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Avoid needless buffer zeroing in std::sys::windows::fs #101236

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merged 1 commit into from
Sep 1, 2022
Merged

Avoid needless buffer zeroing in std::sys::windows::fs #101236

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38 changes: 24 additions & 14 deletions library/std/src/sys/windows/fs.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,7 @@ use crate::os::windows::prelude::*;
use crate::ffi::OsString;
use crate::fmt;
use crate::io::{self, BorrowedCursor, Error, IoSlice, IoSliceMut, SeekFrom};
use crate::mem;
use crate::mem::{self, MaybeUninit};
use crate::os::windows::io::{AsHandle, BorrowedHandle};
use crate::path::{Path, PathBuf};
use crate::ptr;
Expand Down Expand Up @@ -326,7 +326,8 @@ impl File {
cvt(c::GetFileInformationByHandle(self.handle.as_raw_handle(), &mut info))?;
let mut reparse_tag = 0;
if info.dwFileAttributes & c::FILE_ATTRIBUTE_REPARSE_POINT != 0 {
let mut b = Align8([0u8; c::MAXIMUM_REPARSE_DATA_BUFFER_SIZE]);
let mut b =
Align8([MaybeUninit::<u8>::uninit(); c::MAXIMUM_REPARSE_DATA_BUFFER_SIZE]);
if let Ok((_, buf)) = self.reparse_point(&mut b) {
reparse_tag = (*buf).ReparseTag;
}
Expand Down Expand Up @@ -389,7 +390,8 @@ impl File {
attr.file_size = info.AllocationSize as u64;
attr.number_of_links = Some(info.NumberOfLinks);
if attr.file_type().is_reparse_point() {
let mut b = Align8([0; c::MAXIMUM_REPARSE_DATA_BUFFER_SIZE]);
let mut b =
Align8([MaybeUninit::<u8>::uninit(); c::MAXIMUM_REPARSE_DATA_BUFFER_SIZE]);
if let Ok((_, buf)) = self.reparse_point(&mut b) {
attr.reparse_tag = (*buf).ReparseTag;
}
Expand Down Expand Up @@ -463,7 +465,7 @@ impl File {
// avoid narrowing provenance to the actual `REPARSE_DATA_BUFFER`.
fn reparse_point(
&self,
space: &mut Align8<[u8]>,
space: &mut Align8<[MaybeUninit<u8>]>,
) -> io::Result<(c::DWORD, *const c::REPARSE_DATA_BUFFER)> {
unsafe {
let mut bytes = 0;
Expand All @@ -488,7 +490,7 @@ impl File {
}

fn readlink(&self) -> io::Result<PathBuf> {
let mut space = Align8([0u8; c::MAXIMUM_REPARSE_DATA_BUFFER_SIZE]);
let mut space = Align8([MaybeUninit::<u8>::uninit(); c::MAXIMUM_REPARSE_DATA_BUFFER_SIZE]);
let (_bytes, buf) = self.reparse_point(&mut space)?;
unsafe {
let (path_buffer, subst_off, subst_len, relative) = match (*buf).ReparseTag {
Expand Down Expand Up @@ -658,12 +660,16 @@ impl File {

/// A buffer for holding directory entries.
struct DirBuff {
buffer: Box<Align8<[u8; Self::BUFFER_SIZE]>>,
buffer: Box<Align8<[MaybeUninit<u8>; Self::BUFFER_SIZE]>>,
}
impl DirBuff {
const BUFFER_SIZE: usize = 1024;
fn new() -> Self {
Self { buffer: Box::new(Align8([0u8; Self::BUFFER_SIZE])) }
Self {
// Safety: `Align8<[MaybeUninit<u8>; N]>` does not need
// initialization.
buffer: unsafe { Box::new_uninit().assume_init() },
}
}
fn capacity(&self) -> usize {
self.buffer.0.len()
Expand All @@ -676,8 +682,8 @@ impl DirBuff {
DirBuffIter::new(self)
}
}
impl AsRef<[u8]> for DirBuff {
fn as_ref(&self) -> &[u8] {
impl AsRef<[MaybeUninit<u8>]> for DirBuff {
fn as_ref(&self) -> &[MaybeUninit<u8>] {
&self.buffer.0
}
}
Expand All @@ -686,7 +692,7 @@ impl AsRef<[u8]> for DirBuff {
///
/// Currently only returns file names (UTF-16 encoded).
struct DirBuffIter<'a> {
buffer: Option<&'a [u8]>,
buffer: Option<&'a [MaybeUninit<u8>]>,
cursor: usize,
}
impl<'a> DirBuffIter<'a> {
Expand All @@ -701,9 +707,13 @@ impl<'a> Iterator for DirBuffIter<'a> {
let buffer = &self.buffer?[self.cursor..];

// Get the name and next entry from the buffer.
// SAFETY: The buffer contains a `FILE_ID_BOTH_DIR_INFO` struct but the
// last field (the file name) is unsized. So an offset has to be
// used to get the file name slice.
// SAFETY:
// - The buffer contains a `FILE_ID_BOTH_DIR_INFO` struct but the last
// field (the file name) is unsized. So an offset has to be used to
// get the file name slice.
// - The OS has guaranteed initialization of the fields of
// `FILE_ID_BOTH_DIR_INFO` and the trailing filename (for at least
// `FileNameLength` bytes)
let (name, is_directory, next_entry) = unsafe {
let info = buffer.as_ptr().cast::<c::FILE_ID_BOTH_DIR_INFO>();
// Guaranteed to be aligned in documentation for
Expand Down Expand Up @@ -1349,7 +1359,7 @@ fn symlink_junction_inner(original: &Path, junction: &Path) -> io::Result<()> {
let h = f.as_inner().as_raw_handle();

unsafe {
let mut data = Align8([0u8; c::MAXIMUM_REPARSE_DATA_BUFFER_SIZE]);
let mut data = Align8([MaybeUninit::<u8>::uninit(); c::MAXIMUM_REPARSE_DATA_BUFFER_SIZE]);
let data_ptr = data.0.as_mut_ptr();
let db = data_ptr.cast::<c::REPARSE_MOUNTPOINT_DATA_BUFFER>();
let buf = ptr::addr_of_mut!((*db).ReparseTarget).cast::<c::WCHAR>();
Expand Down