nilfs2: add checkpoint tree to nilfs object

To hold multiple versions of a filesystem in one sb instance, a new
on-memory structure is necessary to handle one or more checkpoints.

This adds a red-black tree of checkpoints to nilfs object, and adds
lookup and create functions for them.

Each checkpoint is represented by "nilfs_root" structure, and this
structure has rb_node to configure the rb-tree.

The nilfs_root object is identified with a checkpoint number.  For
each snapshot, a nilfs_root object is allocated and the checkpoint
number of snapshot is assigned to it.  For a regular mount
(i.e. current mode mount), NILFS_CPTREE_CURRENT_CNO constant is
assigned to the corresponding nilfs_root object.

Each nilfs_root object has an ifile inode and some counters.  These
items will displace those of nilfs_sb_info structure in successive
patches.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

2 files changed, 134 insertions, 0 deletions

diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index 6a012b9e1b31..f1d599273d9e 100644
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -89,6 +89,8 @@ static struct the_nilfs *alloc_nilfs(struct block_device *bdev)
         INIT_LIST_HEAD(&nilfs->ns_supers);
         INIT_LIST_HEAD(&nilfs->ns_gc_inodes);
         spin_lock_init(&nilfs->ns_last_segment_lock);
+        nilfs->ns_cptree = RB_ROOT;
+        spin_lock_init(&nilfs->ns_cptree_lock);
         init_rwsem(&nilfs->ns_segctor_sem);
 
         return nilfs;
@@ -809,6 +811,96 @@ int nilfs_near_disk_full(struct the_nilfs *nilfs)
         return ncleansegs <= nilfs->ns_nrsvsegs + nincsegs;
 }
 
+struct nilfs_root *nilfs_lookup_root(struct the_nilfs *nilfs, __u64 cno)
+{
+        struct rb_node *n;
+        struct nilfs_root *root;
+
+        spin_lock(&nilfs->ns_cptree_lock);
+        n = nilfs->ns_cptree.rb_node;
+        while (n) {
+                root = rb_entry(n, struct nilfs_root, rb_node);
+
+                if (cno < root->cno) {
+                        n = n->rb_left;
+                } else if (cno > root->cno) {
+                        n = n->rb_right;
+                } else {
+                        atomic_inc(&root->count);
+                        spin_unlock(&nilfs->ns_cptree_lock);
+                        return root;
+                }
+        }
+        spin_unlock(&nilfs->ns_cptree_lock);
+
+        return NULL;
+}
+
+struct nilfs_root *
+nilfs_find_or_create_root(struct the_nilfs *nilfs, __u64 cno)
+{
+        struct rb_node **p, *parent;
+        struct nilfs_root *root, *new;
+
+        root = nilfs_lookup_root(nilfs, cno);
+        if (root)
+                return root;
+
+        new = kmalloc(sizeof(*root), GFP_KERNEL);
+        if (!new)
+                return NULL;
+
+        spin_lock(&nilfs->ns_cptree_lock);
+
+        p = &nilfs->ns_cptree.rb_node;
+        parent = NULL;
+
+        while (*p) {
+                parent = *p;
+                root = rb_entry(parent, struct nilfs_root, rb_node);
+
+                if (cno < root->cno) {
+                        p = &(*p)->rb_left;
+                } else if (cno > root->cno) {
+                        p = &(*p)->rb_right;
+                } else {
+                        atomic_inc(&root->count);
+                        spin_unlock(&nilfs->ns_cptree_lock);
+                        kfree(new);
+                        return root;
+                }
+        }
+
+        new->cno = cno;
+        new->ifile = NULL;
+        new->nilfs = nilfs;
+        atomic_set(&new->count, 1);
+        atomic_set(&new->inodes_count, 0);
+        atomic_set(&new->blocks_count, 0);
+
+        rb_link_node(&new->rb_node, parent, p);
+        rb_insert_color(&new->rb_node, &nilfs->ns_cptree);
+
+        spin_unlock(&nilfs->ns_cptree_lock);
+
+        return new;
+}
+
+void nilfs_put_root(struct nilfs_root *root)
+{
+        if (atomic_dec_and_test(&root->count)) {
+                struct the_nilfs *nilfs = root->nilfs;
+
+                spin_lock(&nilfs->ns_cptree_lock);
+                rb_erase(&root->rb_node, &nilfs->ns_cptree);
+                spin_unlock(&nilfs->ns_cptree_lock);
+                if (root->ifile)
+                        nilfs_mdt_destroy(root->ifile);
+
+                kfree(root);
+        }
+}
+
 /**
  * nilfs_find_sbinfo - find existing nilfs_sb_info structure
  * @nilfs: nilfs object
diff --git a/fs/nilfs2/the_nilfs.h b/fs/nilfs2/the_nilfs.h
index c7ecd0c623a3..0afede68a9e1 100644
--- a/fs/nilfs2/the_nilfs.h
+++ b/fs/nilfs2/the_nilfs.h
@@ -26,6 +26,7 @@
 
 #include <linux/types.h>
 #include <linux/buffer_head.h>
+#include <linux/rbtree.h>
 #include <linux/fs.h>
 #include <linux/blkdev.h>
 #include <linux/backing-dev.h>
@@ -80,6 +81,8 @@ enum {
  * @ns_cpfile: checkpoint file inode
  * @ns_sufile: segusage file inode
  * @ns_gc_dat: shadow inode of the DAT file inode for GC
+ * @ns_cptree: rb-tree of all mounted checkpoints (nilfs_root)
+ * @ns_cptree_lock: lock protecting @ns_cptree
  * @ns_gc_inodes: dummy inodes to keep live blocks
  * @ns_blocksize_bits: bit length of block size
  * @ns_blocksize: block size
@@ -164,6 +167,10 @@ struct the_nilfs {
         struct inode           *ns_sufile;
         struct inode           *ns_gc_dat;
 
+        /* Checkpoint tree */
+        struct rb_root          ns_cptree;
+        spinlock_t              ns_cptree_lock;
+
         /* GC inode list */
         struct list_head        ns_gc_inodes;
 
@@ -200,6 +207,32 @@ THE_NILFS_FNS(DISCONTINUED, discontinued)
 THE_NILFS_FNS(GC_RUNNING, gc_running)
 THE_NILFS_FNS(SB_DIRTY, sb_dirty)
 
+/**
+ * struct nilfs_root - nilfs root object
+ * @cno: checkpoint number
+ * @rb_node: red-black tree node
+ * @count: refcount of this structure
+ * @nilfs: nilfs object
+ * @ifile: inode file
+ * @root: root inode
+ * @inodes_count: number of inodes
+ * @blocks_count: number of blocks (Reserved)
+ */
+struct nilfs_root {
+        __u64 cno;
+        struct rb_node rb_node;
+
+        atomic_t count;
+        struct the_nilfs *nilfs;
+        struct inode *ifile;
+
+        atomic_t inodes_count;
+        atomic_t blocks_count;
+};
+
+/* Special checkpoint number */
+#define NILFS_CPTREE_CURRENT_CNO        0
+
 /* Minimum interval of periodical update of superblocks (in seconds) */
 #define NILFS_SB_FREQ           10
 
@@ -222,6 +255,10 @@ int init_nilfs(struct the_nilfs *, struct nilfs_sb_info *, char *);
 int load_nilfs(struct the_nilfs *, struct nilfs_sb_info *);
 int nilfs_discard_segments(struct the_nilfs *, __u64 *, size_t);
 int nilfs_count_free_blocks(struct the_nilfs *, sector_t *);
+struct nilfs_root *nilfs_lookup_root(struct the_nilfs *nilfs, __u64 cno);
+struct nilfs_root *nilfs_find_or_create_root(struct the_nilfs *nilfs,
+                                             __u64 cno);
+void nilfs_put_root(struct nilfs_root *root);
 struct nilfs_sb_info *nilfs_find_sbinfo(struct the_nilfs *, int, __u64);
 int nilfs_checkpoint_is_mounted(struct the_nilfs *, __u64, int);
 int nilfs_near_disk_full(struct the_nilfs *);
@@ -235,6 +272,11 @@ static inline void get_nilfs(struct the_nilfs *nilfs)
         atomic_inc(&nilfs->ns_count);
 }
 
+static inline void nilfs_get_root(struct nilfs_root *root)
+{
+        atomic_inc(&root->count);
+}
+
 static inline void
 nilfs_attach_writer(struct the_nilfs *nilfs, struct nilfs_sb_info *sbi)
 {