From: Patrick Donnelly <pdonnell@redhat.com>
Date: Sat, 8 Jun 2024 19:00:27 +0000 (-0400)
Subject: mds: add warning about encoding new fields
X-Git-Tag: testing/wip-jcollin-testing-20240701.061036-squid~5^2~5
X-Git-Url: http://git.apps.os.sepia.ceph.com/?a=commitdiff_plain;h=1a709427535bb2eab5d0083285fecedd64fcf21b;p=ceph-ci.git

mds: add warning about encoding new fields

It's never a good idea to put new fields in the middle of other encoded values
unless you're willing to break all backwards-compatibility.

Signed-off-by: Patrick Donnelly <pdonnell@redhat.com>
(cherry picked from commit d27b1156ae7d38902c76ffa48b6999a779ec5da9)
---

diff --git a/src/mds/CDentry.cc b/src/mds/CDentry.cc
index 8694dfc72a2..9caa7ca92eb 100644
--- a/src/mds/CDentry.cc
+++ b/src/mds/CDentry.cc
@@ -568,6 +568,7 @@ void CDentry::encode_remote(inodeno_t& ino, unsigned char d_type,
 
   // marker, name, ino
   ENCODE_START(2, 1, bl);
+  // WARNING: always put new fields at the end of bl
   encode(ino, bl);
   encode(d_type, bl);
   encode(alternate_name, bl);
diff --git a/src/mds/CDir.cc b/src/mds/CDir.cc
index 3828fe04d7b..ce805ea7ff5 100644
--- a/src/mds/CDir.cc
+++ b/src/mds/CDir.cc
@@ -2500,6 +2500,7 @@ void CDir::_omap_commit_ops(int r, int op_prio, int64_t metapool, version_t vers
       bl.append('i');         // inode
 
       ENCODE_START(2, 1, bl);
+      // WARNING: always put new fields at the end of bl
       encode(item.alternate_name, bl);
       _encode_primary_inode_base(item, dfts, bl);
       ENCODE_FINISH(bl);