From d8c082cdb15d33845cdc2c495469a7cc6aa01d9e Mon Sep 17 00:00:00 2001
From: Justus Winter <4winter@informatik.uni-hamburg.de>
Date: Fri, 16 May 2014 23:06:33 +0200
Subject: [PATCH 08/11] 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_node_netnode): Compute netnode address from node address.
(diskfs_netnode_node): And vice-versa.
---
 libdiskfs/diskfs.h    | 22 ++++++++++++++++++++++
 libdiskfs/node-make.c | 39 ++++++++++++++++++++++++++++++---------
 2 files changed, 52 insertions(+), 9 deletions(-)

diff --git a/libdiskfs/diskfs.h b/libdiskfs/diskfs.h
index 8151ddc..f710d10 100644
--- a/libdiskfs/diskfs.h
+++ b/libdiskfs/diskfs.h
@@ -685,6 +685,28 @@ diskfs_notice_filechange (struct node *np, enum file_changed_type type,
    The new node will have one hard reference and no light references.  */
 struct node *diskfs_make_node (struct disknode *dn);
 
+/* Create a new node structure.  Also allocate SIZE bytes for the
+   disknode.  The address of the disknode can be obtained using
+   diskfs_node_disknode.  The new node will have one hard reference
+   and no light references.  */
+struct node *diskfs_make_node_alloc (size_t size);
+
+/* Return the address of the disknode for NODE.  NODE must have been
+   allocated using diskfs_make_node_alloc.  */
+static inline struct disknode *
+diskfs_node_disknode (struct node *node)
+{
+  return (struct disknode *) ((char *) node + sizeof (struct node));
+}
+
+/* Return the address of the node for DISKNODE.  DISKNODE must have
+   been allocated using diskfs_make_node_alloc.  */
+static inline struct node *
+diskfs_disknode_node (struct disknode *disknode)
+{
+  return (struct node *) ((char *) disknode - sizeof (struct node));
+}
+
 
 /* The library also exports the following functions; they are not generally
    useful unless you are redefining other functions the library provides. */
diff --git a/libdiskfs/node-make.c b/libdiskfs/node-make.c
index 2b6ef2a..ff0cc0d 100644
--- a/libdiskfs/node-make.c
+++ b/libdiskfs/node-make.c
@@ -19,16 +19,9 @@
 #include <fcntl.h>
 
 
-/* Create a and return new node structure with DN as its physical disknode.
-   The node will have one hard reference and no light references.  */
-struct node *
-diskfs_make_node (struct disknode *dn)
+static struct node *
+init_node (struct node *np, struct disknode *dn)
 {
-  struct node *np = malloc (sizeof (struct node));
-
-  if (np == 0)
-    return 0;
-
   np->dn = dn;
   np->dn_set_ctime = 0;
   np->dn_set_atime = 0;
@@ -52,3 +45,31 @@ diskfs_make_node (struct disknode *dn)
 
   return np;
 }
+
+/* Create a and return new node structure with DN as its physical disknode.
+   The node will have one hard reference and no light references.  */
+struct node *
+diskfs_make_node (struct disknode *dn)
+{
+  struct node *np = malloc (sizeof (struct node));
+
+  if (np == 0)
+    return 0;
+
+  return init_node (np, dn);
+}
+
+/* Create a new node structure.  Also allocate SIZE bytes for the
+   disknode.  The address of the disknode can be obtained using
+   diskfs_node_disknode.  The new node will have one hard reference
+   and no light references.  */
+struct node *
+diskfs_make_node_alloc (size_t size)
+{
+  struct node *np = malloc (sizeof (struct node) + size);
+
+  if (np == NULL)
+    return NULL;
+
+  return init_node (np, diskfs_node_disknode (np));
+}
-- 
2.0.0.rc2