binman: Support replacing data in a cbfs

At present binman cannot replace data within a CBFS since it does not
allow rewriting of the files in that CBFS. Implement this by using the
new WriteData() method to handle the case.

Add a header to compressed data so that the amount of compressed data can
be determined without reference to the size of the containing entry. This
allows the entry to be larger that the contents, without causing errors in
decompression. This is necessary to cope with a compressed device tree
being updated in such a way that it shrinks after the entry size is
already set (an obscure case). It is not used with CBFS since it has its
own metadata for this. Increase the number of passes allowed to resolve
the position of entries, to handle this case.

Add a test for this new logic.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/patman/tools.py

@@ -9,6 +9,7 @@ import command
 import glob
 import os
 import shutil
+import struct
 import sys
 import tempfile
 
@@ -377,7 +378,7 @@ def ToBytes(string):
         return string.encode('utf-8')
     return string
 
-def Compress(indata, algo):
+def Compress(indata, algo, with_header=True):
     """Compress some data using a given algorithm
 
     Note that for lzma this uses an old version of the algorithm, not that
@@ -408,9 +409,12 @@ def Compress(indata, algo):
         data = Run('gzip', '-c', fname, binary=True)
     else:
         raise ValueError("Unknown algorithm '%s'" % algo)
+    if with_header:
+        hdr = struct.pack('<I', len(data))
+        data = hdr + data
     return data
 
-def Decompress(indata, algo):
+def Decompress(indata, algo, with_header=True):
     """Decompress some data using a given algorithm
 
     Note that for lzma this uses an old version of the algorithm, not that
@@ -428,6 +432,9 @@ def Decompress(indata, algo):
     """
     if algo == 'none':
         return indata
+    if with_header:
+        data_len = struct.unpack('<I', indata[:4])[0]
+        indata = indata[4:4 + data_len]
     fname = GetOutputFilename('%s.decomp.tmp' % algo)
     with open(fname, 'wb') as fd:
         fd.write(indata)