pramfs: xattr block descriptors tree

diff -Nurp linux-2.6.36-orig/fs/pramfs/desctree.c linux-2.6.36/fs/pramfs/desctree.c
@@ -0,0 +1,184 @@
+/*
+ * FILE NAME fs/pramfs/desctree.c
+ *
+ * BRIEF DESCRIPTION
+ *
+ * Extended attributes block descriptors tree.
+ *
+ * Copyright 2010 Marco Stornelli <[email protected]>
+ *
+ * This file is licensed under the terms of the GNU General Public
+ * License version 2. This program is licensed "as is" without any
+ * warranty of any kind, whether express or implied.
+ */
+
+#include <linux/spinlock.h>
+#include "desctree.h"
+#include "pram.h"
+
+/* xblock_desc_init_always()
+ *
+ * These are initializations that need to be done on every
+ * descriptor allocation as the fields are not initialised
+ * by slab allocation.
+ */
+void xblock_desc_init_always(struct pram_xblock_desc *desc)
+{
+	atomic_set(&desc->refcount, 0);
+	desc->blocknr = 0;
+	desc->flags = 0;
+}
+
+/* xblock_desc_init_once()
+ *
+ * These are initializations that only need to be done
+ * once, because the fields are idempotent across use
+ * of the descriptor, so let the slab aware of that.
+ */
+void xblock_desc_init_once(struct pram_xblock_desc *desc)
+{
+	mutex_init(&desc->lock);
+}
+
+/* __insert_xblock_desc()
+ *
+ * Insert a new descriptor in the tree.
+ *
+ */
+static void __insert_xblock_desc(struct pram_sb_info *sbi,
+				 unsigned long blocknr, struct rb_node *node)
+{
+	struct rb_node **p = &(sbi->desc_tree.rb_node);
+	struct rb_node *parent = NULL;
+	struct pram_xblock_desc *desc;
+
+	while (*p) {
+		parent = *p;
+		desc = rb_entry(parent, struct pram_xblock_desc, node);
+
+		if (blocknr < desc->blocknr)
+			p = &(*p)->rb_left;
+		else if (blocknr > desc->blocknr)
+			p = &(*p)->rb_right;
+		else
+			/* Oops...an other descriptor for the same block ? */
+			BUG();
+	}
+
+	rb_link_node(node, parent, p);
+	rb_insert_color(node, &sbi->desc_tree);
+}
+
+void insert_xblock_desc(struct pram_sb_info *sbi, struct pram_xblock_desc *desc)
+{
+	spin_lock(&sbi->desc_tree_lock);
+	__insert_xblock_desc(sbi, desc->blocknr, &desc->node);
+	spin_unlock(&sbi->desc_tree_lock);
+};
+
+/* __lookup_xblock_desc()
+ *
+ * Search an extended attribute descriptor in the tree via the
+ * block number. It returns the descriptor if it's found or
+ * NULL. If not found it creates a new descriptor if create is not 0.
+ */
+static struct pram_xblock_desc *__lookup_xblock_desc(struct pram_sb_info *sbi,
+					    unsigned long blocknr,
+					    struct kmem_cache *cache,
+					    int create)
+{
+	struct rb_node *n = sbi->desc_tree.rb_node;
+	struct pram_xblock_desc *desc = NULL;
+
+	while (n) {
+		desc = rb_entry(n, struct pram_xblock_desc, node);
+
+		if (blocknr < desc->blocknr)
+			n = n->rb_left;
+		else if (blocknr > desc->blocknr)
+			n = n->rb_right;
+		else {
+			atomic_inc(&desc->refcount);
+			goto out;
+		}
+	}
+
+	/* not found */
+	if (create) {
+		desc = kmem_cache_alloc(cache, GFP_NOFS);
+		if (!desc)
+			return ERR_PTR(-ENOMEM);
+		xblock_desc_init_always(desc);
+		atomic_set(&desc->refcount, 1);
+		desc->blocknr = blocknr;
+		__insert_xblock_desc(sbi, desc->blocknr, &desc->node);
+	}
+out:
+	return desc;
+}
+
+struct pram_xblock_desc *lookup_xblock_desc(struct pram_sb_info *sbi,
+					    unsigned long blocknr,
+					    struct kmem_cache *cache,
+					    int create)
+{
+	struct pram_xblock_desc *desc = NULL;
+
+	spin_lock(&sbi->desc_tree_lock);
+	desc = __lookup_xblock_desc(sbi, blocknr, cache, create);
+	spin_unlock(&sbi->desc_tree_lock);
+	return desc;
+}
+
+/* put_xblock_desc()
+ *
+ * Decrement the reference count and if it reaches zero and the
+ * desciptor has been marked to be free, then we free it.
+ * It returns 0 if the descriptor has been deleted and 1 otherwise.
+ */
+int put_xblock_desc(struct pram_sb_info *sbi, struct pram_xblock_desc *desc)
+{
+	int ret = 1;
+	if (!desc)
+		return ret;
+
+	if (atomic_dec_and_lock(&desc->refcount, &sbi->desc_tree_lock)) {
+		if (test_bit(FREEING, &desc->flags)) {
+			rb_erase(&desc->node, &sbi->desc_tree);
+			pram_dbg("erasing desc for block %lu\n", desc->blocknr);
+			ret = 0;
+		}
+		spin_unlock(&sbi->desc_tree_lock);
+	}
+	return ret;
+};
+
+/* mark_free_desc()
+ *
+ * Mark free a descriptor. The descriptor will be deleted later in the
+ * put_xblock_desc().
+ */
+void mark_free_desc(struct pram_xblock_desc *desc)
+{
+	set_bit(FREEING, &desc->flags);
+}
+
+/* erase_tree()
+ *
+ * Free all objects in the tree.
+ */
+void erase_tree(struct pram_sb_info *sbi, struct kmem_cache *cachep)
+{
+	struct rb_node *n;
+	struct pram_xblock_desc *desc;
+
+	spin_lock(&sbi->desc_tree_lock);
+	n = rb_first(&sbi->desc_tree);
+	while (n) {
+		desc = rb_entry(n, struct pram_xblock_desc, node);
+		rb_erase(n, &sbi->desc_tree);
+		kmem_cache_free(cachep, desc);
+		n = rb_next(n);
+	}
+	spin_unlock(&sbi->desc_tree_lock);
+}

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