diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 2845ed7d6..49c6a4617 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -196,8 +196,8 @@ endif (HAVE_NBD_NETLINK_H AND NL3_LIBRARIES)
 # libvitastor_kv.so
 add_library(vitastor_kv SHARED
 	kv_db.cpp
-	kv_db.h
 )
+set_target_properties(vitastor_kv PROPERTIES PUBLIC_HEADER "vitastor_kv.h")
 target_link_libraries(vitastor_kv
 	vitastor_client
 )
diff --git a/src/kv_cli.cpp b/src/kv_cli.cpp
index 52d3f5427..fd3d7d0af 100644
--- a/src/kv_cli.cpp
+++ b/src/kv_cli.cpp
@@ -12,16 +12,17 @@
 #include <fcntl.h>
 //#include <signal.h>
 
+#include "cluster_client.h"
 #include "epoll_manager.h"
 #include "str_util.h"
-#include "kv_db.h"
+#include "vitastor_kv.h"
 
 const char *exe_name = NULL;
 
 class kv_cli_t
 {
 public:
-    json11::Json::object cfg;
+    std::map<std::string, std::string> cfg;
     std::vector<std::string> cli_cmd;
 
     kv_dbw_t *db = NULL;
@@ -156,7 +157,7 @@ void kv_cli_t::run()
     if (cfg.find("db") != cfg.end())
     {
         bool done = false;
-        handle_cmd({ "open", cfg.at("db").string_value() }, [&done](int res) { if (res != 0) exit(1); done = true; });
+        handle_cmd({ "open", cfg.at("db") }, [&done](int res) { if (res != 0) exit(1); done = true; });
         while (!done)
         {
             ringloop->loop();
diff --git a/src/kv_db.cpp b/src/kv_db.cpp
index aa4ddb73a..7b0bb7db6 100644
--- a/src/kv_db.cpp
+++ b/src/kv_db.cpp
@@ -15,7 +15,7 @@
 
 #include "cluster_client.h"
 #include "str_util.h"
-#include "kv_db.h"
+#include "vitastor_kv.h"
 
 // 0x VITASTOR OPTBTREE
 #define KV_BLOCK_MAGIC 0x761A5106097B18EE
@@ -1969,12 +1969,12 @@ kv_dbw_t::~kv_dbw_t()
     delete db;
 }
 
-void kv_dbw_t::open(inode_t inode_id, json11::Json cfg, std::function<void(int)> cb)
+void kv_dbw_t::open(uint64_t inode_id, std::map<std::string, std::string> cfg, std::function<void(int)> cb)
 {
     db->open(inode_id, cfg, cb);
 }
 
-void kv_dbw_t::set_config(json11::Json cfg)
+void kv_dbw_t::set_config(std::map<std::string, std::string> cfg)
 {
     db->set_config(cfg);
 }
diff --git a/src/kv_stress.cpp b/src/kv_stress.cpp
index e90e47204..4d5fa53d5 100644
--- a/src/kv_stress.cpp
+++ b/src/kv_stress.cpp
@@ -12,9 +12,10 @@
 #include <fcntl.h>
 //#include <signal.h>
 
+#include "cluster_client.h"
 #include "epoll_manager.h"
 #include "str_util.h"
-#include "kv_db.h"
+#include "vitastor_kv.h"
 
 const char *exe_name = NULL;
 
@@ -44,7 +45,7 @@ class kv_test_t
 {
 public:
     // Config
-    json11::Json::object kv_cfg;
+    std::map<std::string, std::string> kv_cfg;
     std::string key_prefix, key_suffix;
     uint64_t inode_id = 0;
     uint64_t op_count = 1000000;
@@ -238,22 +239,22 @@ void kv_test_t::parse_config(json11::Json cfg)
     if (!cfg["stop_on_error"].is_null())
         stop_on_error = cfg["stop_on_error"].bool_value();
     if (!cfg["kv_block_size"].is_null())
-        kv_cfg["kv_block_size"] = cfg["kv_block_size"];
+        kv_cfg["kv_block_size"] = cfg["kv_block_size"].as_string();
     if (!cfg["kv_memory_limit"].is_null())
-        kv_cfg["kv_memory_limit"] = cfg["kv_memory_limit"];
+        kv_cfg["kv_memory_limit"] = cfg["kv_memory_limit"].as_string();
     if (!cfg["kv_allocate_blocks"].is_null())
-        kv_cfg["kv_allocate_blocks"] = cfg["kv_allocate_blocks"];
+        kv_cfg["kv_allocate_blocks"] = cfg["kv_allocate_blocks"].as_string();
     if (!cfg["kv_evict_max_misses"].is_null())
-        kv_cfg["kv_evict_max_misses"] = cfg["kv_evict_max_misses"];
+        kv_cfg["kv_evict_max_misses"] = cfg["kv_evict_max_misses"].as_string();
     if (!cfg["kv_evict_attempts_per_level"].is_null())
-        kv_cfg["kv_evict_attempts_per_level"] = cfg["kv_evict_attempts_per_level"];
+        kv_cfg["kv_evict_attempts_per_level"] = cfg["kv_evict_attempts_per_level"].as_string();
     if (!cfg["kv_evict_unused_age"].is_null())
-        kv_cfg["kv_evict_unused_age"] = cfg["kv_evict_unused_age"];
+        kv_cfg["kv_evict_unused_age"] = cfg["kv_evict_unused_age"].as_string();
     if (!cfg["kv_log_level"].is_null())
     {
         log_level = cfg["kv_log_level"].uint64_value();
         trace = log_level >= 10;
-        kv_cfg["kv_log_level"] = cfg["kv_log_level"];
+        kv_cfg["kv_log_level"] = std::to_string(log_level);
     }
     total_prob = reopen_prob+get_prob+add_prob+update_prob+del_prob+list_prob;
     stat.get.name = "get";
diff --git a/src/nfs_block.cpp b/src/nfs_block.cpp
index de765ab93..71495839a 100644
--- a/src/nfs_block.cpp
+++ b/src/nfs_block.cpp
@@ -2,6 +2,8 @@
 // License: VNPL-1.1 (see README.md for details)
 //
 // NFS proxy over Vitastor block images
+// Presents all images as files
+// Keeps image/file list in memory and is thus unsuitable for a large number of files
 
 #include <sys/time.h>
 
diff --git a/src/nfs_block.h b/src/nfs_block.h
index 7fcf9add2..f523c55ee 100644
--- a/src/nfs_block.h
+++ b/src/nfs_block.h
@@ -2,6 +2,8 @@
 // License: VNPL-1.1 (see README.md for details)
 //
 // NFS proxy over Vitastor block images - header
+// Presents all images as files
+// Keeps image/file list in memory and is thus unsuitable for a large number of files
 
 #pragma once
 
diff --git a/src/nfs_kv.cpp b/src/nfs_kv.cpp
index 1598cca08..6badb5759 100644
--- a/src/nfs_kv.cpp
+++ b/src/nfs_kv.cpp
@@ -256,7 +256,12 @@ void kv_fs_state_t::init(nfs_proxy_t *proxy, json11::Json cfg)
     int open_res = 0;
     bool open_done = false;
     proxy->db = new kv_dbw_t(proxy->cli);
-    proxy->db->open(fs_kv_inode, cfg, [&](int res)
+    std::map<std::string, std::string> kv_cfg;
+    for (auto & kv: cfg.object_items())
+    {
+        kv_cfg[kv.first] = kv.second.as_string();
+    }
+    proxy->db->open(fs_kv_inode, kv_cfg, [&](int res)
     {
         open_done = true;
         open_res = res;
diff --git a/src/nfs_proxy.cpp b/src/nfs_proxy.cpp
index dfbc538de..c93518ea7 100644
--- a/src/nfs_proxy.cpp
+++ b/src/nfs_proxy.cpp
@@ -1,9 +1,7 @@
 // Copyright (c) Vitaliy Filippov, 2019+
 // License: VNPL-1.1 (see README.md for details)
 //
-// Simplified NFS proxy
-// Presents all images as files
-// Keeps image/file list in memory and is thus unsuitable for a large number of files
+// NFS proxy entrypoint, common for both pseudo-FS and Vitastor-KV based FS
 
 #define _XOPEN_SOURCE
 #include <limits.h>
diff --git a/src/nfs_proxy.h b/src/nfs_proxy.h
index 816a73a82..999db70ac 100644
--- a/src/nfs_proxy.h
+++ b/src/nfs_proxy.h
@@ -1,10 +1,15 @@
+// Copyright (c) Vitaliy Filippov, 2019+
+// License: VNPL-1.1 (see README.md for details)
+//
+// Simplified NFS proxy - main entrypoint header
+
 #pragma once
 
 #include "cluster_client.h"
 #include "epoll_manager.h"
 #include "nfs_portmap.h"
 #include "nfs/xdr_impl.h"
-#include "kv_db.h"
+#include "vitastor_kv.h"
 
 #define NFS_ROOT_HANDLE "R"
 #define RPC_INIT_BUF_SIZE 32768
diff --git a/src/vitastor_c.cpp b/src/vitastor_c.cpp
index 7a01b3da8..8099cb741 100644
--- a/src/vitastor_c.cpp
+++ b/src/vitastor_c.cpp
@@ -200,6 +200,11 @@ vitastor_c *vitastor_c_create_epoll_json(const char **options, int options_len)
     return self;
 }
 
+void* vitastor_c_get_internal_client(vitastor_c *client)
+{
+    return client->cli;
+}
+
 void vitastor_c_destroy(vitastor_c *client)
 {
     delete client->cli;
diff --git a/src/vitastor_c.h b/src/vitastor_c.h
index 258fdf857..74a1dff55 100644
--- a/src/vitastor_c.h
+++ b/src/vitastor_c.h
@@ -7,7 +7,7 @@
 #define VITASTOR_QEMU_PROXY_H
 
 // C API wrapper version
-#define VITASTOR_C_API_VERSION 3
+#define VITASTOR_C_API_VERSION 4
 
 #ifndef POOL_ID_BITS
 #define POOL_ID_BITS 16
@@ -41,6 +41,7 @@ vitastor_c *vitastor_c_create_uring(const char *config_path, const char *etcd_ho
     int use_rdma, const char *rdma_device, int rdma_port_num, int rdma_gid_index, int rdma_mtu, int log_level);
 vitastor_c *vitastor_c_create_uring_json(const char **options, int options_len);
 vitastor_c *vitastor_c_create_epoll_json(const char **options, int options_len);
+void* vitastor_c_get_internal_client(vitastor_c *client);
 void vitastor_c_destroy(vitastor_c *client);
 int vitastor_c_is_ready(vitastor_c *client);
 int vitastor_c_uring_register_eventfd(vitastor_c *client);
diff --git a/src/kv_db.h b/src/vitastor_kv.h
similarity index 73%
rename from src/kv_db.h
rename to src/vitastor_kv.h
index 79d0b97c8..97b5f0393 100644
--- a/src/kv_db.h
+++ b/src/vitastor_kv.h
@@ -6,17 +6,27 @@
 
 #pragma once
 
-#include "cluster_client.h"
+#include <stdint.h>
+#include <sys/uio.h>
+
+#include <string>
+#include <map>
+#include <functional>
+
+#define VITASTOR_KV_API_VERSION 1
+
+class cluster_client_t;
 
 struct kv_db_t;
 
 struct kv_dbw_t
 {
+    // cli = vitastor_c_get_internal_client(client)
     kv_dbw_t(cluster_client_t *cli);
     ~kv_dbw_t();
 
-    void open(inode_t inode_id, json11::Json cfg, std::function<void(int)> cb);
-    void set_config(json11::Json cfg);
+    void open(uint64_t inode_id, std::map<std::string, std::string> cfg, std::function<void(int)> cb);
+    void set_config(std::map<std::string, std::string> cfg);
     void close(std::function<void()> cb);
 
     uint64_t get_size();