syncthing/lib/fs/basicfs_xattr_bsdish.go

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// Copyright (C) 2022 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at https://mozilla.org/MPL/2.0/.
//go:build freebsd || netbsd
// +build freebsd netbsd
package fs
import (
"errors"
"fmt"
"sort"
"unsafe"
"golang.org/x/sys/unix"
)
var (
namespaces = [...]int{unix.EXTATTR_NAMESPACE_USER, unix.EXTATTR_NAMESPACE_SYSTEM}
namespacePrefixes = [...]string{unix.EXTATTR_NAMESPACE_USER: "user.", unix.EXTATTR_NAMESPACE_SYSTEM: "system."}
)
func listXattr(path string) ([]string, error) {
var attrs []string
// List the two namespaces explicitly and prefix any results with the
// namespace name.
for _, nsid := range namespaces {
buf := make([]byte, 1024)
size, err := unixLlistxattr(path, buf, nsid)
if errors.Is(err, unix.ERANGE) || size == len(buf) {
// Buffer is too small. Try again with a zero sized buffer to
// get the size, then allocate a buffer of the correct size. We
// include the size == len(buf) because apparently macOS doesn't
// return ERANGE as it should -- no harm done, just an extra
// read if we happened to need precisely 1024 bytes on the first
// pass.
size, err = unixLlistxattr(path, nil, nsid)
if err != nil {
return nil, fmt.Errorf("Listxattr %s: %w", path, err)
}
buf = make([]byte, size)
size, err = unixLlistxattr(path, buf, nsid)
}
if err != nil {
return nil, fmt.Errorf("Listxattr %s: %w", path, err)
}
buf = buf[:size]
// "Each list entry consists of a single byte containing the length
// of the attribute name, followed by the attribute name. The
// attribute name is not terminated by ASCII 0 (nul)."
i := 0
for i < len(buf) {
l := int(buf[i])
i++
if i+l > len(buf) {
// uh-oh
return nil, fmt.Errorf("get xattr %s: attribute length %d at offset %d exceeds buffer length %d", path, l, i, len(buf))
}
if l > 0 {
attrs = append(attrs, namespacePrefixes[nsid]+string(buf[i:i+l]))
i += l
}
}
}
sort.Strings(attrs)
return attrs, nil
}
// This is unix.Llistxattr except taking a namespace parameter to dodge
// https://github.com/golang/go/issues/54357 ("Listxattr on FreeBSD loses
// namespace info")
func unixLlistxattr(link string, dest []byte, nsid int) (sz int, err error) {
d := initxattrdest(dest, 0)
destsiz := len(dest)
s, e := unix.ExtattrListLink(link, nsid, uintptr(d), destsiz)
if e != nil && e == unix.EPERM && nsid != unix.EXTATTR_NAMESPACE_USER {
return 0, nil
} else if e != nil {
return s, e
}
return s, nil
}
var _zero uintptr
func initxattrdest(dest []byte, idx int) (d unsafe.Pointer) {
if len(dest) > idx {
return unsafe.Pointer(&dest[idx])
} else {
return unsafe.Pointer(_zero)
}
}