libdiskfs: add diskfs_make_node_alloc to allocate fat nodes

libdiskfs has two kind of nodes, struct node and struct netnode.
struct node is used to store libdiskfs specific data, while struct
netnode contains user supplied data.  Previously, both objects were
allocated separatly, and a pointer from the node to the netnode
provided a mapping from the former to the latter.

Provide a function diskfs_make_node_alloc that allocates both nodes in
a contiguous region.

This reduces the memory allocation overhead when creating nodes.  It
also makes the relation between node and netnode a simple offset
calculation.  Provide two functions to compute the netnode address
from the node address and vice-versa.

Most notably, this makes implementing a cache on top of libdiskfs
easier.  Auxiliary data for the cache can be stored in the
user-defined netnode, and the fat node can be used as the value.

* libdiskfs/node-make.c (init_node): Move initialization here.
(diskfs_make_node): Use init_node.
(diskfs_make_node_alloc): New function to allocate fat nodes.
* libdiskfs/diskfs.h (diskfs_make_node_alloc): New declaration.
(_diskfs_sizeof_struct_node): Likewise.
(diskfs_node_disknode): Compute disknode address from node address.
(diskfs_disknode_node): And vice-versa.
* libdiskfs/init-init.c (_diskfs_sizeof_struct_node): New variable.

1 files changed, 4 insertions, 0 deletions

diff --git a/libdiskfs/init-init.c b/libdiskfs/init-init.c
index 35be7edd..7a7f2485 100644
--- a/libdiskfs/init-init.c
+++ b/libdiskfs/init-init.c
@@ -25,6 +25,10 @@ the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
 #include <stdio.h>
 #include <maptime.h>
 
+/* For safe inlining of diskfs_node_disknode and
+   diskfs_disknode_node.  */
+size_t const _diskfs_sizeof_struct_node = sizeof (struct node);
+
 mach_port_t diskfs_default_pager;
 mach_port_t diskfs_auth_server_port;
 volatile struct mapped_time_value *diskfs_mtime;