cephfs: add SelectFileystem implementing ceph_select_filesystem

Add SelectFileystem implementing ceph_select_filesystem which can be
used to select a cephfs by name, prior to calling mount, when the ceph
cluster hosts more than one cephfs file system.

Fixes: #262
Fixes: #818
Original-Version-By: "Arvid E. Picciani" <arvid@kraud.cloud>
Original-PR-URL: https://github.com/ceph/go-ceph/pull/819
Signed-off-by: John Mulligan <jmulligan@redhat.com>

cephfs/select_fs.go

@@ -0,0 +1,33 @@
+//go:build ceph_preview
+// +build ceph_preview
+
+package cephfs
+
+/*
+#cgo LDFLAGS: -lcephfs
+#cgo CPPFLAGS: -D_FILE_OFFSET_BITS=64
+#define _GNU_SOURCE
+#include <stdlib.h>
+#include <cephfs/libcephfs.h>
+*/
+import "C"
+
+import (
+	"unsafe"
+)
+
+// SelectFilesystem selects a file system to be mounted. If the ceph cluster
+// supports more than one cephfs this optional function selects which one to
+// use. Can only be called prior to calling Mount. The name of the file system
+// is not validated by this call - if the supplied file system name is not
+// valid then only the subsequent mount call will fail.
+//
+// Implements:
+//  int ceph_select_filesystem(struct ceph_mount_info *cmount, const char *fs_name);
+func (mount *MountInfo) SelectFilesystem(name string) error {
+	cName := C.CString(name)
+	defer C.free(unsafe.Pointer(cName))
+
+	ret := C.ceph_select_filesystem(mount.mount, cName)
+	return getError(ret)
+}