Improve LinuxVersion

Also add error handling to uname() call.

emper/lib/LinuxVersion.cpp

@@ -2,11 +2,12 @@
 // Copyright © 2021 Florian Fischer
 #include "lib/LinuxVersion.hpp"
 
+#include <sys/utsname.h>
+
 #include <cerrno>
 #include <cstdlib>
 
 #include "Common.hpp"
-#include "Debug.hpp"
 
 static auto checked_strtol(const std::string& s) -> long {
 	static const int DECIMAL = 10;
@@ -23,15 +24,30 @@ static auto checked_strtol(const std::string& s) -> long {
 		DIE_MSG("strtol found no digits in " << s);
 	}
 
-	if (endptr != startptr + s.size()) {
-		LOGW("LinuxVersion compare ignored non digits in " << s)
-	}
+	// TODO: We could report remaining bytes of the string by returning
+	// std::string(endptr) together with 'res' (potentially using
+	// std::pair). Not sure if we even need to check if "endptr !=
+	// startptr + s.size()", or if we could always cosntruct
+	// std::string(endptr), potentially constructing the empty string.
 
 	return res;
 }
 
 namespace emper::lib {
 
+std::string LinuxVersion::globalVersion;
+
+LinuxVersion::LinuxVersion() {
+	if (globalVersion.empty()) {
+		struct utsname buf;
+		if (uname(&buf)) {
+			DIE_MSG_ERRNO("Failed to invoke uname()");
+		}
+		globalVersion = std::string(buf.release);
+	}
+	version = globalVersion;
+}
+
 // Returns 1 if s is smaller, -1 if this is smaller, 0 if equal
 auto LinuxVersion::compare(const std::string& s) -> int {
 	size_t dot_pos, dot_pos2;