basic: rework virtualization detection API

Introduce a proper enum, and don't pass around string ids anymore. This
simplifies things quite a bit, and makes virtualization detection more
similar to architecture detection.

src/basic/virt.h

@@ -21,15 +21,51 @@
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
 ***/
 
-int detect_vm(const char **id);
-int detect_container(const char **id);
+#include <stdbool.h>
+
+#include "macro.h"
 
 enum {
         VIRTUALIZATION_NONE = 0,
-        VIRTUALIZATION_VM,
-        VIRTUALIZATION_CONTAINER,
+
+        VIRTUALIZATION_VM_FIRST,
+        VIRTUALIZATION_KVM = VIRTUALIZATION_VM_FIRST,
+        VIRTUALIZATION_QEMU,
+        VIRTUALIZATION_BOCHS,
+        VIRTUALIZATION_XEN,
+        VIRTUALIZATION_UML,
+        VIRTUALIZATION_VMWARE,
+        VIRTUALIZATION_ORACLE,
+        VIRTUALIZATION_MICROSOFT,
+        VIRTUALIZATION_ZVM,
+        VIRTUALIZATION_PARALLELS,
+        VIRTUALIZATION_VM_OTHER,
+        VIRTUALIZATION_VM_LAST = VIRTUALIZATION_VM_OTHER,
+
+        VIRTUALIZATION_CONTAINER_FIRST,
+        VIRTUALIZATION_SYSTEMD_NSPAWN = VIRTUALIZATION_CONTAINER_FIRST,
+        VIRTUALIZATION_LXC_LIBVIRT,
+        VIRTUALIZATION_LXC,
+        VIRTUALIZATION_OPENVZ,
+        VIRTUALIZATION_DOCKER,
+        VIRTUALIZATION_CONTAINER_OTHER,
+        VIRTUALIZATION_CONTAINER_LAST = VIRTUALIZATION_CONTAINER_OTHER,
+
         _VIRTUALIZATION_MAX,
         _VIRTUALIZATION_INVALID = -1
 };
 
-int detect_virtualization(const char **id);
+static inline bool VIRTUALIZATION_IS_VM(int x) {
+        return x >= VIRTUALIZATION_VM_FIRST && x <= VIRTUALIZATION_VM_LAST;
+}
+
+static inline bool VIRTUALIZATION_IS_CONTAINER(int x) {
+        return x >= VIRTUALIZATION_CONTAINER_FIRST && x <= VIRTUALIZATION_CONTAINER_LAST;
+}
+
+int detect_vm(void);
+int detect_container(void);
+int detect_virtualization(void);
+
+const char *virtualization_to_string(int v) _const_;
+int virtualization_from_string(const char *s) _pure_;