Initial reorg.

This is largely the same as #305, but updated for the current tree.

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

@@ -0,0 +1,38 @@
+pub(crate) mod fdentry_impl;
+pub(crate) mod host_impl;
+pub(crate) mod hostcalls_impl;
+
+mod dir;
+
+#[cfg(any(
+    target_os = "macos",
+    target_os = "netbsd",
+    target_os = "freebsd",
+    target_os = "openbsd",
+    target_os = "ios",
+    target_os = "dragonfly"
+))]
+mod bsd;
+#[cfg(target_os = "linux")]
+mod linux;
+
+use crate::{Error, Result};
+use std::ffi::CString;
+use std::fs::{File, OpenOptions};
+use std::path::Path;
+
+pub(crate) fn dev_null() -> Result<File> {
+    OpenOptions::new()
+        .read(true)
+        .write(true)
+        .open("/dev/null")
+        .map_err(Into::into)
+}
+
+pub(crate) fn str_to_cstring(s: &str) -> Result<CString> {
+    CString::new(s.as_bytes()).map_err(|_| Error::EILSEQ)
+}
+
+pub fn preopen_dir<P: AsRef<Path>>(path: P) -> Result<File> {
+    File::open(path).map_err(Into::into)
+}