rbd: add ListMetadata implementing rbd_metadata_list

The function is named ListMetadata but returns a map of all
the metadata assigned to the rbd image. It is named ListMetadata to
match the C librbd api call.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

rbd/metadata.go

@@ -8,6 +8,7 @@ import "C"
 import (
 	"unsafe"
 
+	"github.com/ceph/go-ceph/internal/cutil"
 	"github.com/ceph/go-ceph/internal/retry"
 )
 
@@ -84,3 +85,65 @@ func (image *Image) RemoveMetadata(key string) error {
 
 	return nil
 }
+
+// ListMetadata returns a map containing all metadata assigned to the RBD image.
+//
+// Implements:
+//  int rbd_metadata_list(rbd_image_t image, const char *start, uint64_t max,
+//                        char *keys, size_t *key_len, char *values, size_t *vals_len);
+func (image *Image) ListMetadata() (map[string]string, error) {
+	if err := image.validate(imageIsOpen); err != nil {
+		return nil, err
+	}
+
+	var (
+		err      error
+		keysbuf  []byte
+		keysSize C.size_t
+		valsbuf  []byte
+		valsSize C.size_t
+	)
+	retry.WithSizes(4096, 262144, func(size int) retry.Hint {
+		keysbuf = make([]byte, size)
+		keysSize = C.size_t(size)
+		valsbuf = make([]byte, size)
+		valsSize = C.size_t(size)
+		// the rbd_metadata_list function can use a start point and a limit.
+		// we do not use it and prefer our retry helper and just allocating
+		// buffers large enough to take all the keys and values
+		ret := C.rbd_metadata_list(
+			image.image,
+			(*C.char)(unsafe.Pointer(&empty[0])), // always start at the beginning (no paging)
+			0,                                    // fetch all key-value pairs
+			(*C.char)(unsafe.Pointer(&keysbuf[0])),
+			&keysSize,
+			(*C.char)(unsafe.Pointer(&valsbuf[0])),
+			&valsSize)
+
+		err = getError(ret)
+		nextSize := valsSize
+		if keysSize > nextSize {
+			nextSize = keysSize
+		}
+		return retry.Size(int(nextSize)).If(err == errRange)
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	m := map[string]string{}
+	keys := cutil.SplitBuffer(keysbuf[:keysSize])
+	vals := cutil.SplitBuffer(valsbuf[:valsSize])
+	if len(keys) != len(vals) {
+		// this should not happen (famous last words)
+		return nil, errRange
+	}
+	for i := range keys {
+		m[keys[i]] = vals[i]
+	}
+	return m, nil
+}
+
+// rather than allocate memory every time that ListMetadata is called,
+// define a static byte slice to stand in for the C "empty string"
+var empty = []byte{0}

rbd/metadata_test.go

@@ -39,6 +39,9 @@ func TestImageMetadata(t *testing.T) {
 	value, err = image.GetMetadata(metadataKey)
 	assert.Equal(t, "", value)
 	assert.Equal(t, err, ErrImageNotOpen)
+	// check ListMetadata for unopened image
+	_, err = image.ListMetadata()
+	assert.Equal(t, err, ErrImageNotOpen)
 
 	image, err = OpenImage(ioctx, name, NoSnapshot)
 	assert.NoError(t, err)
@@ -50,6 +53,13 @@ func TestImageMetadata(t *testing.T) {
 	value, err = image.GetMetadata(metadataKey)
 	assert.NoError(t, err)
 	assert.Equal(t, metadataValue, value)
+	// List metadata
+	mm, err := image.ListMetadata()
+	assert.NoError(t, err)
+	assert.Len(t, mm, 1)
+	if assert.Contains(t, mm, metadataKey) {
+		assert.Equal(t, mm[metadataKey], metadataValue)
+	}
 	// Remove the metadata key
 	err = image.RemoveMetadata(metadataKey)
 	assert.NoError(t, err)
@@ -58,6 +68,27 @@ func TestImageMetadata(t *testing.T) {
 	assert.Equal(t, "", value)
 	assert.Error(t, err)
 
+	// Set some additional metadata values
+	m1 := map[string]string{
+		metadataKey:  metadataValue,
+		"k2":         "himalayas",
+		"matterhorn": "alps",
+		"aconcagua":  "andes",
+	}
+	for k, v := range m1 {
+		err = image.SetMetadata(k, v)
+		assert.NoError(t, err)
+	}
+	// Get the metadata value
+	value, err = image.GetMetadata(metadataKey)
+	assert.NoError(t, err)
+	assert.Equal(t, metadataValue, value)
+	// List metadata
+	mm, err = image.ListMetadata()
+	assert.NoError(t, err)
+	assert.Len(t, mm, 4)
+	assert.Equal(t, m1, mm)
+
 	err = image.Close()
 	assert.NoError(t, err)
 	err = image.Remove()