From: Ilya Dryomov <idryomov@gmail.com>
Date: Fri, 10 Nov 2023 10:14:42 +0000 (+0100)
Subject: librbd: resurrect "exists" assert in simple_diff_cb()
X-Git-Tag: v17.2.8~615^2~5
X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=9f1b4008de0705f187dc1d2a09f80cd1f4937a30;p=ceph.git

librbd: resurrect "exists" assert in simple_diff_cb()

This effectively reverts commit 3ccc3bb4bd35 ("librbd: diff_iterate
needs to handle holes in parent images") which just dropped the assert
instead of addressing the root cause of reported crashes.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
(cherry picked from commit bcb107afcd2b0e34b1eefa4767691c5d8d109a82)
---

diff --git a/src/librbd/api/DiffIterate.cc b/src/librbd/api/DiffIterate.cc
index d8760692e1cb..6c86f56b3eea 100644
--- a/src/librbd/api/DiffIterate.cc
+++ b/src/librbd/api/DiffIterate.cc
@@ -150,11 +150,12 @@ private:
 };
 
 int simple_diff_cb(uint64_t off, size_t len, int exists, void *arg) {
-  // it's possible for a discard to create a hole in the parent image -- ignore
-  if (exists) {
-    interval_set<uint64_t> *diff = static_cast<interval_set<uint64_t> *>(arg);
-    diff->insert(off, len);
-  }
+  // This reads the existing extents in a parent from the beginning
+  // of time.  Since images are thin-provisioned, the extents will
+  // always represent data, not holes.
+  ceph_assert(exists);
+  auto diff = static_cast<interval_set<uint64_t>*>(arg);
+  diff->insert(off, len);
   return 0;
 }