diff --git a/lib/libmsg-fs/CMakeLists.txt b/lib/libmsg-fs/CMakeLists.txt
index abcbea3..90c2127 100644
--- a/lib/libmsg-fs/CMakeLists.txt
+++ b/lib/libmsg-fs/CMakeLists.txt
@@ -18,4 +18,4 @@ sysroot_add_library(
 	HEADER_DIR /usr/include
 	LIB_DIR /usr/lib)
 
-target_link_libraries(libmsg-fs libmsg libmango)
+target_link_libraries(libmsg-fs libmsg libmango ulibc)
diff --git a/lib/libmsg-fs/fs.c b/lib/libmsg-fs/fs.c
index e4a0c44..33cf939 100644
--- a/lib/libmsg-fs/fs.c
+++ b/lib/libmsg-fs/fs.c
@@ -1,3 +1,111 @@
-void msg_fs_tmp(void)
+#include <rosetta/msg/fs.h>
+#include <string.h>
+
+kern_status_t rosetta_msg_fs_open_send(
+	kern_handle_t port,
+	const char *path,
+	int flags,
+	int *out_err)
 {
+	size_t path_len = strlen(path);
+
+	struct rosetta_msg_fs_open msg = {0};
+	rosetta_msg_init(&msg.msg_base, ROSETTA_MSG_FS, ROSETTA_MSG_FS_OPEN);
+	uint16_t offset = sizeof msg;
+	msg.msg_request.o_path = offset;
+	msg.msg_request.o_path_len = path_len;
+	msg.msg_request.o_flags = flags;
+
+	struct iovec send_vec[] = {
+		IOVEC(&msg, sizeof msg),
+		IOVEC(path, path_len),
+	};
+
+	struct iovec reply_vec[] = {
+		IOVEC(&msg, sizeof msg),
+	};
+
+	struct msg req = {
+		.msg_data = send_vec,
+		.msg_data_count = sizeof send_vec / sizeof send_vec[0],
+	};
+
+	struct msg resp = {
+		.msg_data = reply_vec,
+		.msg_data_count = sizeof reply_vec / sizeof reply_vec[0],
+	};
+
+	kern_status_t status = msg_send(port, 0, &req, &resp);
+	if (status != KERN_OK) {
+		return status;
+	}
+
+	*out_err = msg.msg_response.o_err;
+
+	return KERN_OK;
+}
+
+kern_status_t rosetta_msg_fs_open_recv(
+	kern_handle_t channel,
+	msgid_t id,
+	struct rosetta_msg_string *out_path,
+	int *out_flags)
+{
+	struct rosetta_msg_fs_open msg;
+	struct iovec vec = IOVEC(&msg, sizeof msg);
+	size_t r = 0;
+
+	kern_status_t status = msg_read(channel, id, 0, &vec, 1, &r);
+	if (status != KERN_OK) {
+		return status;
+	}
+
+	if (r != sizeof msg) {
+		/* TODO better error code for malformed messages */
+		return KERN_INVALID_ARGUMENT;
+	}
+
+	out_path->s_len = msg.msg_request.o_path_len;
+	if (out_path->s_max > 0) {
+		vec.io_base = (virt_addr_t)out_path->s_buf;
+		vec.io_len = out_path->s_max - 1;
+
+		if (vec.io_len > out_path->s_len) {
+			vec.io_len = out_path->s_len;
+		}
+
+		status = msg_read(
+			channel,
+			id,
+			msg.msg_request.o_path,
+			&vec,
+			1,
+			&r);
+		if (status != KERN_OK) {
+			return status;
+		}
+
+		if (r != out_path->s_len) {
+			return KERN_INVALID_ARGUMENT;
+		}
+
+		out_path->s_buf[out_path->s_len] = 0;
+	}
+
+	*out_flags = msg.msg_request.o_flags;
+
+	return KERN_OK;
+}
+
+kern_status_t rosetta_msg_fs_open_reply(
+	kern_handle_t channel,
+	msgid_t id,
+	int err)
+{
+	struct rosetta_msg_fs_open msg = {0};
+	msg.msg_response.o_err = err;
+	struct iovec vec = IOVEC(&msg, sizeof msg);
+
+	struct msg kmsg = {.msg_data = &vec, .msg_data_count = 1};
+	return msg_reply(channel, 0, id, &kmsg);
 }
diff --git a/lib/libmsg-fs/include/rosetta/msg/fs.h b/lib/libmsg-fs/include/rosetta/msg/fs.h
index b258673..8c6c1b7 100644
--- a/lib/libmsg-fs/include/rosetta/msg/fs.h
+++ b/lib/libmsg-fs/include/rosetta/msg/fs.h
@@ -7,21 +7,36 @@
 #define ROSETTA_MSG_FS      0x01409DD2U
 
 /* rosetta.msg.fs.open message ID */
-#define ROSETTA_MSG_FS_OPEN 0x7D837778U
+#define ROSETTA_MSG_FS_OPEN 0x7778U
 
 struct rosetta_msg_fs_open {
 	struct rosetta_msg msg_base;
 	union {
 		struct {
 			uint16_t o_path;
+			uint16_t o_path_len;
 			uint16_t o_flags;
 		} msg_request;
 
 		struct {
 			int o_err;
-			uint16_t o_fd_index;
 		} msg_response;
 	};
 };
 
+extern kern_status_t rosetta_msg_fs_open_send(
+	kern_handle_t port,
+	const char *path,
+	int flags,
+	int *out_err);
+extern kern_status_t rosetta_msg_fs_open_recv(
+	kern_handle_t channel,
+	msgid_t id,
+	struct rosetta_msg_string *out_path,
+	int *out_flags);
+extern kern_status_t rosetta_msg_fs_open_reply(
+	kern_handle_t channel,
+	msgid_t id,
+	int err);
+
 #endif