binman: Change how faked blobs are created

At present fake blobs are created but internally an empty blob is used.
Change it to use the contents of the faked file. Also return whether the
blob was faked, in case the caller needs to know that.

Add a TODO to put fake blobs in their own directory.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>

tools/binman/binman.rst

@@ -1500,7 +1500,8 @@ Some ideas:
 - Figure out how to make Fdt support changing the node order, so that
   Node.AddSubnode() can support adding a node before another, existing node.
   Perhaps it should completely regenerate the flat tree?
-
+- Put faked files into a separate subdir and remove them on start-up, to avoid
+  seeing them as 'real' files on a subsequent run
 
 --
 Simon Glass <sjg@chromium.org>

tools/binman/entry.py

@@ -999,15 +999,18 @@ features to produce new behaviours.
             fname (str): Filename to check
 
         Returns:
-            fname (str): Filename of faked file
+            tuple:
+                fname (str): Filename of faked file
+                bool: True if the blob was faked, False if not
         """
         if self.allow_fake and not pathlib.Path(fname).is_file():
             outfname = tools.get_output_filename(os.path.basename(fname))
             with open(outfname, "wb") as out:
                 out.truncate(1024)
             self.faked = True
-            return outfname
-        return fname
+            tout.info(f"Entry '{self._node.path}': Faked file '{outfname}'")
+            return outfname, True
+        return fname, False
 
     def CheckFakedBlobs(self, faked_blobs_list):
         """Check if any entries in this section have faked external blobs

tools/binman/etype/blob.py

@@ -41,10 +41,11 @@ class Entry_blob(Entry):
             self.external and self.section.GetAllowMissing())
         # Allow the file to be missing
         if not self._pathname:
-            self._pathname = self.check_fake_fname(self._filename)
-            self.SetContents(b'')
+            self._pathname, faked = self.check_fake_fname(self._filename)
             self.missing = True
-            return True
+            if not faked:
+                self.SetContents(b'')
+                return True
 
         self.ReadBlobContents()
         return True

tools/binman/etype/blob_ext_list.py

@@ -37,7 +37,7 @@ class Entry_blob_ext_list(Entry_blob):
         missing = False
         pathnames = []
         for fname in self._filenames:
-            fname = self.check_fake_fname(fname)
+            fname, _ = self.check_fake_fname(fname)
             pathname = tools.get_input_filename(
                 fname, self.external and self.section.GetAllowMissing())
             # Allow the file to be missing