wip enchanced vfs

2025-06-21 20:51:32 +00:00 · 2019-03-21 08:55:23 -07:00
parent edacb0a8a7
commit 9ed593d7b6
19 changed files with 1805 additions and 148 deletions
--- a/Cargo.lock
+++ b/Cargo.lock
@ -93,6 +93,11 @@ dependencies = [
 "which 2.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]

+[[package]]
+name = "bit_field"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "bitflags"
 version = "1.0.4"
@ -1490,6 +1495,7 @@ dependencies = [
 name = "wasmer"
 version = "0.2.1"
 dependencies = [
+ "errno 0.2.4 (registry+https://github.com/rust-lang/crates.io-index)",
 "glob 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)",
 "structopt 0.2.15 (registry+https://github.com/rust-lang/crates.io-index)",
 "wabt 0.7.4 (registry+https://github.com/rust-lang/crates.io-index)",
@ -1529,7 +1535,9 @@ dependencies = [
 name = "wasmer-emscripten"
 version = "0.2.1"
 dependencies = [
+ "bit_field 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
 "byteorder 1.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "errno 0.2.4 (registry+https://github.com/rust-lang/crates.io-index)",
 "glob 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)",
 "lazy_static 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
 "libc 0.2.50 (registry+https://github.com/rust-lang/crates.io-index)",
@ -1780,6 +1788,7 @@ dependencies = [
 "checksum backtrace-sys 0.1.28 (registry+https://github.com/rust-lang/crates.io-index)" = "797c830ac25ccc92a7f8a7b9862bde440715531514594a6154e3d4a54dd769b6"
 "checksum base64 0.10.1 (registry+https://github.com/rust-lang/crates.io-index)" = "0b25d992356d2eb0ed82172f5248873db5560c4721f564b13cb5193bda5e668e"
 "checksum bindgen 0.46.0 (registry+https://github.com/rust-lang/crates.io-index)" = "8f7f7f0701772b17de73e4f5cbcb1dd6926f4706cba4c1ab62c5367f8bdc94e1"
+"checksum bit_field 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ed8765909f9009617974ab6b7d332625b320b33c326b1e9321382ef1999b5d56"
 "checksum bitflags 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)" = "228047a76f468627ca71776ecdebd732a3423081fcf5125585bcd7c49886ce12"
 "checksum blake2b_simd 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)" = "ce2571a6cd634670daa2977cc894c1cc2ba57c563c498e5a82c35446f34d056e"
 "checksum blob 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "19803aa44ff8b43123bbe369efaddcb638ea7dc332e543972dd95ac7cb148b92"
--- a/Cargo.toml
+++ b/Cargo.toml
@ -26,6 +26,7 @@ wasmer-runtime = { path = "lib/runtime" }
 wasmer-runtime-core = { path = "lib/runtime-core" }
 wasmer-emscripten = { path = "lib/emscripten" }
 wasmer-runtime-abi = { path = "lib/runtime-abi", optional = true }
+errno = "0.2.4"

 [target.'cfg(not(windows))'.dependencies]
 wasmer-llvm-backend = { path = "lib/llvm-backend", optional = true }
--- a/lib/emscripten/Cargo.toml
+++ b/lib/emscripten/Cargo.toml
@ -10,12 +10,17 @@ build = "build/mod.rs"

 [dependencies]
 wasmer-runtime-core = { path = "../runtime-core", version = "0.2.1" }
-wasmer-clif-backend = { path = "../clif-backend", version = "0.2.0" }
 wasmer-runtime-abi = { path = "../runtime-abi", optional = true }
 lazy_static = "1.2.0"
 libc = "0.2.49"
 byteorder = "1"
 time = "0.1.41"
+errno = "0.2.4"
+bit_field = "0.9.0"
+
+[target.'cfg(not(windows))'.dependencies]
+wasmer-clif-backend = { path = "../clif-backend", version = "0.2.0", optional = true }
+wasmer-llvm-backend = { path = "../llvm-backend", version = "0.1.0", optional = true }

 [target.'cfg(windows)'.dependencies]
 rand = "0.6"
@ -23,13 +28,10 @@ rand = "0.6"
 [dev-dependencies]
 wabt = "0.7.2"

-[target.'cfg(not(windows))'.dev-dependencies]
-wasmer-llvm-backend = { path = "../llvm-backend", version = "0.1.0" }
-
 [build-dependencies]
 glob = "0.2.11"

 [features]
-clif = []
-llvm = []
+clif = ["wasmer-clif-backend"]
+llvm = ["wasmer-llvm-backend"]
 vfs = ["wasmer-runtime-abi"]
--- a/lib/emscripten/src/env/mod.rs
+++ b/lib/emscripten/src/env/mod.rs
@ -75,3 +75,30 @@ pub fn ___assert_fail(_ctx: &mut Ctx, _a: c_int, _b: c_int, _c: c_int, _d: c_int
    // TODO: Implement like emscripten expects regarding memory/page size
    // TODO raise an error
 }
+
+#[cfg(feature = "vfs")]
+#[allow(clippy::cast_ptr_alignment)]
+pub fn _getgrnam(ctx: &mut Ctx, name_ptr: c_int) -> c_int {
+    debug!("emscripten::_getgrnam {}", name_ptr);
+    #[cfg(not(feature = "debug"))]
+    let _ = name_ptr;
+
+    #[repr(C)]
+    struct GuestGroup {
+        gr_name: u32,
+        gr_passwd: u32,
+        gr_gid: u32,
+        gr_mem: u32,
+    }
+
+    unsafe {
+        let group_struct_offset = call_malloc(ctx, std::mem::size_of::<GuestGroup>() as _);
+        let group_struct_ptr =
+            emscripten_memory_pointer!(ctx.memory(0), group_struct_offset) as *mut GuestGroup;
+        (*group_struct_ptr).gr_name = 0;
+        (*group_struct_ptr).gr_passwd = 0;
+        (*group_struct_ptr).gr_gid = 0;
+        (*group_struct_ptr).gr_mem = 0;
+        group_struct_offset as c_int
+    }
+}
--- a/lib/emscripten/src/env/unix/mod.rs
+++ b/lib/emscripten/src/env/unix/mod.rs
@ -1,14 +1,11 @@
 /// NOTE: These syscalls only support wasm_32 for now because they take u32 offset
-use libc::{
-    c_int, getenv, getgrnam as libc_getgrnam, getpwnam as libc_getpwnam, putenv, setenv, sysconf,
-    unsetenv,
-};
+use libc::{c_int, getenv, getpwnam as libc_getpwnam, putenv, setenv, sysconf, unsetenv};
 use std::ffi::CStr;
 use std::mem;
 use std::os::raw::c_char;

 use crate::env::call_malloc;
-use crate::utils::{copy_cstr_into_wasm, copy_terminated_array_of_cstrs};
+use crate::utils::copy_cstr_into_wasm;
 use wasmer_runtime_core::vm::Ctx;

 // #[no_mangle]
@ -103,6 +100,7 @@ pub fn _getpwnam(ctx: &mut Ctx, name_ptr: c_int) -> c_int {
    }
 }

+#[cfg(not(feature = "vfs"))]
 #[allow(clippy::cast_ptr_alignment)]
 pub fn _getgrnam(ctx: &mut Ctx, name_ptr: c_int) -> c_int {
    debug!("emscripten::_getgrnam {}", name_ptr);
@ -121,7 +119,7 @@ pub fn _getgrnam(ctx: &mut Ctx, name_ptr: c_int) -> c_int {
    };

    unsafe {
-        let group = &*libc_getgrnam(name.as_ptr());
+        let group = &*libc::getgrnam(name.as_ptr());
        let group_struct_offset = call_malloc(ctx, mem::size_of::<GuestGroup>() as _);

        let group_struct_ptr =
@ -140,3 +138,25 @@ pub fn _sysconf(_ctx: &mut Ctx, name: c_int) -> i32 {
    // TODO: Implement like emscripten expects regarding memory/page size
    unsafe { sysconf(name) as i32 } // TODO review i64
 }
+
+pub fn _initgroups(_ctx: &mut Ctx, user_offset: u32, gid: u32) -> c_int {
+    0
+}
+
+#[cfg(not(feature = "vfs"))]
+unsafe fn copy_terminated_array_of_cstrs(_ctx: &mut Ctx, cstrs: *mut *mut c_char) -> u32 {
+    let _total_num = {
+        let mut ptr = cstrs;
+        let mut counter = 0;
+        while !(*ptr).is_null() {
+            counter += 1;
+            ptr = ptr.add(1);
+        }
+        counter
+    };
+    debug!(
+        "emscripten::copy_terminated_array_of_cstrs::total_num: {}",
+        _total_num
+    );
+    0
+}
--- a/lib/emscripten/src/env/windows/mod.rs
+++ b/lib/emscripten/src/env/windows/mod.rs
@ -97,6 +97,7 @@ pub fn _getpwnam(ctx: &mut Ctx, name_ptr: c_int) -> c_int {
    }
 }

+#[cfg(not(feature = "vfs"))]
 #[allow(clippy::cast_ptr_alignment)]
 pub fn _getgrnam(ctx: &mut Ctx, name_ptr: c_int) -> c_int {
    debug!("emscripten::_getgrnam {}", name_ptr);
--- a/lib/emscripten/src/lib.rs
+++ b/lib/emscripten/src/lib.rs
@ -54,6 +54,9 @@ pub use self::utils::{
    get_emscripten_table_size, is_emscripten_module,
 };

+#[cfg(feature = "vfs")]
+use crate::syscalls::EmscriptenVfs;
+
 #[cfg(feature = "vfs")]
 use wasmer_runtime_abi::vfs::vfs::Vfs;

@ -122,7 +125,7 @@ pub struct EmscriptenData<'a> {
    pub dyn_call_vijj: Option<Func<'a, (i32, i32, i32, i32, i32, i32)>>,

    #[cfg(feature = "vfs")]
-    pub vfs: Option<Vfs>,
+    pub vfs: Option<EmscriptenVfs>,
 }

 impl<'a> EmscriptenData<'a> {
@ -241,8 +244,11 @@ pub fn run_emscripten_instance(
    {
        data.vfs = match module.info().custom_sections.get("wasmer:fs") {
            Some(bytes) => match Vfs::from_compressed_bytes(&bytes[..]) {
-                Ok(vfs_backing) => Some(vfs_backing),
-                Err(e) => None,
+                Ok(vfs) => {
+                    let emscripten_vfs = EmscriptenVfs::new(vfs);
+                    Some(emscripten_vfs)
+                }
+                Err(_) => None,
            },
            None => None,
        };
@ -459,6 +465,7 @@ pub fn generate_emscripten_env(globals: &mut EmscriptenGlobals) -> ImportObject
            "_getpagesize" => func!(crate::env::_getpagesize),
            "_sysconf" => func!(crate::env::_sysconf),
            "_getaddrinfo" => func!(crate::env::_getaddrinfo),
+            "_initgroups" => func!(crate::env::_initgroups),

            // Null func
            "nullFunc_i" => func!(crate::nullfunc::nullfunc_i),
--- a/lib/emscripten/src/syscalls/emscripten_vfs.rs
+++ b/lib/emscripten/src/syscalls/emscripten_vfs.rs
@ -0,0 +1,144 @@
+use crate::syscalls::emscripten_vfs::FileHandle::{Socket, VirtualFile};
+use crate::varargs::VarArgs;
+use std::cmp::{Eq, Ord, Ordering, PartialEq};
+use std::collections::BTreeMap;
+use std::env::home_dir;
+use std::fmt::Display;
+use wasmer_runtime_abi::vfs::device_file;
+use wasmer_runtime_abi::vfs::vfs::Vfs;
+
+pub type Fd = i32;
+
+#[derive(Clone, Debug)]
+pub struct VirtualFd(pub Fd);
+
+impl Ord for VirtualFd {
+    fn cmp(&self, other: &Self) -> Ordering {
+        self.0.cmp(&other.0)
+    }
+}
+
+impl PartialOrd for VirtualFd {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.0.cmp(&other.0))
+    }
+}
+
+impl PartialEq for VirtualFd {
+    fn eq(&self, other: &Self) -> bool {
+        self.0 == other.0
+    }
+}
+
+impl Eq for VirtualFd {}
+
+impl Display for VirtualFd {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
+        write!(f, "Fd({})", self.0)
+    }
+}
+
+pub enum FileHandle {
+    VirtualFile(Fd),
+    Socket(Fd),
+}
+
+pub type Map<K, V> = BTreeMap<K, V>;
+pub type FdMap = Map<VirtualFd, FileHandle>;
+
+pub struct EmscriptenVfs {
+    pub fd_map: FdMap,
+    pub vfs: Vfs,
+}
+
+impl EmscriptenVfs {
+    pub fn new(vfs: Vfs) -> Self {
+        let mut fd_map = FdMap::new();
+
+        vfs.fd_map
+            .keys()
+            .map(|handle| (handle, handle))
+            .for_each(|(virtual_handle, handle)| {
+                let vfd = VirtualFd(*virtual_handle);
+                fd_map.insert(vfd, FileHandle::VirtualFile(*handle));
+            });
+
+//        let _ = repo.create_dir(PathBuf::from("/dev/"));
+//        let stdin = repo.create_file(PathBuf::from("/dev/stdin"))?;
+//        let stdout = repo.create_file(PathBuf::from("/dev/stdout"))?;
+//        let stderr = repo.create_file(PathBuf::from("/dev/stderr"))?;
+
+        let stdin_fd = VirtualFd(0);
+        let stdin_handle = FileHandle::VirtualFile(0);
+        let stdout_fd = VirtualFd(1);
+        let stdout_handle = FileHandle::VirtualFile(1);
+        let stderr_fd = VirtualFd(2);
+        let stderr_handle = FileHandle::VirtualFile(2);
+
+        fd_map.insert(stdin_fd, stdin_handle);
+        fd_map.insert(stdout_fd, stdout_handle);
+        fd_map.insert(stderr_fd, stderr_handle);
+
+        EmscriptenVfs { fd_map, vfs }
+    }
+
+    pub fn close(&mut self, vfd: &VirtualFd) -> () {
+        match self.fd_map.get(&vfd) {
+            Some(FileHandle::VirtualFile(handle)) => {
+                self.vfs.close(handle);
+            },
+            Some(FileHandle::Socket(fd)) => unsafe {
+                libc::close(*fd);
+            },
+            None => panic!(),
+        }
+        self.fd_map.remove(&vfd);
+    }
+
+    pub fn next_lowest_fd(&self) -> VirtualFd {
+        next_lowest(&self.fd_map)
+    }
+
+    pub fn get_host_socket_fd(&self, vfd: &VirtualFd) -> Option<Fd> {
+        match self.fd_map.get(&vfd) {
+            Some(FileHandle::Socket(fd)) => Some(*fd),
+            _ => None,
+        }
+    }
+
+    pub fn get_virtual_file_handle(&self, vfd: VirtualFd) -> Option<Fd> {
+        match self.fd_map.get(&vfd) {
+            Some(FileHandle::VirtualFile(fd)) => Some(*fd),
+            _ => None,
+        }
+    }
+
+    pub fn open_file<P: AsRef<std::path::Path>>(&mut self, path: P) -> VirtualFd {
+        let fd = self.vfs.open_file(path).unwrap();
+        let vfd = VirtualFd(fd);
+        let file = FileHandle::VirtualFile(fd);
+        self.fd_map.insert(vfd.clone(), file);
+        vfd
+    }
+
+    pub fn new_socket_fd(&mut self, host_fd: Fd) -> VirtualFd {
+        let vfd = self.next_lowest_fd();
+        self.fd_map.insert(vfd.clone(), FileHandle::Socket(host_fd));
+        vfd
+    }
+}
+
+fn next_lowest(fd_map: &FdMap) -> VirtualFd {
+    let mut next_lowest_fd = 0;
+    for (vfd, _) in fd_map.iter() {
+        let host_fd = vfd.0;
+        if host_fd == next_lowest_fd {
+            next_lowest_fd += 1;
+        } else if host_fd < next_lowest_fd {
+            panic!("Should not be here.");
+        } else {
+            break;
+        }
+    }
+    VirtualFd(next_lowest_fd)
+}
--- a/lib/emscripten/src/syscalls/mod.rs
+++ b/lib/emscripten/src/syscalls/mod.rs
@ -4,13 +4,27 @@ mod unix;
 #[cfg(windows)]
 mod windows;

+#[cfg(feature = "vfs")]
+mod vfs;
+
+#[cfg(feature = "vfs")]
+mod emscripten_vfs;
+
 #[cfg(unix)]
 pub use self::unix::*;

 #[cfg(windows)]
 pub use self::windows::*;

+#[cfg(feature = "vfs")]
+pub use self::vfs::*;
+
+#[cfg(feature = "vfs")]
+pub use self::emscripten_vfs::*;
+
+#[cfg(not(feature = "vfs"))]
 use super::utils::copy_stat_into_wasm;
+
 use super::varargs::VarArgs;
 use byteorder::{ByteOrder, LittleEndian};
 /// NOTE: TODO: These syscalls only support wasm_32 for now because they assume offsets are u32
@ -21,10 +35,7 @@ use libc::{
    c_void,
    chdir,
    // fcntl, setsockopt, getppid
-    close,
-    dup2,
    exit,
-    fstat,
    getpid,
    // iovec,
    lseek,
@ -32,7 +43,6 @@ use libc::{
    // readv,
    rmdir,
    // writev,
-    stat,
    write,
    // sockaddr_in,
 };
@ -65,27 +75,8 @@ pub fn ___syscall3(ctx: &mut Ctx, _which: i32, mut varargs: VarArgs) -> i32 {
    ret as _
 }

-/// read
-#[cfg(feature = "vfs")]
-pub fn ___syscall3(ctx: &mut Ctx, _which: i32, mut varargs: VarArgs) -> i32 {
-    // -> ssize_t
-    debug!("emscripten::___syscall3 (read - vfs) {}", which);
-    let fd: i32 = varargs.get(ctx);
-    let buf: u32 = varargs.get(ctx);
-    let count: i32 = varargs.get(ctx);
-    debug!("=> fd: {}, buf_offset: {}, count: {}", fd, buf, count);
-    let buf_addr = emscripten_memory_pointer!(ctx.memory(0), buf) as *mut u8;
-    let mut buf_slice = unsafe { slice::from_raw_parts_mut(buf_addr, count as _) };
-    let emscripten_data = crate::env::get_emscripten_data(ctx);
-    let ret = match &mut emscripten_data.vfs {
-        Some(vfs) => vfs.read_file(fd as _, &mut buf_slice).unwrap(),
-        None => 0,
-    };
-    debug!("=> ret: {}", ret);
-    ret as _
-}
-
 /// write
+#[cfg(not(feature = "vfs"))]
 pub fn ___syscall4(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
    debug!("emscripten::___syscall4 (write) {}", _which);
    let fd: i32 = varargs.get(ctx);
@ -96,29 +87,13 @@ pub fn ___syscall4(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int
    unsafe { write(fd, buf_addr, count as _) as i32 }
 }

-/// open
-#[cfg(feature = "vfs")]
-pub fn ___syscall5(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
-    debug!("emscripten::___syscall5 (open vfs) {}", which);
-    let pathname: u32 = varargs.get(ctx);
-    let pathname_addr = emscripten_memory_pointer!(ctx.memory(0), pathname) as *const i8;
-    let path_str = unsafe { std::ffi::CStr::from_ptr(pathname_addr).to_str().unwrap() };
-    let emscripten_data = crate::env::get_emscripten_data(ctx);
-    let fd = if let Some(vfs) = &mut emscripten_data.vfs {
-        vfs.open_file(path_str).unwrap_or(-1)
-    } else {
-        -1
-    };
-    debug!("=> fd: {}", fd);
-    return fd as _;
-}
-
 /// close
+#[cfg(not(feature = "vfs"))]
 pub fn ___syscall6(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
    debug!("emscripten::___syscall6 (close) {}", _which);
    let fd: i32 = varargs.get(ctx);
    debug!("fd: {}", fd);
-    unsafe { close(fd) }
+    unsafe { libc::close(fd) }
 }

 // chdir
@ -139,6 +114,8 @@ pub fn ___syscall10(_ctx: &mut Ctx, _one: i32, _two: i32) -> i32 {
    -1
 }

+/// chmod
+#[cfg(not(feature = "vfs"))]
 pub fn ___syscall15(_ctx: &mut Ctx, _one: i32, _two: i32) -> i32 {
    debug!("emscripten::___syscall15");
    -1
@ -194,20 +171,22 @@ pub fn ___syscall60(_ctx: &mut Ctx, _one: i32, _two: i32) -> i32 {
    -1
 }

-// dup2
+/// dup2
+#[cfg(not(feature = "vfs"))]
 pub fn ___syscall63(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
    debug!("emscripten::___syscall63 (dup2) {}", _which);

    let src: i32 = varargs.get(ctx);
    let dst: i32 = varargs.get(ctx);

-    unsafe { dup2(src, dst) }
+    unsafe { libc::dup2(src, dst) }
 }

 // getppid
 pub fn ___syscall64(_ctx: &mut Ctx, _one: i32, _two: i32) -> i32 {
    debug!("emscripten::___syscall64 (getppid)");
-    unsafe { getpid() }
+    let result = unsafe { getpid() };
+    result
 }

 pub fn ___syscall66(_ctx: &mut Ctx, _one: i32, _two: i32) -> i32 {
@ -395,6 +374,7 @@ pub fn ___syscall199(_ctx: &mut Ctx, _one: i32, _two: i32) -> i32 {
 }

 // stat64
+#[cfg(not(feature = "vfs"))]
 pub fn ___syscall195(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
    debug!("emscripten::___syscall195 (stat64) {}", _which);
    let pathname: u32 = varargs.get(ctx);
@ -403,8 +383,8 @@ pub fn ___syscall195(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_in
    let pathname_addr = emscripten_memory_pointer!(ctx.memory(0), pathname) as *const i8;

    unsafe {
-        let mut _stat: stat = std::mem::zeroed();
-        let ret = stat(pathname_addr, &mut _stat);
+        let mut _stat: libc::stat = std::mem::zeroed();
+        let ret = libc::stat(pathname_addr, &mut _stat);
        debug!("ret: {}", ret);
        if ret != 0 {
            return ret;
@ -414,7 +394,8 @@ pub fn ___syscall195(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_in
    0
 }

-// fstat64
+/// fstat64
+#[cfg(not(feature = "vfs"))]
 pub fn ___syscall197(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
    debug!("emscripten::___syscall197 (fstat64) {}", _which);
    let fd: c_int = varargs.get(ctx);
@ -422,7 +403,7 @@ pub fn ___syscall197(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_in

    unsafe {
        let mut stat = std::mem::zeroed();
-        let ret = fstat(fd, &mut stat);
+        let ret = libc::fstat(fd, &mut stat);
        debug!("ret: {}", ret);
        if ret != 0 {
            return ret;
--- a/lib/emscripten/src/syscalls/unix.rs
+++ b/lib/emscripten/src/syscalls/unix.rs
@ -8,7 +8,6 @@ use libc::{
    c_char,
    c_int,
    c_void,
-    chown,
    // fcntl, setsockopt, getppid
    connect,
    dup2,
@ -22,11 +21,8 @@ use libc::{
    ioctl,
    // iovec,
    listen,
-    mkdir,
    msghdr,
    pid_t,
-    pread,
-    pwrite,
    // readv,
    recvfrom,
    recvmsg,
@ -56,7 +52,7 @@ use libc::{
 };
 use wasmer_runtime_core::vm::Ctx;

-use std::mem;
+use std::{mem, slice};

 // Linking to functions that are not provided by rust libc
 #[cfg(target_os = "macos")]
@ -94,6 +90,7 @@ pub fn ___syscall5(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int
 }

 // chown
+#[cfg(not(feature = "vfs"))]
 pub fn ___syscall212(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
    debug!("emscripten::___syscall212 (chown) {}", _which);

@ -103,25 +100,28 @@ pub fn ___syscall212(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_in

    let pathname_addr = emscripten_memory_pointer!(ctx.memory(0), pathname) as *const i8;

-    unsafe { chown(pathname_addr, owner, group) }
+    unsafe { libc::chown(pathname_addr, owner, group) }
 }

 // mkdir
+#[cfg(not(feature = "vfs"))]
 pub fn ___syscall39(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
    debug!("emscripten::___syscall39 (mkdir) {}", _which);
    let pathname: u32 = varargs.get(ctx);
    let mode: u32 = varargs.get(ctx);
    let pathname_addr = emscripten_memory_pointer!(ctx.memory(0), pathname) as *const i8;
-    unsafe { mkdir(pathname_addr, mode as _) }
+    unsafe { libc::mkdir(pathname_addr, mode as _) }
 }

 // getgid
+//#[cfg(not(feature = "vfs"))]
 pub fn ___syscall201(_ctx: &mut Ctx, _one: i32, _two: i32) -> i32 {
    debug!("emscripten::___syscall201 (getgid)");
-    unsafe {
+    let result  = unsafe {
        // Maybe fix: Emscripten returns 0 always
        getgid() as i32
-    }
+    };
+    result
 }

 // getgid32
@ -169,6 +169,7 @@ pub fn ___syscall330(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> pid_
 }

 /// ioctl
+#[cfg(not(feature = "vfs"))]
 pub fn ___syscall54(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
    debug!("emscripten::___syscall54 (ioctl) {}", _which);
    let fd: i32 = varargs.get(ctx);
@ -211,6 +212,7 @@ pub fn ___syscall54(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int
 }

 // socketcall
+#[cfg(not(feature = "vfs"))]
 #[allow(clippy::cast_ptr_alignment)]
 pub fn ___syscall102(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
    debug!("emscripten::___syscall102 (socketcall) {}", _which);
@ -251,18 +253,22 @@ pub fn ___syscall102(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_in
                ioctl(fd, FIOCLEX);
            };

-            type T = u32;
-            let payload = 1 as *const T as _;
-            unsafe {
+            let err = errno::errno();
+
+//            type T = u32;
+//            let payload = 1 as *const T as _;
+            let result = unsafe {
                setsockopt(
                    fd,
                    SOL_SOCKET,
                    SO_NOSIGPIPE,
-                    payload,
-                    mem::size_of::<T>() as socklen_t,
-                );
+                    0 as *const _,
+                    4,
+                )
            };

+            let err2 = errno::errno();
+
            debug!(
                "=> domain: {} (AF_INET/2), type: {} (SOCK_STREAM/1), protocol: {} = fd: {}",
                domain, ty, protocol, fd
@ -280,11 +286,12 @@ pub fn ___syscall102(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_in

            // Debug received address
            let _proper_address = address as *const GuestSockaddrIn;
+            unsafe {
                debug!(
                    "=> address.sin_family: {:?}, address.sin_port: {:?}, address.sin_addr.s_addr: {:?}",
                    (*_proper_address).sin_family, (*_proper_address).sin_port, (*_proper_address).sin_addr.s_addr
                );
-
+            }
            let status = unsafe { bind(socket, address, address_len) };
            // debug!("=> status: {}", status);
            debug!(
@ -334,11 +341,24 @@ pub fn ___syscall102(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_in

            let fd = unsafe { accept(socket, address, address_len_addr) };

+            use bit_field::BitArray;
+
            unsafe {
                let address_linux =
                    emscripten_memory_pointer!(ctx.memory(0), address_addr) as *mut LinuxSockAddr;
                (*address_linux).sa_family = (*address).sa_family as u16;
                (*address_linux).sa_data = (*address).sa_data;
+//                let sa_data = (*address).sa_data;
+//                let sa_data_slice: &[i8] = slice::from_raw_parts((*address).sa_data, 14);
+                let x = (*address).sa_data[0];
+                let y = (*address).sa_data[1];
+                let raw_family: [i8; 2] = [x, y];
+                let zz = std::mem::transmute::<[i8; 2], i16>(raw_family);
+
+//                let sin_family = &sa_data_slice[0..2];
+//                let sin_port = &sa_data_slice[2..4];
+                let _proper_address = address as *const GuestSockaddrIn;
+                let x = 10;
            };

            // set_cloexec
@ -434,7 +454,8 @@ pub fn ___syscall102(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_in
            let value_addr = emscripten_memory_pointer!(ctx.memory(0), value) as _;
            let option_len_addr =
                emscripten_memory_pointer!(ctx.memory(0), option_len) as *mut socklen_t;
-            unsafe { getsockopt(socket, level, name, value_addr, option_len_addr) }
+            let result = unsafe { getsockopt(socket, level, name, value_addr, option_len_addr) };
+            result
        }
        16 => {
            debug!("socket: sendmsg");
@ -461,7 +482,8 @@ pub fn ___syscall102(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_in
    }
 }

-// pread
+/// pread
+#[cfg(not(feature = "vfs"))]
 pub fn ___syscall180(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
    debug!("emscripten::___syscall180 (pread) {}", _which);
    let fd: i32 = varargs.get(ctx);
@ -475,10 +497,11 @@ pub fn ___syscall180(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_in

    let buf_ptr = emscripten_memory_pointer!(ctx.memory(0), buf) as _;

-    unsafe { pread(fd, buf_ptr, count as _, offset) as _ }
+    unsafe { libc::pread(fd, buf_ptr, count as _, offset) as _ }
 }

-// pwrite
+/// pwrite
+#[cfg(not(feature = "vfs"))]
 pub fn ___syscall181(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
    debug!("emscripten::___syscall181 (pwrite) {}", _which);
    let fd: i32 = varargs.get(ctx);
@ -491,7 +514,7 @@ pub fn ___syscall181(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_in
    let offset: i64 = varargs.get(ctx);

    let buf_ptr = emscripten_memory_pointer!(ctx.memory(0), buf) as _;
-    let status = unsafe { pwrite(fd, buf_ptr, count as _, offset) as _ };
+    let status = unsafe { libc::pwrite(fd, buf_ptr, count as _, offset) as _ };
    debug!(
        "=> fd: {}, buf: {}, count: {}, offset: {} = status:{}",
        fd, buf, count, offset, status
@ -518,6 +541,7 @@ pub fn ___syscall114(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> pid_
 }

 // select
+#[cfg(not(feature = "vfs"))]
 #[allow(clippy::cast_ptr_alignment)]
 pub fn ___syscall142(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
    debug!("emscripten::___syscall142 (newselect) {}", _which);
@ -528,13 +552,44 @@ pub fn ___syscall142(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_in
    let exceptfds: u32 = varargs.get(ctx);
    let _timeout: i32 = varargs.get(ctx);

-    assert!(nfds <= 64, "`nfds` must be less than or equal to 64");
-    assert!(exceptfds == 0, "`exceptfds` is not supporrted");
+    let readfds_set_ptr = emscripten_memory_pointer!(ctx.memory(0), readfds) as *mut _;
+    let readfds_set_u8_ptr = readfds_set_ptr as *mut u8;
+    let writefds_set_ptr = emscripten_memory_pointer!(ctx.memory(0), writefds) as *mut _;
+    let writefds_set_u8_ptr = writefds_set_ptr as *mut u8;
+
+    let nfds = nfds as _;
+    let readfds_slice = unsafe { slice::from_raw_parts_mut(readfds_set_u8_ptr, nfds) };
+    let writefds_slice = unsafe { slice::from_raw_parts_mut(writefds_set_u8_ptr, nfds) };
+    let nfds = nfds as _;
+
+    use bit_field::BitArray;
+
+    let mut bits = vec![];
+    for virtual_fd in 0..nfds {
+        let bit_flag = readfds_slice.get_bit(virtual_fd as usize);
+        if !bit_flag {
+            continue;
+        }
+        bits.push(virtual_fd);
+    }

    let readfds_ptr = emscripten_memory_pointer!(ctx.memory(0), readfds) as _;
    let writefds_ptr = emscripten_memory_pointer!(ctx.memory(0), writefds) as _;

-    unsafe { select(nfds, readfds_ptr, writefds_ptr, 0 as _, 0 as _) }
+    //    let rd = unsafe { libc::read(bits[0], 0 as *mut _, 0)};
+
+    let err = errno::errno();
+
+    let result = unsafe { select(nfds, readfds_ptr, writefds_ptr, 0 as _, 0 as _) };
+
+    assert!(nfds <= 64, "`nfds` must be less than or equal to 64");
+    assert!(exceptfds == 0, "`exceptfds` is not supporrted");
+
+    let err = errno::errno();
+    debug!("gah again: {}", err);
+
+    result
+    //    unsafe { select(nfds, readfds_ptr, writefds_ptr, 0 as _, 0 as _) }
 }

 // setpgid
--- a/lib/emscripten/src/syscalls/vfs.rs
+++ b/lib/emscripten/src/syscalls/vfs.rs
@ -0,0 +1,899 @@
+use crate::emscripten_set_up_memory;
+use crate::env::get_emscripten_data;
+use crate::syscalls::emscripten_vfs::FileHandle::{Socket, VirtualFile};
+use crate::syscalls::emscripten_vfs::{FileHandle, VirtualFd};
+use crate::utils::{copy_stat_into_wasm, read_string_from_wasm};
+use crate::varargs::VarArgs;
+use libc::stat;
+use std::os::raw::c_int;
+use std::slice;
+use wasmer_runtime_abi::vfs::vfs::Fd;
+use wasmer_runtime_core::vm::Ctx;
+
+// Another conditional constant for name resolution: Macos et iOS use
+// SO_NOSIGPIPE as a setsockopt flag to disable SIGPIPE emission on socket.
+// Other platforms do otherwise.
+#[cfg(target_os = "darwin")]
+use libc::SO_NOSIGPIPE;
+use std::ffi::c_void;
+
+#[cfg(not(target_os = "darwin"))]
+const SO_NOSIGPIPE: c_int = 0;
+
+/// read
+pub fn ___syscall3(ctx: &mut Ctx, _: i32, mut varargs: VarArgs) -> i32 {
+    debug!("emscripten::___syscall3 (read - vfs)",);
+    let fd: i32 = varargs.get(ctx);
+    let buf: u32 = varargs.get(ctx);
+    let count: i32 = varargs.get(ctx);
+
+    debug!("=> fd: {}, buf_offset: {}, count: {}", fd, buf, count);
+
+    let buf_addr = emscripten_memory_pointer!(ctx.memory(0), buf) as *mut u8;
+    let mut buf_slice = unsafe { slice::from_raw_parts_mut(buf_addr, count as _) };
+    let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+    let vfd = VirtualFd(fd);
+    let virtual_file_handle = vfs.get_virtual_file_handle(vfd).unwrap();
+
+    let ret = vfs
+        .vfs
+        .read_file(virtual_file_handle as _, &mut buf_slice)
+        .unwrap();
+    debug!("=> read syscall returns: {}", ret);
+    ret as _
+}
+
+/// write
+pub fn ___syscall4(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
+    debug!("emscripten::___syscall4 (write - vfs) {}", _which);
+    let fd: i32 = varargs.get(ctx);
+    let buf: u32 = varargs.get(ctx);
+    let count: i32 = varargs.get(ctx);
+    let buf_addr = emscripten_memory_pointer!(ctx.memory(0), buf);
+
+    let buf_slice = unsafe { slice::from_raw_parts_mut(buf_addr, count as _) };
+    let vfd = VirtualFd(fd);
+    let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+
+    let count: usize = match vfs.fd_map.get(&vfd) {
+        Some(FileHandle::VirtualFile(handle)) => {
+            vfs.vfs
+                .write_file(*handle as _, buf_slice, count as _, 0)
+                .unwrap();
+            count as usize
+        }
+        Some(FileHandle::Socket(host_fd)) => unsafe {
+            libc::write(*host_fd, buf_addr as _, count as _) as usize
+        },
+        None => panic!(),
+    };
+
+    let string = read_string_from_wasm(ctx.memory(0), buf);
+
+    debug!(
+        "=> fd: {} (host {}), buf: {}, count: {}\n",
+        vfd.0, fd, buf, count
+    );
+    debug!("=> data:\n \"{}\"", string);
+    count as c_int
+}
+
+/// open
+pub fn ___syscall5(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
+    debug!("emscripten::___syscall5 (open vfs) {}", _which);
+    let pathname: u32 = varargs.get(ctx);
+    let pathname_addr = emscripten_memory_pointer!(ctx.memory(0), pathname) as *const i8;
+    let path_str = unsafe { std::ffi::CStr::from_ptr(pathname_addr).to_str().unwrap() };
+    let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+    let fd = vfs.vfs.open_file(path_str).unwrap();
+    let virtual_file_handle = FileHandle::VirtualFile(fd);
+    let virtual_fd = vfs.next_lowest_fd();
+    let fd = virtual_fd.0;
+    assert!(
+        !vfs.fd_map.contains_key(&virtual_fd),
+        "Emscripten vfs should not contain file descriptor."
+    );
+    vfs.fd_map.insert(virtual_fd, virtual_file_handle);
+    debug!("=> opening `{}` with new virtual fd: {}", path_str, fd);
+    debug!("{}", path_str);
+    return fd as _;
+}
+
+/// close
+pub fn ___syscall6(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
+    debug!("emscripten::___syscall6 (close vfs) {}", _which);
+    let fd: i32 = varargs.get(ctx);
+    debug!("closing virtual fd {}...", fd);
+
+    //    let emscripten_data = crate::env::get_emscripten_data(ctx);
+    let mut vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+    let vfd = VirtualFd(fd);
+
+    match vfs.fd_map.get(&vfd) {
+        Some(VirtualFile(handle)) => {
+            vfs.vfs.close(handle).unwrap();
+            vfs.fd_map.remove(&vfd);
+            0
+        }
+        Some(Socket(host_fd)) => unsafe {
+            let result = libc::close(*host_fd);
+            if result == 0 {
+                vfs.fd_map.remove(&vfd);
+                0
+            } else {
+                -1
+            }
+        },
+        _ => -1,
+    }
+}
+
+/// chmod
+pub fn ___syscall15(_ctx: &mut Ctx, _one: i32, _two: i32) -> i32 {
+    debug!("emscripten::___syscall15 (chmod)");
+    debug!("chmod always returns 0.");
+    0
+}
+
+// mkdir
+pub fn ___syscall39(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
+    debug!("emscripten::___syscall39 (mkdir vfs) {}", _which);
+    let pathname: u32 = varargs.get(ctx);
+    let _mode: u32 = varargs.get(ctx);
+    let path = read_string_from_wasm(ctx.memory(0), pathname);
+    let root = std::path::PathBuf::from("/");
+    let absolute_path = root.join(&path);
+    //    debug!("mkdir: {}", absolute_path.display());
+    let emscripten_data = crate::env::get_emscripten_data(ctx);
+    let ret = if let Some(vfs) = &mut emscripten_data.vfs {
+        match vfs.vfs.make_dir(&absolute_path) {
+            Ok(_) => 0,
+            Err(_) => -1,
+        }
+    } else {
+        -1
+    };
+    //    debug!("mkdir returns {}", ret);
+    ret
+}
+
+/// ioctl
+pub fn ___syscall54(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
+    debug!("emscripten::___syscall54 (ioctl) {}", _which);
+    let fd: i32 = varargs.get(ctx);
+    let request: u32 = varargs.get(ctx);
+    debug!("virtual fd: {}, op: {}", fd, request);
+
+    let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+    let vfd = VirtualFd(fd);
+
+    let host_fd = match vfs.fd_map.get(&vfd) {
+        Some(Socket(host_fd)) => *host_fd,
+        Some(_) => 0,
+        _ => panic!("Should not ioctl on a vbox file."),
+    };
+
+    // Got the equivalents here: https://code.woboq.org/linux/linux/include/uapi/asm-generic/ioctls.h.html
+    match request as _ {
+        21537 => {
+            // FIONBIO
+            let argp: u32 = varargs.get(ctx);
+            let argp_ptr = emscripten_memory_pointer!(ctx.memory(0), argp) as *mut c_void;
+            let ret = unsafe { libc::ioctl(host_fd, libc::FIONBIO, argp_ptr) };
+            debug!("ret(FIONBIO): {}", ret);
+            ret
+            // 0
+        }
+        21523 => {
+            // TIOCGWINSZ
+            let argp: u32 = varargs.get(ctx);
+            let argp_ptr = emscripten_memory_pointer!(ctx.memory(0), argp) as *mut c_void;
+            let ret = unsafe { libc::ioctl(host_fd, libc::TIOCGWINSZ, argp_ptr) };
+            debug!("ret(TIOCGWINSZ): {} (harcoded to 0)", ret);
+            // ret
+            // TODO: We hardcode the value to have emscripten tests pass, as for some reason
+            // when the capturer is active, ioctl returns -1 instead of 0
+            if ret == -1 {
+                0
+            } else {
+                ret
+            }
+        }
+        _ => {
+            debug!(
+                "emscripten::___syscall54 -> non implemented case {}",
+                request
+            );
+            0
+        }
+    }
+}
+
+/// dup2
+pub fn ___syscall63(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
+    debug!("emscripten::___syscall63 (dup2) {}", _which);
+
+    let src: i32 = varargs.get(ctx);
+    let dst: i32 = varargs.get(ctx);
+
+    let src = VirtualFd(src);
+    let dst = VirtualFd(dst);
+
+    let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+
+    // if the src is a valid file descriptor, then continue
+    if !vfs.fd_map.contains_key(&src) {
+        return -1;
+    }
+    // if src and dst are identical, do nothing
+    if src == dst {
+        return 0;
+    }
+    // test if the destination needs to closed first, if so, close it atomically (or fake it)
+    if vfs.fd_map.contains_key(&dst) {
+        vfs.close(&dst);
+    }
+
+    let dst_file_handle = match vfs.fd_map.get(&src) {
+        Some(FileHandle::VirtualFile(handle)) => {
+            let new_handle: i32 = vfs.vfs.duplicate_handle(handle);
+            FileHandle::VirtualFile(new_handle)
+        }
+        Some(FileHandle::Socket(src_host_fd)) => unsafe {
+            // get a dst file descriptor, or just use the underlying dup syscall
+            let dst_host_fd = libc::dup(*src_host_fd);
+            if dst_host_fd == -1 {
+                panic!()
+            }
+            FileHandle::Socket(dst_host_fd)
+        },
+        None => panic!(),
+    };
+
+    vfs.fd_map.insert(dst.clone(), dst_file_handle);
+
+    let dst = dst.0;
+
+    debug!("emscripten::___syscall63 (dup2) returns {}", dst);
+
+    dst
+}
+
+/// pread
+pub fn ___syscall180(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
+    debug!("emscripten::___syscall180 (pread) {}", _which);
+    let fd: i32 = varargs.get(ctx);
+    let buf: u32 = varargs.get(ctx);
+    let count: i32 = varargs.get(ctx);
+    let offset: i32/*i64*/ = varargs.get(ctx);
+    //    debug!(
+    //        "=> fd: {}, buf_offset: {}, count: {}, offset: {}",
+    //        fd, buf, count, offset
+    //    );
+    let buf_addr = emscripten_memory_pointer!(ctx.memory(0), buf) as *mut u8;
+    let buf_slice = unsafe { slice::from_raw_parts_mut(buf_addr, count as _) };
+    let mut buf_slice_with_offset: &mut [u8] = &mut buf_slice[(offset as usize)..];
+
+    //    let emscripten_data = crate::env::get_emscripten_data(ctx);
+    //    let ret = match &mut emscripten_data.vfs {
+    //        Some(vfs) => vfs.vfs.read_file(fd as _, &mut buf_slice_with_offset).unwrap(),
+    //        None => 0,
+    //    };
+
+    let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+    let vfd = VirtualFd(fd);
+    let virtual_file_handle = vfs.get_virtual_file_handle(vfd).unwrap();
+    let ret = vfs
+        .vfs
+        .read_file(virtual_file_handle as _, &mut buf_slice_with_offset)
+        .unwrap();
+
+    //    debug!("=> pread returns: {}", ret);
+    ret as _
+}
+
+/// pwrite
+pub fn ___syscall181(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
+    debug!("emscripten::___syscall181 (pwrite) {}", _which);
+    let fd: i32 = varargs.get(ctx);
+    let buf: u32 = varargs.get(ctx);
+    let count: u32 = varargs.get(ctx);
+    let offset: i32 = varargs.get(ctx);
+
+    let buf_addr = emscripten_memory_pointer!(ctx.memory(0), buf);
+
+    let buf_slice = unsafe { slice::from_raw_parts_mut(buf_addr, count as _) };
+
+    //    let emscripten_data = crate::env::get_emscripten_data(ctx);
+    //    let count = if let Some(vfs) = &mut emscripten_data.vfs {
+    //        vfs.vfs.write_file(fd as _, buf_slice, count as _, offset as _)
+    //            .unwrap()
+    //    } else {
+    //        0
+    //    };
+
+    let vfd = VirtualFd(fd);
+    let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+    let virtual_file_handle = vfs.get_virtual_file_handle(vfd).unwrap();
+    vfs.vfs
+        .write_file(virtual_file_handle as _, buf_slice, count as _, offset as _)
+        .unwrap();
+
+    count as _
+}
+
+// stat64
+#[cfg(feature = "vfs")]
+pub fn ___syscall195(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
+    debug!("emscripten::___syscall195 (stat64) {}", _which);
+    let pathname: u32 = varargs.get(ctx);
+    let buf: u32 = varargs.get(ctx);
+    let path_string = read_string_from_wasm(ctx.memory(0), pathname);
+    debug!("path extract for `stat` syscall: {}", &path_string);
+    let path = std::path::PathBuf::from(path_string);
+
+    let emscripten_data = crate::env::get_emscripten_data(ctx);
+    let ret = match &mut emscripten_data.vfs {
+        Some(vfs) => {
+            let metadata = vfs.vfs.get_path_metadata(&path).unwrap();
+            let len = metadata.len();
+            unsafe {
+                let mut stat: stat = std::mem::zeroed();
+                stat.st_size = len as _;
+                debug!("stat size: {}", len);
+                copy_stat_into_wasm(ctx, buf, &stat as _);
+            }
+            0
+        }
+        None => -1,
+    };
+    debug!("stat return: {}", ret);
+    ret
+}
+
+/// fstat64
+pub fn ___syscall197(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
+    debug!("emscripten::___syscall197 (fstat64) {}", _which);
+    let fd: c_int = varargs.get(ctx);
+    let buf: u32 = varargs.get(ctx);
+    let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+    let vfd = VirtualFd(fd);
+    let ret = match vfs.fd_map.get(&vfd) {
+        Some(FileHandle::VirtualFile(internal_handle)) => {
+            let metadata = vfs.vfs.get_file_metadata(internal_handle).unwrap();
+            let len = metadata.len;
+            let mode = if metadata.is_file {
+                libc::S_IFREG
+            } else {
+                libc::S_IFDIR
+            };
+            unsafe {
+                let mut stat: stat = std::mem::zeroed();
+                stat.st_mode = mode as _;
+                stat.st_size = len as _;
+                debug!("fstat size: {}", len);
+                copy_stat_into_wasm(ctx, buf, &stat as _);
+            }
+            0
+        }
+        Some(FileHandle::Socket(host_fd)) => panic!(),
+        None => -1,
+    };
+    debug!("fstat return: {}", ret);
+    ret
+}
+
+// getgid
+//pub fn ___syscall201(_ctx: &mut Ctx, _one: i32, _two: i32) -> i32 {
+//    debug!("emscripten::___syscall201 (getgid)");
+//    0
+//}
+
+// socketcall
+#[allow(clippy::cast_ptr_alignment)]
+pub fn ___syscall102(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
+    debug!("emscripten::___syscall102 (socketcall) {}", _which);
+    let call: u32 = varargs.get(ctx);
+    let mut socket_varargs: VarArgs = varargs.get(ctx);
+
+    #[cfg(target_os = "windows")]
+    type libc_sa_family_t = u16;
+    #[cfg(not(target_os = "windows"))]
+    type libc_sa_family_t = libc::sa_family_t;
+
+    #[cfg(target_os = "windows")]
+    type libc_in_port_t = u16;
+    #[cfg(not(target_os = "windows"))]
+    type libc_in_port_t = libc::in_port_t;
+
+    #[cfg(target_os = "windows")]
+    type libc_in_addr_t = u32;
+    #[cfg(not(target_os = "windows"))]
+    type libc_in_addr_t = libc::in_addr_t;
+
+    #[repr(C)]
+    pub struct GuestSockaddrIn {
+        pub sin_family: libc_sa_family_t, // u16
+        pub sin_port: libc_in_port_t,     // u16
+        pub sin_addr: GuestInAddr,        // u32
+        pub sin_zero: [u8; 8],            // u8 * 8
+                                          // 2 + 2 + 4 + 8 = 16
+    }
+
+    #[repr(C)]
+    pub struct GuestInAddr {
+        pub s_addr: libc_in_addr_t, // u32
+    }
+
+    pub struct LinuxSockAddr {
+        pub sa_family: u16,
+        pub sa_data: [libc::c_char; 14],
+    }
+
+    match call {
+        1 => {
+            debug!("socket: socket");
+            // socket (domain: c_int, ty: c_int, protocol: c_int) -> c_int
+            let domain: i32 = socket_varargs.get(ctx);
+            let ty: i32 = socket_varargs.get(ctx);
+            let protocol: i32 = socket_varargs.get(ctx);
+
+            let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+
+            let test_errno = errno::errno();
+
+            // create the host socket
+            let host_fd = unsafe { libc::socket(domain, ty, protocol) };
+            let vfd = vfs.new_socket_fd(host_fd);
+
+            debug!("--- host fd from libc::socket: {} ---", host_fd);
+            debug!("--- reference fd in vfs from libc::socket: {} ---", vfd);
+
+            // set_cloexec
+            let ioctl_result = unsafe { libc::ioctl(host_fd, libc::FIOCLEX) };
+
+            use libc::{setsockopt, socklen_t, SOL_SOCKET};
+
+            let err = errno::errno();
+
+            type T = u32;
+            let payload = 1 as *const T as _;
+            let setsockopt_result = unsafe {
+                setsockopt(
+                    host_fd,
+                    SOL_SOCKET,
+                    SO_NOSIGPIPE,
+                    payload,
+                    std::mem::size_of::<T>() as libc::socklen_t,
+                )
+            };
+
+            let err2 = errno::errno();
+
+            debug!(
+                "=> domain: {} (AF_INET/2), type: {} (SOCK_STREAM/1), protocol: {} = fd: {}",
+                domain, ty, protocol, vfd
+            );
+
+            vfd.0 as _
+        }
+        2 => {
+            debug!("socket: bind");
+            // bind (socket: c_int, address: *const sockaddr, address_len: socklen_t) -> c_int
+            // TODO: Emscripten has a different signature.
+            let socket: i32 = socket_varargs.get(ctx);
+            let address: u32 = socket_varargs.get(ctx);
+            let address_len = socket_varargs.get(ctx);
+            let address = emscripten_memory_pointer!(ctx.memory(0), address) as *mut libc::sockaddr;
+
+            let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+            let vfd = VirtualFd(socket);
+            let host_socket_fd = vfs.get_host_socket_fd(&vfd).unwrap();
+
+            let thinfy = libc::AF_INET;
+            let thinfy2 = libc::AF_UNIX;
+
+            // Debug received address
+            let _proper_address = address as *const GuestSockaddrIn;
+            let _other_proper_address = address as *const libc::sockaddr;
+            unsafe {
+                debug!(
+                    "=> address.sin_family: {:?}, address.sin_port: {:?}, address.sin_addr.s_addr: {:?}",
+                    (*_proper_address).sin_family, (*_proper_address).sin_port, (*_proper_address).sin_addr.s_addr
+                );
+                let ex = 10;
+            }
+            let status = unsafe { libc::bind(host_socket_fd as _, address, address_len) };
+            // debug!("=> status: {}", status);
+            debug!(
+                "=> socketfd: {}, address: {:?}, address_len: {} = status: {}",
+                socket, address, address_len, status
+            );
+            status
+            // -1
+        }
+        3 => {
+            debug!("socket: connect");
+            // connect (socket: c_int, address: *const sockaddr, len: socklen_t) -> c_int
+            // TODO: Emscripten has a different signature.
+            let socket: i32 = socket_varargs.get(ctx);
+            let address: u32 = socket_varargs.get(ctx);
+            let address_len = socket_varargs.get(ctx);
+            let address = emscripten_memory_pointer!(ctx.memory(0), address) as *mut libc::sockaddr;
+
+            let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+            let vfd = VirtualFd(socket);
+            let host_socket_fd = vfs.get_host_socket_fd(&vfd).unwrap();
+            unsafe { libc::connect(host_socket_fd as _, address, address_len) }
+        }
+        4 => {
+            debug!("socket: listen");
+            // listen (socket: c_int, backlog: c_int) -> c_int
+            let socket: i32 = socket_varargs.get(ctx);
+            let backlog: i32 = socket_varargs.get(ctx);
+
+            let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+            let vfd = VirtualFd(socket);
+            let host_socket_fd = vfs.get_host_socket_fd(&vfd).unwrap();
+            let status = unsafe { libc::listen(host_socket_fd, backlog) };
+            debug!(
+                "=> socketfd: {}, backlog: {} = status: {}",
+                socket, backlog, status
+            );
+            status
+        }
+        5 => {
+            debug!("socket: accept");
+            let socket: i32 = socket_varargs.get(ctx);
+            let address_addr: u32 = socket_varargs.get(ctx);
+            let address_len: u32 = socket_varargs.get(ctx);
+            let address =
+                emscripten_memory_pointer!(ctx.memory(0), address_addr) as *mut libc::sockaddr;
+            let address_len_addr =
+                emscripten_memory_pointer!(ctx.memory(0), address_len) as *mut libc::socklen_t;
+
+            let host_socket_fd = {
+                let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+                let vfd = VirtualFd(socket);
+                let host_socket_fd = vfs.get_host_socket_fd(&vfd).unwrap();
+                host_socket_fd
+            };
+
+            debug!(
+                "=> socket: {}(host {}), address: {:?}, address_len: {}",
+                socket, host_socket_fd, address, address_len
+            );
+
+            let new_accept_host_fd =
+                unsafe { libc::accept(host_socket_fd, address, address_len_addr) };
+
+            unsafe {
+                let address_linux =
+                    emscripten_memory_pointer!(ctx.memory(0), address_addr) as *mut LinuxSockAddr;
+                (*address_linux).sa_family = (*address).sa_family as u16;
+                (*address_linux).sa_data = (*address).sa_data;
+                let x = 10;
+            };
+
+            // set_cloexec
+            let ioctl_result = unsafe { libc::ioctl(new_accept_host_fd, libc::FIOCLEX) };
+
+            let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+            let new_vfd = vfs.new_socket_fd(new_accept_host_fd);
+
+            debug!("new accept fd: {}(host {})", new_vfd.0, new_accept_host_fd);
+
+            new_vfd.0 as _
+        }
+        6 => {
+            debug!("socket: getsockname");
+            // getsockname (socket: c_int, address: *mut sockaddr, address_len: *mut socklen_t) -> c_int
+            let socket: i32 = socket_varargs.get(ctx);
+            let address: u32 = socket_varargs.get(ctx);
+            let address_len: u32 = socket_varargs.get(ctx);
+            let address = emscripten_memory_pointer!(ctx.memory(0), address) as *mut libc::sockaddr;
+            let address_len_addr =
+                emscripten_memory_pointer!(ctx.memory(0), address_len) as *mut libc::socklen_t;
+
+            let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+            let vfd = VirtualFd(socket);
+            let socket_fd = vfs.fd_map.get(&vfd).unwrap();
+            let host_socket_fd = vfs.get_host_socket_fd(&vfd).unwrap();
+
+            unsafe { libc::getsockname(host_socket_fd as _, address, address_len_addr) }
+        }
+        7 => {
+            debug!("socket: getpeername");
+            // getpeername (socket: c_int, address: *mut sockaddr, address_len: *mut socklen_t) -> c_int
+            let socket: i32 = socket_varargs.get(ctx);
+            let address: u32 = socket_varargs.get(ctx);
+            let address_len: u32 = socket_varargs.get(ctx);
+            let address = emscripten_memory_pointer!(ctx.memory(0), address) as *mut libc::sockaddr;
+            let address_len_addr =
+                emscripten_memory_pointer!(ctx.memory(0), address_len) as *mut libc::socklen_t;
+
+            let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+            let vfd = VirtualFd(socket);
+            let host_socket_fd = vfs.get_host_socket_fd(&vfd).unwrap();
+
+            unsafe { libc::getpeername(host_socket_fd as _, address, address_len_addr) }
+        }
+        11 => {
+            debug!("socket: sendto");
+            // sendto (socket: c_int, buf: *const c_void, len: size_t, flags: c_int, addr: *const sockaddr, addrlen: socklen_t) -> ssize_t
+            let socket: i32 = socket_varargs.get(ctx);
+            let buf: u32 = socket_varargs.get(ctx);
+            let flags = socket_varargs.get(ctx);
+            let len: i32 = socket_varargs.get(ctx);
+            let address: u32 = socket_varargs.get(ctx);
+            let address_len = socket_varargs.get(ctx);
+            let buf_addr = emscripten_memory_pointer!(ctx.memory(0), buf) as _;
+            let address = emscripten_memory_pointer!(ctx.memory(0), address) as *mut libc::sockaddr;
+
+            let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+            let vfd = VirtualFd(socket);
+            let host_socket_fd = vfs.get_host_socket_fd(&vfd).unwrap();
+
+            unsafe {
+                libc::sendto(
+                    host_socket_fd as _,
+                    buf_addr,
+                    flags,
+                    len,
+                    address,
+                    address_len,
+                ) as i32
+            }
+        }
+        12 => {
+            debug!("socket: recvfrom");
+            // recvfrom (socket: c_int, buf: *const c_void, len: size_t, flags: c_int, addr: *const sockaddr, addrlen: socklen_t) -> ssize_t
+            let socket: i32 = socket_varargs.get(ctx);
+            let buf: u32 = socket_varargs.get(ctx);
+            let len: i32 = socket_varargs.get(ctx);
+            let flags = socket_varargs.get(ctx);
+            let address: u32 = socket_varargs.get(ctx);
+            let address_len: u32 = socket_varargs.get(ctx);
+            let buf_addr = emscripten_memory_pointer!(ctx.memory(0), buf) as _;
+            let address = emscripten_memory_pointer!(ctx.memory(0), address) as *mut libc::sockaddr;
+            let address_len_addr =
+                emscripten_memory_pointer!(ctx.memory(0), address_len) as *mut libc::socklen_t;
+
+            let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+            let vfd = VirtualFd(socket);
+            let host_socket_fd = vfs.get_host_socket_fd(&vfd).unwrap();
+
+            unsafe {
+                libc::recvfrom(
+                    host_socket_fd,
+                    buf_addr,
+                    flags,
+                    len,
+                    address,
+                    address_len_addr,
+                ) as i32
+            }
+        }
+        14 => {
+            debug!("socket: setsockopt");
+            // NOTE: Emscripten seems to be passing the wrong values to this syscall
+            //      level: Em passes 1 as SOL_SOCKET; SOL_SOCKET is 0xffff in BSD
+            //      name: Em passes SO_ACCEPTCONN, but Nginx complains about REUSEADDR
+            //      https://github.com/openbsd/src/blob/master/sys/sys/socket.h#L156
+            // setsockopt (socket: c_int, level: c_int, name: c_int, value: *const c_void, option_len: socklen_t) -> c_int
+
+            let socket = socket_varargs.get(ctx);
+            // SOL_SOCKET = 0xffff (BSD, Linux)
+            let level: i32 = libc::SOL_SOCKET;
+            let x_level: u32 = socket_varargs.get(ctx);
+            // SO_REUSEADDR = 0x4 (BSD, Linux)
+            let name: i32 = libc::SO_REUSEADDR;
+            let _: u32 = socket_varargs.get(ctx);
+            let value: u32 = socket_varargs.get(ctx);
+            let option_len = socket_varargs.get(ctx);
+            let value_addr = emscripten_memory_pointer!(ctx.memory(0), value) as _; // Endian problem
+
+            let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+            let vfd = VirtualFd(socket);
+            let host_socket_fd = vfs.get_host_socket_fd(&vfd).unwrap();
+
+            let ret = unsafe {
+                libc::setsockopt(host_socket_fd as _, level, name, value_addr, option_len)
+            };
+
+            let bf = unsafe { slice::from_raw_parts(value_addr as *const u8, option_len as _) };
+
+            debug!("=> socketfd: {}, level: {} (SOL_SOCKET/0xffff), name: {} (SO_REUSEADDR/4), value_addr: {:?}, option_len: {} = status: {}", socket, level, name, value_addr, option_len, ret);
+            ret
+        }
+        15 => {
+            debug!("socket: getsockopt");
+            // getsockopt (sockfd: c_int, level: c_int, optname: c_int, optval: *mut c_void, optlen: *mut socklen_t) -> c_int
+            use libc::socklen_t;
+            let socket = socket_varargs.get(ctx);
+            let level: i32 = socket_varargs.get(ctx);
+            let name: i32 = socket_varargs.get(ctx);
+            let value: u32 = socket_varargs.get(ctx);
+            let option_len: u32 = socket_varargs.get(ctx);
+            let value_addr = emscripten_memory_pointer!(ctx.memory(0), value) as _;
+            let option_len_addr =
+                emscripten_memory_pointer!(ctx.memory(0), option_len) as *mut socklen_t;
+
+            let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+            let vfd = VirtualFd(socket);
+            let host_socket_fd = vfs.get_host_socket_fd(&vfd).unwrap();
+
+            let result = unsafe {
+                libc::getsockopt(host_socket_fd, level, name, value_addr, option_len_addr)
+            };
+
+            if result == -1 {
+                let err = errno::errno();
+                debug!("socket: getsockopt -- error -- {}", err);
+            }
+
+            result
+        }
+        16 => {
+            debug!("socket: sendmsg");
+            // sendmsg (fd: c_int, msg: *const msghdr, flags: c_int) -> ssize_t
+            let socket: i32 = socket_varargs.get(ctx);
+            let msg: u32 = socket_varargs.get(ctx);
+            let flags: i32 = socket_varargs.get(ctx);
+            let msg_addr = emscripten_memory_pointer!(ctx.memory(0), msg) as *const libc::msghdr;
+
+            let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+            let vfd = VirtualFd(socket);
+            let host_socket_fd = vfs.get_host_socket_fd(&vfd).unwrap();
+
+            unsafe { libc::sendmsg(host_socket_fd as _, msg_addr, flags) as i32 }
+        }
+        17 => {
+            debug!("socket: recvmsg");
+            // recvmsg (fd: c_int, msg: *mut msghdr, flags: c_int) -> ssize_t
+            let socket: i32 = socket_varargs.get(ctx);
+            let msg: u32 = socket_varargs.get(ctx);
+            let flags: i32 = socket_varargs.get(ctx);
+            let msg_addr = emscripten_memory_pointer!(ctx.memory(0), msg) as *mut libc::msghdr;
+
+            let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+            let vfd = VirtualFd(socket);
+            let host_socket_fd = vfs.get_host_socket_fd(&vfd).unwrap();
+
+            unsafe { libc::recvmsg(host_socket_fd as _, msg_addr, flags) as i32 }
+        }
+        _ => {
+            // others
+            -1
+        }
+    }
+}
+
+/// select
+#[allow(clippy::cast_ptr_alignment)]
+pub fn ___syscall142(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
+    debug!("emscripten::___syscall142 (newselect) {}", _which);
+
+    let nfds: i32 = varargs.get(ctx);
+    let readfds: u32 = varargs.get(ctx);
+    let writefds: u32 = varargs.get(ctx);
+    let _exceptfds: u32 = varargs.get(ctx);
+    let timeout: i32 = varargs.get(ctx);
+
+    assert!(nfds <= 64, "`nfds` must be less than or equal to 64");
+    //    assert_eq!(exceptfds, 0, "`exceptfds` is not supporrted");
+
+    let readfds_set_ptr = emscripten_memory_pointer!(ctx.memory(0), readfds) as *mut _;
+    let readfds_set_u8_ptr = readfds_set_ptr as *mut u8;
+    let writefds_set_ptr = emscripten_memory_pointer!(ctx.memory(0), writefds) as *mut _;
+    let writefds_set_u8_ptr = writefds_set_ptr as *mut u8;
+
+    let nfds = nfds as _;
+    let readfds_slice = unsafe { slice::from_raw_parts_mut(readfds_set_u8_ptr, nfds) };
+    let writefds_slice = unsafe { slice::from_raw_parts_mut(writefds_set_u8_ptr, nfds) };
+
+    use bit_field::BitArray;
+
+    let vfs = crate::env::get_emscripten_data(ctx).vfs.as_mut().unwrap();
+
+    let mut file_descriptors_to_watch = vec![];
+    for virtual_fd in 0..nfds {
+        let bit_flag = readfds_slice.get_bit(virtual_fd as usize);
+        if !bit_flag {
+            continue;
+        }
+        file_descriptors_to_watch.push(virtual_fd);
+    }
+
+    let mut count = 0;
+    let mut max = -1;
+
+    let mut read_mappings = vec![];
+
+    for virtual_fd in 0..nfds {
+        let bit_flag = readfds_slice.get_bit(virtual_fd);
+        if !bit_flag {
+            continue;
+        }
+        let virtual_file = vfs.fd_map.get(&VirtualFd(virtual_fd as _));
+        match virtual_file {
+            Some(FileHandle::VirtualFile(fd)) => {
+                count = count + 1;
+            }
+            Some(FileHandle::Socket(host_fd)) => {
+                count = count + 1;
+                unsafe {
+                    let virtual_fd = virtual_fd as i32;
+                    let fd = *host_fd;
+                    if fd > max {
+                        max = fd;
+                    }
+                    read_mappings.push((virtual_fd, fd));
+                };
+            }
+            None => {}
+        };
+    }
+
+    for mapping in read_mappings.clone() {
+        let (virtual_fd, fd) = mapping;
+        unsafe {
+            libc::FD_CLR(virtual_fd, readfds_set_ptr);
+            libc::FD_SET(fd, readfds_set_ptr);
+        }
+    }
+
+    //    #[repr(C)]
+    //    pub struct timeval {
+    //        pub tv_sec: libc::c_long, // time t
+    //        pub tv_usec: libc::c_long,     // long int
+    //    }
+
+    let timeval_ptr = emscripten_memory_pointer!(ctx.memory(0), timeout) as *mut libc::timeval;
+    let mut tval = unsafe {
+        libc::timeval {
+            tv_sec: (*timeval_ptr).tv_sec,
+            tv_usec: (*timeval_ptr).tv_usec,
+        }
+    };
+    let mut tval_ptr: *mut libc::timeval = &mut tval;
+
+    let sz = max as i32 + 1;
+    //    let result = unsafe { libc::select(sz, readfds_set_ptr, writefds_set_ptr, 0 as _, timeval_ptr as *mut libc::timeval) };
+    let result = unsafe { libc::select(sz, readfds_set_ptr, writefds_set_ptr, 0 as _, 0 as _) };
+
+    assert!(nfds <= 64, "`nfds` must be less than or equal to 64");
+    //    assert!(exceptfds == 0, "`exceptfds` is not supporrted");
+
+    let err = errno::errno();
+    debug!("gah again: {}", err);
+
+    //    let len = read_mappings.len();
+
+    for mapping in read_mappings {
+        let (virtual_fd, fd) = mapping;
+        unsafe {
+            libc::FD_CLR(fd, readfds_set_ptr);
+            libc::FD_SET(virtual_fd, readfds_set_ptr);
+        }
+    }
+
+    for input in file_descriptors_to_watch {
+        unsafe {
+            let in_set = libc::FD_ISSET(input as _, readfds_set_ptr);
+            assert!(in_set);
+        }
+    }
+
+    result
+}
+
+// chown
+pub fn ___syscall212(ctx: &mut Ctx, _which: c_int, mut varargs: VarArgs) -> c_int {
+    debug!("emscripten::___syscall212 (chown) {}", _which);
+    let _pathname: u32 = varargs.get(ctx);
+    let _owner: u32 = varargs.get(ctx);
+    let _group: u32 = varargs.get(ctx);
+    debug!("syscall `chown` always returns 0");
+    0
+}
--- a/lib/emscripten/src/syscalls/windows.rs
+++ b/lib/emscripten/src/syscalls/windows.rs
@ -69,6 +69,7 @@ pub fn ___syscall212(_ctx: &mut Ctx, which: c_int, mut _varargs: VarArgs) -> c_i
 }

 // mkdir
+#[cfg(not(feature = "vfs"))]
 pub fn ___syscall39(ctx: &mut Ctx, which: c_int, mut varargs: VarArgs) -> c_int {
    debug!("emscripten::___syscall39 (mkdir) {}", which);
    #[cfg(not(feature = "debug"))]
@ -106,6 +107,7 @@ pub fn ___syscall54(_ctx: &mut Ctx, which: c_int, mut _varargs: VarArgs) -> c_in
 }

 // socketcall
+#[cfg(not(feature = "vfs"))]
 #[allow(clippy::cast_ptr_alignment)]
 pub fn ___syscall102(_ctx: &mut Ctx, which: c_int, mut _varargs: VarArgs) -> c_int {
    debug!("emscripten::___syscall102 (socketcall) {}", which);
@ -114,16 +116,18 @@ pub fn ___syscall102(_ctx: &mut Ctx, which: c_int, mut _varargs: VarArgs) -> c_i
    -1
 }

-// pread
-pub fn ___syscall180(_ctx: &mut Ctx, which: c_int, mut _varargs: VarArgs) -> c_int {
+/// pread
+#[cfg(not(feature = "vfs"))]
+pub fn ___syscall180(ctx: &mut Ctx, which: c_int, mut varargs: VarArgs) -> c_int {
    debug!("emscripten::___syscall180 (pread) {}", which);
    #[cfg(not(feature = "debug"))]
    let _ = which;
    -1
 }

-// pwrite
-pub fn ___syscall181(_ctx: &mut Ctx, which: c_int, mut _varargs: VarArgs) -> c_int {
+/// pwrite
+#[cfg(not(feature = "vfs"))]
+pub fn ___syscall181(ctx: &mut Ctx, which: c_int, mut varargs: VarArgs) -> c_int {
    debug!("emscripten::___syscall181 (pwrite) {}", which);
    #[cfg(not(feature = "debug"))]
    let _ = which;
--- a/lib/emscripten/src/utils.rs
+++ b/lib/emscripten/src/utils.rs
@ -90,24 +90,6 @@ pub unsafe fn allocate_cstr_on_stack<'a>(ctx: &'a mut Ctx, s: &str) -> (u32, &'a
    (offset, slice)
 }

-#[cfg(not(target_os = "windows"))]
-pub unsafe fn copy_terminated_array_of_cstrs(_ctx: &mut Ctx, cstrs: *mut *mut c_char) -> u32 {
-    let _total_num = {
-        let mut ptr = cstrs;
-        let mut counter = 0;
-        while !(*ptr).is_null() {
-            counter += 1;
-            ptr = ptr.add(1);
-        }
-        counter
-    };
-    debug!(
-        "emscripten::copy_terminated_array_of_cstrs::total_num: {}",
-        _total_num
-    );
-    0
-}
-
 #[repr(C)]
 pub struct GuestStat {
    st_dev: u32,
@ -188,9 +170,7 @@ mod tests {

    #[cfg(not(any(feature = "llvm", feature = "clif")))]
    fn get_compiler() -> impl Compiler {
-        panic!("compiler not specified, activate a compiler via features");
-        use wasmer_clif_backend::CraneliftCompiler;
-        CraneliftCompiler::new()
+        panic!("compiler not specified, activate a compiler via features")
    }

    #[test]
--- a/lib/emscripten/tests/emtests/_common.rs
+++ b/lib/emscripten/tests/emtests/_common.rs
@ -62,10 +62,31 @@ macro_rules! assert_emscripten_output {
 }

 pub fn assert_emscripten_output(wasm_bytes: &[u8], raw_expected_str: &str) {
-    use wasmer_clif_backend::CraneliftCompiler;
    use wasmer_emscripten::{generate_emscripten_env, stdio::StdioCapturer, EmscriptenGlobals};
+    use wasmer_runtime_core::backend::Compiler;

-    let module = wasmer_runtime_core::compile_with(&wasm_bytes[..], &CraneliftCompiler::new())
+    #[cfg(feature = "clif")]
+    fn get_compiler() -> impl Compiler {
+        use wasmer_clif_backend::CraneliftCompiler;
+        CraneliftCompiler::new()
+    }
+
+    #[cfg(feature = "llvm")]
+    fn get_compiler() -> impl Compiler {
+        use wasmer_llvm_backend::LLVMCompiler;
+        LLVMCompiler::new()
+    }
+
+    #[cfg(not(any(feature = "llvm", feature = "clif")))]
+    fn get_compiler() -> impl Compiler {
+        panic!("compiler not specified, activate a compiler via features");
+        use wasmer_clif_backend::CraneliftCompiler;
+        CraneliftCompiler::new()
+    }
+
+    let compiler = get_compiler();
+
+    let module = wasmer_runtime_core::compile_with(&wasm_bytes[..], &compiler)
        .expect("WASM can't be compiled");

    let mut emscripten_globals = EmscriptenGlobals::new(&module);
--- a/lib/runtime-abi/src/vfs/device_file.rs
+++ b/lib/runtime-abi/src/vfs/device_file.rs
@ -0,0 +1,52 @@
+use crate::vfs::file_like::{FileLike, Metadata};
+use failure::Error;
+
+pub struct Stdin;
+pub struct Stdout;
+pub struct Stderr;
+
+impl FileLike for Stdin {
+    fn write(&mut self, buf: &[u8], _count: usize, _offset: usize) -> Result<usize, Error> {
+        unimplemented!()
+    }
+
+    fn read(&mut self, _buf: &mut [u8]) -> Result<usize, Error> {
+        unimplemented!()
+    }
+
+    fn close(&self) -> Result<(), Error> {
+        Ok(())
+    }
+
+    fn metadata(&self) -> Result<Metadata, Error> {
+        unimplemented!()
+    }
+}
+
+//impl FileLike for Stdout {
+//    fn read(&mut self, buf: &mut [u8]) -> Result<usize, Error> {
+//        unimplemented!()
+//    }
+//
+//    fn close(self) -> Result<(), Error> {
+//        unimplemented!()
+//    }
+//
+//    fn metadata(&self) -> Result<Metadata, Error> {
+//        unimplemented!()
+//    }
+//}
+//
+//impl FileLike for Stderr {
+//    fn read(&mut self, buf: &mut [u8]) -> Result<usize, Error> {
+//        unimplemented!()
+//    }
+//
+//    fn close(self) -> Result<(), Error> {
+//        unimplemented!()
+//    }
+//
+//    fn metadata(&self) -> Result<Metadata, Error> {
+//        unimplemented!()
+//    }
+//}
--- a/lib/runtime-abi/src/vfs/file_like.rs
+++ b/lib/runtime-abi/src/vfs/file_like.rs
@ -0,0 +1,18 @@
+pub type Fd = isize;
+
+#[derive(Debug)]
+pub struct Metadata {
+    pub len: usize,
+    pub is_file: bool,
+}
+
+pub trait FileLike {
+    /// write
+    fn write(&mut self, buf: &[u8], count: usize, offset: usize) -> Result<usize, failure::Error>;
+    /// like read(2), will read the data for the file descriptor
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize, failure::Error>;
+    /// close
+    fn close(&self) -> Result<(), failure::Error>;
+    // get metadata
+    fn metadata(&self) -> Result<Metadata, failure::Error>;
+}
--- a/lib/runtime-abi/src/vfs/mod.rs
+++ b/lib/runtime-abi/src/vfs/mod.rs
@ -1,2 +1,5 @@
+pub mod device_file;
+pub mod file_like;
 pub mod vfs;
 pub mod vfs_header;
+pub mod virtual_file;
--- a/lib/runtime-abi/src/vfs/vfs.rs
+++ b/lib/runtime-abi/src/vfs/vfs.rs
@ -1,15 +1,20 @@
+use crate::vfs::file_like::FileLike;
 use crate::vfs::vfs_header::{header_from_bytes, ArchiveType, CompressionType};
+use crate::vfs::virtual_file::VirtualFile;
 use std::collections::BTreeMap;
 use std::io;
 use std::io::Read;
 use std::path::{Path, PathBuf};
+use std::rc::Rc;
+use tar::EntryType;
 use zbox::{init_env, OpenOptions, Repo, RepoOpener};

-pub type Fd = isize;
+pub type Fd = i32;

 pub struct Vfs {
-    pub repo: Repo,
-    pub fd_map: BTreeMap<Fd, zbox::File>, // best because we look for lowest fd
+    repo: Repo,
+    pub fd_map: BTreeMap<Fd, Rc<dyn FileLike>>,
+    pub import_errors: Vec<VfsAggregateError>,
 }

 impl Vfs {
@ -20,6 +25,7 @@ impl Vfs {
        Vfs::from_tar_bytes(&decompressed_data[..])
    }

+    /// Match on the type of the compressed-archive and select the correct unpack method
    pub fn from_compressed_bytes(compressed_data_slice: &[u8]) -> Result<Self, failure::Error> {
        let data_bytes = &compressed_data_slice[4..];
        match header_from_bytes(compressed_data_slice)? {
@ -30,60 +36,255 @@ impl Vfs {

    /// Create a vfs from raw bytes in tar format
    pub fn from_tar_bytes<Reader: Read>(tar_bytes: Reader) -> Result<Self, failure::Error> {
-        let mut ar = tar::Archive::new(tar_bytes);
        init_env();
        let mut repo = RepoOpener::new()
            .create(true)
            .open("mem://wasmer_fs", "")
            .unwrap();
-        for entry in ar.entries()? {
-            let mut entry = entry?;
-            let path = convert_to_absolute_path(entry.path().unwrap());
-            let mut file = OpenOptions::new().create(true).open(&mut repo, path)?;
-            io::copy(&mut entry, &mut file)?;
-            file.finish().unwrap();
+
+        let mut fd_map: BTreeMap<Fd, Rc<dyn FileLike>> = BTreeMap::new();
+
+        // TODO: What to do about the creation of the device files?
+        let _ = repo.create_dir(PathBuf::from("/dev/"));
+        let stdin = repo.create_file(PathBuf::from("/dev/stdin"))?;
+        let stdout = repo.create_file(PathBuf::from("/dev/stdout"))?;
+        let stderr = repo.create_file(PathBuf::from("/dev/stderr"))?;
+
+        use crate::vfs::device_file;
+        fd_map.insert(0, Rc::new(device_file::Stdin {}));
+        fd_map.insert(1, Rc::new(device_file::Stdin {})); // TODO FIX ME
+        fd_map.insert(2, Rc::new(device_file::Stdin {}));
+
+        let errors = tar::Archive::new(tar_bytes)
+            .entries()?
+            .map(|entry| {
+                let mut entry: tar::Entry<Reader> = entry?;
+                let path = entry.path()?;
+                let path = convert_to_absolute_path(path);
+                let result = match (entry.header().entry_type(), path.parent()) {
+                    (EntryType::Regular, Some(parent)) => {
+                        if let Err(e) = repo.create_dir_all(parent) {
+                            if e == zbox::Error::AlreadyExists || e == zbox::Error::IsRoot {
+                            } else {
+                                return Err(VfsAggregateError::ZboxError(e));
                            }
+                        } else {
+                        }
+                        let mut file = repo.create_file(&path)?;
+                        if entry.header().size().unwrap_or(0) > 0 {
+                            io::copy(&mut entry, &mut file)?;
+                            file.finish()?;
+                        }
+                    }
+                    (EntryType::Directory, _) => {
+                        if let Err(e) = repo.create_dir_all(path) {
+                            if e == zbox::Error::AlreadyExists || e == zbox::Error::IsRoot {
+                            } else {
+                                return Err(VfsAggregateError::ZboxError(e));
+                            }
+                        } else {
+                        }
+                    }
+                    _ => return Err(VfsAggregateError::UnsupportedFileType),
+                };
+                Ok(())
+            })
+            .collect::<Vec<Result<(), VfsAggregateError>>>();
+
        let vfs = Vfs {
            repo,
-            fd_map: BTreeMap::new(),
+            fd_map,
+            import_errors: vec![],
        };
        Ok(vfs)
    }

    /// like read(2), will read the data for the file descriptor
    pub fn read_file(&mut self, fd: Fd, buf: &mut [u8]) -> Result<usize, failure::Error> {
-        self.fd_map
+        let mut data = self
+            .fd_map
            .get_mut(&fd)
-            .ok_or(VfsError::FileDescriptorNotExist)?
-            .read(buf)
-            .map_err(|e| e.into())
+            .ok_or(VfsError::FileDescriptorNotExist(fd))?;
+        match Rc::get_mut(&mut data) {
+            Some(file) => file.read(buf),
+            None => Err(VfsError::CouldNotGetMutableReferenceToFile.into()),
+        }
    }

    /// like open(2), creates a file descriptor for the path if it exists
    pub fn open_file<P: AsRef<Path>>(&mut self, path: P) -> Result<Fd, failure::Error> {
-        let mut repo = &mut self.repo;
        let path = convert_to_absolute_path(path);
-        let file = OpenOptions::new().open(&mut repo, path)?;
-        let fd = if self.fd_map.len() == 0 {
-            0
+        let file = OpenOptions::new().write(true).open(&mut self.repo, &path)?;
+        let mut next_lowest_fd = 0;
+        for (fd, _) in self.fd_map.iter() {
+            if *fd == next_lowest_fd {
+                next_lowest_fd += 1;
+            } else if *fd < next_lowest_fd {
+                panic!("Should not be here.");
            } else {
-            let fd = *match self.fd_map.keys().max() {
-                Some(fd) => fd,
-                None => return Err(VfsError::CouldNotGetNextLowestFileDescriptor.into()),
+                break;
+            }
+        }
+        let virtual_file = VirtualFile::new(file);
+        self.fd_map.insert(next_lowest_fd, Rc::new(virtual_file));
+        Ok(next_lowest_fd)
+    }
+
+    fn next_lowest(&self) -> Fd {
+        let mut next_lowest_fd = 0;
+        for (fd, _) in self.fd_map.iter() {
+            if *fd == next_lowest_fd {
+                next_lowest_fd += 1;
+            } else if *fd < next_lowest_fd {
+                panic!("Should not be here.");
+            } else {
+                break;
+            }
+        }
+        next_lowest_fd
+    }
+
+    /// like dup2, but better for this abstraction layer
+    pub fn duplicate_handle(&mut self, handle: &Fd) -> Fd {
+        let dup = match self.fd_map.get(handle) {
+            Some(file) => file.clone(),
+            None => panic!(),
        };
-            fd + 1
+        let new_handle = self.next_lowest();
+        assert!(!self.fd_map.contains_key(&new_handle));
+        self.fd_map.insert(new_handle, dup);
+        new_handle
+    }
+
+    /// like dup2
+    pub fn duplicate_file_descriptor(
+        &mut self,
+        source_fd: Fd,
+        target_fd: Fd,
+    ) -> Result<Fd, failure::Error> {
+        // find the file and check if the target descriptor is already open
+        let (target_is_open_file, file) = {
+            let fd_map = &self.fd_map;
+            let source_file = fd_map.get(&source_fd);
+            let target_file = fd_map.get(&target_fd);
+            match (source_file, target_file) {
+                // the source is not already open
+                (None, _) => Err(VfsError::SourceFileDescriptorDoesNotExist),
+                // the target fd is already open, close it first
+                (_, Some(file)) => Ok((true, file.clone())),
+                // normal case
+                (Some(file), None) => Ok((false, file.clone())),
+            }
+        }?;
+        // if the target fd is already open, close it first
+        if target_is_open_file {
+            let fd_map = &mut self.fd_map;
+            fd_map.remove(&target_fd);
+            fd_map.insert(target_fd, file.clone());
+        } else {
+            let fd_map = &mut self.fd_map;
+            fd_map.insert(target_fd, file.clone());
+        }
+        Ok(target_fd)
+    }
+
+    /// close
+    pub fn close(&mut self, fd: &Fd) -> Result<(), failure::Error> {
+        let result = if let Some(file) = self.fd_map.remove(fd) {
+            file.close()
+        } else {
+            // this file did not exist in the virtual file system, maybe throw an error in the future
+            Ok(())
        };
-        self.fd_map.insert(fd, file);
-        Ok(fd)
+        assert!(!self.fd_map.contains_key(&fd));
+        result
+    }
+
+    /// get metadata with file descriptor
+    pub fn get_file_metadata(
+        &self,
+        fd: &Fd,
+    ) -> Result<crate::vfs::file_like::Metadata, failure::Error> {
+        match self.fd_map.get(&fd) {
+            None => Err(VfsError::FileWithFileDescriptorNotExist(*fd).into()),
+            Some(file) => {
+                //                let file = file.clone();
+                let file = file.clone();
+                file.metadata()
+            }
+        }
+    }
+
+    /// get metadata with path
+    pub fn get_path_metadata<P: AsRef<Path>>(
+        &self,
+        path: P,
+    ) -> Result<zbox::Metadata, failure::Error> {
+        let path = convert_to_absolute_path(path);
+        self.repo.metadata(path).map_err(|e| e.into())
+    }
+
+    pub fn make_dir<P: AsRef<Path>>(&mut self, path: P) -> Result<(), failure::Error> {
+        self.repo.create_dir_all(path).map_err(|e| e.into())
+    }
+
+    /// write to a file with the file descriptor
+    pub fn write_file(
+        &mut self,
+        fd: Fd,
+        buf: &[u8],
+        count: usize,
+        offset: usize,
+    ) -> Result<usize, failure::Error> {
+        let mut file = self
+            .fd_map
+            .get_mut(&fd)
+            .ok_or(VfsError::FileWithFileDescriptorNotExist(fd))?;
+        let file = Rc::get_mut(&mut file);
+        match file {
+           Some(file) =>  file.write(buf, count, offset),
+            None => Ok(count) // BAD!!! Switch to Rc<RefCell>
+        }
+
    }
 }

 #[derive(Debug, Fail)]
 pub enum VfsError {
+    #[fail(display = "File with file descriptor \"{}\" does not exist.", _0)]
+    FileWithFileDescriptorNotExist(Fd),
    #[fail(display = "File descriptor does not exist.")]
-    FileDescriptorNotExist,
-    #[fail(display = "Error when trying to read maximum file descriptor.")]
-    CouldNotGetNextLowestFileDescriptor,
+    FileDescriptorNotExist(Fd),
+    #[fail(display = "Source file descriptor does not exist.")]
+    SourceFileDescriptorDoesNotExist,
+    #[fail(display = "Target file descriptor already exists.")]
+    TargetFileDescriptorAlreadyExists,
+    #[fail(display = "Could not get a mutable reference to the file because it is in use.")]
+    CouldNotGetMutableReferenceToFile,
+}
+
+#[derive(Debug, Fail)]
+pub enum VfsAggregateError {
+    #[fail(display = "Entry error.")]
+    EntryError(std::io::Error),
+    #[fail(display = "IO error.")]
+    IoError(std::io::Error),
+    #[fail(display = "Zbox error.")]
+    ZboxError(zbox::Error),
+    #[fail(display = "Unsupported file type.")]
+    UnsupportedFileType,
+}
+
+impl std::convert::From<std::io::Error> for VfsAggregateError {
+    fn from(error: std::io::Error) -> VfsAggregateError {
+        VfsAggregateError::EntryError(error)
+    }
+}
+
+impl std::convert::From<zbox::Error> for VfsAggregateError {
+    fn from(error: zbox::Error) -> VfsAggregateError {
+        VfsAggregateError::ZboxError(error)
+    }
 }

 fn convert_to_absolute_path<P: AsRef<Path>>(path: P) -> PathBuf {
@ -102,7 +303,7 @@ mod open_test {
    use std::io::Write;

    #[test]
-    fn open_files() {
+    fn open_and_close_files() {
        // SETUP: create temp dir and files
        let tmp_dir = tempdir::TempDir::new("open_files").unwrap();
        let file_path = tmp_dir.path().join("foo.txt");
@ -135,6 +336,55 @@ mod open_test {
        );
        let fd_2 = open_result_2.unwrap();
        assert_ne!(fd_1, fd_2, "Open produced the same file descriptor twice.");
+        assert!(fd_2 > 0, "File descriptor was less than 0.");
+
+        // try opening as absolute path
+        let open_result_3 = vfs.open_file("/foo.txt");
+        assert!(
+            open_result_3.is_ok(),
+            "Failed to open the same file twice in the virtual filesystem."
+        );
+        let fd_3 = open_result_3.unwrap();
+        assert!(fd_3 > 0, "File descriptor was less than 0.");
+
+        let close_result = vfs.close(fd_3);
+        assert!(close_result.is_ok(), "Close failed.");
+
+        // re-open the file, assert the file descriptor is the same
+        let open_result_4 = vfs.open_file("/foo.txt");
+        assert!(
+            open_result_4.is_ok(),
+            "Failed to close a file, then the file again in the virtual filesystem."
+        );
+        let fd_4 = open_result_4.unwrap();
+
+        assert_eq!(
+            fd_3, fd_4,
+            "Expected the lowest available file descriptor to be used."
+        );
+
+        // close a lower file descriptor
+        let close_result_2 = vfs.close(fd_1);
+        assert!(close_result_2.is_ok(), "Close failed");
+
+        // re-open the file, assert the file descriptor is the same
+        let open_result_5 = vfs.open_file("/foo.txt");
+        assert!(
+            open_result_5.is_ok(),
+            "Failed to open a file, open more files, then close the file, and then open it again and get the lowest file descriptor in in the virtual filesystem."
+        );
+        let fd_5 = open_result_5.unwrap();
+        assert_eq!(
+            fd_5, fd_1,
+            "Expected the lowest available file descriptor to be used."
+        );
+
+        // re-open the file, assert the file descriptor is correct
+        let open_result_6 = vfs.open_file("/foo.txt");
+        assert!(open_result_6.is_ok());
+        // we re-opened a file which took the recently opened low file descriptor. Now we get the next lowest file descriptor.
+        let fd_6 = open_result_6.unwrap();
+        assert_eq!(fd_6, fd_4 + 1);
    }

    #[test]
@ -171,6 +421,7 @@ mod open_test {
 #[cfg(test)]
 mod read_test {
    use crate::vfs::vfs::Vfs;
+    use std::fs;
    use std::fs::File;
    use std::io::Write;
    use tempdir;
@ -186,6 +437,14 @@ mod read_test {
            vfs_result.is_ok(),
            "Failed to create file system from empty archive"
        );
+        // assert import errors
+        let vfs = vfs_result.unwrap();
+        assert_eq!(
+            vfs.import_errors.len(),
+            0,
+            "Expected no import errors. Found {} errors.",
+            vfs.import_errors.len()
+        );
    }

    #[test]
@ -214,6 +473,14 @@ mod read_test {
        assert!(read_result.is_ok(), "Failed to read file from vfs");
        let expected_data = "foo foo foo\n".as_bytes();
        assert_eq!(actual_data, expected_data, "Contents were not equal");
+
+        // assert import errors
+        assert_eq!(
+            vfs.import_errors.len(),
+            0,
+            "Expected no import errors. Found {} errors.",
+            vfs.import_errors.len()
+        );
    }

    #[test]
@ -258,5 +525,130 @@ mod read_test {
            &bar_actual_data, bar_expected_data,
            "Contents of `bar.txt` is not correct"
        );
+        // assert import errors
+        assert_eq!(
+            vfs.import_errors.len(),
+            0,
+            "Expected no import errors. Found {} errors.",
+            vfs.import_errors.len()
+        );
+    }
+
+    #[test]
+    fn two_nested_files_in_archive() {
+        // SETUP: create temp dir and files
+        let tmp_dir = tempdir::TempDir::new("two_nested_files_in_archive").unwrap();
+        let baz_dir_path = tmp_dir.path().join("foo").join("bar");
+        fs::create_dir_all(baz_dir_path.clone()).unwrap();
+        let quuz_dir_path = tmp_dir.path().join("qux").join("quuz");
+        fs::create_dir_all(quuz_dir_path.clone()).unwrap();
+        let baz_file_path = baz_dir_path.join("baz.txt");
+        let quuz_file_path = quuz_dir_path.join("quuz.txt");
+        let mut baz_tmp_file = File::create(baz_file_path.clone()).unwrap();
+        let mut quuz_tmp_file = File::create(quuz_file_path.clone()).unwrap();
+        writeln!(baz_tmp_file, "baz baz baz baz").unwrap();
+        writeln!(quuz_tmp_file, "quuz").unwrap();
+        let tar_data = vec![];
+        let mut ar = tar::Builder::new(tar_data);
+        ar.append_path_with_name(baz_file_path, "foo/bar/baz.txt")
+            .unwrap();
+        ar.append_path_with_name(quuz_file_path, "qux/quux/quuz.txt")
+            .unwrap();
+        let archive = ar.into_inner().unwrap();
+        // SETUP: create virtual filesystem with tar data
+        let vfs_result = Vfs::from_tar_bytes(&archive[..]);
+        // ASSERT:
+        assert!(
+            vfs_result.is_ok(),
+            "Failed to create file system from archive"
+        );
+        let mut vfs = vfs_result.unwrap();
+        // read the file
+        let baz_fd = vfs.open_file("foo/bar/baz.txt").unwrap();
+        let quuz_fd = vfs.open_file("qux/quux/quuz.txt").unwrap();
+        let mut baz_actual_data: [u8; 16] = [0; 16];
+        let baz_read_result = vfs.read_file(baz_fd, &mut baz_actual_data);
+        let mut quuz_actual_data: [u8; 5] = [0; 5];
+        let quuz_read_result = vfs.read_file(quuz_fd, &mut quuz_actual_data);
+        assert!(
+            baz_read_result.is_ok(),
+            "Failed to read foo/bar/baz.txt from vfs"
+        );
+        assert!(
+            quuz_read_result.is_ok(),
+            "Failed to read qux/quux/quuz.txt from vfs"
+        );
+        let baz_expected_data: &[u8; 16] = b"baz baz baz baz\n";
+        let quuz_expected_data: &[u8; 5] = b"quuz\n";
+        assert_eq!(
+            &baz_actual_data, baz_expected_data,
+            "Contents of `foo/bar/baz.txt` is not correct"
+        );
+        assert_eq!(
+            &quuz_actual_data, quuz_expected_data,
+            "Contents of `qux/quux/quuz.txt` is not correct"
+        );
+        // assert import errors
+        assert_eq!(
+            vfs.import_errors.len(),
+            0,
+            "Expected no import errors. Found {} errors.",
+            vfs.import_errors.len()
+        );
+    }
+}
+
+#[cfg(test)]
+mod dup_test {
+    use crate::vfs::vfs::{Fd, Vfs};
+    use std::fs::File;
+    use std::io::Write;
+    use std::sync::Arc;
+
+    #[test]
+    fn duplicates_file_descriptor() {
+        // SETUP: create temp dir and files
+        let tmp_dir = tempdir::TempDir::new("two_files_in_archive").unwrap();
+        let foo_file_path = tmp_dir.path().join("foo.txt");
+        let bar_file_path = tmp_dir.path().join("bar.txt");
+        let mut foo_tmp_file = File::create(foo_file_path.clone()).unwrap();
+        let mut bar_tmp_file = File::create(bar_file_path.clone()).unwrap();
+        writeln!(foo_tmp_file, "foo foo foo").unwrap();
+        writeln!(bar_tmp_file, "bar bar").unwrap();
+        let tar_data = vec![];
+        let mut ar = tar::Builder::new(tar_data);
+        ar.append_path_with_name(foo_file_path, "foo.txt").unwrap();
+        ar.append_path_with_name(bar_file_path, "bar.txt").unwrap();
+        let archive = ar.into_inner().unwrap();
+        // SETUP: create virtual filesystem with tar data
+        let vfs_result = Vfs::from_tar_bytes(&archive[..]);
+        // ASSERT:
+        assert!(
+            vfs_result.is_ok(),
+            "Failed to create file system from archive"
+        );
+        let mut vfs = vfs_result.unwrap();
+
+        let source_fd = vfs.open_file("foo.txt").unwrap();
+        let target_fd: Fd = 10;
+        assert_ne!(
+            source_fd, target_fd,
+            "Test setup failed. The source descriptor is identical to desired target descriptor."
+        );
+
+        let mut fds = vec![];
+        fds.push(Arc::new(100));
+        fds.push(Arc::new(200));
+
+        let result = vfs.duplicate_file_descriptor(source_fd, target_fd);
+
+        assert!(result.is_ok(), "Failed to duplicated file descriptor.");
+        // assert import errors
+        assert_eq!(
+            vfs.import_errors.len(),
+            0,
+            "Expected no import errors. Found {} errors.",
+            vfs.import_errors.len()
+        );
    }
 }
--- a/lib/runtime-abi/src/vfs/virtual_file.rs
+++ b/lib/runtime-abi/src/vfs/virtual_file.rs
@ -0,0 +1,41 @@
+use failure::Error;
+
+use crate::vfs::file_like::{FileLike, Metadata};
+
+pub struct VirtualFile {
+    zbox_file: zbox::File,
+}
+
+impl VirtualFile {
+    pub fn new(file: zbox::File) -> Self {
+        VirtualFile { zbox_file: file }
+    }
+}
+
+impl FileLike for VirtualFile {
+    fn write(&mut self, buf: &[u8], count: usize, offset: usize) -> Result<usize, Error> {
+        use std::io::{Seek, SeekFrom};
+        self.zbox_file.seek(SeekFrom::Start(offset as u64))?;
+        let _ = self.zbox_file.write_once(&buf[..count])?;
+        Ok(count)
+    }
+
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize, Error> {
+        use std::io::Read;
+        self.zbox_file.read(buf).map_err(|e| e.into())
+    }
+
+    fn close(&self) -> Result<(), Error> {
+        Ok(())
+    }
+
+    fn metadata(&self) -> Result<Metadata, Error> {
+        self.zbox_file
+            .metadata()
+            .map(|m| Metadata {
+                len: m.len(),
+                is_file: m.is_file(),
+            })
+            .map_err(|e: zbox::Error| e.into())
+    }
+}