[archiso] Change cowfile_size= behavior

Move from percent to explicit size and set a default of 256M (sparse)
Signed-off-by: Gerardo Exequiel Pozzi <vmlinuz386@gmail.com>

archiso/initcpio/hooks/archiso

@@ -11,19 +11,13 @@ _mnt_fs() {
     ro_dev=$(losetup --find --show --read-only "${img}")
     echo ${ro_dev} >> /run/archiso/used_block_devices
     ro_dev_size=$(blockdev --getsz ${ro_dev})
-    if [[ "${cowfile_size}" == "100" ]]; then
-        rw_dev_size=${ro_dev_size}
-    else
-        # size calculation done in this way to avoid integer overflow when ro_dev_size is > 10.2G
-        rw_dev_size=$((ro_dev_size/100*cowfile_size))
-    fi
 
     if [[ "${cow_persistent}" == "P" ]]; then
         if [[ -f "/run/archiso/cowspace/${cow_directory}/${img_name}.cow" ]]; then
             msg ":: Found '/run/archiso/cowspace/${cow_directory}/${img_name}.cow', using as persistent."
         else
             msg ":: Creating '/run/archiso/cowspace/${cow_directory}/${img_name}.cow' as persistent."
-            dd of="/run/archiso/cowspace/${cow_directory}/${img_name}.cow" count=0 seek=${rw_dev_size} &> /dev/null
+            truncate -s "${cowfile_size}" "/run/archiso/cowspace/${cow_directory}/${img_name}.cow"
         fi
     else
         if [[ -f "/run/archiso/cowspace/${cow_directory}/${img_name}.cow" ]]; then
@@ -31,13 +25,13 @@ _mnt_fs() {
             rm -f "/run/archiso/cowspace/${cow_directory}/${img_name}.cow"
         fi
         msg ":: Creating '/run/archiso/cowspace/${cow_directory}/${img_name}.cow' as non-persistent."
-        dd of="/run/archiso/cowspace/${cow_directory}/${img_name}.cow" count=0 seek=${rw_dev_size} &> /dev/null
+        truncate -s "${cowfile_size}" "/run/archiso/cowspace/${cow_directory}/${img_name}.cow"
     fi
 
     rw_dev=$(losetup --find --show "/run/archiso/cowspace/${cow_directory}/${img_name}.cow")
     echo ${rw_dev} >> /run/archiso/used_block_devices
 
-    echo "0 ${ro_dev_size} snapshot ${ro_dev} ${rw_dev} ${cow_persistent} 8" | dmsetup create ${dm_snap_name}
+    dmsetup create ${dm_snap_name} --table "0 ${ro_dev_size} snapshot ${ro_dev} ${rw_dev} ${cow_persistent} 8"
 
     _mnt_dev "/dev/mapper/${dm_snap_name}" "${newroot}${mnt}" "-w"
     echo $(readlink -f /dev/mapper/${dm_snap_name}) >> /run/archiso/used_block_devices
@@ -108,9 +102,7 @@ run_hook() {
     [[ -z "${dm_snap_prefix}" ]] && dm_snap_prefix="arch"
     [[ -z "${archisodevice}" ]] && archisodevice="/dev/disk/by-label/${archisolabel}"
     if [[ -z "${cowfile_size}" ]]; then
-        cowfile_size="100"
-    else
-        cowfile_size=${cowfile_size/%}
+        cowfile_size="256M"
     fi
 
     if [[ -n "${cow_label}" ]]; then

archiso/initcpio/install/archiso

@@ -12,6 +12,7 @@ build() {
     add_binary dmsetup
     add_binary losetup
     add_binary mountpoint
+    add_binary truncate
 
     add_file /usr/lib/udev/rules.d/60-cdrom_id.rules
     add_file /usr/lib/udev/rules.d/10-dm.rules

docs/README.bootparams

@@ -31,27 +31,26 @@ INDEX
                     and continue booting if ok.
                     Default: (unset)
 * cow_label=        Set the filesystem label where COW (dm-snapshot)
-                    files must be stored.
+                    file must be stored.
                     Default: (unset)
-* cow_device=       Set the device node where COW (dm-snapshot) files
+* cow_device=       Set the device node where COW (dm-snapshot) file
                     must be stored.
                     Default: (unset) or "/dev/disk/by-label/${cow_label}"
 * cow_directory=    Set a directory inside ${cow_device}.
                     Default: "/persistent_${archisolabel}/${arch}"
-* cow_persistent=   Set if snapshots are persistent "P" or non-persistent "N".
+* cow_persistent=   Set if snapshot is persistent "P" or non-persistent "N".
                     Default: "N" (if no ${cow_device} is used) otherwise "P".
 * cowspace_size=    Set the size of tmpfs /cowspace. This space is used for
                     Copy-On-Write files of dm-snapshot.
                     Size is in bytes (suffix with "k", "m" and "g") or
                     in percentage of available RAM.
                     Default: "75%"
-* cowfile_size=     Set the size for all files to be used as COW (dm-snapshot),
-                    in percentage of the ro-device.fs file. This is mostly useful
-                    when cow_device= is used and filesystem does not support
-                    sparse files (ie VFAT).
-                    Default: "100%"
+* cowfile_size=     Set the size for COW file (dm-snapshot).
+                    The argument is an integer and optional unit.
+                    Units are M,G (powers of 1024) or MB,GB (powers of 1000).
+                    Default: "256M"
 * copytoram_size=   Set the size of tmpfs. This space is used for
-                    copy of all SquashFS images used, if copytoram=y.
+                    airootfs.sfs image if copytoram=y.
                     Size is in bytes (suffix with "k", "m" and "g") or
                     in percentage of available RAM.
                     Default: "75%"