btrfs: add fs context handling functions

We are going to use the fs context to hold the mount options, so
allocate the btrfs_fs_context when we're asked to init the fs context,
and free it in the free callback.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/super.c

@@ -2642,10 +2642,44 @@ static void btrfs_kill_super(struct super_block *sb)
 	btrfs_free_fs_info(fs_info);
 }
 
-static const struct fs_context_operations btrfs_fs_context_ops __maybe_unused = {
+static void btrfs_free_fs_context(struct fs_context *fc)
+{
+	struct btrfs_fs_context *ctx = fc->fs_private;
+
+	if (!ctx)
+		return;
+
+	kfree(ctx->subvol_name);
+	kfree(ctx);
+}
+
+static const struct fs_context_operations btrfs_fs_context_ops = {
 	.parse_param	= btrfs_parse_param,
+	.free		= btrfs_free_fs_context,
 };
 
+static int __maybe_unused btrfs_init_fs_context(struct fs_context *fc)
+{
+	struct btrfs_fs_context *ctx;
+
+	ctx = kzalloc(sizeof(struct btrfs_fs_context), GFP_KERNEL);
+	if (!ctx)
+		return -ENOMEM;
+
+	ctx->thread_pool_size = min_t(unsigned long, num_online_cpus() + 2, 8);
+	ctx->max_inline = BTRFS_DEFAULT_MAX_INLINE;
+	ctx->commit_interval = BTRFS_DEFAULT_COMMIT_INTERVAL;
+	ctx->subvol_objectid = BTRFS_FS_TREE_OBJECTID;
+#ifndef CONFIG_BTRFS_FS_POSIX_ACL
+	ctx->noacl = true;
+#endif
+
+	fc->fs_private = ctx;
+	fc->ops = &btrfs_fs_context_ops;
+
+	return 0;
+}
+
 static struct file_system_type btrfs_fs_type = {
 	.owner		= THIS_MODULE,
 	.name		= "btrfs",