@@ -5,6 +5,13 @@ package daemon

 import (

 	"strings"

 	"testing"

+

+	containertypes "github.com/docker/docker/api/types/container"

+	"github.com/docker/docker/container"

+	"github.com/docker/docker/oci"

+	"github.com/docker/docker/pkg/idtools"

+

+	"github.com/stretchr/testify/assert"

 )

 const mountsFixture = `142 78 0:38 / / rw,relatime - aufs none rw,si=573b861da0b3a05b,dio

@@ -102,3 +109,51 @@ func TestNotCleanupMounts(t *testing.T) {

 		t.Fatal("Expected not to clean up /dev/shm")

 	}

 }

+

+// TestTmpfsDevShmSizeOverride checks that user-specified /dev/tmpfs mount

+// size is not overriden by the default shmsize (that should only be used

+// for default /dev/shm (as in "shareable" and "private" ipc modes).

+// https://github.com/moby/moby/issues/35271

+func TestTmpfsDevShmSizeOverride(t *testing.T) {

+	size := "777m"

+	mnt := "/dev/shm"

+

+	d := Daemon{

+		idMappings: &idtools.IDMappings{},

+	}

+	c := &container.Container{

+		HostConfig: &containertypes.HostConfig{

+			ShmSize: 48 * 1024, // size we should NOT end up with

+		},

+	}

+	ms := []container.Mount{

+		{

+			Source:      "tmpfs",

+			Destination: mnt,

+			Data:        "size=" + size,

+		},

+	}

+

+	// convert ms to spec

+	spec := oci.DefaultSpec()

+	err := setMounts(&d, &spec, c, ms)

+	assert.NoError(t, err)

+

+	// Check the resulting spec for the correct size

+	found := false

+	for _, m := range spec.Mounts {

+		if m.Destination == mnt {

+			for _, o := range m.Options {

+				if !strings.HasPrefix(o, "size=") {

+					continue

+				}

+				t.Logf("%+v\n", m.Options)

+				assert.Equal(t, "size="+size, o)

+				found = true

+			}

+		}

+	}

+	if !found {

+		t.Fatal("/dev/shm not found in spec, or size option missing")

+	}

+}