From 730b9c5afb03bd054adbac03a00b8946bf2e814f Mon Sep 17 00:00:00 2001
From: Ilya Dryomov <idryomov@gmail.com>
Date: Wed, 27 Dec 2023 16:18:50 +0100
Subject: [PATCH] include/intarith: introduce round_down_to()

Same as with round_up_to(), d isn't required to be a power of two.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
(cherry picked from commit 94bf3a5d74cfd61e0bd881ca2863fe2205f27767)
---
 src/include/intarith.h        | 4 ++++
 src/librbd/api/DiffIterate.cc | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/include/intarith.h b/src/include/intarith.h
index d3eaff15635f7..f43981a6530f4 100644
--- a/src/include/intarith.h
+++ b/src/include/intarith.h
@@ -22,6 +22,10 @@ constexpr inline std::make_unsigned_t<std::common_type_t<T, U>> div_round_up(T n
   return (n + d - 1) / d;
 }
 
+template<typename T, typename U>
+constexpr inline std::make_unsigned_t<std::common_type_t<T, U>> round_down_to(T n, U d) {
+  return n - n % d;
+}
 
 template<typename T, typename U>
 constexpr inline std::make_unsigned_t<std::common_type_t<T, U>> round_up_to(T n, U d) {
diff --git a/src/librbd/api/DiffIterate.cc b/src/librbd/api/DiffIterate.cc
index 6c86f56b3eea3..d2003101f28b2 100644
--- a/src/librbd/api/DiffIterate.cc
+++ b/src/librbd/api/DiffIterate.cc
@@ -291,7 +291,7 @@ int DiffIterate<I>::execute() {
   uint64_t left = m_length;
 
   while (left > 0) {
-    uint64_t period_off = off - (off % period);
+    uint64_t period_off = round_down_to(off, period);
     uint64_t read_len = std::min(period_off + period - off, left);
 
     if (fast_diff_enabled) {
-- 
2.39.5