Implement fool protection for FS pools

src/cli_pool_modify.cpp

@@ -112,6 +112,24 @@ resume_1:
                 return;
             }
 
+            if (new_cfg.find("used_for_fs") != new_cfg.end() && !force)
+            {
+                // Check that pool doesn't have images
+                auto img_it = parent->cli->st_cli.inode_config.lower_bound(INODE_WITH_POOL(pool_id, 0));
+                if (img_it != parent->cli->st_cli.inode_config.end() && INODE_POOL(img_it->first) == pool_id &&
+                    img_it->second.name == new_cfg["used_for_fs"].string_value())
+                {
+                    // Only allow metadata image to exist in the FS pool
+                    img_it++;
+                }
+                if (img_it != parent->cli->st_cli.inode_config.end() && INODE_POOL(img_it->first) == pool_id)
+                {
+                    result = (cli_result_t){ .err = ENOENT, .text = "Pool "+pool_name+" has block images, delete them before using it for VitastorFS" };
+                    state = 100;
+                    return;
+                }
+            }
+
             // Update pool
             auto pls = kv.value.object_items();
             pls[std::to_string(pool_id)] = new_cfg;