syscallcompat: add Fstatat + emulation + test

Fstatat has recently been added to x/sys/unix. Make
it available for use in gocryptfs.

1 files changed, 20 insertions, 0 deletions

diff --git a/internal/syscallcompat/emulate.go b/internal/syscallcompat/emulate.go
index 96776e2..e5aeae7 100644
--- a/internal/syscallcompat/emulate.go
+++ b/internal/syscallcompat/emulate.go
@@ -210,3 +210,23 @@ func emulateMkdirat(dirfd int, path string, mode uint32) (err error) {
 	}
 	return syscall.Mkdir(path, mode)
 }
+
+// emulateFstatat emulates the syscall for platforms that don't have it
+// in the kernel (darwin).
+func emulateFstatat(dirfd int, path string, stat *unix.Stat_t, flags int) (err error) {
+	if !filepath.IsAbs(path) {
+		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(dirfd)
+		if err != nil {
+			return err
+		}
+		defer syscall.Fchdir(cwd)
+	}
+	return unix.Lstat(path, stat)
+}