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unix/kernel_copy.rs: copy_file_range_candidate allows empty output files #114373

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Aug 4, 2023
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unix/kernel_copy.rs: copy_file_range_candidate allows empty output files #114373

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18 changes: 14 additions & 4 deletions library/std/src/sys/unix/kernel_copy.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -89,6 +89,12 @@ enum FdMeta {
NoneObtained,
}

#[derive(PartialEq)]
enum FdHandle {
Input,
Output,
}

impl FdMeta {
fn maybe_fifo(&self) -> bool {
match self {
Expand All @@ -114,12 +120,14 @@ impl FdMeta {
}
}

fn copy_file_range_candidate(&self) -> bool {
fn copy_file_range_candidate(&self, f: FdHandle) -> 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,
FdMeta::Metadata(meta) if f == FdHandle::Input && meta.is_file() && meta.len() > 0 => {
true
}
FdMeta::Metadata(meta) if f == FdHandle::Output && meta.is_file() => true,
_ => false,
}
}
Expand Down Expand Up @@ -197,7 +205,9 @@ impl<R: CopyRead, W: CopyWrite> SpecCopy for Copier<'_, '_, R, W> {
written += flush()?;
let max_write = reader.min_limit();

if input_meta.copy_file_range_candidate() && output_meta.copy_file_range_candidate() {
if input_meta.copy_file_range_candidate(FdHandle::Input)
&& output_meta.copy_file_range_candidate(FdHandle::Output)
{
let result = copy_regular_files(readfd, writefd, max_write);
result.update_take(reader);

Expand Down
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