Expose compression algorithms via MOSDBoot. Implements 22420.

Modifies Compressor to expose a set of strings (already hardcoded)
that are accessible elsewhere.

Adds metadata to MOSDBoost containing a list of compression algorithms
made available via the plugin interface.

Fixes: http://tracker.ceph.com/issues/22420

Signed-off-by: Jesse Williamson <jwilliamson@suse.de>

src/compressor/Compressor.cc

@@ -23,40 +23,21 @@
 #include "common/dout.h"
 
 const char * Compressor::get_comp_alg_name(int a) {
-  switch (a) {
-  case COMP_ALG_NONE: return "none";
-  case COMP_ALG_SNAPPY: return "snappy";
-  case COMP_ALG_ZLIB: return "zlib";
-  case COMP_ALG_ZSTD: return "zstd";
-#ifdef HAVE_LZ4
-  case COMP_ALG_LZ4: return "lz4";
-#endif
-#ifdef HAVE_BROTLI
-  case COMP_ALG_BROTLI: return "brotli";
-#endif
-  default: return "???";
-  }
+
+  if(a < 0 || a >= COMP_ALG_LAST) 
+   return "???"; // It would be nice to revise this...
+
+  return compression_algorithm_names[a];
 }
 
 boost::optional<Compressor::CompressionAlgorithm> Compressor::get_comp_alg_type(const std::string &s) {
-  if (s == "snappy")
-    return COMP_ALG_SNAPPY;
-  if (s == "zlib")
-    return COMP_ALG_ZLIB;
-  if (s == "zstd")
-    return COMP_ALG_ZSTD;
-#ifdef HAVE_LZ4
-  if (s == "lz4")
-    return COMP_ALG_LZ4;
-#endif
-#ifdef HAVE_BROTLI
-  if (s == "brotli")
-    return COMP_ALG_BROTLI;
-#endif
-  if (s == "" || s == "none")
-    return COMP_ALG_NONE;
 
-  return boost::optional<CompressionAlgorithm>();
+  for (int pos = 0; pos != sizeof(compression_algorithm_names); ++pos) {
+	if(compression_algorithm_names[pos] == s)
+	 return { static_cast<CompressionAlgorithm>(pos) };
+  }
+
+  return {};
 }
 
 const char *Compressor::get_comp_mode_name(int m) {

src/compressor/Compressor.h

@@ -42,6 +42,17 @@ class Compressor {
 #endif
     COMP_ALG_LAST	//the last value for range checks
   };
+
+  // The names in this array must match the above values:
+  constexpr static char const* const compression_algorithm_names[] = {
+	"none",
+	"snappy",
+	"zlib",
+	"zstd",
+	"lz4",
+	"brotli",
+  };
+
   // compression options
   enum CompressionMode {
     COMP_NONE,                  ///< compress never

src/osd/OSD.cc

@@ -12,14 +12,19 @@
  * Foundation.  See file COPYING.
  *
  */
+
 #include "acconfig.h"
-#include <unistd.h>
+
+#include <cerrno>
+#include <cctype>
 #include <fstream>
 #include <iostream>
-#include <errno.h>
+#include <algorithm>
+
+#include <unistd.h>
+
 #include <sys/stat.h>
 #include <signal.h>
-#include <ctype.h>
 #include <boost/scoped_ptr.hpp>
 
 #ifdef HAVE_SYS_PARAM_H
@@ -47,6 +52,7 @@
 #include "common/io_priority.h"
 #include "common/pick_address.h"
 #include "common/SubProcess.h"
+#include "common/PluginRegistry.h"
 
 #include "os/ObjectStore.h"
 #ifdef HAVE_LIBFUSE
@@ -55,7 +61,6 @@
 
 #include "PrimaryLogPG.h"
 
-
 #include "msg/Messenger.h"
 #include "msg/Message.h"
 
@@ -5536,6 +5541,28 @@ void OSD::_send_boot()
   set_state(STATE_BOOTING);
 }
 
+std::string OSD::_collect_compression_algorithms()
+{
+  const auto& compression_algorithm_names = Compressor::compression_algorithm_names;
+  const auto& plugin_registry = cct->get_plugin_registry()->plugins;
+
+  if(0 == plugin_registry.size())
+   return std::string();
+
+  ostringstream os;
+  for_each(begin(compression_algorithm_names), end(compression_algorithm_names),
+  		  [&os, &plugin_registry](const auto& algorithm_name) {
+  		   if (plugin_registry.end() != plugin_registry.find(algorithm_name))
+  			os << algorithm_name << ',';
+  		  });
+
+  string s(os.str());
+
+  s.erase(s.find_last_of(','));
+
+  return s;
+}
+
 void OSD::_collect_metadata(map<string,string> *pm)
 {
   // config info
@@ -5544,6 +5571,7 @@ void OSD::_collect_metadata(map<string,string> *pm)
     // not applicable for bluestore
     (*pm)["osd_journal"] = journal_path;
   }
+
   (*pm)["front_addr"] = stringify(client_messenger->get_myaddr());
   (*pm)["back_addr"] = stringify(cluster_messenger->get_myaddr());
   (*pm)["hb_front_addr"] = stringify(hb_front_server_messenger->get_myaddr());
@@ -5566,6 +5594,10 @@ void OSD::_collect_metadata(map<string,string> *pm)
   set<string> devnames;
   store->get_devices(&devnames);
   (*pm)["devices"] = stringify(devnames);
+
+  // Other information:
+  (*pm)["supported_compression_algorithms"] = _collect_compression_algorithms();
+
   dout(10) << __func__ << " " << *pm << dendl;
 }
 

src/osd/OSD.h

@@ -1927,6 +1927,7 @@ class OSD : public Dispatcher,
   void _preboot(epoch_t oldest, epoch_t newest);
   void _send_boot();
   void _collect_metadata(map<string,string> *pmeta);
+	void _collect_compression_algorithms(map<string,string>& pmeta);
 
   void start_waiting_for_healthy();
   bool _is_healthy();