feat: block-device mounts

This PR adds capability to mount virtual and passthrough disks
as block devices inside containers.

We add a new "blockdev://" prefix to OCI `Mount.ContainerPath`,
which indicates that the source should be mounted as a blcok
device.

A new `BlockDev` field has been added to `mountConfig` used by
`mountManager`, which indicates that the SCSI attachment should
be mounted as a block device.

The GCS has also been updated to handle `BlockDev`. Instead of
mounting the filesystem, GCS creates a symlink to the block device
corresponding to the SCSI attachment. The symlink path is set
by shim as a source of bind mount in OCI container spec. GCS
resolves the symlink and adds the corresponding device cgroup.
Without the cgroup, the container won't be able to work with the
block device.

We chose a symlink approach instead of bind mounting the device
directly, because the shim doesn't know the path at which the
device will appear inside UVM. For this to work, we either need
to encode the SCSI controller/LUN in the OCI mount's HostPath or
update the communication protocol between the shim and GCS, where
GCS would either return the device path, or add capability for
the shim to query for it.

Below are some CRI container config examples for physical and
virtual disks:

Passthrough physical disk:
```json
{
    ...
    "mounts": [
        {
            "host_path": "\\\\.\\PHYSICALDRIVE1",
            "container_path": "blockdev:///my/block/mount",
            "readonly": false
        }
    ]
    ...
}
```

Virtual VHD disk:
```json
{
    ...
    "mounts": [
        {
            "host_path": "C:\\path\\to\\my\\disk.vhdx",
            "container_path": "blockdev:///my/block/mount",
            "readonly": false
        }
    ]
    ...
}
```

Signed-off-by: Maksim An <maksiman@microsoft.com>

internal/guest/runtime/hcsv2/uvm.go

@@ -1005,6 +1005,7 @@ func modifyMappedVirtualDisk(
 				VerityInfo:       verityInfo,
 				EnsureFilesystem: mvd.EnsureFilesystem,
 				Filesystem:       mvd.Filesystem,
+				BlockDev:         mvd.BlockDev,
 			}
 			return scsi.Mount(mountCtx, mvd.Controller, mvd.Lun, mvd.Partition, mvd.MountPath,
 				mvd.ReadOnly, mvd.Options, config)
@@ -1022,6 +1023,7 @@ func modifyMappedVirtualDisk(
 				VerityInfo:       verityInfo,
 				EnsureFilesystem: mvd.EnsureFilesystem,
 				Filesystem:       mvd.Filesystem,
+				BlockDev:         mvd.BlockDev,
 			}
 			if err := scsi.Unmount(ctx, mvd.Controller, mvd.Lun, mvd.Partition,
 				mvd.MountPath, config); err != nil {

internal/guest/runtime/hcsv2/workload_container.go

@@ -5,10 +5,12 @@ package hcsv2
 
 import (
 	"context"
+	"fmt"
 	"os"
 	"path/filepath"
 	"strings"
 
+	"github.com/opencontainers/runc/libcontainer/devices"
 	oci "github.com/opencontainers/runtime-spec/specs-go"
 	"github.com/pkg/errors"
 	"go.opencensus.io/trace"
@@ -84,6 +86,44 @@ func updateHugePageMounts(sbid string, spec *oci.Spec) error {
 	return nil
 }
 
+func updateBlockDeviceMounts(spec *oci.Spec) error {
+	for i, m := range spec.Mounts {
+		if !strings.HasPrefix(m.Destination, guestpath.BlockDevMountPrefix) {
+			continue
+		}
+		permissions := "rwm"
+		for _, o := range m.Options {
+			if o == "ro" {
+				permissions = "r"
+			}
+		}
+
+		// For block device mounts, the source will be a symlink. Resolve it first
+		// before passing to `DeviceFromPath`, which expects a real device path.
+		rPath, err := os.Readlink(m.Source)
+		if err != nil {
+			return fmt.Errorf("failed to readlink %s: %w", m.Source, err)
+		}
+
+		sourceDevice, err := devices.DeviceFromPath(rPath, permissions)
+		if err != nil {
+			return fmt.Errorf("failed to get device from path: %w", err)
+		}
+
+		deviceCgroup := oci.LinuxDeviceCgroup{
+			Allow:  true,
+			Type:   string(sourceDevice.Type),
+			Major:  &sourceDevice.Major,
+			Minor:  &sourceDevice.Minor,
+			Access: string(sourceDevice.Permissions),
+		}
+
+		spec.Linux.Resources.Devices = append(spec.Linux.Resources.Devices, deviceCgroup)
+		spec.Mounts[i].Destination = strings.TrimPrefix(m.Destination, guestpath.BlockDevMountPrefix)
+	}
+	return nil
+}
+
 func specHasGPUDevice(spec *oci.Spec) bool {
 	for _, d := range spec.Windows.Devices {
 		if d.IDType == "gpu" {
@@ -115,6 +155,10 @@ func setupWorkloadContainerSpec(ctx context.Context, sbid, id string, spec *oci.
 		return errors.Wrapf(err, "failed to update hugepages mounts for container %v in sandbox %v", id, sbid)
 	}
 
+	if err = updateBlockDeviceMounts(spec); err != nil {
+		return fmt.Errorf("failed to update block device mounts for container %v in sandbox %v: %w", id, sbid, err)
+	}
+
 	// Add default mounts for container networking (e.g. /etc/hostname, /etc/hosts),
 	// if spec didn't override them explicitly.
 	networkingMounts := specInternal.GenerateWorkloadContainerNetworkMounts(sbid, spec)

internal/guest/storage/scsi/scsi.go

@@ -112,6 +112,7 @@ type Config struct {
 	VerityInfo       *guestresource.DeviceVerityInfo
 	EnsureFilesystem bool
 	Filesystem       string
+	BlockDev         bool
 }
 
 // Mount creates a mount from the SCSI device on `controller` index `lun` to
@@ -163,6 +164,22 @@ func Mount(
 		}
 	}
 
+	// create and symlink block device mount target
+	if config.BlockDev {
+		parent := filepath.Dir(target)
+		log.G(ctx).WithField("parent", parent).Debug("creating parent directory for block device mount")
+		if err := osMkdirAll(parent, 0700); err != nil {
+			return err
+		}
+		defer func() {
+			if err != nil {
+				_ = os.Remove(target)
+			}
+		}()
+		log.G(ctx).Debug("creating symlink for block device mount")
+		return os.Symlink(source, target)
+	}
+
 	if err := osMkdirAll(target, 0700); err != nil {
 		return err
 	}
@@ -280,6 +297,15 @@ func Unmount(
 		trace.Int64Attribute("partition", int64(partition)),
 		trace.StringAttribute("target", target))
 
+	// skip unmount logic for block devices, since they are just symlinks
+	if config.BlockDev {
+		log.G(ctx).Debug("removing symlink for block device mount")
+		if err := os.Remove(target); err != nil {
+			return fmt.Errorf("failed to remove symlink: %w", err)
+		}
+		return nil
+	}
+
 	// unmount target
 	if err := storageUnmountPath(ctx, target, true); err != nil {
 		return errors.Wrapf(err, "unmount failed: %s", target)

internal/guestpath/paths.go

@@ -13,6 +13,9 @@ const (
 	// HugePagesMountPrefix is mount prefix used in container spec to mark a
 	// huge-pages mount
 	HugePagesMountPrefix = "hugepages://"
+	// BlockDevMountPrefix is mount prefix used in container spec to mark a
+	// block-device mount.
+	BlockDevMountPrefix = "blockdev://"
 	// PipePrefix is the mount prefix used in container spec to mark a named pipe
 	PipePrefix = `\\.\pipe`
 	// LCOWMountPathPrefixFmt is the path format in the LCOW UVM where

internal/hcsoci/resources_lcow.go

@@ -83,22 +83,27 @@ func allocateLinuxResources(ctx context.Context, coi *createOptionsInternal, r *
 			}
 
 			l := log.G(ctx).WithField("mount", fmt.Sprintf("%+v", mount))
+
+			isBlockDev := strings.HasPrefix(mount.Destination, guestpath.BlockDevMountPrefix)
 			if mount.Type == MountTypePhysicalDisk {
 				l.Debug("hcsshim::allocateLinuxResources Hot-adding SCSI physical disk for OCI mount")
 				scsiMount, err := coi.HostingSystem.SCSIManager.AddPhysicalDisk(
 					ctx,
 					hostPath,
 					readOnly,
 					coi.HostingSystem.ID(),
-					&scsi.MountConfig{Options: mount.Options},
+					&scsi.MountConfig{Options: mount.Options, BlockDev: isBlockDev},
 				)
 				if err != nil {
 					return errors.Wrapf(err, "adding SCSI physical disk mount %+v", mount)
 				}
-
 				uvmPathForFile = scsiMount.GuestPath()
 				r.Add(scsiMount)
-				coi.Spec.Mounts[i].Type = "none"
+				mt := "none"
+				if isBlockDev {
+					mt = "bind"
+				}
+				coi.Spec.Mounts[i].Type = mt
 			} else if mount.Type == MountTypeVirtualDisk {
 				l.Debug("hcsshim::allocateLinuxResources Hot-adding SCSI virtual disk for OCI mount")
 
@@ -109,15 +114,19 @@ func allocateLinuxResources(ctx context.Context, coi *createOptionsInternal, r *
 					hostPath,
 					readOnly,
 					coi.HostingSystem.ID(),
-					&scsi.MountConfig{Options: mount.Options},
+					&scsi.MountConfig{Options: mount.Options, BlockDev: isBlockDev},
 				)
 				if err != nil {
 					return errors.Wrapf(err, "adding SCSI virtual disk mount %+v", mount)
 				}
 
 				uvmPathForFile = scsiMount.GuestPath()
 				r.Add(scsiMount)
-				coi.Spec.Mounts[i].Type = "none"
+				mt := "none"
+				if isBlockDev {
+					mt = "bind"
+				}
+				coi.Spec.Mounts[i].Type = mt
 			} else if strings.HasPrefix(mount.Source, guestpath.SandboxMountPrefix) {
 				// Mounts that map to a path in UVM are specified with 'sandbox://' prefix.
 				// example: sandbox:///a/dirInUvm destination:/b/dirInContainer

internal/protocol/guestresource/resources.go

@@ -85,6 +85,7 @@ type LCOWMappedVirtualDisk struct {
 	ReadOnly   bool     `json:"ReadOnly,omitempty"`
 	Encrypted  bool     `json:"Encrypted,omitempty"`
 	Options    []string `json:"Options,omitempty"`
+	BlockDev   bool     `json:"BlockDev,omitempty"`
 	// Deprecated: verity info is read by the guest
 	VerityInfo       *DeviceVerityInfo `json:"VerityInfo,omitempty"`
 	EnsureFilesystem bool              `json:"EnsureFilesystem,omitempty"`

internal/uvm/scsi/backend.go

@@ -196,6 +196,7 @@ func mountRequest(controller, lun uint, path string, config *mountConfig, osType
 			Options:          config.options,
 			EnsureFilesystem: config.ensureFilesystem,
 			Filesystem:       config.filesystem,
+			BlockDev:         config.blockDev,
 		}
 	default:
 		return guestrequest.ModificationRequest{}, fmt.Errorf("unsupported os type: %s", osType)
@@ -221,6 +222,7 @@ func unmountRequest(controller, lun uint, path string, config *mountConfig, osTy
 			Lun:        uint8(lun),
 			Partition:  config.partition,
 			Controller: uint8(controller),
+			BlockDev:   config.blockDev,
 		}
 	default:
 		return guestrequest.ModificationRequest{}, fmt.Errorf("unsupported os type: %s", osType)

internal/uvm/scsi/manager.go

@@ -83,6 +83,9 @@ type MountConfig struct {
 	// mounted as.
 	// This is only supported for LCOW.
 	Filesystem string
+	// BlockDev indicates if the device should be mounted as a block device.
+	// This is only supported for LCOW.
+	BlockDev bool
 }
 
 // Mount represents a SCSI device that has been attached to a VM, and potentially
@@ -157,6 +160,7 @@ func (m *Manager) AddVirtualDisk(
 			options:          mc.Options,
 			ensureFilesystem: mc.EnsureFilesystem,
 			filesystem:       mc.Filesystem,
+			blockDev:         mc.BlockDev,
 		}
 	}
 	return m.add(ctx,
@@ -202,6 +206,7 @@ func (m *Manager) AddPhysicalDisk(
 			options:          mc.Options,
 			ensureFilesystem: mc.EnsureFilesystem,
 			filesystem:       mc.Filesystem,
+			blockDev:         mc.BlockDev,
 		}
 	}
 	return m.add(ctx,

internal/uvm/scsi/mount.go

@@ -41,6 +41,7 @@ type mountConfig struct {
 	partition        uint64
 	readOnly         bool
 	encrypted        bool
+	blockDev         bool
 	options          []string
 	ensureFilesystem bool
 	filesystem       string