libceph: introduce reference counted string

The data structure is for storing namesapce string. It allows namespace
string to be shared between cephfs inodes with same layout. This data
structure can also be referenced by OSD request.
Signed-off-by: Yan, Zheng <zyan@redhat.com>

include/linux/ceph/libceph.h

@@ -21,6 +21,7 @@
 #include <linux/ceph/mon_client.h>
 #include <linux/ceph/osd_client.h>
 #include <linux/ceph/ceph_fs.h>
+#include <linux/ceph/string_table.h>
 
 /*
  * mount options

include/linux/ceph/string_table.h

+#ifndef _FS_CEPH_STRING_TABLE_H
+#define _FS_CEPH_STRING_TABLE_H
+
+#include <linux/types.h>
+#include <linux/kref.h>
+#include <linux/rbtree.h>
+#include <linux/rcupdate.h>
+
+struct ceph_string {
+	struct kref kref;
+	union {
+		struct rb_node node;
+		struct rcu_head rcu;
+	};
+	size_t len;
+	char str[];
+};
+
+extern void ceph_release_string(struct kref *ref);
+extern struct ceph_string *ceph_find_or_create_string(const char *str,
+						      size_t len);
+extern bool ceph_strings_empty(void);
+
+static inline struct ceph_string *ceph_get_string(struct ceph_string *str)
+{
+	kref_get(&str->kref);
+	return str;
+}
+
+static inline void ceph_put_string(struct ceph_string *str)
+{
+	if (!str)
+		return;
+	kref_put(&str->kref, ceph_release_string);
+}
+
+static inline int ceph_compare_string(struct ceph_string *cs,
+				      const char* str, size_t len)
+{
+	size_t cs_len = cs ? cs->len : 0;
+	if (cs_len != len)
+		return cs_len - len;
+	if (len == 0)
+		return 0;
+	return strncmp(cs->str, str, len);
+}
+
+#define ceph_try_get_string(x)					\
+({								\
+	struct ceph_string *___str;				\
+	rcu_read_lock();					\
+	for (;;) {						\
+		___str = rcu_dereference(x);			\
+		if (!___str ||					\
+		    kref_get_unless_zero(&___str->kref))	\
+			break;					\
+	}							\
+	rcu_read_unlock();					\
+	(___str);						\
+})
+
+#endif

net/ceph/Makefile

@@ -11,5 +11,5 @@ libceph-y := ceph_common.o messenger.o msgpool.o buffer.o pagelist.o \
 	crypto.o armor.o \
 	auth_x.o \
 	ceph_fs.o ceph_strings.o ceph_hash.o \
-	pagevec.o snapshot.o
+	pagevec.o snapshot.o string_table.o
 

net/ceph/ceph_common.c

@@ -747,6 +747,8 @@ static int __init init_ceph_lib(void)
 static void __exit exit_ceph_lib(void)
 {
 	dout("exit_ceph_lib\n");
+	WARN_ON(!ceph_strings_empty());
+
 	ceph_osdc_cleanup();
 	ceph_msgr_exit();
 	ceph_crypto_shutdown();

net/ceph/string_table.c

+#include <linux/slab.h>
+#include <linux/gfp.h>
+#include <linux/string.h>
+#include <linux/spinlock.h>
+#include <linux/ceph/string_table.h>
+
+static DEFINE_SPINLOCK(string_tree_lock);
+static struct rb_root string_tree = RB_ROOT;
+
+struct ceph_string *ceph_find_or_create_string(const char* str, size_t len)
+{
+	struct ceph_string *cs, *exist;
+	struct rb_node **p, *parent;
+	int ret;
+
+	exist = NULL;
+	spin_lock(&string_tree_lock);
+	p = &string_tree.rb_node;
+	while (*p) {
+		exist = rb_entry(*p, struct ceph_string, node);
+		ret = ceph_compare_string(exist, str, len);
+		if (ret > 0)
+			p = &(*p)->rb_left;
+		else if (ret < 0)
+			p = &(*p)->rb_right;
+		else
+			break;
+		exist = NULL;
+	}
+	if (exist && !kref_get_unless_zero(&exist->kref)) {
+		rb_erase(&exist->node, &string_tree);
+		RB_CLEAR_NODE(&exist->node);
+		exist = NULL;
+	}
+	spin_unlock(&string_tree_lock);
+	if (exist)
+		return exist;
+
+	cs = kmalloc(sizeof(*cs) + len + 1, GFP_NOFS);
+	if (!cs)
+		return NULL;
+
+	kref_init(&cs->kref);
+	cs->len = len;
+	memcpy(cs->str, str, len);
+	cs->str[len] = 0;
+
+retry:
+	exist = NULL;
+	parent = NULL;
+	p = &string_tree.rb_node;
+	spin_lock(&string_tree_lock);
+	while (*p) {
+		parent = *p;
+		exist = rb_entry(*p, struct ceph_string, node);
+		ret = ceph_compare_string(exist, str, len);
+		if (ret > 0)
+			p = &(*p)->rb_left;
+		else if (ret < 0)
+			p = &(*p)->rb_right;
+		else
+			break;
+		exist = NULL;
+	}
+	ret = 0;
+	if (!exist) {
+		rb_link_node(&cs->node, parent, p);
+		rb_insert_color(&cs->node, &string_tree);
+	} else if (!kref_get_unless_zero(&exist->kref)) {
+		rb_erase(&exist->node, &string_tree);
+		RB_CLEAR_NODE(&exist->node);
+		ret = -EAGAIN;
+	}
+	spin_unlock(&string_tree_lock);
+	if (ret == -EAGAIN)
+		goto retry;
+
+	if (exist) {
+		kfree(cs);
+		cs = exist;
+	}
+
+	return cs;
+}
+EXPORT_SYMBOL(ceph_find_or_create_string);
+
+static void ceph_free_string(struct rcu_head *head)
+{
+	struct ceph_string *cs = container_of(head, struct ceph_string, rcu);
+	kfree(cs);
+}
+
+void ceph_release_string(struct kref *ref)
+{
+	struct ceph_string *cs = container_of(ref, struct ceph_string, kref);
+
+	spin_lock(&string_tree_lock);
+	if (!RB_EMPTY_NODE(&cs->node)) {
+		rb_erase(&cs->node, &string_tree);
+		RB_CLEAR_NODE(&cs->node);
+	}
+	spin_unlock(&string_tree_lock);
+
+	call_rcu(&cs->rcu, ceph_free_string);
+}
+EXPORT_SYMBOL(ceph_release_string);
+
+bool ceph_strings_empty(void)
+{
+	return RB_EMPTY_ROOT(&string_tree);
+}