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Commitb092569

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Auto merge of#122079 - tbu-:pr_copy_file_range_probe, r=the8472
Less syscalls for the `copy_file_range` probeIf it's obvious from the actual syscall results themselves that the syscall is supported or unsupported, don't do an extra syscall with an invalid file descriptor.CC#122052
2 parents785eb65 +7d67ee5 commitb092569

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1 file changed

+48
-19
lines changed

1 file changed

+48
-19
lines changed

‎library/std/src/sys/pal/unix/kernel_copy.rs‎

Lines changed: 48 additions & 19 deletions
Original file line numberDiff line numberDiff line change
@@ -560,6 +560,12 @@ pub(super) fn copy_regular_files(reader: RawFd, writer: RawFd, max_len: u64) ->
560560
// We store the availability in a global to avoid unnecessary syscalls
561561
staticHAS_COPY_FILE_RANGE:AtomicU8 =AtomicU8::new(NOT_PROBED);
562562

563+
letmut have_probed =matchHAS_COPY_FILE_RANGE.load(Ordering::Relaxed){
564+
NOT_PROBED =>false,
565+
UNAVAILABLE =>returnCopyResult::Fallback(0),
566+
_ =>true,
567+
};
568+
563569
syscall!{
564570
fn copy_file_range(
565571
fd_in: libc::c_int,
@@ -571,25 +577,22 @@ pub(super) fn copy_regular_files(reader: RawFd, writer: RawFd, max_len: u64) ->
571577
) -> libc::ssize_t
572578
}
573579

574-
matchHAS_COPY_FILE_RANGE.load(Ordering::Relaxed){
575-
NOT_PROBED =>{
576-
// EPERM can indicate seccomp filters or an immutable file.
577-
// To distinguish these cases we probe with invalid file descriptors which should result in EBADF if the syscall is supported
578-
// and some other error (ENOSYS or EPERM) if it's not available
579-
let result =unsafe{
580-
cvt(copy_file_range(INVALID_FD, ptr::null_mut(),INVALID_FD, ptr::null_mut(),1,0))
581-
};
582-
583-
ifmatches!(result.map_err(|e| e.raw_os_error()),Err(Some(EBADF))){
584-
HAS_COPY_FILE_RANGE.store(AVAILABLE,Ordering::Relaxed);
585-
}else{
586-
HAS_COPY_FILE_RANGE.store(UNAVAILABLE,Ordering::Relaxed);
587-
returnCopyResult::Fallback(0);
588-
}
580+
fnprobe_copy_file_range_support() ->u8{
581+
// In some cases, we cannot determine availability from the first
582+
// `copy_file_range` call. In this case, we probe with an invalid file
583+
// descriptor so that the results are easily interpretable.
584+
matchunsafe{
585+
cvt(copy_file_range(INVALID_FD, ptr::null_mut(),INVALID_FD, ptr::null_mut(),1,0))
586+
.map_err(|e| e.raw_os_error())
587+
}{
588+
Err(Some(EPERM |ENOSYS)) =>UNAVAILABLE,
589+
Err(Some(EBADF)) =>AVAILABLE,
590+
Ok(_) =>panic!("unexpected copy_file_range probe success"),
591+
// Treat other errors as the syscall
592+
// being unavailable.
593+
Err(_) =>UNAVAILABLE,
589594
}
590-
UNAVAILABLE =>returnCopyResult::Fallback(0),
591-
_ =>{}
592-
};
595+
}
593596

594597
letmut written =0u64;
595598
while written < max_len{
@@ -604,6 +607,11 @@ pub(super) fn copy_regular_files(reader: RawFd, writer: RawFd, max_len: u64) ->
604607
cvt(copy_file_range(reader, ptr::null_mut(), writer, ptr::null_mut(), bytes_to_copy,0))
605608
};
606609

610+
if !have_probed && copy_result.is_ok(){
611+
have_probed =true;
612+
HAS_COPY_FILE_RANGE.store(AVAILABLE,Ordering::Relaxed);
613+
}
614+
607615
match copy_result{
608616
Ok(0)if written ==0 =>{
609617
// fallback to work around several kernel bugs where copy_file_range will fail to
@@ -619,7 +627,28 @@ pub(super) fn copy_regular_files(reader: RawFd, writer: RawFd, max_len: u64) ->
619627
returnmatch err.raw_os_error(){
620628
// when file offset + max_length > u64::MAX
621629
Some(EOVERFLOW) =>CopyResult::Fallback(written),
622-
Some(ENOSYS |EXDEV |EINVAL |EPERM |EOPNOTSUPP |EBADF)if written ==0 =>{
630+
Some(raw_os_error @(ENOSYS |EXDEV |EINVAL |EPERM |EOPNOTSUPP |EBADF))
631+
if written ==0 =>
632+
{
633+
if !have_probed{
634+
let available =ifmatches!(raw_os_error,ENOSYS |EOPNOTSUPP |EPERM){
635+
// EPERM can indicate seccomp filters or an
636+
// immutable file. To distinguish these
637+
// cases we probe with invalid file
638+
// descriptors which should result in EBADF
639+
// if the syscall is supported and EPERM or
640+
// ENOSYS if it's not available.
641+
//
642+
// For EOPNOTSUPP, see below. In the case of
643+
// ENOSYS, we try to cover for faulty FUSE
644+
// drivers.
645+
probe_copy_file_range_support()
646+
}else{
647+
AVAILABLE
648+
};
649+
HAS_COPY_FILE_RANGE.store(available,Ordering::Relaxed);
650+
}
651+
623652
// Try fallback io::copy if either:
624653
// - Kernel version is < 4.5 (ENOSYS¹)
625654
// - Files are mounted on different fs (EXDEV)

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