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basicfs_xattr_unix.go
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basicfs_xattr_unix.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 !windows && !dragonfly && !illumos && !solaris && !openbsd
// +build !windows,!dragonfly,!illumos,!solaris,!openbsd
package fs
import (
"bytes"
"errors"
"fmt"
"sync"
"syscall"
"github.com/syncthing/syncthing/lib/protocol"
"golang.org/x/sys/unix"
)
func (f *BasicFilesystem) GetXattr(path string, xattrFilter XattrFilter) ([]protocol.Xattr, error) {
path, err := f.rooted(path)
if err != nil {
return nil, fmt.Errorf("get xattr %s: %w", path, err)
}
attrs, err := listXattr(path)
if err != nil {
return nil, fmt.Errorf("get xattr %s: %w", path, err)
}
res := make([]protocol.Xattr, 0, len(attrs))
var totSize int
for _, attr := range attrs {
if !xattrFilter.Permit(attr) {
l.Debugf("get xattr %s: skipping attribute %q denied by filter", path, attr)
continue
}
val, err := getXattr(path, attr)
var errNo syscall.Errno
if errors.As(err, &errNo) && errNo == 0x5d {
// ENOATTR, returned on BSD when asking for an attribute that
// doesn't exist (any more?)
continue
} else if err != nil {
return nil, fmt.Errorf("get xattr %s: %w", path, err)
}
if max := xattrFilter.GetMaxSingleEntrySize(); max > 0 && len(attr)+len(val) > max {
l.Debugf("get xattr %s: attribute %q exceeds max size", path, attr)
continue
}
totSize += len(attr) + len(val)
if max := xattrFilter.GetMaxTotalSize(); max > 0 && totSize > max {
l.Debugf("get xattr %s: attribute %q would cause max size to be exceeded", path, attr)
continue
}
res = append(res, protocol.Xattr{
Name: attr,
Value: val,
})
}
return res, nil
}
var xattrBufPool = sync.Pool{
New: func() any { return make([]byte, 1024) },
}
func getXattr(path, name string) ([]byte, error) {
buf := xattrBufPool.Get().([]byte)
defer func() {
// Put the buffer back in the pool, or not if we're not supposed to
// (we returned it to the caller).
if buf != nil {
xattrBufPool.Put(buf)
}
}()
size, err := unix.Lgetxattr(path, name, buf)
if errors.Is(err, unix.ERANGE) {
// Buffer was too small. Figure out how large it needs to be, and
// allocate.
size, err = unix.Lgetxattr(path, name, nil)
if err != nil {
return nil, fmt.Errorf("Lgetxattr %s %q: %w", path, name, err)
}
if size > len(buf) {
xattrBufPool.Put(buf)
buf = make([]byte, size)
}
size, err = unix.Lgetxattr(path, name, buf)
}
if err != nil {
return nil, fmt.Errorf("Lgetxattr %s %q: %w", path, name, err)
}
if size >= len(buf)/4*3 {
// The buffer is adequately sized (at least three quarters of it is
// used), return it as-is.
val := buf[:size]
buf = nil // Don't put it back in the pool.
return val, nil
}
// The buffer is larger than required, copy the data to a new buffer of
// the correct size. This avoids having lots of 1024-sized allocations
// sticking around when 24 bytes or whatever would be enough.
val := make([]byte, size)
copy(val, buf)
return val, nil
}
func (f *BasicFilesystem) SetXattr(path string, xattrs []protocol.Xattr, xattrFilter XattrFilter) error {
// Index the new attribute set.
xattrsIdx := make(map[string]int)
for i, xa := range xattrs {
xattrsIdx[xa.Name] = i
}
// Get and index the existing attribute set
current, err := f.GetXattr(path, xattrFilter)
if err != nil {
return fmt.Errorf("set xattrs %s: GetXattr: %w", path, err)
}
currentIdx := make(map[string]int)
for i, xa := range current {
currentIdx[xa.Name] = i
}
path, err = f.rooted(path)
if err != nil {
return fmt.Errorf("set xattrs %s: %w", path, err)
}
// Remove all existing xattrs that are not in the new set
for _, xa := range current {
if _, ok := xattrsIdx[xa.Name]; !ok {
if err := unix.Lremovexattr(path, xa.Name); err != nil {
return fmt.Errorf("set xattrs %s: Removexattr %q: %w", path, xa.Name, err)
}
}
}
// Set all xattrs that are different in the new set
for _, xa := range xattrs {
if old, ok := currentIdx[xa.Name]; ok && bytes.Equal(xa.Value, current[old].Value) {
continue
}
if err := unix.Lsetxattr(path, xa.Name, xa.Value, 0); err != nil {
return fmt.Errorf("set xattrs %s: Setxattr %q: %w", path, xa.Name, err)
}
}
return nil
}
func compact(ss []string) []string {
i := 0
for _, s := range ss {
if s != "" {
ss[i] = s
i++
}
}
return ss[:i]
}