libsqfs: add a threshold for extended directory inodes with index

mksquashfs generates extended inodes if a directory contains 256
entries. libsquashfs so far only generated extended inodes if there
is no other way to encode it. Mimic the behaviour of mksquashfs by
adding a threshold.

For this to work, the "sqfs_inode_set_xattr_index" function has to
be changed to not immediately try to demote inodes to basic types.
The fstree serialization is modified to do that itself if the index
is 0xFFFFFFFF and the target is not a directory inode.

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

1 files changed, 4 insertions, 3 deletions

diff --git a/include/sqfs/inode.h b/include/sqfs/inode.h
index 8df7158..7f4e7b5 100644
--- a/include/sqfs/inode.h
+++ b/include/sqfs/inode.h
@@ -576,9 +576,10 @@ SQFS_API int sqfs_inode_get_xattr_index(const sqfs_inode_generic_t *inode,
  *
  * @memberof sqfs_inode_generic_t
  *
- * For basic inodes, this function promes the inodes to extended inodes if the
- * index is not 0xFFFFFFFF. If the index is 0xFFFFFFFF, the function tries to
- * demote extended inode to a basic inode after setting the index.
+ * For basic inodes, this function promotes the inodes to extended inodes if
+ * the index is not 0xFFFFFFFF. The function does not try to demote extended
+ * inodes if the index is 0xFFFFFFFF, because that would cause additional
+ * information like a directory index to be lost.
  *
  * @param inode A pointer to an inode.
  * @param index The extended attribute index.