copyFile with bufferSize instead of hardcoded value (#22769)

- `copyFile` allows to specify `bufferSize` instead of hardcoded wrong
value. Tiny diff.


# Performance

- 1200% Performance improvement.


# Check it yourself

Execute:

```bash
for i in $(seq 0 10); do
  bs=$((1024*2**$i))
  printf "%7s Kb\t" $bs
  timeout --foreground -sINT 2 dd bs=$bs if=/dev/zero of=/dev/null 2>&1 | sed -n 's/.* \([0-9.,]* [GM]B\/s\)/\1/p'
done
```

(This script can be ported to PowerShell for Windows I guess, it works
in Windows MinGW Bash anyways).


# Stats

- Hardcoded `8192` or `8000` Kb bufferSize gives `5` GB/s.
- Setting `262144` Kb bufferSize gives `65` GB/s (script suggestion).

---------

Co-authored-by: Andreas Rumpf <rumpf_a@web.de>

1 files changed, 1 insertions, 0 deletions

diff --git a/changelog.md b/changelog.md
index 74020e8fa..1fb6377a2 100644
--- a/changelog.md
+++ b/changelog.md
@@ -8,6 +8,7 @@
 
 [//]: # "Changes:"
 
+- Changed `std/osfiles.copyFile` to allow to specify `bufferSize` instead of a hardcoded one.
 
 [//]: # "Additions:"