Make fd_tell host independent

src/hostcalls/fs.rs

@@ -340,15 +340,19 @@ pub fn fd_tell(
     trace!("fd_tell(fd={:?}, newoffset={:#x?})", fd, newoffset);
 
     let fd = dec_fd(fd);
-    let fd = match wasi_ctx
+    let mut fd = match wasi_ctx
         .get_fd_entry(fd, host::__WASI_RIGHT_FD_TELL, 0)
         .and_then(|fe| fe.fd_object.descriptor.as_file())
     {
         Ok(f) => f,
         Err(e) => return return_enc_errno(e),
     };
-    let host_offset = match hostcalls_impl::fd_tell(fd) {
+
-        Ok(host_offset) => host_offset,
+    let host_offset = match fd
+        .seek(SeekFrom::Current(0))
+        .map_err(|err| err.raw_os_error().map_or(host::__WASI_EIO, errno_from_host))
+    {
+        Ok(offset) => offset,
         Err(e) => return return_enc_errno(e),
     };
 

src/sys/unix/hostcalls_impl/fs.rs

@@ -27,14 +27,6 @@ pub(crate) fn fd_pwrite(file: &File, buf: &[u8], offset: host::__wasi_filesize_t
         .map_err(|e| e.raw_os_error().map_or(host::__WASI_EIO, errno_from_host))
 }
 
-pub(crate) fn fd_tell(file: &File) -> Result<u64> {
-    use nix::unistd::{lseek, Whence};
-    match lseek(file.as_raw_fd(), 0, Whence::SeekCur) {
-        Ok(newoffset) => Ok(newoffset as u64),
-        Err(e) => Err(host_impl::errno_from_nix(e.as_errno().unwrap())),
-    }
-}
-
 pub(crate) fn fd_fdstat_get(fd: &File) -> Result<host::__wasi_fdflags_t> {
     use nix::fcntl::{fcntl, OFlag, F_GETFL};
     match fcntl(fd.as_raw_fd(), F_GETFL).map(OFlag::from_bits_truncate) {

src/sys/windows/hostcalls_impl/fs.rs

@@ -46,10 +46,6 @@ pub(crate) fn fd_pwrite(file: &File, buf: &[u8], offset: host::__wasi_filesize_t
         .map_err(|err| err.raw_os_error().map_or(host::__WASI_EIO, errno_from_host))
 }
 
-pub(crate) fn fd_tell(file: &File) -> Result<u64> {
-    unimplemented!("fd_tell")
-}
-
 pub(crate) fn fd_fdstat_get(fd: &File) -> Result<host::__wasi_fdflags_t> {
     use winx::file::AccessRight;
     match winx::file::get_file_access_rights(fd.as_raw_handle())