[archiso] Add dm_snap_prefix= boot param.

Default value is "arch". This implies that all device mapper node
for snapshot devices will be for example: arch_root-image.

This helps AIF to hidden these devices from "Device Configuration".
Signed-off-by: Gerardo Exequiel Pozzi <vmlinuz386@yahoo.com.ar>

README

@@ -43,6 +43,8 @@ INDEX
                     Size is in bytes (suffix with "k", "m" and "g") or
                     in percentage of available RAM.
                     Default: "75%"
+* dm_snap_prefix=   Set a prefix for device-mapper snapshot node names.
+                    Default: "arch"
 * arch=             Force an architecture type (i686 | x86_64).
                     Do not set it for normal operations.
                     Useful for running a 64 bit kernel / 32 bit userspace.

archiso/hooks/archiso

@@ -29,6 +29,7 @@ _mnt_fs() {
     local mnt="${2}"
     local img_fullname="${img##*/}";
     local img_name="${img_fullname%%.*}"
+    local dm_snap_name="${dm_snap_prefix}_${img_name}"
     local ro_dev ro_dev_size ro_dev_fs_type rw_dev
 
     mkdir -p "${mnt}"
@@ -42,11 +43,11 @@ _mnt_fs() {
     _next_loop_dev
     rw_dev=$(_make_loop_dev "/cowspace/${img_name}.cow")
 
-    echo "0 ${ro_dev_size} snapshot ${ro_dev} ${rw_dev} N 8" | dmsetup create ${img_name}
+    echo "0 ${ro_dev_size} snapshot ${ro_dev} ${rw_dev} N 8" | dmsetup create ${dm_snap_name}
 
-    msg ":: Mounting '/dev/mapper/${img_name}' (${ro_dev_fs_type}) to '${mnt}'"
-    if ! mount -t "${ro_dev_fs_type}" "/dev/mapper/${img_name}" "${mnt}" ; then
-        echo "ERROR: while mounting '/dev/mapper/${img_name}' to '${mnt}'"
+    msg ":: Mounting '/dev/mapper/${dm_snap_name}' (${ro_dev_fs_type}) to '${mnt}'"
+    if ! mount -t "${ro_dev_fs_type}" "/dev/mapper/${dm_snap_name}" "${mnt}" ; then
+        echo "ERROR: while mounting '/dev/mapper/${dm_snap_name}' to '${mnt}'"
         launch_interactive_shell
     fi
 }
@@ -81,6 +82,7 @@ run_hook() {
     [[ -z "${cowspace_size}" ]] && cowspace_size="75%"
     [[ -z "${copytoram_size}" ]] && copytoram_size="75%"
     [[ -z "${archisobasedir}" ]] && archisobasedir="arch"
+    [[ -z "${dm_snap_prefix}" ]] && dm_snap_prefix="arch"
     [[ -z "${archisodevice}" ]] && archisodevice="/dev/disk/by-label/${archisolabel}"
     if [[ -z "${aitab}" ]]; then
         aitab="/bootmnt/${archisobasedir}/aitab"