[PATCH v2 2/3] binman: Generate preload header and sign data only once

[yan wang <yan.wang@softathome.com>]

From: Paul HENRYS <paul.henrys_ext@softathome.com>

To optimize preload generation, generate the header and signatures only
after all data has been collected. This avoids signing the data multiple
times.

Since header_size is known upfront (from __init__), set the preload
header size in `ObtainContents()` to avoid an extra packing pass when
ProcessContentsUpdate() detects the size changed from 0 to header_size.

This reduces unnecessary repacking and signing operations.

Signed-off-by: Paul HENRYS <paul.henrys_ext@softathome.com>
---
Changes for v2:
- Set contents_size knowing header_size in ObtainContents()

 tools/binman/etype/pre_load.py | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/tools/binman/etype/pre_load.py b/tools/binman/etype/pre_load.py
index 00f1a896767..34a7bc1b985 100644
--- a/tools/binman/etype/pre_load.py
+++ b/tools/binman/etype/pre_load.py
@@ -152,14 +152,14 @@ class Entry_pre_load(Entry_collection):
         return data + pad
 
     def ObtainContents(self):
-        """Obtain a placeholder for the header contents"""
-        # wait that the image is available
-        self.image = self.GetContents(False)
-        if self.image is None:
-            return False
-        self.SetContents(self._CreateHeader())
+        """Only set the known size of the preload header. The data will be
+        generated later on in ProcessContents() when the data from every entries
+        can be retrieved.
+        """
+        self.contents_size = self.header_size
         return True
 
     def ProcessContents(self):
+        self.image = self.GetContents(True)
         data = self._CreateHeader()
         return self.ProcessContentsUpdate(data)
-- 
2.43.0