nilfs2: add helper functions to delete blocks from dat file

This adds delete functions for data blocks of metadata files using bitmap
based allocator.  nilfs_palloc_delete_entry_block() deletes an entry block
(e.g.  block storing dat entries), and nilfs_palloc_delete_bitmap_block()
deletes a bitmap block, respectively.

These helpers are intended to be used in the successive change on
deallocator of block addresses ("nilfs2: free unused dat file blocks
during garbage collection").
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/nilfs2/alloc.c

@@ -235,6 +235,26 @@ static int nilfs_palloc_get_block(struct inode *inode, unsigned long blkoff,
 	return ret;
 }
 
+/**
+ * nilfs_palloc_delete_block - delete a block on the persistent allocator file
+ * @inode: inode of metadata file using this allocator
+ * @blkoff: block offset
+ * @prev: nilfs_bh_assoc struct of the last used buffer
+ * @lock: spin lock protecting @prev
+ */
+static int nilfs_palloc_delete_block(struct inode *inode, unsigned long blkoff,
+				     struct nilfs_bh_assoc *prev,
+				     spinlock_t *lock)
+{
+	spin_lock(lock);
+	if (prev->bh && blkoff == prev->blkoff) {
+		brelse(prev->bh);
+		prev->bh = NULL;
+	}
+	spin_unlock(lock);
+	return nilfs_mdt_delete_block(inode, blkoff);
+}
+
 /**
  * nilfs_palloc_get_desc_block - get buffer head of a group descriptor block
  * @inode: inode of metadata file using this allocator
@@ -273,6 +293,22 @@ static int nilfs_palloc_get_bitmap_block(struct inode *inode,
 				      &cache->prev_bitmap, &cache->lock);
 }
 
+/**
+ * nilfs_palloc_delete_bitmap_block - delete a bitmap block
+ * @inode: inode of metadata file using this allocator
+ * @group: group number
+ */
+static int nilfs_palloc_delete_bitmap_block(struct inode *inode,
+					    unsigned long group)
+{
+	struct nilfs_palloc_cache *cache = NILFS_MDT(inode)->mi_palloc_cache;
+
+	return nilfs_palloc_delete_block(inode,
+					 nilfs_palloc_bitmap_blkoff(inode,
+								    group),
+					 &cache->prev_bitmap, &cache->lock);
+}
+
 /**
  * nilfs_palloc_get_entry_block - get buffer head of an entry block
  * @inode: inode of metadata file using this allocator
@@ -291,6 +327,20 @@ int nilfs_palloc_get_entry_block(struct inode *inode, __u64 nr,
 				      &cache->prev_entry, &cache->lock);
 }
 
+/**
+ * nilfs_palloc_delete_entry_block - delete an entry block
+ * @inode: inode of metadata file using this allocator
+ * @nr: serial number of the entry
+ */
+static int nilfs_palloc_delete_entry_block(struct inode *inode, __u64 nr)
+{
+	struct nilfs_palloc_cache *cache = NILFS_MDT(inode)->mi_palloc_cache;
+
+	return nilfs_palloc_delete_block(inode,
+					 nilfs_palloc_entry_blkoff(inode, nr),
+					 &cache->prev_entry, &cache->lock);
+}
+
 /**
  * nilfs_palloc_block_get_group_desc - get kernel address of a group descriptor
  * @inode: inode of metadata file using this allocator