ext4: add a function which updates the super block during online resizing

This patch adds a function named ext4_update_super() which updates
super block so the newly created block groups are visible to the file
system.  This code is copied from ext4_group_add().

The function will be used by new resize implementation.
Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/resize.c

@@ -1142,6 +1142,100 @@ static int ext4_setup_new_descs(handle_t *handle, struct super_block *sb,
 	return err;
 }
 
+/*
+ * ext4_update_super() updates the super block so that the newly added
+ * groups can be seen by the filesystem.
+ *
+ * @sb: super block
+ * @flex_gd: new added groups
+ */
+static void ext4_update_super(struct super_block *sb,
+			     struct ext4_new_flex_group_data *flex_gd)
+{
+	ext4_fsblk_t blocks_count = 0;
+	ext4_fsblk_t free_blocks = 0;
+	ext4_fsblk_t reserved_blocks = 0;
+	struct ext4_new_group_data *group_data = flex_gd->groups;
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	struct ext4_super_block *es = sbi->s_es;
+	int i;
+
+	BUG_ON(flex_gd->count == 0 || group_data == NULL);
+	/*
+	 * Make the new blocks and inodes valid next.  We do this before
+	 * increasing the group count so that once the group is enabled,
+	 * all of its blocks and inodes are already valid.
+	 *
+	 * We always allocate group-by-group, then block-by-block or
+	 * inode-by-inode within a group, so enabling these
+	 * blocks/inodes before the group is live won't actually let us
+	 * allocate the new space yet.
+	 */
+	for (i = 0; i < flex_gd->count; i++) {
+		blocks_count += group_data[i].blocks_count;
+		free_blocks += group_data[i].free_blocks_count;
+	}
+
+	reserved_blocks = ext4_r_blocks_count(es) * 100;
+	do_div(reserved_blocks, ext4_blocks_count(es));
+	reserved_blocks *= blocks_count;
+	do_div(reserved_blocks, 100);
+
+	ext4_blocks_count_set(es, ext4_blocks_count(es) + blocks_count);
+	le32_add_cpu(&es->s_inodes_count, EXT4_INODES_PER_GROUP(sb) *
+		     flex_gd->count);
+
+	/*
+	 * We need to protect s_groups_count against other CPUs seeing
+	 * inconsistent state in the superblock.
+	 *
+	 * The precise rules we use are:
+	 *
+	 * * Writers must perform a smp_wmb() after updating all
+	 *   dependent data and before modifying the groups count
+	 *
+	 * * Readers must perform an smp_rmb() after reading the groups
+	 *   count and before reading any dependent data.
+	 *
+	 * NB. These rules can be relaxed when checking the group count
+	 * while freeing data, as we can only allocate from a block
+	 * group after serialising against the group count, and we can
+	 * only then free after serialising in turn against that
+	 * allocation.
+	 */
+	smp_wmb();
+
+	/* Update the global fs size fields */
+	sbi->s_groups_count += flex_gd->count;
+
+	/* Update the reserved block counts only once the new group is
+	 * active. */
+	ext4_r_blocks_count_set(es, ext4_r_blocks_count(es) +
+				reserved_blocks);
+
+	/* Update the free space counts */
+	percpu_counter_add(&sbi->s_freeclusters_counter,
+			   EXT4_B2C(sbi, free_blocks));
+	percpu_counter_add(&sbi->s_freeinodes_counter,
+			   EXT4_INODES_PER_GROUP(sb) * flex_gd->count);
+
+	if (EXT4_HAS_INCOMPAT_FEATURE(sb,
+				      EXT4_FEATURE_INCOMPAT_FLEX_BG) &&
+	    sbi->s_log_groups_per_flex) {
+		ext4_group_t flex_group;
+		flex_group = ext4_flex_group(sbi, group_data[0].group);
+		atomic_add(EXT4_B2C(sbi, free_blocks),
+			   &sbi->s_flex_groups[flex_group].free_clusters);
+		atomic_add(EXT4_INODES_PER_GROUP(sb) * flex_gd->count,
+			   &sbi->s_flex_groups[flex_group].free_inodes);
+	}
+
+	if (test_opt(sb, DEBUG))
+		printk(KERN_DEBUG "EXT4-fs: added group %u:"
+		       "%llu blocks(%llu free %llu reserved)\n", flex_gd->count,
+		       blocks_count, free_blocks, reserved_blocks);
+}
+
 /* Add group descriptor data to an existing or new group descriptor block.
  * Ensure we handle all possible error conditions _before_ we start modifying
  * the filesystem, because we cannot abort the transaction and not have it