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, 1 insertions, 0 deletions

diff --git a/lib/sqfshelper/statistics.c b/lib/sqfshelper/statistics.c
index 3f9f595..fb70615 100644
--- a/lib/sqfshelper/statistics.c
+++ b/lib/sqfshelper/statistics.c
@@ -55,6 +55,7 @@ static void notify_fragment_discard(void *user, const sqfs_block_t *block)
 }
 
 static const sqfs_block_hooks_t hooks = {
+	.size = sizeof(hooks),
 	.post_block_write = post_block_write,
 	.pre_fragment_store = pre_fragment_store,
 	.notify_blocks_erased = notify_blocks_erased,