wasi-common error cleanup: part 1, yanix (#1226)

* Reuse std::io::Error for raw *nix errno

This commit removes custom `yanix::Errno` and instead (as was
previously suggested) reuses `std::io::Error` to generate and wrap
raw *nix errno value.

* Update wasi-common to use new Yanix error type

This commit updates `wasi-common` to use new way of handling raw
OS error in `yanix`; i.e., via re-use of `std::io::Error` instead
of a custom `Errno` enum.

* Fix formatting

* Unwrap if io::Error created from raw OS error

This commit calls `unwrap` on `err` if that one was created via
`io::Error::last_os_error()`. It also refactors error matching
in several syscalls on the BSD platform (mainly).

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

@@ -1,8 +1,8 @@
 use crate::{
     dir::{Dir, Entry, EntryExt, SeekLoc},
-    Errno, Result,
+    Result,
 };
-use std::ops::Deref;
+use std::{io, ops::Deref};
 
 #[derive(Copy, Clone, Debug)]
 pub(crate) struct EntryImpl {
@@ -19,16 +19,17 @@ impl Deref for EntryImpl {
 }
 
 pub(crate) fn iter_impl(dir: &Dir) -> Option<Result<EntryImpl>> {
-    let errno = Errno::last();
+    let errno = io::Error::last_os_error();
     let dirent = unsafe { libc::readdir(dir.as_raw().as_ptr()) };
     if dirent.is_null() {
-        if errno != Errno::last() {
+        let curr_errno = io::Error::last_os_error();
+        if errno.raw_os_error() != curr_errno.raw_os_error() {
             // TODO This should be verified on different BSD-flavours.
             //
             // According to 4.3BSD/POSIX.1-2001 man pages, there was an error
             // if the errno value has changed at some point during the sequence
             // of readdir calls.
-            Some(Err(Errno::last().into()))
+            Some(Err(curr_errno.into()))
         } else {
             // Not an error. We've simply reached the end of the stream.
             None

crates/wasi-common/yanix/src/sys/bsd/fadvise.rs

@@ -1,4 +1,4 @@
-use crate::{Errno, Result};
+use crate::{Error, Result};
 use std::{convert::TryInto, os::unix::prelude::*};
 
 #[cfg(not(any(target_os = "freebsd", target_os = "netbsd")))]
@@ -48,7 +48,7 @@ pub unsafe fn posix_fadvise(
         ra_offset: offset,
         ra_count: len.try_into()?,
     };
-    Errno::from_success_code(libc::fcntl(fd, libc::F_RDADVISE, &advisory))
+    Error::from_success_code(libc::fcntl(fd, libc::F_RDADVISE, &advisory))
 }
 
 #[cfg(any(target_os = "freebsd", target_os = "netbsd"))]
@@ -58,7 +58,7 @@ pub unsafe fn posix_fadvise(
     len: libc::off_t,
     advice: PosixFadviseAdvice,
 ) -> Result<()> {
-    Errno::from_success_code(libc::posix_fadvise(fd, offset, len, advice as libc::c_int))
+    Error::from_success_code(libc::posix_fadvise(fd, offset, len, advice as libc::c_int))
 }
 
 // On BSDs without support we leave it as no-op

crates/wasi-common/yanix/src/sys/bsd/file.rs

@@ -1,5 +1,5 @@
-use crate::{Errno, Result};
-use std::os::unix::prelude::*;
+use crate::Result;
+use std::{io, os::unix::prelude::*};
 
 pub unsafe fn isatty(fd: RawFd) -> Result<bool> {
     let res = libc::isatty(fd);
@@ -8,9 +8,13 @@ pub unsafe fn isatty(fd: RawFd) -> Result<bool> {
         Ok(true)
     } else {
         // ... otherwise 0 is returned, and errno is set to indicate the error.
-        let errno = Errno::last();
-        if errno == Errno::ENOTTY {
-            Ok(false)
+        let errno = io::Error::last_os_error();
+        if let Some(raw_errno) = errno.raw_os_error() {
+            if raw_errno == libc::ENOTTY {
+                Ok(false)
+            } else {
+                Err(errno.into())
+            }
         } else {
             Err(errno.into())
         }