Improve ABI backward & forward compatibillity

 - Padd the compressor config union
    - 128 bytes aught to be enough for everyone, i.e. future compressors.
    - Insist that the padding space is initialized to 0. If a field gets
      added to an existing compressor, it can test for 0 as a sentinel
      value.
 - Add a size field to the hook structure, aka "the Microsoft way".
    - The explanation is in the comment.
    - Don't make the Microsoft mistake of checking for >=, insist on *exact*
      size match. Future users will need a fallback if their hooks are
      rejected. But at least they will be rejected instead of silently not
      being used.
 - Add an unsupported flag check to the dir tree reader.
 - Add a basic abi unit test that, for now, checks the size of the compressor
   config struct fields.

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

1 files changed, 6 insertions, 2 deletions

diff --git a/lib/sqfs/data_writer/common.c b/lib/sqfs/data_writer/common.c
index 059ef41..a19eb6d 100644
--- a/lib/sqfs/data_writer/common.c
+++ b/lib/sqfs/data_writer/common.c
@@ -157,9 +157,13 @@ int sqfs_data_writer_write_fragment_table(sqfs_data_writer_t *proc,
 	return 0;
 }
 
-void sqfs_data_writer_set_hooks(sqfs_data_writer_t *proc, void *user_ptr,
-				const sqfs_block_hooks_t *hooks)
+int sqfs_data_writer_set_hooks(sqfs_data_writer_t *proc, void *user_ptr,
+			       const sqfs_block_hooks_t *hooks)
 {
+	if (hooks->size != sizeof(*hooks))
+		return SQFS_ERROR_UNSUPPORTED;
+
 	proc->hooks = hooks;
 	proc->user_ptr = user_ptr;
+	return 0;
 }