syscallcompat: add Readlinkat

We need readlinkat to implement Readlink
symlink-race-free.

1 files changed, 29 insertions, 0 deletions

diff --git a/internal/syscallcompat/sys_common_test.go b/internal/syscallcompat/sys_common_test.go
new file mode 100644
index 0000000..bc694ba
--- /dev/null
+++ b/internal/syscallcompat/sys_common_test.go
@@ -0,0 +1,29 @@
+package syscallcompat
+
+import (
+	"bytes"
+	"os"
+	"syscall"
+	"testing"
+)
+
+func TestReadlinkat(t *testing.T) {
+	for _, targetLen := range []int{100, 500, 4000} {
+		target := string(bytes.Repeat([]byte("x"), targetLen))
+		err := os.Symlink(target, tmpDir+"/readlinkat")
+		if err != nil {
+			t.Fatal(err)
+		}
+		target2, err := Readlinkat(tmpDirFd, "readlinkat")
+		if err != nil {
+			t.Fatal(err)
+		}
+		if target != target2 {
+			t.Errorf("target=%q != target2=%q", target, target2)
+		}
+		err = syscall.Unlink(tmpDir + "/readlinkat")
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+}