From bf90e768792ddad2126f1777c90264fd842f6dd7 Mon Sep 17 00:00:00 2001
From: Venky Shankar <vshankar@redhat.com>
Date: Mon, 19 Oct 2020 05:02:21 -0400
Subject: [PATCH] mds: include metadata in SnapInfo structure

This is a free-flowing key/value metadata attached to a snapshot
and persisted in `SnapInfo` structure. The idea is to allow
custom metadata to be persisted when creating a snapshot.

Initial users for this feature would be cephfs-mirror daemon. The
idea is to persist the primary filesystems snapshot ID on snapshot
creation in secondary filesystem. This allows identification of
snapshot renames and recreates.

Signed-off-by: Venky Shankar <vshankar@redhat.com>
---
 src/mds/snap.cc | 14 ++++++++++++--
 src/mds/snap.h  |  2 ++
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/src/mds/snap.cc b/src/mds/snap.cc
index 3da4cda2b4b..f988ca51367 100644
--- a/src/mds/snap.cc
+++ b/src/mds/snap.cc
@@ -24,21 +24,25 @@
 
 void SnapInfo::encode(bufferlist& bl) const
 {
-  ENCODE_START(2, 2, bl);
+  ENCODE_START(3, 2, bl);
   encode(snapid, bl);
   encode(ino, bl);
   encode(stamp, bl);
   encode(name, bl);
+  encode(metadata, bl);
   ENCODE_FINISH(bl);
 }
 
 void SnapInfo::decode(bufferlist::const_iterator& bl)
 {
-  DECODE_START_LEGACY_COMPAT_LEN(2, 2, 2, bl);
+  DECODE_START_LEGACY_COMPAT_LEN(3, 2, 2, bl);
   decode(snapid, bl);
   decode(ino, bl);
   decode(stamp, bl);
   decode(name, bl);
+  if (struct_v >= 3) {
+    decode(metadata, bl);
+  }
   DECODE_FINISH(bl);
 }
 
@@ -48,6 +52,11 @@ void SnapInfo::dump(Formatter *f) const
   f->dump_unsigned("ino", ino);
   f->dump_stream("stamp") << stamp;
   f->dump_string("name", name);
+  f->open_object_section("metadata");
+  for (auto &[key, value] : metadata) {
+    f->dump_string(key, value);
+  }
+  f->close_section();
 }
 
 void SnapInfo::generate_test_instances(std::list<SnapInfo*>& ls)
@@ -58,6 +67,7 @@ void SnapInfo::generate_test_instances(std::list<SnapInfo*>& ls)
   ls.back()->ino = 2;
   ls.back()->stamp = utime_t(3, 4);
   ls.back()->name = "foo";
+  ls.back()->metadata = {{"foo", "bar"}};
 }
 
 ostream& operator<<(ostream& out, const SnapInfo &sn)
diff --git a/src/mds/snap.h b/src/mds/snap.h
index 346f787e37c..f8b5b701af4 100644
--- a/src/mds/snap.h
+++ b/src/mds/snap.h
@@ -15,6 +15,7 @@
 #ifndef CEPH_MDS_SNAP_H
 #define CEPH_MDS_SNAP_H
 
+#include <map>
 #include <string_view>
 
 #include "mdstypes.h"
@@ -39,6 +40,7 @@ struct SnapInfo {
   std::string name;
 
   mutable std::string long_name; ///< cached _$ino_$name
+  std::map<std::string,std::string> metadata;
 };
 WRITE_CLASS_ENCODER(SnapInfo)
 
-- 
2.39.5