From 7b0d56fe98a4ae449d26af0b83d00271a179db6e Mon Sep 17 00:00:00 2001
From: Sebastian Lackner <sebastian@fds-team.de>
Date: Mon, 14 Jan 2019 02:51:50 +0100
Subject: [PATCH] syscallcompat: Drop Symlinkat emulation on macOS.

---
 internal/syscallcompat/emulate.go         | 20 -----------
 internal/syscallcompat/emulate_test.go    | 41 -----------------------
 internal/syscallcompat/sys_common.go      |  5 +++
 internal/syscallcompat/sys_common_test.go | 40 ++++++++++++++++++++++
 internal/syscallcompat/sys_darwin.go      |  4 ---
 internal/syscallcompat/sys_linux.go       |  5 ---
 6 files changed, 45 insertions(+), 70 deletions(-)

diff --git a/internal/syscallcompat/emulate.go b/internal/syscallcompat/emulate.go
index dc8cf6d..a98a0ce 100644
--- a/internal/syscallcompat/emulate.go
+++ b/internal/syscallcompat/emulate.go
@@ -30,26 +30,6 @@ func emulateMknodat(dirfd int, path string, mode uint32, dev int) error {
 	return syscall.Mknod(path, mode, dev)
 }
 
-// emulateSymlinkat emulates the syscall for platforms that don't have it
-// in the kernel (darwin).
-func emulateSymlinkat(oldpath string, newdirfd int, newpath string) (err error) {
-	if !filepath.IsAbs(newpath) {
-		chdirMutex.Lock()
-		defer chdirMutex.Unlock()
-		cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
-		if err != nil {
-			return err
-		}
-		defer syscall.Close(cwd)
-		err = syscall.Fchdir(newdirfd)
-		if err != nil {
-			return err
-		}
-		defer syscall.Fchdir(cwd)
-	}
-	return syscall.Symlink(oldpath, newpath)
-}
-
 // emulateMkdirat emulates the syscall for platforms that don't have it
 // in the kernel (darwin).
 func emulateMkdirat(dirfd int, path string, mode uint32) (err error) {
diff --git a/internal/syscallcompat/emulate_test.go b/internal/syscallcompat/emulate_test.go
index 6fe5f3e..6db37f8 100644
--- a/internal/syscallcompat/emulate_test.go
+++ b/internal/syscallcompat/emulate_test.go
@@ -2,8 +2,6 @@ package syscallcompat
 
 import (
 	"os"
-	"runtime"
-	"syscall"
 	"testing"
 
 	"golang.org/x/sys/unix"
@@ -29,45 +27,6 @@ func TestEmulateMknodat(t *testing.T) {
 	}
 }
 
-// symlinkCheckMode looks if the mode bits in "st" say that this is a symlink.
-// Calls t.Fatal() if not.
-func symlinkCheckMode(t *testing.T, st syscall.Stat_t) {
-	if runtime.GOOS == "darwin" {
-		// On MacOS, symlinks don't carry their own permissions, so
-		// only check the file type.
-		if st.Mode&syscall.S_IFMT != syscall.S_IFLNK {
-			t.Fatalf("This is not a symlink: mode = 0%o", st.Mode)
-		}
-		return
-	}
-	if st.Mode != 0120777 {
-		t.Fatalf("Wrong mode, have 0%o, want 0120777", st.Mode)
-	}
-}
-
-func TestEmulateSymlinkat(t *testing.T) {
-	err := emulateSymlinkat("/foo/bar/baz", tmpDirFd, "symlink1")
-	if err != nil {
-		t.Fatal(err)
-	}
-	var st syscall.Stat_t
-	err = syscall.Lstat(tmpDir+"/symlink1", &st)
-	if err != nil {
-		t.Fatal(err)
-	}
-	symlinkCheckMode(t, st)
-	// Test with absolute path
-	err = emulateSymlinkat("/foo/bar/baz", -1, tmpDir+"/symlink2")
-	if err != nil {
-		t.Fatal(err)
-	}
-	err = syscall.Lstat(tmpDir+"/symlink2", &st)
-	if err != nil {
-		t.Fatal(err)
-	}
-	symlinkCheckMode(t, st)
-}
-
 func TestEmulateMkdirat(t *testing.T) {
 	err := emulateMkdirat(tmpDirFd, "mkdirat", 0700)
 	if err != nil {
diff --git a/internal/syscallcompat/sys_common.go b/internal/syscallcompat/sys_common.go
index 9514830..21bac56 100644
--- a/internal/syscallcompat/sys_common.go
+++ b/internal/syscallcompat/sys_common.go
@@ -87,6 +87,11 @@ func Linkat(olddirfd int, oldpath string, newdirfd int, newpath string, flags in
 	return unix.Linkat(olddirfd, oldpath, newdirfd, newpath, flags)
 }
 
+// Symlinkat syscall.
+func Symlinkat(oldpath string, newdirfd int, newpath string) (err error) {
+	return unix.Symlinkat(oldpath, newdirfd, newpath)
+}
+
 const XATTR_SIZE_MAX = 65536
 
 // Make the buffer 1kB bigger so we can detect overflows
diff --git a/internal/syscallcompat/sys_common_test.go b/internal/syscallcompat/sys_common_test.go
index 4556279..78283e6 100644
--- a/internal/syscallcompat/sys_common_test.go
+++ b/internal/syscallcompat/sys_common_test.go
@@ -3,6 +3,7 @@ package syscallcompat
 import (
 	"bytes"
 	"os"
+	"runtime"
 	"syscall"
 	"testing"
 
@@ -207,3 +208,42 @@ func TestFchmodat(t *testing.T) {
 		t.Errorf("chmod on symlink affected symlink target: New mode=%#0o", st.Mode)
 	}
 }
+
+// symlinkCheckMode looks if the mode bits in "st" say that this is a symlink.
+// Calls t.Fatal() if not.
+func symlinkCheckMode(t *testing.T, st syscall.Stat_t) {
+	if runtime.GOOS == "darwin" {
+		// On MacOS, symlinks don't carry their own permissions, so
+		// only check the file type.
+		if st.Mode&syscall.S_IFMT != syscall.S_IFLNK {
+			t.Fatalf("This is not a symlink: mode = 0%o", st.Mode)
+		}
+		return
+	}
+	if st.Mode != 0120777 {
+		t.Fatalf("Wrong mode, have 0%o, want 0120777", st.Mode)
+	}
+}
+
+func TestSymlinkat(t *testing.T) {
+	err := Symlinkat("/foo/bar/baz", tmpDirFd, "symlink1")
+	if err != nil {
+		t.Fatal(err)
+	}
+	var st syscall.Stat_t
+	err = syscall.Lstat(tmpDir+"/symlink1", &st)
+	if err != nil {
+		t.Fatal(err)
+	}
+	symlinkCheckMode(t, st)
+	// Test with absolute path
+	err = Symlinkat("/foo/bar/baz", -1, tmpDir+"/symlink2")
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = syscall.Lstat(tmpDir+"/symlink2", &st)
+	if err != nil {
+		t.Fatal(err)
+	}
+	symlinkCheckMode(t, st)
+}
diff --git a/internal/syscallcompat/sys_darwin.go b/internal/syscallcompat/sys_darwin.go
index be85fee..2780ef6 100644
--- a/internal/syscallcompat/sys_darwin.go
+++ b/internal/syscallcompat/sys_darwin.go
@@ -102,10 +102,6 @@ func Fchmodat(dirfd int, path string, mode uint32, flags int) (err error) {
 	return unix.Fchmodat(dirfd, path, mode, flags)
 }
 
-func Symlinkat(oldpath string, newdirfd int, newpath string) (err error) {
-	return emulateSymlinkat(oldpath, newdirfd, newpath)
-}
-
 func SymlinkatUser(oldpath string, newdirfd int, newpath string, context *fuse.Context) (err error) {
 	if context != nil {
 		runtime.LockOSThread()
diff --git a/internal/syscallcompat/sys_linux.go b/internal/syscallcompat/sys_linux.go
index cacec6a..0b34aa1 100644
--- a/internal/syscallcompat/sys_linux.go
+++ b/internal/syscallcompat/sys_linux.go
@@ -154,11 +154,6 @@ func Fchmodat(dirfd int, path string, mode uint32, flags int) (err error) {
 	return syscall.Chmod(procPath, mode)
 }
 
-// Symlinkat syscall.
-func Symlinkat(oldpath string, newdirfd int, newpath string) (err error) {
-	return unix.Symlinkat(oldpath, newdirfd, newpath)
-}
-
 // SymlinkatUser runs the Symlinkat syscall in the context of a different user.
 func SymlinkatUser(oldpath string, newdirfd int, newpath string, context *fuse.Context) (err error) {
 	if context != nil {