ds-identify: fake dmidecode support on OpenBSD

use sysctl's hw hierarchy, because it contains pretty much all we use
from dmidecode. Unlike dmidecode, we don't need to set
`kern.allowkmem=1` for this to work.

tools/ds-identify

@@ -210,6 +210,27 @@ get_kenv_field() {
     _RET="$val"
 }
 
+get_sysctl_field() {
+    local sys_field="$1" sysctl_field="" val=""
+    command -v sysctl >/dev/null 2>&1 || {
+        warn "No sysctl program. Cannot read $sys_field."
+        return 1
+    }
+    case "$sys_field" in
+        chassis_vendor) kenv_field='hw.vendor';;
+        chassis_serial) kenv_field='hw.type';;
+        chassis_version) kenv_field='hw.uuid';;
+        sys_vendor) kenv_field='hw.vendor';;
+        product_name) kenv_field='hw.product';;
+        product_serial) kenv_field='hw.uuid';;
+        product_uuid) kenv_field='hw.uuid';;
+        *) error "Unknown field $sys_field. Cannot call sysctl."
+           return 1;;
+    esac
+    val=$(sysctl -nq "$kenv_field" 2>/dev/null) || return 1
+    _RET="$val"
+}
+
 dmi_decode() {
     local sys_field="$1" dmi_field="" val=""
     command -v dmidecode >/dev/null 2>&1 || {
@@ -237,6 +258,11 @@ get_dmi_field() {
         return $?
     fi
 
+    if [ "$DI_UNAME_KERNEL_NAME" = "OpenBSD" ]; then
+        get_sysctl_field "$1" || _RET="$ERROR"
+        return $?
+    fi
+
     local path="${PATH_SYS_CLASS_DMI_ID}/$1"
     if [ -d "${PATH_SYS_CLASS_DMI_ID}" ]; then
         if [ -f "$path" ] && [ -r "$path" ]; then