gadget,tests: add support for volume-assignment syntax in gadget.yaml…

…, this will allow the gadget yaml to specify specific disk mappings when either installing or updating the system

gadget/device_darwin.go

@@ -28,3 +28,7 @@ var errNotImplemented = errors.New("not implemented")
 func FindDeviceForStructure(vs *VolumeStructure) (string, error) {
 	return "", errNotImplemented
 }
+
+func ResolveDeviceForStructure(device string) (string, error) {
+	return "", errNotImplemented
+}

gadget/device_linux.go

@@ -31,38 +31,10 @@ import (
 
 var evalSymlinks = filepath.EvalSymlinks
 
-// FindDeviceForStructure attempts to find an existing block device matching
-// given volume structure, by inspecting its name and, optionally, the
-// filesystem label. Assumes that the host's udev has set up device symlinks
-// correctly.
-func FindDeviceForStructure(vs *VolumeStructure) (string, error) {
-	var candidates []string
-
-	if vs.Name != "" {
-		byPartlabel := filepath.Join(dirs.GlobalRootDir, "/dev/disk/by-partlabel/", disks.BlkIDEncodeLabel(vs.Name))
-		candidates = append(candidates, byPartlabel)
-	}
-	if vs.HasFilesystem() {
-		fsLabel := vs.Label
-		if fsLabel == "" && vs.Name != "" {
-			// when image is built and the structure has no
-			// filesystem label, the structure name will be used by
-			// default as the label
-			fsLabel = vs.Name
-		}
-		if fsLabel != "" {
-			candLabel, err := disks.CandidateByLabelPath(fsLabel)
-			if err == nil {
-				candidates = append(candidates, candLabel)
-			} else {
-				logger.Debugf("no by-label candidate for %q: %v", fsLabel, err)
-			}
-		}
-	}
-
+func resolveMaybeDiskPaths(diskPaths []string) (string, error) {
 	var found string
 	var match string
-	for _, candidate := range candidates {
+	for _, candidate := range diskPaths {
 		if !osutil.FileExists(candidate) {
 			continue
 		}
@@ -91,3 +63,48 @@ func FindDeviceForStructure(vs *VolumeStructure) (string, error) {
 
 	return found, nil
 }
+
+func discoverDeviceDiskCandidatesForStructure(vs *VolumeStructure) (candidates []string) {
+	if vs.Name != "" {
+		byPartlabel := filepath.Join(dirs.GlobalRootDir, "/dev/disk/by-partlabel/", disks.BlkIDEncodeLabel(vs.Name))
+		candidates = append(candidates, byPartlabel)
+	}
+	if vs.HasFilesystem() {
+		fsLabel := vs.Label
+		if fsLabel == "" && vs.Name != "" {
+			// when image is built and the structure has no
+			// filesystem label, the structure name will be used by
+			// default as the label
+			fsLabel = vs.Name
+		}
+		if fsLabel != "" {
+			candLabel, err := disks.CandidateByLabelPath(fsLabel)
+			if err == nil {
+				candidates = append(candidates, candLabel)
+			} else {
+				logger.Debugf("no by-label candidate for %q: %v", fsLabel, err)
+			}
+		}
+	}
+	return candidates
+}
+
+// FindDeviceForStructure attempts to find an existing block device matching
+// given volume structure, by inspecting its name and, optionally, the
+// filesystem label. Assumes that the host's udev has set up device symlinks
+// correctly.
+func FindDeviceForStructure(vs *VolumeStructure) (string, error) {
+	candidates := discoverDeviceDiskCandidatesForStructure(vs)
+	return resolveMaybeDiskPaths(candidates)
+}
+
+// ResolveDeviceForStructure is an opposite to FindDeviceForStructure that allows
+// supplying a device path to resolve a specific disk. Calling this without a filter
+// (i.e device == ""), will return an error
+// The device path must be a path into /dev/disk/**
+func ResolveDeviceForStructure(device string) (string, error) {
+	if device == "" {
+		return "", fmt.Errorf("internal error: device must be supplied")
+	}
+	return resolveMaybeDiskPaths([]string{device})
+}

gadget/device_test.go

@@ -21,6 +21,7 @@ package gadget_test
 
 import (
 	"errors"
+	"fmt"
 	"os"
 	"path/filepath"
 
@@ -244,3 +245,47 @@ func (d *deviceSuite) TestDeviceFindBadEvalSymlinks(c *C) {
 	c.Check(err, ErrorMatches, `cannot read device link: failed`)
 	c.Check(found, Equals, "")
 }
+
+func (d *deviceSuite) TestResolveDeviceEmptyBase(c *C) {
+	found, err := gadget.ResolveDeviceForStructure("")
+	c.Check(err, ErrorMatches, `internal error: device must be supplied`)
+	c.Check(found, Equals, "")
+}
+
+func (d *deviceSuite) TestResolveDeviceBaseDeviceNotSymlink(c *C) {
+	// only the by-filesystem-label symlink
+	fakedevice := filepath.Join(d.dir, "/dev/fakedevice")
+	c.Assert(os.Symlink(fakedevice, filepath.Join(d.dir, "/dev/disk/by-label/foo")), IsNil)
+	c.Assert(os.Symlink("../../fakedevice", filepath.Join(d.dir, "/dev/disk/by-partlabel/relative")), IsNil)
+
+	found, err := gadget.ResolveDeviceForStructure(fakedevice)
+	c.Check(err, ErrorMatches, fmt.Sprintf(`candidate %s/dev/fakedevice is not a symlink`, d.dir))
+	c.Check(found, Equals, "")
+}
+
+func (d *deviceSuite) TestResolveDeviceMatchesBaseDeviceAsSymlink(c *C) {
+	// only the by-filesystem-label symlink
+	fakedevice := filepath.Join(d.dir, "/dev/fakedevice")
+	c.Assert(os.Symlink(fakedevice, filepath.Join(d.dir, "/dev/disk/by-label/foo")), IsNil)
+	c.Assert(os.Symlink("../../fakedevice", filepath.Join(d.dir, "/dev/disk/by-partlabel/relative")), IsNil)
+
+	found, err := gadget.ResolveDeviceForStructure(filepath.Join(d.dir, "/dev/disk/by-label/foo"))
+	c.Check(err, IsNil)
+	c.Check(found, Equals, filepath.Join(d.dir, "/dev/fakedevice"))
+}
+
+func (d *deviceSuite) TestResolveDeviceNoMatchesBaseDevice(c *C) {
+	// fake two devices
+	// only the by-filesystem-label symlink
+	fakedevice0 := filepath.Join(d.dir, "/dev/fakedevice")
+	fakedevice1 := filepath.Join(d.dir, "/dev/fakedevice1")
+
+	c.Assert(os.Symlink(fakedevice0, filepath.Join(d.dir, "/dev/disk/by-label/foo")), IsNil)
+	c.Assert(os.Symlink(fakedevice1, filepath.Join(d.dir, "/dev/disk/by-label/bar")), IsNil)
+
+	c.Assert(os.Symlink("../../fakedevice", filepath.Join(d.dir, "/dev/disk/by-partlabel/relative")), IsNil)
+
+	found, err := gadget.ResolveDeviceForStructure(fakedevice1)
+	c.Check(err, ErrorMatches, `device not found`)
+	c.Check(found, Equals, "")
+}

gadget/export_test.go

@@ -19,7 +19,10 @@
 
 package gadget
 
-import "github.com/snapcore/snapd/gadget/quantity"
+import (
+	"github.com/snapcore/snapd/gadget/quantity"
+	"github.com/snapcore/snapd/testutil"
+)
 
 type (
 	MountedFilesystemUpdater = mountedFilesystemUpdater
@@ -97,3 +100,9 @@ func NewInvalidOffsetError(offset, lowerBound, upperBound quantity.Offset) *Inva
 func (v *Volume) YamlIdxToStructureIdx(yamlIdx int) (int, error) {
 	return v.yamlIdxToStructureIdx(yamlIdx)
 }
+
+func MockFindVolumesMatchingDeviceAssignment(f func(gi *Info) (map[string]DeviceVolume, error)) (restore func()) {
+	r := testutil.Backup(&FindVolumesMatchingDeviceAssignment)
+	FindVolumesMatchingDeviceAssignment = f
+	return r
+}