p9: Remove dependency on sys_util

The read_dir utility was only used by p9. Other code uses fs::read_dir,
so we can move it from base::unix into p9.

BUG=b:229114164
TEST=presubmit

Change-Id: I9bd12b11233582245db8251aeb3d4480170a2d48
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3584628
Reviewed-by: Allen Webb <allenwebb@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Dennis Kempin <denniskempin@google.com>

base/src/unix/mod.rs

@@ -38,7 +38,6 @@ mod poll;
 mod priority;
 pub mod rand;
 mod raw_fd;
-pub mod read_dir;
 mod sched;
 pub mod scoped_signal_handler;
 mod shm;

common/p9/Cargo.toml

@@ -6,7 +6,6 @@ edition = "2021"
 
 [dependencies]
 libc = "*"
-sys_util = { path = "../sys_util" } # provided by ebuild
 wire_format_derive = { path = "wire_format_derive", version = "*" }
 
 [features]

common/p9/src/lib.rs

@@ -14,3 +14,15 @@ mod server;
 pub mod fuzzing;
 
 pub use server::*;
+
+#[macro_export]
+macro_rules! syscall {
+    ($e:expr) => {{
+        let res = $e;
+        if res < 0 {
+            Err(std::io::Error::last_os_error())
+        } else {
+            Ok(res)
+        }
+    }};
+}

common/p9/src/server/mod.rs

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+mod read_dir;
+
 use std::cmp::min;
 use std::collections::{btree_map, BTreeMap};
 use std::ffi::{CStr, CString};
@@ -14,9 +16,9 @@ use std::os::unix::fs::FileExt;
 use std::os::unix::io::{AsRawFd, FromRawFd, RawFd};
 use std::path::Path;
 
-use sys_util::{read_dir::read_dir, syscall};
-
 use crate::protocol::*;
+use crate::syscall;
+use read_dir::read_dir;
 
 // Tlopen and Tlcreate flags.  Taken from "include/net/9p/9p.h" in the linux tree.
 const P9_RDONLY: u32 = 0o00000000;

common/p9/src/server/read_dir.rs

@@ -4,8 +4,6 @@
 
 use std::{ffi::CStr, io::Result, mem::size_of, os::unix::io::AsRawFd};
 
-use data_model::DataInit;
-
 use crate::syscall;
 
 #[repr(C, packed)]
@@ -16,7 +14,25 @@ struct LinuxDirent64 {
     d_reclen: libc::c_ushort,
     d_ty: libc::c_uchar,
 }
-unsafe impl DataInit for LinuxDirent64 {}
+
+impl LinuxDirent64 {
+    // Note: Taken from data_model::DataInit
+    fn from_slice(data: &[u8]) -> Option<&Self> {
+        // Early out to avoid an unneeded `align_to` call.
+        if data.len() != size_of::<Self>() {
+            return None;
+        }
+        // The `align_to` method ensures that we don't have any unaligned references.
+        // This aliases a pointer, but because the pointer is from a const slice reference,
+        // there are no mutable aliases.
+        // Finally, the reference returned can not outlive data because they have equal implicit
+        // lifetime constraints.
+        match unsafe { data.align_to::<Self>() } {
+            ([], [mid], []) => Some(mid),
+            _ => None,
+        }
+    }
+}
 
 pub struct DirEntry<'r> {
     pub ino: libc::ino64_t,
@@ -45,8 +61,7 @@ impl<'d, D: AsRawFd> ReadDir<'d, D> {
                     self.buf.as_mut_ptr() as *mut LinuxDirent64,
                     self.buf.len() as libc::c_int,
                 )
-            })
-            .map_err(|e| e.into());
+            });
             match res {
                 Ok(end) => {
                     self.current = 0;