[ImageBuilder v2 1/2] scripts/common: Introduce phandle_next and get_next_phandle()

[Michal Orzel <michal.orzel@xxxxxxx>]

When dealing with device trees, we need to have a solution to add
custom phandles to the nodes we create/modify. Add a global variable
phandle_next to act as a countdown counter starting with the highest
valid phandle value 0xfffffffe. Add a new function get_next_phandle
to get a value of the next available phandle and set it to a variable
whose name is passed as a first argument. The global counter will be
decremented with each call to this function.

Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
---
To make the interface to phandle_next as simple as possible, we just
need a single function that will get us the next phandle and update the
global counter. That is why we cannot use the following:
- "phandle=$(get_next_phandle)" as a subshell cannot modify the environment
  of its parent shell,
- making use of return statement as it only works with values up to 255

The current solution with passing a variable name to a function that
will modify its value using eval is the simplest one and serves our purpose.

Changes in v2:
- new patch
---
 scripts/common | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/scripts/common b/scripts/common
index 68938beb8557..25c041270c29 100644
--- a/scripts/common
+++ b/scripts/common
@@ -13,6 +13,9 @@
 tmp_files=()
 tmp_dirs=()
 
+# Highest valid phandle. Will be decremented with each call to get_next_phandle
+phandle_next="0xfffffffe"
+
 function remove_tmp_files()
 {
     for i in "${tmp_files[@]}"
@@ -26,6 +29,14 @@ function remove_tmp_files()
     done
 }
 
+# Get next phandle and set it as a value (in hex) of a variable whose name is
+# passed as a first argument. Decrement global counter phandle_next.
+function get_next_phandle()
+{
+    eval "$1=$(printf "0x%x" $phandle_next)"
+    phandle_next=$(( $phandle_next - 1 ))
+}
+
 function sanity_check_partial_dts()
 {
     local domU_passthrough_path="$1"
-- 
2.25.1