[PATCH v2 01/10] pylibfdt: Fix FdtSw.as_fdt() when buffer is nearly full

[Douglas Anderson]

`FdtSw.as_fdt()` calls `fdt_finish()` on a copy of `self._fdt` without
using `self.check_space()`. Because `fdt_finish()` appends the 4-byte
`FDT_END` token, `as_fdt()` raises `FdtException(FDT_ERR_NOSPACE)` if
fewer than 4 bytes of free space remain in `self._fdt` after the final
`end_node()`.

Wrap `fdt_finish()` in a `while self.check_space(fdt_finish(fdtsw)):`
loop so `FdtSw.as_fdt()` automatically resizes the buffer when needed,
matching the rest of `FdtSw`'s methods.

Assisted-by: Gemini:gemini-pro-prerelease
Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
---

Changes in v2:
- New patch fixing FdtSw.as_fdt() buffer resize when < 4 bytes remain

 pylibfdt/libfdt.i       | 3 ++-
 tests/pylibfdt_tests.py | 8 ++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/pylibfdt/libfdt.i b/pylibfdt/libfdt.i
index b41c03f4932a..46f28f67290d 100644
--- a/pylibfdt/libfdt.i
+++ b/pylibfdt/libfdt.i
@@ -959,7 +959,8 @@ class FdtSw(FdtRo):
             Fdt object allowing access to the newly created device tree
         """
         fdtsw = bytearray(self._fdt)
-        check_err(fdt_finish(fdtsw))
+        while self.check_space(fdt_finish(fdtsw)):
+            fdtsw = bytearray(self._fdt)
         return Fdt(fdtsw)
 
     def check_space(self, val):
diff --git a/tests/pylibfdt_tests.py b/tests/pylibfdt_tests.py
index 0e1660753477..1b65961491bf 100644
--- a/tests/pylibfdt_tests.py
+++ b/tests/pylibfdt_tests.py
@@ -646,6 +646,14 @@ class PyLibfdtSwTests(unittest.TestCase):
         # Make sure we did at least two resizes
         self.assertTrue(len(fdt.as_bytearray()) > FdtSw.INC_SIZE * 2)
 
+        # Check that as_fdt() resizes when fewer than 4 bytes remain for FDT_END
+        sw_exact = FdtSw(76)
+        sw_exact.finish_reservemap()
+        sw_exact.begin_node('')
+        sw_exact.end_node()
+        fdt_exact = sw_exact.as_fdt()
+        self.assertEqual(80, fdt_exact.totalsize())
+
 
 class PyLibfdtRoTests(unittest.TestCase):
     """Test class for read-only pylibfdt access functions
-- 
2.56.0.313.g2479322e68-goog