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Auto merge of #75272 - the8472:spec-copy, r=KodrAus

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specialize io::copy to use copy_file_range, splice or sendfile

Fixes #74426.
Also covers #60689 but only as an optimization instead of an official API.

The specialization only covers std-owned structs so it should avoid the problems with #71091

Currently linux-only but it should be generalizable to other unix systems that have sendfile/sosplice and similar.

There is a bit of optimization potential around the syscall count. Right now it may end up doing more syscalls than the naive copy loop when doing short (<8KiB) copies between file descriptors.

The test case executes the following:

```
[pid 103776] statx(3, "", AT_STATX_SYNC_AS_STAT|AT_EMPTY_PATH, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0644, stx_size=17, ...}) = 0
[pid 103776] write(4, "wxyz", 4)        = 4
[pid 103776] write(4, "iklmn", 5)       = 5
[pid 103776] copy_file_range(3, NULL, 4, NULL, 5, 0) = 5

```

0-1 `stat` calls to identify the source file type. 0 if the type can be inferred from the struct from which the FD was extracted
𝖬 `write` to drain the `BufReader`/`BufWriter` wrappers. only happen when buffers are present. 𝖬 ≾ number of wrappers present. If there is a write buffer it may absorb the read buffer contents first so only result in a single write. Vectored writes would also be an option but that would require more invasive changes to `BufWriter`.
𝖭 `copy_file_range`/`splice`/`sendfile` until file size, EOF or the byte limit from `Take` is reached. This should generally be *much* more efficient than the read-write loop and also have other benefits such as DMA offload or extent sharing.

## Benchmarks

```

OLD

test io::tests::bench_file_to_file_copy         ... bench:      21,002 ns/iter (+/- 750) = 6240 MB/s    [ext4]
test io::tests::bench_file_to_file_copy         ... bench:      35,704 ns/iter (+/- 1,108) = 3671 MB/s  [btrfs]
test io::tests::bench_file_to_socket_copy       ... bench:      57,002 ns/iter (+/- 4,205) = 2299 MB/s
test io::tests::bench_socket_pipe_socket_copy   ... bench:     142,640 ns/iter (+/- 77,851) = 918 MB/s

NEW

test io::tests::bench_file_to_file_copy         ... bench:      14,745 ns/iter (+/- 519) = 8889 MB/s    [ext4]
test io::tests::bench_file_to_file_copy         ... bench:       6,128 ns/iter (+/- 227) = 21389 MB/s   [btrfs]
test io::tests::bench_file_to_socket_copy       ... bench:      13,767 ns/iter (+/- 3,767) = 9520 MB/s
test io::tests::bench_socket_pipe_socket_copy   ... bench:      26,471 ns/iter (+/- 6,412) = 4951 MB/s
```
This commit is contained in:
bors 2020-11-14 12:01:55 +00:00
commit 30e49a9ead
11 changed files with 930 additions and 152 deletions
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2
library/std/src/fs.rs
View File

@ -1656,7 +1656,7 @@ pub fn rename<P: AsRef<Path>, Q: AsRef<Path>>(from: P, to: Q) -> io::Result<()>
/// the length of the `to` file as reported by `metadata`.
///
/// If you’re wanting to copy the contents of one file to another and you’re
/// working with [`File`]s, see the [`io::copy`] function.
/// working with [`File`]s, see the [`io::copy()`] function.
///
/// # Platform-specific behavior
///

88
library/std/src/io/copy.rs Normal file
View File

@ -0,0 +1,88 @@
use crate::io::{self, ErrorKind, Read, Write};
use crate::mem::MaybeUninit;
/// Copies the entire contents of a reader into a writer.
///
/// This function will continuously read data from `reader` and then
/// write it into `writer` in a streaming fashion until `reader`
/// returns EOF.
///
/// On success, the total number of bytes that were copied from
/// `reader` to `writer` is returned.
///
/// If you’re wanting to copy the contents of one file to another and you’re
/// working with filesystem paths, see the [`fs::copy`] function.
///
/// [`fs::copy`]: crate::fs::copy
///
/// # Errors
///
/// This function will return an error immediately if any call to [`read`] or
/// [`write`] returns an error. All instances of [`ErrorKind::Interrupted`] are
/// handled by this function and the underlying operation is retried.
///
/// [`read`]: Read::read
/// [`write`]: Write::write
///
/// # Examples
///
/// ```
/// use std::io;
///
/// fn main() -> io::Result<()> {
/// let mut reader: &[u8] = b"hello";
/// let mut writer: Vec<u8> = vec![];
///
/// io::copy(&mut reader, &mut writer)?;
///
/// assert_eq!(&b"hello"[..], &writer[..]);
/// Ok(())
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn copy<R: ?Sized, W: ?Sized>(reader: &mut R, writer: &mut W) -> io::Result<u64>
where
R: Read,
W: Write,
{
cfg_if::cfg_if! {
if #[cfg(any(target_os = "linux", target_os = "android"))] {
crate::sys::kernel_copy::copy_spec(reader, writer)
} else {
generic_copy(reader, writer)
}
}
}
/// The general read-write-loop implementation of
/// `io::copy` that is used when specializations are not available or not applicable.
pub(crate) fn generic_copy<R: ?Sized, W: ?Sized>(reader: &mut R, writer: &mut W) -> io::Result<u64>
where
R: Read,
W: Write,
{
let mut buf = MaybeUninit::<[u8; super::DEFAULT_BUF_SIZE]>::uninit();
// FIXME: #42788
//
// - This creates a (mut) reference to a slice of
// _uninitialized_ integers, which is **undefined behavior**
//
// - Only the standard library gets to soundly "ignore" this,
// based on its privileged knowledge of unstable rustc
// internals;
unsafe {
reader.initializer().initialize(buf.assume_init_mut());
}
let mut written = 0;
loop {
let len = match reader.read(unsafe { buf.assume_init_mut() }) {
Ok(0) => return Ok(written),
Ok(len) => len,
Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
Err(e) => return Err(e),
};
writer.write_all(unsafe { &buf.assume_init_ref()[..len] })?;
written += len as u64;
}
}

5
library/std/src/io/mod.rs
View File

@ -266,6 +266,8 @@ pub use self::buffered::IntoInnerError;
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::buffered::{BufReader, BufWriter, LineWriter};
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::copy::copy;
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::cursor::Cursor;
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::error::{Error, ErrorKind, Result};
@ -279,11 +281,12 @@ pub use self::stdio::{_eprint, _print};
#[doc(no_inline, hidden)]
pub use self::stdio::{set_panic, set_print, LocalOutput};
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::util::{copy, empty, repeat, sink, Empty, Repeat, Sink};
pub use self::util::{empty, repeat, sink, Empty, Repeat, Sink};
pub(crate) use self::stdio::clone_io;
mod buffered;
pub(crate) mod copy;
mod cursor;
mod error;
mod impls;

8
library/std/src/io/stdio.rs
View File

@ -409,6 +409,14 @@ impl Read for Stdin {
}
}
// only used by platform-dependent io::copy specializations, i.e. unused on some platforms
#[cfg(any(target_os = "linux", target_os = "android"))]
impl StdinLock<'_> {
pub(crate) fn as_mut_buf(&mut self) -> &mut BufReader<impl Read> {
&mut self.inner
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Read for StdinLock<'_> {
fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {

2
library/std/src/io/tests.rs
View File

@ -1,7 +1,7 @@
use super::{repeat, Cursor, SeekFrom};
use crate::cmp::{self, min};
use crate::io::prelude::*;
use crate::io::{self, IoSlice, IoSliceMut};
use crate::io::{BufRead, Read, Seek, Write};
use crate::ops::Deref;
#[test]

73
library/std/src/io/util.rs
View File

@ -4,78 +4,7 @@
mod tests;
use crate::fmt;
use crate::io::{self, BufRead, ErrorKind, Initializer, IoSlice, IoSliceMut, Read, Write};
use crate::mem::MaybeUninit;
/// Copies the entire contents of a reader into a writer.
///
/// This function will continuously read data from `reader` and then
/// write it into `writer` in a streaming fashion until `reader`
/// returns EOF.
///
/// On success, the total number of bytes that were copied from
/// `reader` to `writer` is returned.
///
/// If you’re wanting to copy the contents of one file to another and you’re
/// working with filesystem paths, see the [`fs::copy`] function.
///
/// [`fs::copy`]: crate::fs::copy
///
/// # Errors
///
/// This function will return an error immediately if any call to [`read`] or
/// [`write`] returns an error. All instances of [`ErrorKind::Interrupted`] are
/// handled by this function and the underlying operation is retried.
///
/// [`read`]: Read::read
/// [`write`]: Write::write
///
/// # Examples
///
/// ```
/// use std::io;
///
/// fn main() -> io::Result<()> {
/// let mut reader: &[u8] = b"hello";
/// let mut writer: Vec<u8> = vec![];
///
/// io::copy(&mut reader, &mut writer)?;
///
/// assert_eq!(&b"hello"[..], &writer[..]);
/// Ok(())
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn copy<R: ?Sized, W: ?Sized>(reader: &mut R, writer: &mut W) -> io::Result<u64>
where
R: Read,
W: Write,
{
let mut buf = MaybeUninit::<[u8; super::DEFAULT_BUF_SIZE]>::uninit();
// FIXME: #42788
//
// - This creates a (mut) reference to a slice of
// _uninitialized_ integers, which is **undefined behavior**
//
// - Only the standard library gets to soundly "ignore" this,
// based on its privileged knowledge of unstable rustc
// internals;
unsafe {
reader.initializer().initialize(buf.assume_init_mut());
}
let mut written = 0;
loop {
let len = match reader.read(unsafe { buf.assume_init_mut() }) {
Ok(0) => return Ok(written),
Ok(len) => len,
Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
Err(e) => return Err(e),
};
writer.write_all(unsafe { &buf.assume_init_ref()[..len] })?;
written += len as u64;
}
}
use crate::io::{self, BufRead, Initializer, IoSlice, IoSliceMut, Read, Write};
/// A reader which is always at EOF.
///

1
library/std/src/lib.rs
View File

@ -317,6 +317,7 @@
#![feature(toowned_clone_into)]
#![feature(total_cmp)]
#![feature(trace_macros)]
#![feature(try_blocks)]
#![feature(try_reserve)]
#![feature(unboxed_closures)]
#![feature(unsafe_block_in_unsafe_fn)]

85
library/std/src/sys/unix/fs.rs
View File

@ -1204,88 +1204,19 @@ pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
#[cfg(any(target_os = "linux", target_os = "android"))]
pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
use crate::cmp;
use crate::sync::atomic::{AtomicBool, Ordering};
// Kernel prior to 4.5 don't have copy_file_range
// We store the availability in a global to avoid unnecessary syscalls
static HAS_COPY_FILE_RANGE: AtomicBool = AtomicBool::new(true);
unsafe fn copy_file_range(
fd_in: libc::c_int,
off_in: *mut libc::loff_t,
fd_out: libc::c_int,
off_out: *mut libc::loff_t,
len: libc::size_t,
flags: libc::c_uint,
) -> libc::c_long {
libc::syscall(libc::SYS_copy_file_range, fd_in, off_in, fd_out, off_out, len, flags)
}
let (mut reader, reader_metadata) = open_from(from)?;
let max_len = u64::MAX;
let (mut writer, _) = open_to_and_set_permissions(to, reader_metadata)?;
let has_copy_file_range = HAS_COPY_FILE_RANGE.load(Ordering::Relaxed);
let mut written = 0u64;
while written < max_len {
let copy_result = if has_copy_file_range {
let bytes_to_copy = cmp::min(max_len - written, usize::MAX as u64) as usize;
let copy_result = unsafe {
// We actually don't have to adjust the offsets,
// because copy_file_range adjusts the file offset automatically
cvt(copy_file_range(
reader.as_raw_fd(),
ptr::null_mut(),
writer.as_raw_fd(),
ptr::null_mut(),
bytes_to_copy,
0,
))
};
if let Err(ref copy_err) = copy_result {
match copy_err.raw_os_error() {
Some(libc::ENOSYS | libc::EPERM | libc::EOPNOTSUPP) => {
HAS_COPY_FILE_RANGE.store(false, Ordering::Relaxed);
}
_ => {}
}
}
copy_result
} else {
Err(io::Error::from_raw_os_error(libc::ENOSYS))
};
match copy_result {
Ok(0) if written == 0 => {
// fallback to work around several kernel bugs where copy_file_range will fail to
// copy any bytes and return 0 instead of an error if
// - reading virtual files from the proc filesystem which appear to have 0 size
// but are not empty. noted in coreutils to affect kernels at least up to 5.6.19.
// - copying from an overlay filesystem in docker. reported to occur on fedora 32.
return io::copy(&mut reader, &mut writer);
}
Ok(0) => return Ok(written), // reached EOF
Ok(ret) => written += ret as u64,
Err(err) => {
match err.raw_os_error() {
Some(
libc::ENOSYS | libc::EXDEV | libc::EINVAL | libc::EPERM | libc::EOPNOTSUPP,
) => {
// Try fallback io::copy if either:
// - Kernel version is < 4.5 (ENOSYS)
// - Files are mounted on different fs (EXDEV)
// - copy_file_range is broken in various ways on RHEL/CentOS 7 (EOPNOTSUPP)
// - copy_file_range is disallowed, for example by seccomp (EPERM)
// - copy_file_range cannot be used with pipes or device nodes (EINVAL)
assert_eq!(written, 0);
return io::copy(&mut reader, &mut writer);
}
_ => return Err(err),
}
}
}
use super::kernel_copy::{copy_regular_files, CopyResult};
match copy_regular_files(reader.as_raw_fd(), writer.as_raw_fd(), max_len) {
CopyResult::Ended(result) => result,
CopyResult::Fallback(written) => match io::copy::generic_copy(&mut reader, &mut writer) {
Ok(bytes) => Ok(bytes + written),
Err(e) => Err(e),
},
}
Ok(written)
}
#[cfg(any(target_os = "macos", target_os = "ios"))]

603
library/std/src/sys/unix/kernel_copy.rs Normal file
View File

@ -0,0 +1,603 @@
//! This module contains specializations that can offload `io::copy()` operations on file descriptor
//! containing types (`File`, `TcpStream`, etc.) to more efficient syscalls than `read(2)` and `write(2)`.
//!
//! Specialization is only applied to wholly std-owned types so that user code can't observe
//! that the `Read` and `Write` traits are not used.
//!
//! Since a copy operation involves a reader and writer side where each can consist of different types
//! and also involve generic wrappers (e.g. `Take`, `BufReader`) it is not practical to specialize
//! a single method on all possible combinations.
//!
//! Instead readers and writers are handled separately by the `CopyRead` and `CopyWrite` specialization
//! traits and then specialized on by the `Copier::copy` method.
//!
//! `Copier` uses the specialization traits to unpack the underlying file descriptors and
//! additional prerequisites and constraints imposed by the wrapper types.
//!
//! Once it has obtained all necessary pieces and brought any wrapper types into a state where they
//! can be safely bypassed it will attempt to use the `copy_file_range(2)`,
//! `sendfile(2)` or `splice(2)` syscalls to move data directly between file descriptors.
//! Since those syscalls have requirements that cannot be fully checked in advance and
//! gathering additional information about file descriptors would require additional syscalls
//! anyway it simply attempts to use them one after another (guided by inaccurate hints) to
//! figure out which one works and and falls back to the generic read-write copy loop if none of them
//! does.
//! Once a working syscall is found for a pair of file descriptors it will be called in a loop
//! until the copy operation is completed.
//!
//! Advantages of using these syscalls:
//!
//! * fewer context switches since reads and writes are coalesced into a single syscall
//! and more bytes are transferred per syscall. This translates to higher throughput
//! and fewer CPU cycles, at least for sufficiently large transfers to amortize the initial probing.
//! * `copy_file_range` creates reflink copies on CoW filesystems, thus moving less data and
//! consuming less disk space
//! * `sendfile` and `splice` can perform zero-copy IO under some circumstances while
//! a naive copy loop would move every byte through the CPU.
//!
//! Drawbacks:
//!
//! * copy operations smaller than the default buffer size can under some circumstances, especially
//! on older kernels, incur more syscalls than the naive approach would. As mentioned above
//! the syscall selection is guided by hints to minimize this possibility but they are not perfect.
//! * optimizations only apply to std types. If a user adds a custom wrapper type, e.g. to report
//! progress, they can hit a performance cliff.
//! * complexity
use crate::cmp::min;
use crate::convert::TryInto;
use crate::fs::{File, Metadata};
use crate::io::copy::generic_copy;
use crate::io::{
BufRead, BufReader, BufWriter, Error, Read, Result, StderrLock, StdinLock, StdoutLock, Take,
Write,
};
use crate::mem::ManuallyDrop;
use crate::net::TcpStream;
use crate::os::unix::fs::FileTypeExt;
use crate::os::unix::io::{AsRawFd, FromRawFd, RawFd};
use crate::process::{ChildStderr, ChildStdin, ChildStdout};
use crate::ptr;
use crate::sync::atomic::{AtomicBool, Ordering};
use crate::sys::cvt;
#[cfg(test)]
mod tests;
pub(crate) fn copy_spec<R: Read + ?Sized, W: Write + ?Sized>(
read: &mut R,
write: &mut W,
) -> Result<u64> {
let copier = Copier { read, write };
SpecCopy::copy(copier)
}
/// This type represents either the inferred `FileType` of a `RawFd` based on the source
/// type from which it was extracted or the actual metadata
///
/// The methods on this type only provide hints, due to `AsRawFd` and `FromRawFd` the inferred
/// type may be wrong.
enum FdMeta {
/// We obtained the FD from a type that can contain any type of `FileType` and queried the metadata
/// because it is cheaper than probing all possible syscalls (reader side)
Metadata(Metadata),
Socket,
Pipe,
/// We don't have any metadata, e.g. because the original type was `File` which can represent
/// any `FileType` and we did not query the metadata either since it did not seem beneficial
/// (writer side)
NoneObtained,
}
impl FdMeta {
fn maybe_fifo(&self) -> bool {
match self {
FdMeta::Metadata(meta) => meta.file_type().is_fifo(),
FdMeta::Socket => false,
FdMeta::Pipe => true,
FdMeta::NoneObtained => true,
}
}
fn potential_sendfile_source(&self) -> bool {
match self {
// procfs erronously shows 0 length on non-empty readable files.
// and if a file is truly empty then a `read` syscall will determine that and skip the write syscall
// thus there would be benefit from attempting sendfile
FdMeta::Metadata(meta)
if meta.file_type().is_file() && meta.len() > 0
|| meta.file_type().is_block_device() =>
{
true
}
_ => false,
}
}
fn copy_file_range_candidate(&self) -> bool {
match self {
// copy_file_range will fail on empty procfs files. `read` can determine whether EOF has been reached
// without extra cost and skip the write, thus there is no benefit in attempting copy_file_range
FdMeta::Metadata(meta) if meta.is_file() && meta.len() > 0 => true,
FdMeta::NoneObtained => true,
_ => false,
}
}
}
struct CopyParams(FdMeta, Option<RawFd>);
struct Copier<'a, 'b, R: Read + ?Sized, W: Write + ?Sized> {
read: &'a mut R,
write: &'b mut W,
}
trait SpecCopy {
fn copy(self) -> Result<u64>;
}
impl<R: Read + ?Sized, W: Write + ?Sized> SpecCopy for Copier<'_, '_, R, W> {
default fn copy(self) -> Result<u64> {
generic_copy(self.read, self.write)
}
}
impl<R: CopyRead, W: CopyWrite> SpecCopy for Copier<'_, '_, R, W> {
fn copy(self) -> Result<u64> {
let (reader, writer) = (self.read, self.write);
let r_cfg = reader.properties();
let w_cfg = writer.properties();
// before direct operations on file descriptors ensure that all source and sink buffers are empty
let mut flush = || -> crate::io::Result<u64> {
let bytes = reader.drain_to(writer, u64::MAX)?;
// BufWriter buffered bytes have already been accounted for in earlier write() calls
writer.flush()?;
Ok(bytes)
};
let mut written = 0u64;
if let (CopyParams(input_meta, Some(readfd)), CopyParams(output_meta, Some(writefd))) =
(r_cfg, w_cfg)
{
written += flush()?;
let max_write = reader.min_limit();
if input_meta.copy_file_range_candidate() && output_meta.copy_file_range_candidate() {
let result = copy_regular_files(readfd, writefd, max_write);
match result {
CopyResult::Ended(Ok(bytes_copied)) => return Ok(bytes_copied + written),
CopyResult::Ended(err) => return err,
CopyResult::Fallback(bytes) => written += bytes,
}
}
// on modern kernels sendfile can copy from any mmapable type (some but not all regular files and block devices)
// to any writable file descriptor. On older kernels the writer side can only be a socket.
// So we just try and fallback if needed.
// If current file offsets + write sizes overflow it may also fail, we do not try to fix that and instead
// fall back to the generic copy loop.
if input_meta.potential_sendfile_source() {
let result = sendfile_splice(SpliceMode::Sendfile, readfd, writefd, max_write);
match result {
CopyResult::Ended(Ok(bytes_copied)) => return Ok(bytes_copied + written),
CopyResult::Ended(err) => return err,
CopyResult::Fallback(bytes) => written += bytes,
}
}
if input_meta.maybe_fifo() || output_meta.maybe_fifo() {
let result = sendfile_splice(SpliceMode::Splice, readfd, writefd, max_write);
match result {
CopyResult::Ended(Ok(bytes_copied)) => return Ok(bytes_copied + written),
CopyResult::Ended(err) => return err,
CopyResult::Fallback(0) => { /* use the fallback below */ }
CopyResult::Fallback(_) => {
unreachable!("splice should not return > 0 bytes on the fallback path")
}
}
}
}
// fallback if none of the more specialized syscalls wants to work with these file descriptors
match generic_copy(reader, writer) {
Ok(bytes) => Ok(bytes + written),
err => err,
}
}
}
#[rustc_specialization_trait]
trait CopyRead: Read {
/// Implementations that contain buffers (i.e. `BufReader`) must transfer data from their internal
/// buffers into `writer` until either the buffers are emptied or `limit` bytes have been
/// transferred, whichever occurs sooner.
/// If nested buffers are present the outer buffers must be drained first.
///
/// This is necessary to directly bypass the wrapper types while preserving the data order
/// when operating directly on the underlying file descriptors.
fn drain_to<W: Write>(&mut self, _writer: &mut W, _limit: u64) -> Result<u64> {
Ok(0)
}
/// The minimum of the limit of all `Take<_>` wrappers, `u64::MAX` otherwise.
/// This method does not account for data `BufReader` buffers and would underreport
/// the limit of a `Take<BufReader<Take<_>>>` type. Thus its result is only valid
/// after draining the buffers via `drain_to`.
fn min_limit(&self) -> u64 {
u64::MAX
}
/// Extracts the file descriptor and hints/metadata, delegating through wrappers if necessary.
fn properties(&self) -> CopyParams;
}
#[rustc_specialization_trait]
trait CopyWrite: Write {
/// Extracts the file descriptor and hints/metadata, delegating through wrappers if necessary.
fn properties(&self) -> CopyParams;
}
impl<T> CopyRead for &mut T
where
T: CopyRead,
{
fn drain_to<W: Write>(&mut self, writer: &mut W, limit: u64) -> Result<u64> {
(**self).drain_to(writer, limit)
}
fn min_limit(&self) -> u64 {
(**self).min_limit()
}
fn properties(&self) -> CopyParams {
(**self).properties()
}
}
impl<T> CopyWrite for &mut T
where
T: CopyWrite,
{
fn properties(&self) -> CopyParams {
(**self).properties()
}
}
impl CopyRead for File {
fn properties(&self) -> CopyParams {
CopyParams(fd_to_meta(self), Some(self.as_raw_fd()))
}
}
impl CopyRead for &File {
fn properties(&self) -> CopyParams {
CopyParams(fd_to_meta(*self), Some(self.as_raw_fd()))
}
}
impl CopyWrite for File {
fn properties(&self) -> CopyParams {
CopyParams(FdMeta::NoneObtained, Some(self.as_raw_fd()))
}
}
impl CopyWrite for &File {
fn properties(&self) -> CopyParams {
CopyParams(FdMeta::NoneObtained, Some(self.as_raw_fd()))
}
}
impl CopyRead for TcpStream {
fn properties(&self) -> CopyParams {
// avoid the stat syscall since we can be fairly sure it's a socket
CopyParams(FdMeta::Socket, Some(self.as_raw_fd()))
}
}
impl CopyRead for &TcpStream {
fn properties(&self) -> CopyParams {
// avoid the stat syscall since we can be fairly sure it's a socket
CopyParams(FdMeta::Socket, Some(self.as_raw_fd()))
}
}
impl CopyWrite for TcpStream {
fn properties(&self) -> CopyParams {
// avoid the stat syscall since we can be fairly sure it's a socket
CopyParams(FdMeta::Socket, Some(self.as_raw_fd()))
}
}
impl CopyWrite for &TcpStream {
fn properties(&self) -> CopyParams {
// avoid the stat syscall since we can be fairly sure it's a socket
CopyParams(FdMeta::Socket, Some(self.as_raw_fd()))
}
}
impl CopyWrite for ChildStdin {
fn properties(&self) -> CopyParams {
CopyParams(FdMeta::Pipe, Some(self.as_raw_fd()))
}
}
impl CopyRead for ChildStdout {
fn properties(&self) -> CopyParams {
CopyParams(FdMeta::Pipe, Some(self.as_raw_fd()))
}
}
impl CopyRead for ChildStderr {
fn properties(&self) -> CopyParams {
CopyParams(FdMeta::Pipe, Some(self.as_raw_fd()))
}
}
impl CopyRead for StdinLock<'_> {
fn drain_to<W: Write>(&mut self, writer: &mut W, outer_limit: u64) -> Result<u64> {
let buf_reader = self.as_mut_buf();
let buf = buf_reader.buffer();
let buf = &buf[0..min(buf.len(), outer_limit.try_into().unwrap_or(usize::MAX))];
let bytes_drained = buf.len();
writer.write_all(buf)?;
buf_reader.consume(bytes_drained);
Ok(bytes_drained as u64)
}
fn properties(&self) -> CopyParams {
CopyParams(fd_to_meta(self), Some(self.as_raw_fd()))
}
}
impl CopyWrite for StdoutLock<'_> {
fn properties(&self) -> CopyParams {
CopyParams(FdMeta::NoneObtained, Some(self.as_raw_fd()))
}
}
impl CopyWrite for StderrLock<'_> {
fn properties(&self) -> CopyParams {
CopyParams(FdMeta::NoneObtained, Some(self.as_raw_fd()))
}
}
impl<T: CopyRead> CopyRead for Take<T> {
fn drain_to<W: Write>(&mut self, writer: &mut W, outer_limit: u64) -> Result<u64> {
let local_limit = self.limit();
let combined_limit = min(outer_limit, local_limit);
let bytes_drained = self.get_mut().drain_to(writer, combined_limit)?;
// update limit since read() was bypassed
self.set_limit(local_limit - bytes_drained);
Ok(bytes_drained)
}
fn min_limit(&self) -> u64 {
min(Take::limit(self), self.get_ref().min_limit())
}
fn properties(&self) -> CopyParams {
self.get_ref().properties()
}
}
impl<T: CopyRead> CopyRead for BufReader<T> {
fn drain_to<W: Write>(&mut self, writer: &mut W, outer_limit: u64) -> Result<u64> {
let buf = self.buffer();
let buf = &buf[0..min(buf.len(), outer_limit.try_into().unwrap_or(usize::MAX))];
let bytes = buf.len();
writer.write_all(buf)?;
self.consume(bytes);
let remaining = outer_limit - bytes as u64;
// in case of nested bufreaders we also need to drain the ones closer to the source
let inner_bytes = self.get_mut().drain_to(writer, remaining)?;
Ok(bytes as u64 + inner_bytes)
}
fn min_limit(&self) -> u64 {
self.get_ref().min_limit()
}
fn properties(&self) -> CopyParams {
self.get_ref().properties()
}
}
impl<T: CopyWrite> CopyWrite for BufWriter<T> {
fn properties(&self) -> CopyParams {
self.get_ref().properties()
}
}
fn fd_to_meta<T: AsRawFd>(fd: &T) -> FdMeta {
let fd = fd.as_raw_fd();
let file: ManuallyDrop<File> = ManuallyDrop::new(unsafe { File::from_raw_fd(fd) });
match file.metadata() {
Ok(meta) => FdMeta::Metadata(meta),
Err(_) => FdMeta::NoneObtained,
}
}
pub(super) enum CopyResult {
Ended(Result<u64>),
Fallback(u64),
}
/// linux-specific implementation that will attempt to use copy_file_range for copy offloading
/// as the name says, it only works on regular files
///
/// Callers must handle fallback to a generic copy loop.
/// `Fallback` may indicate non-zero number of bytes already written
/// if one of the files' cursor +`max_len` would exceed u64::MAX (`EOVERFLOW`).
pub(super) fn copy_regular_files(reader: RawFd, writer: RawFd, max_len: u64) -> CopyResult {
use crate::cmp;
// Kernel prior to 4.5 don't have copy_file_range
// We store the availability in a global to avoid unnecessary syscalls
static HAS_COPY_FILE_RANGE: AtomicBool = AtomicBool::new(true);
unsafe fn copy_file_range(
fd_in: libc::c_int,
off_in: *mut libc::loff_t,
fd_out: libc::c_int,
off_out: *mut libc::loff_t,
len: libc::size_t,
flags: libc::c_uint,
) -> libc::c_long {
libc::syscall(libc::SYS_copy_file_range, fd_in, off_in, fd_out, off_out, len, flags)
}
let has_copy_file_range = HAS_COPY_FILE_RANGE.load(Ordering::Relaxed);
let mut written = 0u64;
while written < max_len {
let copy_result = if has_copy_file_range {
let bytes_to_copy = cmp::min(max_len - written, usize::MAX as u64);
// cap to 1GB chunks in case u64::MAX is passed as max_len and the file has a non-zero seek position
// this allows us to copy large chunks without hitting EOVERFLOW,
// unless someone sets a file offset close to u64::MAX - 1GB, in which case a fallback would be required
let bytes_to_copy = cmp::min(bytes_to_copy as usize, 0x4000_0000usize);
let copy_result = unsafe {
// We actually don't have to adjust the offsets,
// because copy_file_range adjusts the file offset automatically
cvt(copy_file_range(
reader,
ptr::null_mut(),
writer,
ptr::null_mut(),
bytes_to_copy,
0,
))
};
if let Err(ref copy_err) = copy_result {
match copy_err.raw_os_error() {
Some(libc::ENOSYS | libc::EPERM | libc::EOPNOTSUPP) => {
HAS_COPY_FILE_RANGE.store(false, Ordering::Relaxed);
}
_ => {}
}
}
copy_result
} else {
Err(Error::from_raw_os_error(libc::ENOSYS))
};
match copy_result {
Ok(0) if written == 0 => {
// fallback to work around several kernel bugs where copy_file_range will fail to
// copy any bytes and return 0 instead of an error if
// - reading virtual files from the proc filesystem which appear to have 0 size
// but are not empty. noted in coreutils to affect kernels at least up to 5.6.19.
// - copying from an overlay filesystem in docker. reported to occur on fedora 32.
return CopyResult::Fallback(0);
}
Ok(0) => return CopyResult::Ended(Ok(written)), // reached EOF
Ok(ret) => written += ret as u64,
Err(err) => {
return match err.raw_os_error() {
// when file offset + max_length > u64::MAX
Some(libc::EOVERFLOW) => CopyResult::Fallback(written),
Some(
libc::ENOSYS | libc::EXDEV | libc::EINVAL | libc::EPERM | libc::EOPNOTSUPP,
) => {
// Try fallback io::copy if either:
// - Kernel version is < 4.5 (ENOSYS)
// - Files are mounted on different fs (EXDEV)
// - copy_file_range is broken in various ways on RHEL/CentOS 7 (EOPNOTSUPP)
// - copy_file_range is disallowed, for example by seccomp (EPERM)
// - copy_file_range cannot be used with pipes or device nodes (EINVAL)
assert_eq!(written, 0);
CopyResult::Fallback(0)
}
_ => CopyResult::Ended(Err(err)),
};
}
}
}
CopyResult::Ended(Ok(written))
}
#[derive(PartialEq)]
enum SpliceMode {
Sendfile,
Splice,
}
/// performs splice or sendfile between file descriptors
/// Does _not_ fall back to a generic copy loop.
fn sendfile_splice(mode: SpliceMode, reader: RawFd, writer: RawFd, len: u64) -> CopyResult {
static HAS_SENDFILE: AtomicBool = AtomicBool::new(true);
static HAS_SPLICE: AtomicBool = AtomicBool::new(true);
syscall! {
fn splice(
srcfd: libc::c_int,
src_offset: *const i64,
dstfd: libc::c_int,
dst_offset: *const i64,
len: libc::size_t,
flags: libc::c_int
) -> libc::ssize_t
}
match mode {
SpliceMode::Sendfile if !HAS_SENDFILE.load(Ordering::Relaxed) => {
return CopyResult::Fallback(0);
}
SpliceMode::Splice if !HAS_SPLICE.load(Ordering::Relaxed) => {
return CopyResult::Fallback(0);
}
_ => (),
}
let mut written = 0u64;
while written < len {
// according to its manpage that's the maximum size sendfile() will copy per invocation
let chunk_size = crate::cmp::min(len - written, 0x7ffff000_u64) as usize;
let result = match mode {
SpliceMode::Sendfile => {
cvt(unsafe { libc::sendfile(writer, reader, ptr::null_mut(), chunk_size) })
}
SpliceMode::Splice => cvt(unsafe {
splice(reader, ptr::null_mut(), writer, ptr::null_mut(), chunk_size, 0)
}),
};
match result {
Ok(0) => break, // EOF
Ok(ret) => written += ret as u64,
Err(err) => {
return match err.raw_os_error() {
Some(libc::ENOSYS | libc::EPERM) => {
// syscall not supported (ENOSYS)
// syscall is disallowed, e.g. by seccomp (EPERM)
match mode {
SpliceMode::Sendfile => HAS_SENDFILE.store(false, Ordering::Relaxed),
SpliceMode::Splice => HAS_SPLICE.store(false, Ordering::Relaxed),
}
assert_eq!(written, 0);
CopyResult::Fallback(0)
}
Some(libc::EINVAL) => {
// splice/sendfile do not support this particular file descriptor (EINVAL)
assert_eq!(written, 0);
CopyResult::Fallback(0)
}
Some(os_err) if mode == SpliceMode::Sendfile && os_err == libc::EOVERFLOW => {
CopyResult::Fallback(written)
}
_ => CopyResult::Ended(Err(err)),
};
}
}
}
CopyResult::Ended(Ok(written))
}

213
library/std/src/sys/unix/kernel_copy/tests.rs Normal file
View File

@ -0,0 +1,213 @@
use crate::env::temp_dir;
use crate::fs::OpenOptions;
use crate::io;
use crate::io::Result;
use crate::io::SeekFrom;
use crate::io::{BufRead, Read, Seek, Write};
use crate::os::unix::io::AsRawFd;
#[test]
fn copy_specialization() -> Result<()> {
use crate::io::{BufReader, BufWriter};
let path = crate::env::temp_dir();
let source_path = path.join("copy-spec.source");
let sink_path = path.join("copy-spec.sink");
let result: Result<()> = try {
let mut source = crate::fs::OpenOptions::new()
.read(true)
.write(true)
.create(true)
.truncate(true)
.open(&source_path)?;
source.write_all(b"abcdefghiklmnopqr")?;
source.seek(SeekFrom::Start(8))?;
let mut source = BufReader::with_capacity(8, source.take(5));
source.fill_buf()?;
assert_eq!(source.buffer(), b"iklmn");
source.get_mut().set_limit(6);
source.get_mut().get_mut().seek(SeekFrom::Start(1))?; // "bcdefg"
let mut source = source.take(10); // "iklmnbcdef"
let mut sink = crate::fs::OpenOptions::new()
.read(true)
.write(true)
.create(true)
.truncate(true)
.open(&sink_path)?;
sink.write_all(b"000000")?;
let mut sink = BufWriter::with_capacity(5, sink);
sink.write_all(b"wxyz")?;
assert_eq!(sink.buffer(), b"wxyz");
let copied = crate::io::copy(&mut source, &mut sink)?;
assert_eq!(copied, 10);
assert_eq!(sink.buffer().len(), 0);
let mut sink = sink.into_inner()?;
sink.seek(SeekFrom::Start(0))?;
let mut copied = Vec::new();
sink.read_to_end(&mut copied)?;
assert_eq!(&copied, b"000000wxyziklmnbcdef");
};
let rm1 = crate::fs::remove_file(source_path);
let rm2 = crate::fs::remove_file(sink_path);
result.and(rm1).and(rm2)
}
#[bench]
fn bench_file_to_file_copy(b: &mut test::Bencher) {
const BYTES: usize = 128 * 1024;
let src_path = temp_dir().join("file-copy-bench-src");
let mut src = crate::fs::OpenOptions::new()
.create(true)
.truncate(true)
.read(true)
.write(true)
.open(src_path)
.unwrap();
src.write(&vec![0u8; BYTES]).unwrap();
let sink_path = temp_dir().join("file-copy-bench-sink");
let mut sink = crate::fs::OpenOptions::new()
.create(true)
.truncate(true)
.write(true)
.open(sink_path)
.unwrap();
b.bytes = BYTES as u64;
b.iter(|| {
src.seek(SeekFrom::Start(0)).unwrap();
sink.seek(SeekFrom::Start(0)).unwrap();
assert_eq!(BYTES as u64, io::copy(&mut src, &mut sink).unwrap());
});
}
#[bench]
fn bench_file_to_socket_copy(b: &mut test::Bencher) {
const BYTES: usize = 128 * 1024;
let src_path = temp_dir().join("pipe-copy-bench-src");
let mut src = OpenOptions::new()
.create(true)
.truncate(true)
.read(true)
.write(true)
.open(src_path)
.unwrap();
src.write(&vec![0u8; BYTES]).unwrap();
let sink_drainer = crate::net::TcpListener::bind("localhost:0").unwrap();
let mut sink = crate::net::TcpStream::connect(sink_drainer.local_addr().unwrap()).unwrap();
let mut sink_drainer = sink_drainer.accept().unwrap().0;
crate::thread::spawn(move || {
let mut sink_buf = vec![0u8; 1024 * 1024];
loop {
sink_drainer.read(&mut sink_buf[..]).unwrap();
}
});
b.bytes = BYTES as u64;
b.iter(|| {
src.seek(SeekFrom::Start(0)).unwrap();
assert_eq!(BYTES as u64, io::copy(&mut src, &mut sink).unwrap());
});
}
#[cfg(any(target_os = "linux", target_os = "android"))]
#[bench]
fn bench_socket_pipe_socket_copy(b: &mut test::Bencher) {
use super::CopyResult;
use crate::io::ErrorKind;
use crate::process::{ChildStdin, ChildStdout};
use crate::sys_common::FromInner;
let (read_end, write_end) = crate::sys::pipe::anon_pipe().unwrap();
let mut read_end = ChildStdout::from_inner(read_end);
let write_end = ChildStdin::from_inner(write_end);
let acceptor = crate::net::TcpListener::bind("localhost:0").unwrap();
let mut remote_end = crate::net::TcpStream::connect(acceptor.local_addr().unwrap()).unwrap();
let local_end = crate::sync::Arc::new(acceptor.accept().unwrap().0);
// the data flow in this benchmark:
//
// socket(tx) local_source
// remote_end (write) +--------> (splice to)
// write_end
// +
// |
// | pipe
// v
// read_end
// remote_end (read) <---------+ (splice to) *
// socket(rx) local_end
//
// * benchmark loop using io::copy
crate::thread::spawn(move || {
let mut sink_buf = vec![0u8; 1024 * 1024];
remote_end.set_nonblocking(true).unwrap();
loop {
match remote_end.write(&mut sink_buf[..]) {
Err(err) if err.kind() == ErrorKind::WouldBlock => {}
Ok(_) => {}
err => {
err.expect("write failed");
}
};
match remote_end.read(&mut sink_buf[..]) {
Err(err) if err.kind() == ErrorKind::WouldBlock => {}
Ok(_) => {}
err => {
err.expect("read failed");
}
};
}
});
// check that splice works, otherwise the benchmark would hang
let probe = super::sendfile_splice(
super::SpliceMode::Splice,
local_end.as_raw_fd(),
write_end.as_raw_fd(),
1,
);
match probe {
CopyResult::Ended(Ok(1)) => {
// splice works
}
_ => {
eprintln!("splice failed, skipping benchmark");
return;
}
}
let local_source = local_end.clone();
crate::thread::spawn(move || {
loop {
super::sendfile_splice(
super::SpliceMode::Splice,
local_source.as_raw_fd(),
write_end.as_raw_fd(),
u64::MAX,
);
}
});
const BYTES: usize = 128 * 1024;
b.bytes = BYTES as u64;
b.iter(|| {
assert_eq!(
BYTES as u64,
io::copy(&mut (&mut read_end).take(BYTES as u64), &mut &*local_end).unwrap()
);
});
}

2
library/std/src/sys/unix/mod.rs
View File

@ -51,6 +51,8 @@ pub mod fd;
pub mod fs;
pub mod futex;
pub mod io;
#[cfg(any(target_os = "linux", target_os = "android"))]
pub mod kernel_copy;
#[cfg(target_os = "l4re")]
mod l4re;
pub mod memchr;