Support fd_fdstat_get and fd_renumber on stdin/stdout/stderr (#631)

* Support fd_fdstat_get on stdin/stdout/stderr.

Add a routine for obtaining an `OsFile` containing a file descriptor for
stdin/stdout/stderr so that we can do fd_fdstat_get on them.

* Add a testcase for fd_fdstat_get etc. on stdin etc.

* Don't dup file descriptors in fd_renumber.

* Fix compilation on macOS

* Rename OsFile to OsHandle

This commits renames `OsFile` to `OsHandle` which seems to make
more sense semantically as it is permitted to hold a valid OS handle
to OS entities other than simply file/dir (e.g., socket, stream, etc.).
As such, this commit also renames methods on `Descriptor` struct
from `as_actual_file` to `as_file` as this in reality does pertain
ops on FS entities such as files/dirs, and `as_file` to `as_os_handle`
as in this case it can be anything, from file, through a socket, to
a stream.

* Fix compilation on Linux

* Introduce `OsHandleRef` for borrowing OS resources.

To prevent a `ManuallyDrop<OsHandleRef>` from outliving the resource it
holds on to, create an `OsHandleRef` class parameterized on the lifetime
of the `Descriptor`.

* Fix scoping to pub-priv and backport to snapshot_0

crates/test-programs/wasi-tests/src/bin/stdio.rs

@@ -0,0 +1,31 @@
+use libc;
+use std::mem::MaybeUninit;
+use std::{env, process};
+use wasi::wasi_unstable;
+use wasi_tests::wasi_wrappers::wasi_fd_fdstat_get;
+
+unsafe fn test_stdio() {
+    for fd in &[
+        wasi_unstable::STDIN_FD,
+        wasi_unstable::STDOUT_FD,
+        wasi_unstable::STDERR_FD,
+    ] {
+        let mut fdstat: wasi_unstable::FdStat = MaybeUninit::zeroed().assume_init();
+        let status = wasi_fd_fdstat_get(*fd, &mut fdstat);
+        assert_eq!(
+            status,
+            wasi_unstable::raw::__WASI_ESUCCESS,
+            "fd_fdstat_get on stdio"
+        );
+
+        assert!(
+            wasi_unstable::fd_renumber(*fd, *fd + 100).is_ok(),
+            "renumbering stdio",
+        );
+    }
+}
+
+fn main() {
+    // Run the tests.
+    unsafe { test_stdio() }
+}

crates/wasi-common/src/fdentry.rs

@@ -1,61 +1,44 @@
 use crate::sys::dev_null;
-use crate::sys::fdentry_impl::{determine_type_and_access_rights, OsFile};
+use crate::sys::fdentry_impl::{
+    descriptor_as_oshandle, determine_type_and_access_rights, OsHandle,
+};
 use crate::{wasi, Error, Result};
+use std::marker::PhantomData;
+use std::mem::ManuallyDrop;
+use std::ops::{Deref, DerefMut};
 use std::path::PathBuf;
 use std::{fs, io};
 
 #[derive(Debug)]
 pub(crate) enum Descriptor {
-    OsFile(OsFile),
+    OsHandle(OsHandle),
     Stdin,
     Stdout,
     Stderr,
 }
 
 impl Descriptor {
-    pub(crate) fn as_file(&self) -> Result<&OsFile> {
+    /// Return a reference to the `OsHandle` treating it as an actual file/dir, and
+    /// allowing operations which require an actual file and not just a stream or
+    /// socket file descriptor.
+    pub(crate) fn as_file(&self) -> Result<&OsHandle> {
         match self {
-            Self::OsFile(file) => Ok(file),
+            Self::OsHandle(file) => Ok(file),
             _ => Err(Error::EBADF),
         }
     }
 
-    pub(crate) fn as_file_mut(&mut self) -> Result<&mut OsFile> {
+    /// Like `as_file`, but return a mutable reference.
+    pub(crate) fn as_file_mut(&mut self) -> Result<&mut OsHandle> {
         match self {
-            Self::OsFile(file) => Ok(file),
+            Self::OsHandle(file) => Ok(file),
             _ => Err(Error::EBADF),
         }
     }
 
-    pub(crate) fn is_file(&self) -> bool {
+    /// Return an `OsHandle`, which may be a stream or socket file descriptor.
-        match self {
+    pub(crate) fn as_os_handle<'descriptor>(&'descriptor self) -> OsHandleRef<'descriptor> {
-            Self::OsFile(_) => true,
+        descriptor_as_oshandle(self)
-            _ => false,
-        }
-    }
-
-    #[allow(unused)]
-    pub(crate) fn is_stdin(&self) -> bool {
-        match self {
-            Self::Stdin => true,
-            _ => false,
-        }
-    }
-
-    #[allow(unused)]
-    pub(crate) fn is_stdout(&self) -> bool {
-        match self {
-            Self::Stdout => true,
-            _ => false,
-        }
-    }
-
-    #[allow(unused)]
-    pub(crate) fn is_stderr(&self) -> bool {
-        match self {
-            Self::Stderr => true,
-            _ => false,
-        }
     }
 }
 
@@ -82,7 +65,7 @@ impl FdEntry {
         unsafe { determine_type_and_access_rights(&file) }.map(
             |(file_type, rights_base, rights_inheriting)| Self {
                 file_type,
-                descriptor: Descriptor::OsFile(OsFile::from(file)),
+                descriptor: Descriptor::OsHandle(OsHandle::from(file)),
                 rights_base,
                 rights_inheriting,
                 preopen_path: None,
@@ -90,10 +73,6 @@ impl FdEntry {
         )
     }
 
-    pub(crate) fn duplicate(file: &fs::File) -> Result<Self> {
-        Self::from(file.try_clone()?)
-    }
-
     pub(crate) fn duplicate_stdin() -> Result<Self> {
         unsafe { determine_type_and_access_rights(&io::stdin()) }.map(
             |(file_type, rights_base, rights_inheriting)| Self {
@@ -184,3 +163,35 @@ impl FdEntry {
         }
     }
 }
+
+/// This allows an `OsHandle` to be temporarily borrowed from a
+/// `Descriptor`. The `Descriptor` continues to own the resource,
+/// and `OsHandleRef`'s lifetime parameter ensures that it doesn't
+/// outlive the `Descriptor`.
+pub(crate) struct OsHandleRef<'descriptor> {
+    handle: ManuallyDrop<OsHandle>,
+    _ref: PhantomData<&'descriptor Descriptor>,
+}
+
+impl<'descriptor> OsHandleRef<'descriptor> {
+    pub(crate) fn new(handle: ManuallyDrop<OsHandle>) -> Self {
+        OsHandleRef {
+            handle,
+            _ref: PhantomData,
+        }
+    }
+}
+
+impl<'descriptor> Deref for OsHandleRef<'descriptor> {
+    type Target = fs::File;
+
+    fn deref(&self) -> &Self::Target {
+        &self.handle
+    }
+}
+
+impl<'descriptor> DerefMut for OsHandleRef<'descriptor> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.handle
+    }
+}

crates/wasi-common/src/hostcalls_impl/fs.rs

@@ -161,7 +161,7 @@ pub(crate) unsafe fn fd_read(
         .get_fd_entry_mut(fd)?
         .as_descriptor_mut(wasi::__WASI_RIGHTS_FD_READ, 0)?
     {
-        Descriptor::OsFile(file) => file.read_vectored(&mut iovs),
+        Descriptor::OsHandle(file) => file.read_vectored(&mut iovs),
         Descriptor::Stdin => io::stdin().lock().read_vectored(&mut iovs),
         _ => return Err(Error::EBADF),
     };
@@ -180,33 +180,25 @@ pub(crate) unsafe fn fd_renumber(
 ) -> Result<()> {
     trace!("fd_renumber(from={:?}, to={:?})", from, to);
 
-    if !wasi_ctx.contains_fd_entry(from) || !wasi_ctx.contains_fd_entry(to) {
+    if !wasi_ctx.contains_fd_entry(from) {
         return Err(Error::EBADF);
     }
 
-    let from_fe = wasi_ctx.get_fd_entry(from)?;
-    let to_fe = wasi_ctx.get_fd_entry(to)?;
-
     // Don't allow renumbering over a pre-opened resource.
     // TODO: Eventually, we do want to permit this, once libpreopen in
     // userspace is capable of removing entries from its tables as well.
-    if from_fe.preopen_path.is_some() || to_fe.preopen_path.is_some() {
+    let from_fe = wasi_ctx.get_fd_entry(from)?;
+    if from_fe.preopen_path.is_some() {
+        return Err(Error::ENOTSUP);
+    }
+    if let Ok(to_fe) = wasi_ctx.get_fd_entry(to) {
+        if to_fe.preopen_path.is_some() {
             return Err(Error::ENOTSUP);
         }
-
-    // check if stdio fds
-    // TODO should we renumber stdio fds?
-    if !from_fe.as_descriptor(0, 0)?.is_file() || !to_fe.as_descriptor(0, 0)?.is_file() {
-        return Err(Error::EBADF);
     }
 
-    let fe_from_dup = from_fe
+    let fe = wasi_ctx.remove_fd_entry(from)?;
-        .as_descriptor(0, 0)?
+    wasi_ctx.insert_fd_entry_at(to, fe);
-        .as_file()
-        .and_then(|file| FdEntry::duplicate(file))?;
-
-    wasi_ctx.insert_fd_entry_at(to, fe_from_dup);
-    wasi_ctx.remove_fd_entry(from)?;
 
     Ok(())
 }
@@ -279,9 +271,12 @@ pub(crate) unsafe fn fd_fdstat_get(
     trace!("fd_fdstat_get(fd={:?}, fdstat_ptr={:#x?})", fd, fdstat_ptr);
 
     let mut fdstat = dec_fdstat_byref(memory, fdstat_ptr)?;
-    let wasi_fd = wasi_ctx.get_fd_entry(fd)?.as_descriptor(0, 0)?.as_file()?;
+    let host_fd = wasi_ctx
+        .get_fd_entry(fd)?
+        .as_descriptor(0, 0)?
+        .as_os_handle();
 
-    let fs_flags = hostcalls_impl::fd_fdstat_get(wasi_fd)?;
+    let fs_flags = hostcalls_impl::fd_fdstat_get(&host_fd)?;
 
     let fe = wasi_ctx.get_fd_entry(fd)?;
     fdstat.fs_filetype = fe.file_type;
@@ -301,9 +296,12 @@ pub(crate) unsafe fn fd_fdstat_set_flags(
 ) -> Result<()> {
     trace!("fd_fdstat_set_flags(fd={:?}, fdflags={:#x?})", fd, fdflags);
 
-    let fd = wasi_ctx.get_fd_entry(fd)?.as_descriptor(0, 0)?.as_file()?;
+    let fd = wasi_ctx
+        .get_fd_entry(fd)?
+        .as_descriptor(0, 0)?
+        .as_os_handle();
 
-    hostcalls_impl::fd_fdstat_set_flags(fd, fdflags)
+    hostcalls_impl::fd_fdstat_set_flags(&fd, fdflags)
 }
 
 pub(crate) unsafe fn fd_fdstat_set_rights(
@@ -365,7 +363,7 @@ pub(crate) unsafe fn fd_write(
         .get_fd_entry_mut(fd)?
         .as_descriptor_mut(wasi::__WASI_RIGHTS_FD_WRITE, 0)?
     {
-        Descriptor::OsFile(file) => file.write_vectored(&iovs)?,
+        Descriptor::OsHandle(file) => file.write_vectored(&iovs)?,
         Descriptor::Stdin => return Err(Error::EBADF),
         Descriptor::Stdout => {
             // lock for the duration of the scope

crates/wasi-common/src/old/snapshot_0/fdentry.rs

@@ -1,61 +1,44 @@
 use crate::old::snapshot_0::sys::dev_null;
-use crate::old::snapshot_0::sys::fdentry_impl::{determine_type_and_access_rights, OsFile};
+use crate::old::snapshot_0::sys::fdentry_impl::{
+    descriptor_as_oshandle, determine_type_and_access_rights, OsHandle,
+};
 use crate::old::snapshot_0::{wasi, Error, Result};
+use std::marker::PhantomData;
+use std::mem::ManuallyDrop;
+use std::ops::{Deref, DerefMut};
 use std::path::PathBuf;
 use std::{fs, io};
 
 #[derive(Debug)]
 pub(crate) enum Descriptor {
-    OsFile(OsFile),
+    OsHandle(OsHandle),
     Stdin,
     Stdout,
     Stderr,
 }
 
 impl Descriptor {
-    pub(crate) fn as_file(&self) -> Result<&OsFile> {
+    /// Return a reference to the `OsHandle` treating it as an actual file/dir, and
+    /// allowing operations which require an actual file and not just a stream or
+    /// socket file descriptor.
+    pub(crate) fn as_file(&self) -> Result<&OsHandle> {
         match self {
-            Self::OsFile(file) => Ok(file),
+            Self::OsHandle(file) => Ok(file),
             _ => Err(Error::EBADF),
         }
     }
 
-    pub(crate) fn as_file_mut(&mut self) -> Result<&mut OsFile> {
+    /// Like `as_file`, but return a mutable reference.
+    pub(crate) fn as_file_mut(&mut self) -> Result<&mut OsHandle> {
         match self {
-            Self::OsFile(file) => Ok(file),
+            Self::OsHandle(file) => Ok(file),
             _ => Err(Error::EBADF),
         }
     }
 
-    pub(crate) fn is_file(&self) -> bool {
+    /// Return an `OsHandle`, which may be a stream or socket file descriptor.
-        match self {
+    pub(crate) fn as_os_handle<'descriptor>(&'descriptor self) -> OsHandleRef<'descriptor> {
-            Self::OsFile(_) => true,
+        descriptor_as_oshandle(self)
-            _ => false,
-        }
-    }
-
-    #[allow(unused)]
-    pub(crate) fn is_stdin(&self) -> bool {
-        match self {
-            Self::Stdin => true,
-            _ => false,
-        }
-    }
-
-    #[allow(unused)]
-    pub(crate) fn is_stdout(&self) -> bool {
-        match self {
-            Self::Stdout => true,
-            _ => false,
-        }
-    }
-
-    #[allow(unused)]
-    pub(crate) fn is_stderr(&self) -> bool {
-        match self {
-            Self::Stderr => true,
-            _ => false,
-        }
     }
 }
 
@@ -82,7 +65,7 @@ impl FdEntry {
         unsafe { determine_type_and_access_rights(&file) }.map(
             |(file_type, rights_base, rights_inheriting)| Self {
                 file_type,
-                descriptor: Descriptor::OsFile(OsFile::from(file)),
+                descriptor: Descriptor::OsHandle(OsHandle::from(file)),
                 rights_base,
                 rights_inheriting,
                 preopen_path: None,
@@ -90,10 +73,6 @@ impl FdEntry {
         )
     }
 
-    pub(crate) fn duplicate(file: &fs::File) -> Result<Self> {
-        Self::from(file.try_clone()?)
-    }
-
     pub(crate) fn duplicate_stdin() -> Result<Self> {
         unsafe { determine_type_and_access_rights(&io::stdin()) }.map(
             |(file_type, rights_base, rights_inheriting)| Self {
@@ -184,3 +163,35 @@ impl FdEntry {
         }
     }
 }
+
+/// This allows an `OsHandle` to be temporarily borrowed from a
+/// `Descriptor`. The `Descriptor` continues to own the resource,
+/// and `OsHandleRef`'s lifetime parameter ensures that it doesn't
+/// outlive the `Descriptor`.
+pub(crate) struct OsHandleRef<'descriptor> {
+    handle: ManuallyDrop<OsHandle>,
+    _ref: PhantomData<&'descriptor Descriptor>,
+}
+
+impl<'descriptor> OsHandleRef<'descriptor> {
+    pub(crate) fn new(handle: ManuallyDrop<OsHandle>) -> Self {
+        OsHandleRef {
+            handle,
+            _ref: PhantomData,
+        }
+    }
+}
+
+impl<'descriptor> Deref for OsHandleRef<'descriptor> {
+    type Target = fs::File;
+
+    fn deref(&self) -> &Self::Target {
+        &self.handle
+    }
+}
+
+impl<'descriptor> DerefMut for OsHandleRef<'descriptor> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.handle
+    }
+}

crates/wasi-common/src/old/snapshot_0/hostcalls_impl/fs.rs

@@ -161,7 +161,7 @@ pub(crate) unsafe fn fd_read(
         .get_fd_entry_mut(fd)?
         .as_descriptor_mut(wasi::__WASI_RIGHTS_FD_READ, 0)?
     {
-        Descriptor::OsFile(file) => file.read_vectored(&mut iovs),
+        Descriptor::OsHandle(file) => file.read_vectored(&mut iovs),
         Descriptor::Stdin => io::stdin().lock().read_vectored(&mut iovs),
         _ => return Err(Error::EBADF),
     };
@@ -180,33 +180,25 @@ pub(crate) unsafe fn fd_renumber(
 ) -> Result<()> {
     trace!("fd_renumber(from={:?}, to={:?})", from, to);
 
-    if !wasi_ctx.contains_fd_entry(from) || !wasi_ctx.contains_fd_entry(to) {
+    if !wasi_ctx.contains_fd_entry(from) {
         return Err(Error::EBADF);
     }
 
-    let from_fe = wasi_ctx.get_fd_entry(from)?;
-    let to_fe = wasi_ctx.get_fd_entry(to)?;
-
     // Don't allow renumbering over a pre-opened resource.
     // TODO: Eventually, we do want to permit this, once libpreopen in
     // userspace is capable of removing entries from its tables as well.
-    if from_fe.preopen_path.is_some() || to_fe.preopen_path.is_some() {
+    let from_fe = wasi_ctx.get_fd_entry(from)?;
+    if from_fe.preopen_path.is_some() {
+        return Err(Error::ENOTSUP);
+    }
+    if let Ok(to_fe) = wasi_ctx.get_fd_entry(to) {
+        if to_fe.preopen_path.is_some() {
             return Err(Error::ENOTSUP);
         }
-
-    // check if stdio fds
-    // TODO should we renumber stdio fds?
-    if !from_fe.as_descriptor(0, 0)?.is_file() || !to_fe.as_descriptor(0, 0)?.is_file() {
-        return Err(Error::EBADF);
     }
 
-    let fe_from_dup = from_fe
+    let fe = wasi_ctx.remove_fd_entry(from)?;
-        .as_descriptor(0, 0)?
+    wasi_ctx.insert_fd_entry_at(to, fe);
-        .as_file()
-        .and_then(|file| FdEntry::duplicate(file))?;
-
-    wasi_ctx.insert_fd_entry_at(to, fe_from_dup);
-    wasi_ctx.remove_fd_entry(from)?;
 
     Ok(())
 }
@@ -279,9 +271,12 @@ pub(crate) unsafe fn fd_fdstat_get(
     trace!("fd_fdstat_get(fd={:?}, fdstat_ptr={:#x?})", fd, fdstat_ptr);
 
     let mut fdstat = dec_fdstat_byref(memory, fdstat_ptr)?;
-    let wasi_fd = wasi_ctx.get_fd_entry(fd)?.as_descriptor(0, 0)?.as_file()?;
+    let host_fd = wasi_ctx
+        .get_fd_entry(fd)?
+        .as_descriptor(0, 0)?
+        .as_os_handle();
 
-    let fs_flags = hostcalls_impl::fd_fdstat_get(wasi_fd)?;
+    let fs_flags = hostcalls_impl::fd_fdstat_get(&host_fd)?;
 
     let fe = wasi_ctx.get_fd_entry(fd)?;
     fdstat.fs_filetype = fe.file_type;
@@ -301,9 +296,12 @@ pub(crate) unsafe fn fd_fdstat_set_flags(
 ) -> Result<()> {
     trace!("fd_fdstat_set_flags(fd={:?}, fdflags={:#x?})", fd, fdflags);
 
-    let fd = wasi_ctx.get_fd_entry(fd)?.as_descriptor(0, 0)?.as_file()?;
+    let fd = wasi_ctx
+        .get_fd_entry(fd)?
+        .as_descriptor(0, 0)?
+        .as_os_handle();
 
-    hostcalls_impl::fd_fdstat_set_flags(fd, fdflags)
+    hostcalls_impl::fd_fdstat_set_flags(&fd, fdflags)
 }
 
 pub(crate) unsafe fn fd_fdstat_set_rights(
@@ -365,7 +363,7 @@ pub(crate) unsafe fn fd_write(
         .get_fd_entry_mut(fd)?
         .as_descriptor_mut(wasi::__WASI_RIGHTS_FD_WRITE, 0)?
     {
-        Descriptor::OsFile(file) => file.write_vectored(&iovs)?,
+        Descriptor::OsHandle(file) => file.write_vectored(&iovs)?,
         Descriptor::Stdin => return Err(Error::EBADF),
         Descriptor::Stdout => {
             // lock for the duration of the scope

crates/wasi-common/src/old/snapshot_0/sys/unix/bsd/hostcalls_impl.rs

@@ -1,4 +1,4 @@
-use super::osfile::OsFile;
+use super::oshandle::OsHandle;
 use crate::old::snapshot_0::hostcalls_impl::PathGet;
 use crate::old::snapshot_0::sys::host_impl;
 use crate::old::snapshot_0::sys::unix::str_to_cstring;
@@ -140,23 +140,23 @@ pub(crate) fn path_rename(resolved_old: PathGet, resolved_new: PathGet) -> Resul
 }
 
 pub(crate) fn fd_readdir(
-    os_file: &mut OsFile,
+    os_handle: &mut OsHandle,
     host_buf: &mut [u8],
     cookie: wasi::__wasi_dircookie_t,
 ) -> Result<usize> {
-    use crate::old::snapshot_0::sys::unix::bsd::osfile::DirStream;
+    use crate::old::snapshot_0::sys::unix::bsd::oshandle::DirStream;
     use libc::{fdopendir, readdir, rewinddir, seekdir, telldir};
     use nix::errno::Errno;
     use std::ffi::CStr;
     use std::mem::ManuallyDrop;
     use std::sync::Mutex;
 
-    let dir_stream = match os_file.dir_stream {
+    let dir_stream = match os_handle.dir_stream {
         Some(ref mut dir_stream) => dir_stream,
         None => {
-            let file = os_file.file.try_clone()?;
+            let file = os_handle.file.try_clone()?;
             let dir_ptr = unsafe { fdopendir(file.as_raw_fd()) };
-            os_file.dir_stream.get_or_insert(Mutex::new(DirStream {
+            os_handle.dir_stream.get_or_insert(Mutex::new(DirStream {
                 file: ManuallyDrop::new(file),
                 dir_ptr,
             }))

crates/wasi-common/src/old/snapshot_0/sys/unix/bsd/mod.rs

@@ -1,6 +1,6 @@
 pub(crate) mod filetime;
 pub(crate) mod hostcalls_impl;
-pub(crate) mod osfile;
+pub(crate) mod oshandle;
 
 pub(crate) mod fdentry_impl {
     use crate::old::snapshot_0::{sys::host_impl, Result};

crates/wasi-common/src/old/snapshot_0/sys/unix/bsd/oshandle.rs

@@ -17,12 +17,12 @@ impl Drop for DirStream {
 }
 
 #[derive(Debug)]
-pub(crate) struct OsFile {
+pub(crate) struct OsHandle {
     pub(crate) file: fs::File,
     pub(crate) dir_stream: Option<Mutex<DirStream>>,
 }
 
-impl From<fs::File> for OsFile {
+impl From<fs::File> for OsHandle {
     fn from(file: fs::File) -> Self {
         Self {
             file,
@@ -31,13 +31,13 @@ impl From<fs::File> for OsFile {
     }
 }
 
-impl AsRawFd for OsFile {
+impl AsRawFd for OsHandle {
     fn as_raw_fd(&self) -> RawFd {
         self.file.as_raw_fd()
     }
 }
 
-impl Deref for OsFile {
+impl Deref for OsHandle {
     type Target = fs::File;
 
     fn deref(&self) -> &Self::Target {
@@ -45,7 +45,7 @@ impl Deref for OsFile {
     }
 }
 
-impl DerefMut for OsFile {
+impl DerefMut for OsHandle {
     fn deref_mut(&mut self) -> &mut Self::Target {
         &mut self.file
     }

crates/wasi-common/src/old/snapshot_0/sys/unix/fdentry_impl.rs

@@ -1,11 +1,13 @@
-use crate::old::snapshot_0::fdentry::Descriptor;
+use crate::old::snapshot_0::fdentry::{Descriptor, OsHandleRef};
 use crate::old::snapshot_0::{wasi, Error, Result};
+use std::fs::File;
 use std::io;
+use std::mem::ManuallyDrop;
 use std::os::unix::prelude::{AsRawFd, FileTypeExt, FromRawFd, RawFd};
 
 cfg_if::cfg_if! {
     if #[cfg(target_os = "linux")] {
-        pub(crate) use super::linux::osfile::*;
+        pub(crate) use super::linux::oshandle::*;
         pub(crate) use super::linux::fdentry_impl::*;
     } else if #[cfg(any(
             target_os = "macos",
@@ -15,7 +17,7 @@ cfg_if::cfg_if! {
             target_os = "ios",
             target_os = "dragonfly"
     ))] {
-        pub(crate) use super::bsd::osfile::*;
+        pub(crate) use super::bsd::oshandle::*;
         pub(crate) use super::bsd::fdentry_impl::*;
     }
 }
@@ -23,7 +25,7 @@ cfg_if::cfg_if! {
 impl AsRawFd for Descriptor {
     fn as_raw_fd(&self) -> RawFd {
         match self {
-            Self::OsFile(file) => file.as_raw_fd(),
+            Self::OsHandle(file) => file.as_raw_fd(),
             Self::Stdin => io::stdin().as_raw_fd(),
             Self::Stdout => io::stdout().as_raw_fd(),
             Self::Stderr => io::stderr().as_raw_fd(),
@@ -31,6 +33,14 @@ impl AsRawFd for Descriptor {
     }
 }
 
+pub(crate) fn descriptor_as_oshandle<'lifetime>(
+    desc: &'lifetime Descriptor,
+) -> OsHandleRef<'lifetime> {
+    OsHandleRef::new(ManuallyDrop::new(OsHandle::from(unsafe {
+        File::from_raw_fd(desc.as_raw_fd())
+    })))
+}
+
 /// This function is unsafe because it operates on a raw file descriptor.
 pub(crate) unsafe fn determine_type_and_access_rights<Fd: AsRawFd>(
     fd: &Fd,

crates/wasi-common/src/old/snapshot_0/sys/unix/linux/hostcalls_impl.rs

@@ -1,5 +1,5 @@
 use super::super::dir::{Dir, Entry, SeekLoc};
-use super::osfile::OsFile;
+use super::oshandle::OsHandle;
 use crate::old::snapshot_0::hostcalls_impl::{Dirent, PathGet};
 use crate::old::snapshot_0::sys::host_impl;
 use crate::old::snapshot_0::sys::unix::str_to_cstring;
@@ -115,11 +115,11 @@ pub(crate) fn fd_readdir_impl(
 // This should actually be common code with Windows,
 // but there's BSD stuff remaining
 pub(crate) fn fd_readdir(
-    os_file: &mut OsFile,
+    os_handle: &mut OsHandle,
     mut host_buf: &mut [u8],
     cookie: wasi::__wasi_dircookie_t,
 ) -> Result<usize> {
-    let iter = fd_readdir_impl(os_file, cookie)?;
+    let iter = fd_readdir_impl(os_handle, cookie)?;
     let mut used = 0;
     for dirent in iter {
         let dirent_raw = dirent?.to_wasi_raw()?;

crates/wasi-common/src/old/snapshot_0/sys/unix/linux/mod.rs

@@ -1,6 +1,6 @@
 pub(crate) mod filetime;
 pub(crate) mod hostcalls_impl;
-pub(crate) mod osfile;
+pub(crate) mod oshandle;
 
 pub(crate) mod fdentry_impl {
     use crate::old::snapshot_0::{sys::host_impl, Result};

crates/wasi-common/src/old/snapshot_0/sys/unix/linux/oshandle.rs

@@ -3,21 +3,21 @@ use std::ops::{Deref, DerefMut};
 use std::os::unix::prelude::{AsRawFd, RawFd};
 
 #[derive(Debug)]
-pub(crate) struct OsFile(fs::File);
+pub(crate) struct OsHandle(fs::File);
 
-impl From<fs::File> for OsFile {
+impl From<fs::File> for OsHandle {
     fn from(file: fs::File) -> Self {
         Self(file)
     }
 }
 
-impl AsRawFd for OsFile {
+impl AsRawFd for OsHandle {
     fn as_raw_fd(&self) -> RawFd {
         self.0.as_raw_fd()
     }
 }
 
-impl Deref for OsFile {
+impl Deref for OsHandle {
     type Target = fs::File;
 
     fn deref(&self) -> &Self::Target {
@@ -25,7 +25,7 @@ impl Deref for OsFile {
     }
 }
 
-impl DerefMut for OsFile {
+impl DerefMut for OsHandle {
     fn deref_mut(&mut self) -> &mut Self::Target {
         &mut self.0
     }

crates/wasi-common/src/old/snapshot_0/sys/windows/fdentry_impl.rs

@@ -1,26 +1,27 @@
-use crate::old::snapshot_0::fdentry::Descriptor;
+use crate::old::snapshot_0::fdentry::{Descriptor, OsHandleRef};
 use crate::old::snapshot_0::{wasi, Error, Result};
 use std::fs::File;
 use std::io;
+use std::mem::ManuallyDrop;
 use std::ops::{Deref, DerefMut};
 use std::os::windows::prelude::{AsRawHandle, FromRawHandle, RawHandle};
 
 #[derive(Debug)]
-pub(crate) struct OsFile(File);
+pub(crate) struct OsHandle(File);
 
-impl From<File> for OsFile {
+impl From<File> for OsHandle {
     fn from(file: File) -> Self {
         Self(file)
     }
 }
 
-impl AsRawHandle for OsFile {
+impl AsRawHandle for OsHandle {
     fn as_raw_handle(&self) -> RawHandle {
         self.0.as_raw_handle()
     }
 }
 
-impl Deref for OsFile {
+impl Deref for OsHandle {
     type Target = File;
 
     fn deref(&self) -> &Self::Target {
@@ -28,7 +29,7 @@ impl Deref for OsFile {
     }
 }
 
-impl DerefMut for OsFile {
+impl DerefMut for OsHandle {
     fn deref_mut(&mut self) -> &mut Self::Target {
         &mut self.0
     }
@@ -37,7 +38,7 @@ impl DerefMut for OsFile {
 impl AsRawHandle for Descriptor {
     fn as_raw_handle(&self) -> RawHandle {
         match self {
-            Self::OsFile(file) => file.as_raw_handle(),
+            Self::OsHandle(file) => file.as_raw_handle(),
             Self::Stdin => io::stdin().as_raw_handle(),
             Self::Stdout => io::stdout().as_raw_handle(),
             Self::Stderr => io::stderr().as_raw_handle(),
@@ -45,6 +46,14 @@ impl AsRawHandle for Descriptor {
     }
 }
 
+pub(crate) fn descriptor_as_oshandle<'lifetime>(
+    desc: &'lifetime Descriptor,
+) -> OsHandleRef<'lifetime> {
+    OsHandleRef::new(ManuallyDrop::new(OsHandle::from(unsafe {
+        File::from_raw_handle(desc.as_raw_handle())
+    })))
+}
+
 /// This function is unsafe because it operates on a raw file handle.
 pub(crate) unsafe fn determine_type_and_access_rights<Handle: AsRawHandle>(
     handle: &Handle,

crates/wasi-common/src/old/snapshot_0/sys/windows/hostcalls_impl/fs.rs

@@ -7,7 +7,7 @@ use crate::old::snapshot_0::helpers::systemtime_to_timestamp;
 use crate::old::snapshot_0::hostcalls_impl::{
     fd_filestat_set_times_impl, Dirent, FileType, PathGet,
 };
-use crate::old::snapshot_0::sys::fdentry_impl::{determine_type_rights, OsFile};
+use crate::old::snapshot_0::sys::fdentry_impl::{determine_type_rights, OsHandle};
 use crate::old::snapshot_0::sys::host_impl::{self, path_from_host};
 use crate::old::snapshot_0::sys::hostcalls_impl::fs_helpers::PathGetExt;
 use crate::old::snapshot_0::{wasi, Error, Result};
@@ -261,11 +261,11 @@ pub(crate) fn fd_readdir_impl(
 
 // This should actually be common code with Linux
 pub(crate) fn fd_readdir(
-    os_file: &mut OsFile,
+    os_handle: &mut OsHandle,
     mut host_buf: &mut [u8],
     cookie: wasi::__wasi_dircookie_t,
 ) -> Result<usize> {
-    let iter = fd_readdir_impl(os_file, cookie)?;
+    let iter = fd_readdir_impl(os_handle, cookie)?;
     let mut used = 0;
     for dirent in iter {
         let dirent_raw = dirent?.to_wasi_raw()?;

crates/wasi-common/src/sys/unix/bsd/hostcalls_impl.rs

@@ -1,5 +1,5 @@
 use super::super::dir::{Dir, Entry, SeekLoc};
-use super::osfile::OsFile;
+use super::oshandle::OsHandle;
 use crate::hostcalls_impl::{Dirent, PathGet};
 use crate::sys::host_impl;
 use crate::sys::unix::str_to_cstring;
@@ -205,12 +205,12 @@ pub(crate) fn fd_advise(
 }
 
 pub(crate) fn fd_readdir<'a>(
-    os_file: &'a mut OsFile,
+    os_handle: &'a mut OsHandle,
     cookie: wasi::__wasi_dircookie_t,
 ) -> Result<impl Iterator<Item = Result<Dirent>> + 'a> {
     use std::sync::Mutex;
 
-    let dir = match os_file.dir {
+    let dir = match os_handle.dir {
         Some(ref mut dir) => dir,
         None => {
             // We need to duplicate the fd, because `opendir(3)`:
@@ -219,9 +219,9 @@ pub(crate) fn fd_readdir<'a>(
             //     descriptor, or to modify the state of the associated description other
             //     than by means of closedir(), readdir(), readdir_r(), or rewinddir(),
             //     the behaviour is undefined.
-            let fd = (*os_file).try_clone()?;
+            let fd = (*os_handle).try_clone()?;
             let dir = Dir::from(fd)?;
-            os_file.dir.get_or_insert(Mutex::new(dir))
+            os_handle.dir.get_or_insert(Mutex::new(dir))
         }
     };
     let mut dir = dir.lock().unwrap();

crates/wasi-common/src/sys/unix/bsd/mod.rs

@@ -1,6 +1,6 @@
 pub(crate) mod filetime;
 pub(crate) mod hostcalls_impl;
-pub(crate) mod osfile;
+pub(crate) mod oshandle;
 
 pub(crate) mod fdentry_impl {
     use crate::{sys::host_impl, Result};

crates/wasi-common/src/sys/unix/bsd/oshandle.rs

@@ -5,9 +5,9 @@ use std::os::unix::prelude::{AsRawFd, RawFd};
 use std::sync::Mutex;
 
 #[derive(Debug)]
-pub(crate) struct OsFile {
+pub(crate) struct OsHandle {
     pub(crate) file: fs::File,
-    // In case that this `OsFile` actually refers to a directory,
+    // In case that this `OsHandle` actually refers to a directory,
     // when the client makes a `fd_readdir` syscall on this descriptor,
     // we will need to cache the `libc::DIR` pointer manually in order
     // to be able to seek on it later. While on Linux, this is handled
@@ -21,19 +21,19 @@ pub(crate) struct OsFile {
     pub(crate) dir: Option<Mutex<Dir>>,
 }
 
-impl From<fs::File> for OsFile {
+impl From<fs::File> for OsHandle {
     fn from(file: fs::File) -> Self {
         Self { file, dir: None }
     }
 }
 
-impl AsRawFd for OsFile {
+impl AsRawFd for OsHandle {
     fn as_raw_fd(&self) -> RawFd {
         self.file.as_raw_fd()
     }
 }
 
-impl Deref for OsFile {
+impl Deref for OsHandle {
     type Target = fs::File;
 
     fn deref(&self) -> &Self::Target {
@@ -41,7 +41,7 @@ impl Deref for OsFile {
     }
 }
 
-impl DerefMut for OsFile {
+impl DerefMut for OsHandle {
     fn deref_mut(&mut self) -> &mut Self::Target {
         &mut self.file
     }

crates/wasi-common/src/sys/unix/fdentry_impl.rs

@@ -1,11 +1,13 @@
-use crate::fdentry::Descriptor;
+use crate::fdentry::{Descriptor, OsHandleRef};
 use crate::{wasi, Error, Result};
+use std::fs::File;
 use std::io;
+use std::mem::ManuallyDrop;
 use std::os::unix::prelude::{AsRawFd, FileTypeExt, FromRawFd, RawFd};
 
 cfg_if::cfg_if! {
     if #[cfg(target_os = "linux")] {
-        pub(crate) use super::linux::osfile::*;
+        pub(crate) use super::linux::oshandle::*;
         pub(crate) use super::linux::fdentry_impl::*;
     } else if #[cfg(any(
             target_os = "macos",
@@ -15,7 +17,7 @@ cfg_if::cfg_if! {
             target_os = "ios",
             target_os = "dragonfly"
     ))] {
-        pub(crate) use super::bsd::osfile::*;
+        pub(crate) use super::bsd::oshandle::*;
         pub(crate) use super::bsd::fdentry_impl::*;
     }
 }
@@ -23,7 +25,7 @@ cfg_if::cfg_if! {
 impl AsRawFd for Descriptor {
     fn as_raw_fd(&self) -> RawFd {
         match self {
-            Self::OsFile(file) => file.as_raw_fd(),
+            Self::OsHandle(file) => file.as_raw_fd(),
             Self::Stdin => io::stdin().as_raw_fd(),
             Self::Stdout => io::stdout().as_raw_fd(),
             Self::Stderr => io::stderr().as_raw_fd(),
@@ -31,6 +33,14 @@ impl AsRawFd for Descriptor {
     }
 }
 
+pub(crate) fn descriptor_as_oshandle<'lifetime>(
+    desc: &'lifetime Descriptor,
+) -> OsHandleRef<'lifetime> {
+    OsHandleRef::new(ManuallyDrop::new(OsHandle::from(unsafe {
+        File::from_raw_fd(desc.as_raw_fd())
+    })))
+}
+
 /// This function is unsafe because it operates on a raw file descriptor.
 pub(crate) unsafe fn determine_type_and_access_rights<Fd: AsRawFd>(
     fd: &Fd,

crates/wasi-common/src/sys/unix/linux/mod.rs

@@ -1,6 +1,6 @@
 pub(crate) mod filetime;
 pub(crate) mod hostcalls_impl;
-pub(crate) mod osfile;
+pub(crate) mod oshandle;
 
 pub(crate) mod fdentry_impl {
     use crate::{sys::host_impl, Result};

crates/wasi-common/src/sys/unix/linux/oshandle.rs

@@ -3,21 +3,21 @@ use std::ops::{Deref, DerefMut};
 use std::os::unix::prelude::{AsRawFd, RawFd};
 
 #[derive(Debug)]
-pub(crate) struct OsFile(fs::File);
+pub(crate) struct OsHandle(fs::File);
 
-impl From<fs::File> for OsFile {
+impl From<fs::File> for OsHandle {
     fn from(file: fs::File) -> Self {
         Self(file)
     }
 }
 
-impl AsRawFd for OsFile {
+impl AsRawFd for OsHandle {
     fn as_raw_fd(&self) -> RawFd {
         self.0.as_raw_fd()
     }
 }
 
-impl Deref for OsFile {
+impl Deref for OsHandle {
     type Target = fs::File;
 
     fn deref(&self) -> &Self::Target {
@@ -25,7 +25,7 @@ impl Deref for OsFile {
     }
 }
 
-impl DerefMut for OsFile {
+impl DerefMut for OsHandle {
     fn deref_mut(&mut self) -> &mut Self::Target {
         &mut self.0
     }

crates/wasi-common/src/sys/windows/fdentry_impl.rs

@@ -1,26 +1,27 @@
-use crate::fdentry::Descriptor;
+use crate::fdentry::{Descriptor, OsHandleRef};
 use crate::{wasi, Error, Result};
 use std::fs::File;
 use std::io;
+use std::mem::ManuallyDrop;
 use std::ops::{Deref, DerefMut};
 use std::os::windows::prelude::{AsRawHandle, FromRawHandle, RawHandle};
 
 #[derive(Debug)]
-pub(crate) struct OsFile(File);
+pub(crate) struct OsHandle(File);
 
-impl From<File> for OsFile {
+impl From<File> for OsHandle {
     fn from(file: File) -> Self {
         Self(file)
     }
 }
 
-impl AsRawHandle for OsFile {
+impl AsRawHandle for OsHandle {
     fn as_raw_handle(&self) -> RawHandle {
         self.0.as_raw_handle()
     }
 }
 
-impl Deref for OsFile {
+impl Deref for OsHandle {
     type Target = File;
 
     fn deref(&self) -> &Self::Target {
@@ -28,7 +29,7 @@ impl Deref for OsFile {
     }
 }
 
-impl DerefMut for OsFile {
+impl DerefMut for OsHandle {
     fn deref_mut(&mut self) -> &mut Self::Target {
         &mut self.0
     }
@@ -37,7 +38,7 @@ impl DerefMut for OsFile {
 impl AsRawHandle for Descriptor {
     fn as_raw_handle(&self) -> RawHandle {
         match self {
-            Self::OsFile(file) => file.as_raw_handle(),
+            Self::OsHandle(file) => file.as_raw_handle(),
             Self::Stdin => io::stdin().as_raw_handle(),
             Self::Stdout => io::stdout().as_raw_handle(),
             Self::Stderr => io::stderr().as_raw_handle(),
@@ -45,6 +46,14 @@ impl AsRawHandle for Descriptor {
     }
 }
 
+pub(crate) fn descriptor_as_oshandle<'lifetime>(
+    desc: &'lifetime Descriptor,
+) -> OsHandleRef<'lifetime> {
+    OsHandleRef::new(ManuallyDrop::new(OsHandle::from(unsafe {
+        File::from_raw_handle(desc.as_raw_handle())
+    })))
+}
+
 /// This function is unsafe because it operates on a raw file handle.
 pub(crate) unsafe fn determine_type_and_access_rights<Handle: AsRawHandle>(
     handle: &Handle,

crates/wasi-common/src/sys/windows/hostcalls_impl/fs.rs

@@ -5,7 +5,7 @@ use crate::ctx::WasiCtx;
 use crate::fdentry::FdEntry;
 use crate::helpers::systemtime_to_timestamp;
 use crate::hostcalls_impl::{fd_filestat_set_times_impl, Dirent, FileType, PathGet};
-use crate::sys::fdentry_impl::{determine_type_rights, OsFile};
+use crate::sys::fdentry_impl::determine_type_rights;
 use crate::sys::host_impl::{self, path_from_host};
 use crate::sys::hostcalls_impl::fs_helpers::PathGetExt;
 use crate::{wasi, Error, Result};