mounts: Ignore existing mounts if they cannot be honored

In case we use an hypervisor that cannot support filesystem sharing,
we copy files over to the VM rootfs through the gRPC protocol. This
is a nice workaround, but it only works with regular files, which
means no device file, no socket file, no directory, etc... can be
sent this way.

This is a limitation that we accept here, by simply ignoring those
non-regular files.

Fixes #1068

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
Signed-off-by: Eric Ernst <eric.ernst@intel.com>

virtcontainers/container.go

@@ -431,10 +431,10 @@ func (c *Container) createContainersDirs() error {
 	return nil
 }
 
-func (c *Container) shareFiles(m Mount, idx int, hostSharedDir, guestSharedDir string) (string, error) {
+func (c *Container) shareFiles(m Mount, idx int, hostSharedDir, guestSharedDir string) (string, bool, error) {
 	randBytes, err := utils.GenerateRandomBytes(8)
 	if err != nil {
-		return "", err
+		return "", false, err
 	}
 
 	filename := fmt.Sprintf("%s-%s-%s", c.id, hex.EncodeToString(randBytes), filepath.Base(m.Destination))
@@ -445,20 +445,35 @@ func (c *Container) shareFiles(m Mount, idx int, hostSharedDir, guestSharedDir s
 	caps := c.sandbox.hypervisor.capabilities()
 	if !caps.isFsSharingSupported() {
 		c.Logger().Debug("filesystem sharing is not supported, files will be copied")
+
+		fileInfo, err := os.Stat(m.Source)
+		if err != nil {
+			return "", false, err
+		}
+
+		// Ignore the mount if this is not a regular file (excludes
+		// directory, socket, device, ...) as it cannot be handled by
+		// a simple copy. But this should not be treated as an error,
+		// only as a limitation.
+		if !fileInfo.Mode().IsRegular() {
+			c.Logger().WithField("ignored-file", m.Source).Debug("Ignoring non-regular file as FS sharing not supported")
+			return "", true, nil
+		}
+
 		if err := c.sandbox.agent.copyFile(m.Source, guestDest); err != nil {
-			return "", err
+			return "", false, err
 		}
 	} else {
 		// These mounts are created in the shared dir
 		mountDest := filepath.Join(hostSharedDir, c.sandbox.id, filename)
 		if err := bindMount(c.ctx, m.Source, mountDest, false); err != nil {
-			return "", err
+			return "", false, err
 		}
 		// Save HostPath mount value into the mount list of the container.
 		c.mounts[idx].HostPath = mountDest
 	}
 
-	return guestDest, nil
+	return guestDest, false, nil
 }
 
 // mountSharedDirMounts handles bind-mounts by bindmounting to the host shared
@@ -466,8 +481,9 @@ func (c *Container) shareFiles(m Mount, idx int, hostSharedDir, guestSharedDir s
 // It also updates the container mount list with the HostPath info, and store
 // container mounts to the storage. This way, we will have the HostPath info
 // available when we will need to unmount those mounts.
-func (c *Container) mountSharedDirMounts(hostSharedDir, guestSharedDir string) ([]Mount, error) {
+func (c *Container) mountSharedDirMounts(hostSharedDir, guestSharedDir string) ([]Mount, []Mount, error) {
 	var sharedDirMounts []Mount
+	var ignoredMounts []Mount
 	for idx, m := range c.mounts {
 		if isSystemMount(m.Destination) || m.Type != "bind" {
 			continue
@@ -485,12 +501,12 @@ func (c *Container) mountSharedDirMounts(hostSharedDir, guestSharedDir string) (
 		if len(m.BlockDeviceID) > 0 {
 			// Attach this block device, all other devices passed in the config have been attached at this point
 			if err := c.sandbox.devManager.AttachDevice(m.BlockDeviceID, c.sandbox); err != nil {
-				return nil, err
+				return nil, nil, err
 			}
 
 			if err := c.sandbox.storeSandboxDevices(); err != nil {
 				//TODO: roll back?
-				return nil, err
+				return nil, nil, err
 			}
 			continue
 		}
@@ -502,9 +518,15 @@ func (c *Container) mountSharedDirMounts(hostSharedDir, guestSharedDir string) (
 			continue
 		}
 
-		guestDest, err := c.shareFiles(m, idx, hostSharedDir, guestSharedDir)
+		guestDest, ignore, err := c.shareFiles(m, idx, hostSharedDir, guestSharedDir)
 		if err != nil {
-			return nil, err
+			return nil, nil, err
+		}
+
+		// Expand the list of mounts to ignore.
+		if ignore {
+			ignoredMounts = append(ignoredMounts, Mount{Source: m.Source})
+			continue
 		}
 
 		// Check if mount is readonly, let the agent handle the readonly mount
@@ -528,10 +550,10 @@ func (c *Container) mountSharedDirMounts(hostSharedDir, guestSharedDir string) (
 	}
 
 	if err := c.storeMounts(); err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 
-	return sharedDirMounts, nil
+	return sharedDirMounts, ignoredMounts, nil
 }
 
 func (c *Container) unmountHostMounts() error {

virtcontainers/hyperstart_agent.go

@@ -549,7 +549,7 @@ func (h *hyper) startOneContainer(sandbox *Sandbox, c *Container) error {
 	//TODO : Enter mount namespace
 
 	// Handle container mounts
-	newMounts, err := c.mountSharedDirMounts(defaultSharedDir, "")
+	newMounts, _, err := c.mountSharedDirMounts(defaultSharedDir, "")
 	if err != nil {
 		bindUnmountAllRootfs(c.ctx, defaultSharedDir, sandbox)
 		return err

virtcontainers/kata_agent.go

@@ -719,6 +719,30 @@ func (k *kataAgent) replaceOCIMountSource(spec *specs.Spec, guestMounts []Mount)
 	return nil
 }
 
+func (k *kataAgent) removeIgnoredOCIMount(spec *specs.Spec, ignoredMounts []Mount) error {
+	var mounts []specs.Mount
+
+	for _, m := range spec.Mounts {
+		found := false
+		for _, ignoredMount := range ignoredMounts {
+			if ignoredMount.Source == m.Source {
+				k.Logger().WithField("removed-mount", m.Source).Debug("Removing OCI mount")
+				found = true
+				break
+			}
+		}
+
+		if !found {
+			mounts = append(mounts, m)
+		}
+	}
+
+	// Replace the OCI mounts with the updated list.
+	spec.Mounts = mounts
+
+	return nil
+}
+
 func (k *kataAgent) replaceOCIMountsForStorages(spec *specs.Spec, volumeStorages []*grpc.Storage) error {
 	ociMounts := spec.Mounts
 	var index int
@@ -981,7 +1005,7 @@ func (k *kataAgent) createContainer(sandbox *Sandbox, c *Container) (p *Process,
 	}
 
 	// Handle container mounts
-	newMounts, err := c.mountSharedDirMounts(kataHostSharedDir, kataGuestSharedDir)
+	newMounts, ignoredMounts, err := c.mountSharedDirMounts(kataHostSharedDir, kataGuestSharedDir)
 	if err != nil {
 		return nil, err
 	}
@@ -995,6 +1019,11 @@ func (k *kataAgent) createContainer(sandbox *Sandbox, c *Container) (p *Process,
 		return nil, err
 	}
 
+	// Remove all mounts that should be ignored from the spec
+	if err = k.removeIgnoredOCIMount(ociSpec, ignoredMounts); err != nil {
+		return nil, err
+	}
+
 	// Append container devices for block devices passed with --device.
 	ctrDevices = k.appendDevices(ctrDevices, c)
 
@@ -1769,6 +1798,12 @@ func (k *kataAgent) copyFile(src, dst string) error {
 		Gid:      int32(st.Gid),
 	}
 
+	// Handle the special case where the file is empty
+	if fileSize == 0 {
+		_, err = k.sendReq(cpReq)
+		return err
+	}
+
 	// Copy file by parts if it's needed
 	remainingBytes := fileSize
 	offset := int64(0)

virtcontainers/sandbox_test.go

@@ -1706,10 +1706,12 @@ func TestPreAddDevice(t *testing.T) {
 		},
 	}
 
-	mounts, err := container.mountSharedDirMounts("", "")
+	mounts, ignoreMounts, err := container.mountSharedDirMounts("", "")
 	assert.Nil(t, err)
 	assert.Equal(t, len(mounts), 0,
 		"mounts should contain nothing because it only contains a block device")
+	assert.Equal(t, len(ignoreMounts), 0,
+		"ignoreMounts should contain nothing because it only contains a block device")
 }
 
 func TestGetNetNs(t *testing.T) {