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