pkg/fileutils: fix Lexists on FreeBSD

The faccessat system call does not support AT_SYMLINK_NOFOLLOW on
FreeBSD versions before 15.0. This works around the limitation by
falling back to os.Lstat if faccessat returns an EINVAL error.

Signed-off-by: Doug Rabson <dfr@rabson.org>

pkg/fileutils/exists_freebsd.go

@@ -0,0 +1,37 @@
+package fileutils
+
+import (
+	"errors"
+	"os"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+// Exists checks whether a file or directory exists at the given path.
+// If the path is a symlink, the symlink is followed.
+func Exists(path string) error {
+	// It uses unix.Faccessat which is a faster operation compared to os.Stat for
+	// simply checking the existence of a file.
+	err := unix.Faccessat(unix.AT_FDCWD, path, unix.F_OK, 0)
+	if err != nil {
+		return &os.PathError{Op: "faccessat", Path: path, Err: err}
+	}
+	return nil
+}
+
+// Lexists checks whether a file or directory exists at the given path.
+// If the path is a symlink, the symlink itself is checked.
+func Lexists(path string) error {
+	// FreeBSD before 15.0 does not support the AT_SYMLINK_NOFOLLOW flag for
+	// faccessat. In this case, the call to faccessat will return EINVAL and
+	// we fall back to using Lstat.
+	err := unix.Faccessat(unix.AT_FDCWD, path, unix.F_OK, unix.AT_SYMLINK_NOFOLLOW)
+	if err != nil && errors.Is(err, syscall.EINVAL) {
+		_, err = os.Lstat(path)
+	}
+	if err != nil {
+		return &os.PathError{Op: "faccessat", Path: path, Err: err}
+	}
+	return nil
+}

pkg/fileutils/exists_unix.go

@@ -1,5 +1,5 @@
-//go:build !windows
-// +build !windows
+//go:build !windows && !freebsd
+// +build !windows,!freebsd
 
 package fileutils