add boot params archisoflags= and cow_flags= for mount options

Having files on btrfs subvolumes requires to give mount options. Add
boot params archisoflags= and cow_flags= for this purpose. Boot
parameters could look like this:

... archisodevice=/dev/sdaX archisoflags=subvolume=isos
cow_device=/dev/sdaX cow_flags=subvolume=persist ...

Signed-off-by: Christian Hesse <mail@eworm.de>

archiso/initcpio/hooks/archiso

@@ -110,6 +110,7 @@ run_hook() {
     [[ -z "${archisobasedir}" ]] && archisobasedir="arch"
     [[ -z "${dm_snap_prefix}" ]] && dm_snap_prefix="arch"
     [[ -z "${archisodevice}" ]] && archisodevice="/dev/disk/by-label/${archisolabel}"
+    [[ -z "${archisoflags}" ]] && archisoflags="defaults"
     [[ -z "${cow_spacesize}" ]] && cow_spacesize="256M"
 
     if [[ -n "${cow_label}" ]]; then
@@ -121,6 +122,7 @@ run_hook() {
         cow_persistent="N"
     fi
 
+    [[ -z "${cow_flags}" ]] && cow_flags="defaults"
     [[ -z "${cow_directory}" ]] && cow_directory="persistent_${archisolabel}/${arch}"
     [[ -z "${cow_chunksize}" ]] && cow_chunksize="8"
 
@@ -135,7 +137,7 @@ archiso_mount_handler() {
     local newroot="${1}"
 
     if ! mountpoint -q "/run/archiso/bootmnt"; then
-        _mnt_dev "${archisodevice}" "/run/archiso/bootmnt" "-r"
+        _mnt_dev -o "${archisoflags}" "${archisodevice}" "/run/archiso/bootmnt" "-r"
         if [[ "${copytoram}" != "y" ]]; then
             echo $(readlink -f ${archisodevice}) >> /run/archiso/used_block_devices
         fi
@@ -164,7 +166,7 @@ archiso_mount_handler() {
     fi
 
     if [[ -n "${cow_device}" ]]; then
-        _mnt_dev "${cow_device}" "/run/archiso/cowspace" "-r"
+        _mnt_dev -o "${cow_flags}" "${cow_device}" "/run/archiso/cowspace" "-r"
         echo $(readlink -f ${cow_device}) >> /run/archiso/used_block_devices
         mount -o remount,rw "/run/archiso/cowspace"
     else

docs/README.bootparams

@@ -21,6 +21,8 @@ INDEX
                     Default: (unset)
 * archisodevice=    Set the device node where archiso medium is located.
                     Default: "/dev/disk/by-label/${archisolabel}"
+* archisoflags=     Set extra mount options, e.g. for btrfs subvolumes.
+                    Default: defaults
 * archisobasedir=   Set the base directory where all files reside.
                     Default: "arch"
 * copytoram=        If set to "y" or just "copytoram" without arguments,
@@ -35,6 +37,8 @@ INDEX
                     Default: (unset)
 * cow_device=       Like cow_label= but using device node.
                     Default: (unset) or "/dev/disk/by-label/${cow_label}"
+* cow_flags=        Set extra mount options, e.g. for btrfs subvolumes.
+                    Default: defaults
 * cow_directory=    Set a directory inside ${cow_device}.
                     Default: "/persistent_${archisolabel}/${arch}"
 * cow_persistent=   Set if snapshot is persistent "P" or non-persistent "N".