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, 100 insertions, 4 deletions

diff --git a/fs/nilfs2/mdt.c b/fs/nilfs2/mdt.c
index 73e5da3b097..0066468609d 100644
--- a/fs/nilfs2/mdt.c
+++ b/fs/nilfs2/mdt.c
@@ -398,16 +398,22 @@ int nilfs_mdt_fetch_dirty(struct inode *inode)
 static int
 nilfs_mdt_write_page(struct page *page, struct writeback_control *wbc)
 {
-        struct inode *inode = container_of(page->mapping,
-                                           struct inode, i_data);
-        struct super_block *sb = inode->i_sb;
-        struct the_nilfs *nilfs = NILFS_MDT(inode)->mi_nilfs;
+        struct inode *inode;
+        struct super_block *sb;
+        struct the_nilfs *nilfs;
         struct nilfs_sb_info *writer = NULL;
         int err = 0;
 
         redirty_page_for_writepage(wbc, page);
         unlock_page(page);
 
+        inode = page->mapping->host;
+        if (!inode)
+                return 0;
+
+        sb = inode->i_sb;
+        nilfs = NILFS_MDT(inode)->mi_nilfs;
+
         if (page->mapping->assoc_mapping)
                 return 0; /* Do not request flush for shadow page cache */
         if (!sb) {
@@ -567,6 +573,96 @@ void nilfs_mdt_set_shadow(struct inode *orig, struct inode *shadow)
                 &NILFS_I(orig)->i_btnode_cache;
 }
 
+static const struct address_space_operations shadow_map_aops = {
+        .sync_page              = block_sync_page,
+};
+
+/**
+ * nilfs_mdt_setup_shadow_map - setup shadow map and bind it to metadata file
+ * @inode: inode of the metadata file
+ * @shadow: shadow mapping
+ */
+int nilfs_mdt_setup_shadow_map(struct inode *inode,
+                               struct nilfs_shadow_map *shadow)
+{
+        struct nilfs_mdt_info *mi = NILFS_MDT(inode);
+        struct backing_dev_info *bdi = NILFS_I_NILFS(inode)->ns_bdi;
+
+        INIT_LIST_HEAD(&shadow->frozen_buffers);
+        nilfs_mapping_init_once(&shadow->frozen_data);
+        nilfs_mapping_init(&shadow->frozen_data, bdi, &shadow_map_aops);
+        nilfs_mapping_init_once(&shadow->frozen_btnodes);
+        nilfs_mapping_init(&shadow->frozen_btnodes, bdi, &shadow_map_aops);
+        mi->mi_shadow = shadow;
+        return 0;
+}
+
+/**
+ * nilfs_mdt_save_to_shadow_map - copy bmap and dirty pages to shadow map
+ * @inode: inode of the metadata file
+ */
+int nilfs_mdt_save_to_shadow_map(struct inode *inode)
+{
+        struct nilfs_mdt_info *mi = NILFS_MDT(inode);
+        struct nilfs_inode_info *ii = NILFS_I(inode);
+        struct nilfs_shadow_map *shadow = mi->mi_shadow;
+        int ret;
+
+        ret = nilfs_copy_dirty_pages(&shadow->frozen_data, inode->i_mapping);
+        if (ret)
+                goto out;
+
+        ret = nilfs_copy_dirty_pages(&shadow->frozen_btnodes,
+                                     &ii->i_btnode_cache);
+        if (ret)
+                goto out;
+
+        nilfs_bmap_save(ii->i_bmap, &shadow->bmap_store);
+ out:
+        return ret;
+}
+
+/**
+ * nilfs_mdt_restore_from_shadow_map - restore dirty pages and bmap state
+ * @inode: inode of the metadata file
+ */
+void nilfs_mdt_restore_from_shadow_map(struct inode *inode)
+{
+        struct nilfs_mdt_info *mi = NILFS_MDT(inode);
+        struct nilfs_inode_info *ii = NILFS_I(inode);
+        struct nilfs_shadow_map *shadow = mi->mi_shadow;
+
+        down_write(&mi->mi_sem);
+
+        if (mi->mi_palloc_cache)
+                nilfs_palloc_clear_cache(inode);
+
+        nilfs_clear_dirty_pages(inode->i_mapping);
+        nilfs_copy_back_pages(inode->i_mapping, &shadow->frozen_data);
+
+        nilfs_clear_dirty_pages(&ii->i_btnode_cache);
+        nilfs_copy_back_pages(&ii->i_btnode_cache, &shadow->frozen_btnodes);
+
+        nilfs_bmap_restore(ii->i_bmap, &shadow->bmap_store);
+
+        up_write(&mi->mi_sem);
+}
+
+/**
+ * nilfs_mdt_clear_shadow_map - truncate pages in shadow map caches
+ * @inode: inode of the metadata file
+ */
+void nilfs_mdt_clear_shadow_map(struct inode *inode)
+{
+        struct nilfs_mdt_info *mi = NILFS_MDT(inode);
+        struct nilfs_shadow_map *shadow = mi->mi_shadow;
+
+        down_write(&mi->mi_sem);
+        truncate_inode_pages(&shadow->frozen_data, 0);
+        truncate_inode_pages(&shadow->frozen_btnodes, 0);
+        up_write(&mi->mi_sem);
+}
+
 static void nilfs_mdt_clear(struct inode *inode)
 {
         struct nilfs_inode_info *ii = NILFS_I(inode);