[thin_dump] --format custom=<shared lib>

Allow people to use their own emitters held in a shared library.

Put a trivial emitter in contrib/ as an example.

thin-provisioning/shared_library_emitter.cc

@@ -0,0 +1,29 @@
+#include "thin-provisioning/shared_library_emitter.h"
+
+#include <dlfcn.h>
+#include <stdexcept>
+
+using namespace std;
+using namespace thin_provisioning;
+
+//----------------------------------------------------------------
+
+emitter::ptr
+thin_provisioning::create_custom_emitter(string const &shared_lib, ostream &out)
+{
+	emitter::ptr (*create_fn)(ostream &out);
+	void *handle = dlopen(shared_lib.c_str(), RTLD_LAZY);
+	if (!handle)
+		throw runtime_error(dlerror());
+
+	dlerror();    // Clear any existing error
+	create_fn = reinterpret_cast<emitter::ptr (*)(ostream &)>(dlsym(handle, "create_emitter"));
+
+	char *error = dlerror();
+	if (error)
+		throw runtime_error(error);
+
+	return create_fn(out);
+}
+
+//----------------------------------------------------------------

thin-provisioning/shared_library_emitter.h

@@ -0,0 +1,14 @@
+#ifndef THIN_PROVISIONING_SHARED_LIBRARY_EMITTER_H
+#define THIN_PROVISIONING_SHARED_LIBRARY_EMITTER_H
+
+#include "thin-provisioning/emitter.h"
+
+//----------------------------------------------------------------
+
+namespace thin_provisioning {
+	emitter::ptr create_custom_emitter(std::string const &shared_lib, std::ostream &out);
+}
+
+//----------------------------------------------------------------
+
+#endif

thin-provisioning/thin_dump.cc

@@ -21,13 +21,14 @@
 #include <getopt.h>
 #include <libgen.h>
 
-#include "human_readable_format.h"
-#include "metadata_dumper.h"
-#include "metadata.h"
-#include "xml_format.h"
-#include "version.h"
-#include "thin-provisioning/commands.h"
 #include "persistent-data/file_utils.h"
+#include "thin-provisioning/commands.h"
+#include "thin-provisioning/human_readable_format.h"
+#include "thin-provisioning/metadata.h"
+#include "thin-provisioning/metadata_dumper.h"
+#include "thin-provisioning/shared_library_emitter.h"
+#include "thin-provisioning/xml_format.h"
+#include "version.h"
 
 using namespace boost;
 using namespace persistent_data;
@@ -56,6 +57,10 @@ namespace {
 		return md;
 	}
 
+	bool begins_with(string const &str, string const &prefix) {
+		return str.substr(0, prefix.length()) == prefix;
+	}
+
 	emitter::ptr create_emitter(string const &format, ostream &out) {
 		emitter::ptr e;
 
@@ -65,9 +70,13 @@ namespace {
 		else if (format == "human_readable")
 			e = create_human_readable_emitter(out);
 
+		else if (begins_with(format, "custom="))
+			e = create_custom_emitter(format.substr(7), out);
+
 		else {
-			cerr << "unknown format '" << format << "'" << endl;
-			exit(1);
+			ostringstream msg;
+			msg << "unknown format '" << format << "'";
+			throw runtime_error(msg.str());
 		}
 
 		return e;