[WIP] Partial bot skeleton, non-functional though

vendor/github.com/cockroachdb/pebble/vfs/default_linux_arm.go

@@ -0,0 +1,73 @@
+// Copyright 2023 The LevelDB-Go and Pebble Authors. All rights reserved. Use
+// of this source code is governed by a BSD-style license that can be found in
+// the LICENSE file.
+
+//go:build linux && arm
+// +build linux,arm
+
+package vfs
+
+import (
+	"os"
+	"syscall"
+
+	"github.com/cockroachdb/errors"
+	"golang.org/x/sys/unix"
+)
+
+func wrapOSFileImpl(f *os.File) File {
+	lf := &linuxOnArmFile{File: f, fd: f.Fd()}
+	if lf.fd != InvalidFd {
+		lf.useSyncRange = isSyncRangeSupported(lf.fd)
+	}
+	return lf
+}
+
+func (defaultFS) OpenDir(name string) (File, error) {
+	f, err := os.OpenFile(name, syscall.O_CLOEXEC, 0)
+	if err != nil {
+		return nil, errors.WithStack(err)
+	}
+	return &linuxOnArmDir{f}, nil
+}
+
+// Assert that linuxOnArmFile and linuxOnArmDir implement vfs.File.
+var (
+	_ File = (*linuxOnArmDir)(nil)
+	_ File = (*linuxOnArmFile)(nil)
+)
+
+type linuxOnArmDir struct {
+	*os.File
+}
+
+func (d *linuxOnArmDir) Prefetch(offset int64, length int64) error      { return nil }
+func (d *linuxOnArmDir) Preallocate(offset, length int64) error         { return nil }
+func (d *linuxOnArmDir) SyncData() error                                { return d.Sync() }
+func (d *linuxOnArmDir) SyncTo(offset int64) (fullSync bool, err error) { return false, nil }
+
+type linuxOnArmFile struct {
+	*os.File
+	fd           uintptr
+	useSyncRange bool
+}
+
+func (f *linuxOnArmFile) Prefetch(offset int64, length int64) error {
+	_, _, err := unix.Syscall(unix.SYS_READAHEAD, uintptr(f.fd), uintptr(offset), uintptr(length))
+	return err
+}
+
+func (f *linuxOnArmFile) Preallocate(offset, length int64) error { return nil }
+
+func (f *linuxOnArmFile) SyncData() error {
+	// TODO(radu): does arm support unix.Fdatasync?
+	return f.Sync()
+}
+
+func (f *linuxOnArmFile) SyncTo(int64) (fullSync bool, err error) {
+	// syscall.SyncFileRange is not defined form arm (see https://github.com/cockroachdb/pebble/issues/171).
+	if err = f.Sync(); err != nil {
+		return false, err
+	}
+	return true, nil
+}