docker: default device.container_path to host_path (#16811)

* docker: default device.container_path to host_path

Matches docker cli behavior.

Fixes #16754

.changelog/16811.txt

@@ -0,0 +1,3 @@
+```release-note:improvement
+driver/docker: Default `devices.container_path` to `devices.host_path` like Docker's CLI
+```

drivers/docker/config.go

@@ -504,6 +504,11 @@ func (d DockerDevice) toDockerDevice() (docker.Device, error) {
 		return dd, fmt.Errorf("host path must be set in configuration for devices")
 	}
 
+	// Docker's CLI defaults to HostPath in this case. See #16754
+	if dd.PathInContainer == "" {
+		dd.PathInContainer = d.HostPath
+	}
+
 	if dd.CgroupPermissions == "" {
 		dd.CgroupPermissions = "rwm"
 	}

drivers/docker/config_test.go

@@ -216,6 +216,7 @@ config {
   devices = [
     {"host_path"="/dev/null", "container_path"="/tmp/container-null", cgroup_permissions="rwm"},
     {"host_path"="/dev/random", "container_path"="/tmp/container-random"},
+    {"host_path"="/dev/bus/usb"},
   ]
   dns_search_domains = ["sub.example.com", "sub2.example.com"]
   dns_options = ["debug", "attempts:10"]
@@ -372,6 +373,11 @@ config {
 				ContainerPath:     "/tmp/container-random",
 				CgroupPermissions: "",
 			},
+			{
+				HostPath:          "/dev/bus/usb",
+				ContainerPath:     "",
+				CgroupPermissions: "",
+			},
 		},
 		DNSSearchDomains: []string{"sub.example.com", "sub2.example.com"},
 		DNSOptions:       []string{"debug", "attempts:10"},

drivers/docker/driver.go

@@ -1035,7 +1035,7 @@ func (d *Driver) createContainerConfig(task *drivers.TaskConfig, driverConfig *T
 		hostConfig.ShmSize = driverConfig.ShmSize
 	}
 
-	// Setup devices
+	// Setup devices from Docker-specific config
 	for _, device := range driverConfig.Devices {
 		dd, err := device.toDockerDevice()
 		if err != nil {
@@ -1043,6 +1043,8 @@ func (d *Driver) createContainerConfig(task *drivers.TaskConfig, driverConfig *T
 		}
 		hostConfig.Devices = append(hostConfig.Devices, dd)
 	}
+
+	// Setup devices from Nomad device plugins
 	for _, device := range task.Devices {
 		hostConfig.Devices = append(hostConfig.Devices, docker.Device{
 			PathOnHost:        device.HostPath,

drivers/docker/driver_test.go

@@ -2471,23 +2471,43 @@ func TestDockerDriver_Device_Success(t *testing.T) {
 		t.Skip("test device mounts only on linux")
 	}
 
-	hostPath := "/dev/random"
-	containerPath := "/dev/myrandom"
-	perms := "rwm"
-
-	expectedDevice := docker.Device{
-		PathOnHost:        hostPath,
-		PathInContainer:   containerPath,
-		CgroupPermissions: perms,
-	}
-	config := DockerDevice{
-		HostPath:      hostPath,
-		ContainerPath: containerPath,
+	cases := []struct {
+		Name     string
+		Input    DockerDevice
+		Expected docker.Device
+	}{
+		{
+			Name: "AllSet",
+			Input: DockerDevice{
+				HostPath:          "/dev/random",
+				ContainerPath:     "/dev/hostrandom",
+				CgroupPermissions: "rwm",
+			},
+			Expected: docker.Device{
+				PathOnHost:        "/dev/random",
+				PathInContainer:   "/dev/hostrandom",
+				CgroupPermissions: "rwm",
+			},
+		},
+		{
+			Name: "OnlyHost",
+			Input: DockerDevice{
+				HostPath: "/dev/random",
+			},
+			Expected: docker.Device{
+				PathOnHost:        "/dev/random",
+				PathInContainer:   "/dev/random",
+				CgroupPermissions: "rwm",
+			},
+		},
 	}
 
+	for i := range cases {
+		tc := cases[i]
+		t.Run(tc.Name, func(t *testing.T) {
 			task, cfg, _ := dockerTask(t)
 
-	cfg.Devices = []DockerDevice{config}
+			cfg.Devices = []DockerDevice{tc.Input}
 			require.NoError(t, task.EncodeConcreteDriverConfig(cfg))
 
 			client, driver, handle, cleanup := dockerSetup(t, task, nil)
@@ -2498,7 +2518,9 @@ func TestDockerDriver_Device_Success(t *testing.T) {
 			require.NoError(t, err)
 
 			require.NotEmpty(t, container.HostConfig.Devices, "Expected one device")
-	require.Equal(t, expectedDevice, container.HostConfig.Devices[0], "Incorrect device ")
+			require.Equal(t, tc.Expected, container.HostConfig.Devices[0], "Incorrect device ")
+		})
+	}
 }
 
 func TestDockerDriver_Entrypoint(t *testing.T) {