
+            tries=$((tries-1))
+        done
+    fi
+
+    mdadm "$dev" --fail "$disk" || return 1
+    tries=100
+    while ! mdadm "$dev" --remove "$disk"; do
+        [ $tries -gt 0 ] || return 1
+        sleep 1
+        tries=$((tries-1))
+    done
+    return 0
+}