From 2232fe8da3dcd4796e6db060ba61ba9c70a2a3f5 Mon Sep 17 00:00:00 2001 From: xstaticxgpx Date: Wed, 2 Aug 2023 09:58:30 -0400 Subject: [PATCH] unix/kernel_copy.rs: copy_file_range_candidate allows empty output files This is for https://github.com/rust-lang/rust/issues/114341 The `meta.len() > 0` condition here is intended for inputs only, ie. when input is in the `/proc` filesystem as documented. That inaccurately included empty output files which are then shunted to the sendfile() routine leading to higher than nescessary IO util in some cases, specifically with CoW filesystems like btrfs. Further, `NoneObtained` is not relevant in this context, so remove it. Simply, determine what is input or output given the passed enum Unit. --- library/std/src/sys/unix/kernel_copy.rs | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/library/std/src/sys/unix/kernel_copy.rs b/library/std/src/sys/unix/kernel_copy.rs index 7d49bbdcbe063..4d17a1b000229 100644 --- a/library/std/src/sys/unix/kernel_copy.rs +++ b/library/std/src/sys/unix/kernel_copy.rs @@ -89,6 +89,12 @@ enum FdMeta { NoneObtained, } +#[derive(PartialEq)] +enum FdHandle { + Input, + Output, +} + impl FdMeta { fn maybe_fifo(&self) -> bool { match self { @@ -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, } } @@ -197,7 +205,9 @@ impl 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);