rbd: add feature check to see if GroupSnapGetInfo is available

The go-ceph rbd package provides the GroupSnapGetInfo function, but it
may return ErrUnsupported when called. Returning this error after
advertising the support for VolumeGroupSnapshot seems ugly.

In order to advertise support for VolumeGroupSnapshot,
SupportsGroupSnapGetInfo() can be used, which detects the required C
function of librbd.

Signed-off-by: Niels de Vos <ndevos@ibm.com>

internal/rbd/features/dlsym.go

@@ -0,0 +1,48 @@
+/*
+Copyright 2024 The Ceph-CSI Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package features
+
+/*
+#cgo LDFLAGS: -ldl
+#include <stdlib.h>
+#include <dlfcn.h>
+*/
+import "C"
+
+import (
+	"fmt"
+	"unsafe"
+)
+
+// dlsym checks if the given symbol is provided by the currently loaded
+// libraries. If the symbol is available, no error is returned.
+func dlsym(symbol string) error {
+	c_symbol := C.CString(symbol)
+	//nolint:nlreturn // linter complains about missing empty line!?
+	defer C.free(unsafe.Pointer(c_symbol))
+
+	// clear dlerror before looking up the symbol
+	C.dlerror()
+	_ = C.dlsym(nil, c_symbol)
+	e := C.dlerror()
+	err := C.GoString(e)
+	if err != "" {
+		return fmt.Errorf("dlsym: %s", err)
+	}
+
+	return nil
+}

internal/rbd/features/features.go

@@ -0,0 +1,58 @@
+/*
+Copyright 2024 The Ceph-CSI Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package features
+
+/*
+#cgo LDFLAGS: -lrbd
+#include <rbd/librbd.h>
+*/
+import "C"
+
+import (
+	"strings"
+	"sync"
+)
+
+var (
+	groupGetSnapInfoOnce      sync.Once
+	errGroupGetSnapInfo       error
+	groupGetSnapInfoSupported = false
+)
+
+// SupportsGroupSnapGetInfo detects if librbd has the rbd_group_snap_get_info
+// function.
+func SupportsGroupSnapGetInfo() (bool, error) {
+	groupGetSnapInfoOnce.Do(func() {
+		// make sure librbd.so.x is loaded, might not (yet) be the case
+		// if no rbd functions are called
+		var opts C.rbd_image_options_t
+		//nolint:gocritic // ignore result of rbd_image_options functions
+		C.rbd_image_options_create(&opts)
+		C.rbd_image_options_destroy(opts)
+
+		// check for rbd_group_snap_get_info() in loaded libs/symbols
+		errGroupGetSnapInfo = dlsym("rbd_group_snap_get_info")
+
+		if errGroupGetSnapInfo == nil {
+			groupGetSnapInfoSupported = true
+		} else if strings.Contains(errGroupGetSnapInfo.Error(), "undefined symbol") {
+			errGroupGetSnapInfo = nil
+		}
+	})
+
+	return groupGetSnapInfoSupported, errGroupGetSnapInfo
+}

internal/rbd/features/features_test.go

@@ -0,0 +1,32 @@
+/*
+Copyright 2024 ceph-csi authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package features
+
+import (
+	"testing"
+)
+
+func TestSupportsGroupSnapGetInfo(t *testing.T) {
+	t.Parallel()
+
+	supported, err := SupportsGroupSnapGetInfo()
+	if err != nil {
+		t.Errorf("failed to check support for GroupSnapGetInfo: %v", err)
+	}
+
+	t.Logf("GroupSnapGetInfo supported: %t", supported)
+}