Use user-provided Listxattr buffer sizexattr_user_buffer

This huge buffer showed up big time in ./profiling/ls.bash
and caused a 2x LS benchmark slowdown.

Instead of the fixed-size buffer, use the buffer size
hint the user has provided us.

We return inaccurate (larger than actual, which should be safe)
numbers when the user has provided no buffer (size probe).

1 files changed, 4 insertions, 6 deletions

diff --git a/internal/fusefrontend_reverse/node_xattr_linux.go b/internal/fusefrontend_reverse/node_xattr_linux.go
index 3c574f5..226ace4 100644
--- a/internal/fusefrontend_reverse/node_xattr_linux.go
+++ b/internal/fusefrontend_reverse/node_xattr_linux.go
@@ -5,6 +5,7 @@ import (
 	"syscall"
 
 	"github.com/hanwen/go-fuse/v2/fs"
+	"golang.org/x/sys/unix"
 
 	"github.com/rfjakob/gocryptfs/v2/internal/syscallcompat"
 )
@@ -27,7 +28,7 @@ func (n *Node) getXAttr(cAttr string) (out []byte, errno syscall.Errno) {
 	return pData, 0
 }
 
-func (n *Node) listXAttr() (out []string, errno syscall.Errno) {
+func (n *Node) listXAttr(buf []byte) (sz int, errno syscall.Errno) {
 	d, errno := n.prepareAtSyscall("")
 	if errno != 0 {
 		return
@@ -35,9 +36,6 @@ func (n *Node) listXAttr() (out []string, errno syscall.Errno) {
 	defer syscall.Close(d.dirfd)
 
 	procPath := fmt.Sprintf("/proc/self/fd/%d/%s", d.dirfd, d.pName)
-	pNames, err := syscallcompat.Llistxattr(procPath)
-	if err != nil {
-		return nil, fs.ToErrno(err)
-	}
-	return pNames, 0
+	sz, err := unix.Llistxattr(procPath, buf)
+	return sz, fs.ToErrno(err)
 }