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Less syscalls for the copy_file_range probe #122079

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merged 3 commits into from
May 26, 2024
Merged

Less syscalls for the copy_file_range probe #122079

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214c498
Less syscalls for the `copy_file_range` probe
tbu- Mar 6, 2024
5073475
Be stricter with `copy_file_range` probe results
tbu- Mar 6, 2024
7d67ee5
Lift the probe code of `copy_file_range` into a function
tbu- Apr 27, 2024
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71 changes: 48 additions & 23 deletions library/std/src/sys/pal/unix/kernel_copy.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -560,6 +560,12 @@ pub(super) fn copy_regular_files(reader: RawFd, writer: RawFd, max_len: u64) ->
// We store the availability in a global to avoid unnecessary syscalls
static HAS_COPY_FILE_RANGE: AtomicU8 = AtomicU8::new(NOT_PROBED);

let mut have_probed = match HAS_COPY_FILE_RANGE.load(Ordering::Relaxed) {
NOT_PROBED => false,
UNAVAILABLE => return CopyResult::Fallback(0),
_ => true,
};

syscall! {
fn copy_file_range(
fd_in: libc::c_int,
Expand All @@ -571,26 +577,6 @@ pub(super) fn copy_regular_files(reader: RawFd, writer: RawFd, max_len: u64) ->
) -> libc::ssize_t
}

match HAS_COPY_FILE_RANGE.load(Ordering::Relaxed) {
NOT_PROBED => {
// EPERM can indicate seccomp filters or an immutable file.
// To distinguish these cases we probe with invalid file descriptors which should result in EBADF if the syscall is supported
// and some other error (ENOSYS or EPERM) if it's not available
let result = unsafe {
cvt(copy_file_range(INVALID_FD, ptr::null_mut(), INVALID_FD, ptr::null_mut(), 1, 0))
};

if matches!(result.map_err(|e| e.raw_os_error()), Err(Some(EBADF))) {
HAS_COPY_FILE_RANGE.store(AVAILABLE, Ordering::Relaxed);
} else {
HAS_COPY_FILE_RANGE.store(UNAVAILABLE, Ordering::Relaxed);
return CopyResult::Fallback(0);
}
}
UNAVAILABLE => return CopyResult::Fallback(0),
_ => {}
};

let mut written = 0u64;
while written < max_len {
let bytes_to_copy = cmp::min(max_len - written, usize::MAX as u64);
Expand All @@ -604,6 +590,11 @@ pub(super) fn copy_regular_files(reader: RawFd, writer: RawFd, max_len: u64) ->
cvt(copy_file_range(reader, ptr::null_mut(), writer, ptr::null_mut(), bytes_to_copy, 0))
};

if !have_probed && copy_result.is_ok() {
have_probed = true;
HAS_COPY_FILE_RANGE.store(AVAILABLE, Ordering::Relaxed);
}

match copy_result {
Ok(0) if written == 0 => {
// fallback to work around several kernel bugs where copy_file_range will fail to
Expand All @@ -616,10 +607,44 @@ pub(super) fn copy_regular_files(reader: RawFd, writer: RawFd, max_len: u64) ->
Ok(0) => return CopyResult::Ended(written), // reached EOF
Ok(ret) => written += ret as u64,
Err(err) => {
return match err.raw_os_error() {
let raw_os_error = match err.raw_os_error() {
Some(raw) => raw,
_ => return CopyResult::Error(err, written),
};
return match raw_os_error {
// when file offset + max_length > u64::MAX
Some(EOVERFLOW) => CopyResult::Fallback(written),
Some(ENOSYS | EXDEV | EINVAL | EPERM | EOPNOTSUPP | EBADF) if written == 0 => {
EOVERFLOW => CopyResult::Fallback(written),
ENOSYS | EXDEV | EINVAL | EPERM | EOPNOTSUPP | EBADF if written == 0 => {
if !have_probed {
if raw_os_error == ENOSYS {
HAS_COPY_FILE_RANGE.store(UNAVAILABLE, Ordering::Relaxed);
} else {
// EPERM can indicate seccomp filters or an
// immutable file. To distinguish these cases
// we probe with invalid file descriptors which
// should result in EBADF if the syscall is
// supported and some other error (ENOSYS or
// EPERM) if it's not available.
let result = unsafe {
cvt(copy_file_range(
INVALID_FD,
ptr::null_mut(),
INVALID_FD,
ptr::null_mut(),
1,
0,
))
};

if matches!(result.map_err(|e| e.raw_os_error()), Err(Some(EBADF)))
{
HAS_COPY_FILE_RANGE.store(AVAILABLE, Ordering::Relaxed);
} else {
HAS_COPY_FILE_RANGE.store(UNAVAILABLE, Ordering::Relaxed);
}
}
}

// Try fallback io::copy if either:
// - Kernel version is < 4.5 (ENOSYS¹)
// - Files are mounted on different fs (EXDEV)
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