os-dirent_namelen_linux.go

//go:build linux && !appengine
// +build linux,!appengine

// Copyright (c) 2015-2021 MinIO, Inc.
//
// This file is part of MinIO Object Storage stack
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package cmd

import (
	"bytes"
	"fmt"
	"syscall"
	"unsafe"
)

func direntNamlen(dirent *syscall.Dirent) (uint64, error) {
	const fixedHdr = uint16(unsafe.Offsetof(syscall.Dirent{}.Name))
	nameBuf := (*[unsafe.Sizeof(dirent.Name)]byte)(unsafe.Pointer(&dirent.Name[0]))
	const nameBufLen = uint16(len(nameBuf))
	limit := dirent.Reclen - fixedHdr
	if limit > nameBufLen {
		limit = nameBufLen
	}
	// Avoid bugs in long file names
	// https://github.com/golang/tools/commit/5f9a5413737ba4b4f692214aebee582b47c8be74
	nameLen := bytes.IndexByte(nameBuf[:limit], 0)
	if nameLen < 0 {
		return 0, fmt.Errorf("failed to find terminating 0 byte in dirent")
	}
	return uint64(nameLen), nil
}