Misc yanix fixes (#715)

* Correctly handle possibly misaligned pointers in readdir

This reapplies #615, which was inadvertently reverted.

* Tidy up unneeded `self::` qualifiers.

* Make Dir's contents private.

Also remove the `unsafe` from `impl_iter`. With `Dir`'s field being
private, we can rely on the pointer being only what we've assigned to
it.

* Make `poll`'s timeout argument a `libc::c_int`.

This clarifies that there are no subsequent conversions before calling the
underlying libc API.

* Use clock_gettime instead of clock_getres to get the time.

* Mark FileType::from_raw as safe.

It handles unknown values, so it can be marked safe.

crates/wasi-common/yanix/src/dir.rs

@@ -8,7 +8,7 @@ use std::{ffi::CStr, ops::Deref, ptr};
 pub use crate::sys::EntryExt;
 
 #[derive(Clone, Debug, Eq, Hash, PartialEq)]
-pub struct Dir(pub(crate) ptr::NonNull<libc::DIR>);
+pub struct Dir(ptr::NonNull<libc::DIR>);
 
 impl Dir {
     /// Takes the ownership of the passed-in descriptor-based object,
@@ -51,6 +51,12 @@ impl Dir {
         let loc = unsafe { libc::telldir(self.0.as_ptr()) };
         SeekLoc(loc)
     }
+
+    /// For use by platform-specific implementation code. Returns the raw
+    /// underlying state.
+    pub(crate) fn as_raw(&self) -> ptr::NonNull<libc::DIR> {
+        self.0
+    }
 }
 
 unsafe impl Send for Dir {}
@@ -78,7 +84,7 @@ impl Entry {
 
     /// Returns the type of this directory entry.
     pub fn file_type(&self) -> FileType {
-        unsafe { FileType::from_raw(self.0.d_type) }
+        FileType::from_raw(self.0.d_type)
     }
 }
 
@@ -107,7 +113,7 @@ pub enum FileType {
 }
 
 impl FileType {
-    pub unsafe fn from_raw(file_type: u8) -> Self {
+    pub fn from_raw(file_type: u8) -> Self {
         match file_type {
             libc::DT_CHR => Self::CharacterDevice,
             libc::DT_DIR => Self::Directory,
@@ -153,6 +159,6 @@ where
     type Item = Result<Entry>;
 
     fn next(&mut self) -> Option<Self::Item> {
-        unsafe { iter_impl(&self.0).map(|x| x.map(Entry)) }
+        iter_impl(&self.0).map(|x| x.map(Entry))
     }
 }