base-files: rework mtd_get_mac_text()

It's necessary to be able to specify the length
for MAC addresses that are stored in flash, for example,
in a case where it is stored without any delimiter.

Let both offset and length have default values.

Add a sanity check related to partition size.

Also, clean up syntax and unnecessary lines.

Signed-off-by: Michael Pratt <mcpratt@pm.me>

diff --git a/package/base-files/files/lib/functions/system.sh b/package/base-files/files/lib/functions/system.sh
index 94ccc02bb8ed2e093c997f032cdf14fa1e3bb2c8..d06354b01f45ef0f66859076846d5315d701a3eb 100644 (file)
--- a/package/base-files/files/lib/functions/system.sh
+++ b/package/base-files/files/lib/functions/system.sh
@@ -141,10 +141,10 @@ mtd_get_mac_uci_config_ubi() {
 }
 
 mtd_get_mac_text() {
-       local mtdname=$1
-       local offset=$(($2))
+       local mtdname="$1"
+       local offset=$((${2:-0}))
+       local length="${3:-17}"
        local part
-       local mac_dirty
 
        part=$(find_mtd_part "$mtdname")
        if [ -z "$part" ]; then
@@ -152,15 +152,9 @@ mtd_get_mac_text() {
                return
        fi
 
-       if [ -z "$offset" ]; then
-               echo "mtd_get_mac_text: offset missing!" >&2
-               return
-       fi
+       [ $((offset + length)) -le $(mtd_get_part_size "$mtdname") ] || return
 
-       mac_dirty=$(dd if="$part" bs=1 skip="$offset" count=17 2>/dev/null)
-
-       # "canonicalize" mac
-       [ -n "$mac_dirty" ] && macaddr_canonicalize "$mac_dirty"
+       macaddr_canonicalize $(dd bs=1 if="$part" skip="$offset" count="$length" 2>/dev/null)
 }
 
 mtd_get_mac_binary() {