Fix #8259 - Can't reuse symlink'd bindmount

volumes.Get was not checking for symlinked paths meanwhile when adding a
new volume it was following the symlink.
So when trying to use a bind-mount that is a symlink, the volume is
added with the correct path, but when another container tries to use the
same volume it got a "Volume exists" error because volumes.Get returned
nil and as such attempted to create a new volume.

Docker-DCO-1.1-Signed-off-by: Brian Goff <cpuguy83@gmail.com> (github: cpuguy83)

integration-cli/docker_cli_run_test.go

@@ -2221,3 +2221,34 @@ func TestRunRedirectStdout(t *testing.T) {
 
 	logDone("run - redirect stdout")
 }
+
+// Regression test for https://github.com/docker/docker/issues/8259
+func TestRunReuseBindVolumeThatIsSymlink(t *testing.T) {
+	tmpDir, err := ioutil.TempDir(os.TempDir(), "testlink")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	linkPath := os.TempDir() + "/testlink2"
+	if err := os.Symlink(tmpDir, linkPath); err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(linkPath)
+
+	// Create first container
+	cmd := exec.Command(dockerBinary, "run", "-v", fmt.Sprintf("%s:/tmp/test", linkPath), "busybox", "ls", "-lh", "/tmp/test")
+	if _, err := runCommand(cmd); err != nil {
+		t.Fatal(err)
+	}
+
+	// Create second container with same symlinked path
+	// This will fail if the referenced issue is hit with a "Volume exists" error
+	cmd = exec.Command(dockerBinary, "run", "-v", fmt.Sprintf("%s:/tmp/test", linkPath), "busybox", "ls", "-lh", "/tmp/test")
+	if out, _, err := runCommandWithOutput(cmd); err != nil {
+		t.Fatal(err, out)
+	}
+
+	deleteAllContainers()
+	logDone("run - can remount old bindmount volume")
+}