Add support for packing sparse files

This commit adds support for packing sparse files into squashfs images
as follows:

 - In the data writer: simply detect zero blocks and write a zero to the
   block size field and don't emit any data. Record the number of bytes
   saved this way. For fragments, set the fragment offset to invalid.
 - In the inode writer: write out the number of bytes saved for sparse
   files. If there should be a fragment but there is none, append a block
   count of 0.
 - In the data reader: if the block size is 0, read nothing from disk and
   emit an empty block. Do the same if the fragment is missing.
 - In the inode reader: restore the number of bytes saved for sparse files.

The sparse files can be packed and unpacked, but the unpacking will not
create sparse files for now.

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

1 files changed, 1 insertions, 0 deletions

diff --git a/lib/sqfs/tree_node_from_inode.c b/lib/sqfs/tree_node_from_inode.c
index f9a6599..9c96701 100644
--- a/lib/sqfs/tree_node_from_inode.c
+++ b/lib/sqfs/tree_node_from_inode.c
@@ -113,6 +113,7 @@ tree_node_t *tree_node_from_inode(sqfs_inode_generic_t *inode,
 		out->name += sizeof(file_info_t);
 
 		out->data.file->size = inode->data.file_ext.file_size;
+		out->data.file->sparse = inode->data.file_ext.sparse;
 		out->data.file->startblock = inode->data.file_ext.blocks_start;
 		out->data.file->fragment = inode->data.file_ext.fragment_idx;
 		out->data.file->fragment_offset =