From dabc61110a5773262614fc77d3653674aac421f7 Mon Sep 17 00:00:00 2001
From: Haomai Wang <haomaiwang@gmail.com>
Date: Thu, 9 Jul 2015 13:32:03 +0800
Subject: [PATCH 1/2] UnittestBuffer: Add bufferlist zero test case

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
(cherry picked from commit 577acf665948e531e50d36f5780ea19351a5bf65)
---
 src/test/bufferlist.cc | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/test/bufferlist.cc b/src/test/bufferlist.cc
index 787ce7e4297741..fdc7014332f530 100644
--- a/src/test/bufferlist.cc
+++ b/src/test/bufferlist.cc
@@ -2221,6 +2221,17 @@ TEST(BufferList, zero) {
     bl.zero((unsigned)3, (unsigned)3);
     EXPECT_EQ(0, ::memcmp("ABC\0\0\0GHIKLM", bl.c_str(), 9));
   }
+  {
+    bufferlist bl;
+    bufferptr ptr1(4);
+    bufferptr ptr2(4);
+    memset(ptr1.c_str(), 'a', 4);
+    memset(ptr2.c_str(), 'b', 4);
+    bl.append(ptr1);
+    bl.append(ptr2);
+    bl.zero((unsigned)2, (unsigned)4);
+    EXPECT_EQ(0, ::memcmp("aa\0\0\0\0bb", bl.c_str(), 8));
+  }
 }
 
 TEST(BufferList, EmptyAppend) {

From 0fde3a2465e156ebf9a5cdc6adc45d66d6d647fc Mon Sep 17 00:00:00 2001
From: Haomai Wang <haomaiwang@gmail.com>
Date: Thu, 9 Jul 2015 13:42:42 +0800
Subject: [PATCH 2/2] buffer: Fix bufferlist::zero bug with special case

Fixes: #12252
Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
(cherry picked from commit 43f583d160ccaf879eaf0f3020e77860cf8d1df0)
---
 src/common/buffer.cc | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/src/common/buffer.cc b/src/common/buffer.cc
index 88656e836bd29f..2a91ec34bf84d3 100644
--- a/src/common/buffer.cc
+++ b/src/common/buffer.cc
@@ -1165,12 +1165,23 @@ static simple_spinlock_t buffer_debug_lock = SIMPLE_SPINLOCK_INITIALIZER;
 	 it != _buffers.end();
 	 ++it) {
       if (p + it->length() > o) {
-	if (p >= o && p+it->length() <= o+l)
-	  it->zero();                         // all
-	else if (p >= o) 
-	  it->zero(0, o+l-p);                 // head
-	else
-	  it->zero(o-p, it->length()-(o-p));  // tail
+        if (p >= o && p+it->length() <= o+l) {
+          // 'o'------------- l -----------|
+          //      'p'-- it->length() --|
+	  it->zero();
+        } else if (p >= o) {
+          // 'o'------------- l -----------|
+          //    'p'------- it->length() -------|
+	  it->zero(0, o+l-p);
+        } else if (p + it->length() <= o+l) {
+          //     'o'------------- l -----------|
+          // 'p'------- it->length() -------|
+	  it->zero(o-p, it->length()-(o-p));
+        } else {
+          //       'o'----------- l -----------|
+          // 'p'---------- it->length() ----------|
+          it->zero(o-p, l);
+        }
       }
       p += it->length();
       if (o+l <= p)