nilfs2: add routines to roll back state of DAT file

This adds optional function to metadata files which makes a copy of
bmap, page caches, and b-tree node cache, and rolls back to the copy
as needed.

This enhancement is intended to displace gcdat inode that provides a
similar function in a different way.

In this patch, nilfs_shadow_map structure is added to store a copy of
the foregoing states.  nilfs_mdt_setup_shadow_map relates this
structure to a metadata file.  And, nilfs_mdt_save_to_shadow_map() and
nilfs_mdt_restore_from_shadow_map() provides save and restore
functions respectively.  Finally, nilfs_mdt_clear_shadow_map() clears
states of nilfs_shadow_map.

The copy of b-tree node cache and page cache is made by duplicating
only dirty pages into corresponding caches in nilfs_shadow_map.  Their
restoration is done by clearing dirty pages from original caches and
by copying dirty pages back from nilfs_shadow_map.

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

1 files changed, 14 insertions, 0 deletions

diff --git a/fs/nilfs2/mdt.h b/fs/nilfs2/mdt.h
index f44560224bd1..e7f0d158c527 100644
--- a/fs/nilfs2/mdt.h
+++ b/fs/nilfs2/mdt.h
@@ -28,6 +28,13 @@
 #include "nilfs.h"
 #include "page.h"
 
+struct nilfs_shadow_map {
+        struct nilfs_bmap_store bmap_store;
+        struct address_space frozen_data;
+        struct address_space frozen_btnodes;
+        struct list_head frozen_buffers;
+};
+
 /**
  * struct nilfs_mdt_info - on-memory private data of meta data files
  * @mi_nilfs: back pointer to the_nilfs struct
@@ -37,6 +44,7 @@
  * @mi_first_entry_offset: offset to the first entry
  * @mi_entries_per_block: number of entries in a block
  * @mi_palloc_cache: persistent object allocator cache
+ * @mi_shadow: shadow of bmap and page caches
  * @mi_blocks_per_group: number of blocks in a group
  * @mi_blocks_per_desc_block: number of blocks per descriptor block
  */
@@ -48,6 +56,7 @@ struct nilfs_mdt_info {
         unsigned                mi_first_entry_offset;
         unsigned long           mi_entries_per_block;
         struct nilfs_palloc_cache *mi_palloc_cache;
+        struct nilfs_shadow_map *mi_shadow;
         unsigned long           mi_blocks_per_group;
         unsigned long           mi_blocks_per_desc_block;
 };
@@ -86,6 +95,11 @@ void nilfs_mdt_destroy(struct inode *);
 void nilfs_mdt_set_entry_size(struct inode *, unsigned, unsigned);
 void nilfs_mdt_set_shadow(struct inode *, struct inode *);
 
+int nilfs_mdt_setup_shadow_map(struct inode *inode,
+                               struct nilfs_shadow_map *shadow);
+int nilfs_mdt_save_to_shadow_map(struct inode *inode);
+void nilfs_mdt_restore_from_shadow_map(struct inode *inode);
+void nilfs_mdt_clear_shadow_map(struct inode *inode);
 
 #define nilfs_mdt_mark_buffer_dirty(bh) nilfs_mark_buffer_dirty(bh)