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, 25 insertions, 0 deletions

diff --git a/fs/nilfs2/page.c b/fs/nilfs2/page.c
index aab11db2cb08..6384ac14c0c8 100644
--- a/fs/nilfs2/page.c
+++ b/fs/nilfs2/page.c
@@ -513,6 +513,31 @@ unsigned nilfs_page_count_clean_buffers(struct page *page,
         }
         return nc;
 }
+ 
+void nilfs_mapping_init_once(struct address_space *mapping)
+{
+        memset(mapping, 0, sizeof(*mapping));
+        INIT_RADIX_TREE(&mapping->page_tree, GFP_ATOMIC);
+        spin_lock_init(&mapping->tree_lock);
+        INIT_LIST_HEAD(&mapping->private_list);
+        spin_lock_init(&mapping->private_lock);
+
+        spin_lock_init(&mapping->i_mmap_lock);
+        INIT_RAW_PRIO_TREE_ROOT(&mapping->i_mmap);
+        INIT_LIST_HEAD(&mapping->i_mmap_nonlinear);
+}
+
+void nilfs_mapping_init(struct address_space *mapping,
+                        struct backing_dev_info *bdi,
+                        const struct address_space_operations *aops)
+{
+        mapping->host = NULL;
+        mapping->flags = 0;
+        mapping_set_gfp_mask(mapping, GFP_NOFS);
+        mapping->assoc_mapping = NULL;
+        mapping->backing_dev_info = bdi;
+        mapping->a_ops = aops;
+}
 
 /*
  * NILFS2 needs clear_page_dirty() in the following two cases: