osdc/Striper: relax assert in assemble_result() for raw buffers

The previous commit uncovered an old bug, introduced in commit
9867804 ("Striper: Add function 'assemble_result(CephContext *cct,
char *buffer, size_t len)' in StripedReadResult.").  The buffer is
allowed to be NULL when assemble_result() is called -- it becomes
a problem only if some data was read.

Strengthen ZeroLengthRead and ZeroLengthWrite tests to cover both
a bogus pointer and a NULL pointer for buffer.

Signed-off-by: Ilya Dryomov <[email protected]>

Author: idryomov

src/osdc/Striper.cc

@@ -485,13 +485,14 @@ void Striper::StripedReadResult::assemble_result(CephContext *cct,
 
 void Striper::StripedReadResult::assemble_result(CephContext *cct, char *buffer, size_t length)
 {
-
-  ceph_assert(buffer && length == total_intended_len);
+  ceph_assert(length == total_intended_len);
 
   map<uint64_t,pair<bufferlist,uint64_t> >::reverse_iterator p = partial.rbegin();
   if (p == partial.rend())
     return;
 
+  ceph_assert(buffer);
+
   uint64_t curr = length;
   uint64_t end = p->first + p->second.second;
   while (p != partial.rend()) {

src/test/librbd/test_librbd.cc

@@ -8683,8 +8683,12 @@ TEST_F(TestLibRBD, ZeroLengthWrite)
   ASSERT_EQ(0, create_image(ioctx, name.c_str(), size, &order));
   ASSERT_EQ(0, rbd_open(ioctx, name.c_str(), &image, NULL));
 
-  char read_data[1];
+  const char data[] = "blah";
+  ASSERT_EQ(0, rbd_write(image, 0, 0, data));
+  ASSERT_EQ(0, rbd_write(image, 0, 0, (char*)0x123));
   ASSERT_EQ(0, rbd_write(image, 0, 0, NULL));
+
+  char read_data[1];
   ASSERT_EQ(1, rbd_read(image, 0, 1, read_data));
   ASSERT_EQ('\0', read_data[0]);
 
@@ -8736,6 +8740,8 @@ TEST_F(TestLibRBD, ZeroLengthRead)
 
   char read_data[1];
   ASSERT_EQ(0, rbd_read(image, 0, 0, read_data));
+  ASSERT_EQ(0, rbd_read(image, 0, 0, (char*)0x123));
+  ASSERT_EQ(0, rbd_read(image, 0, 0, NULL));
 
   ASSERT_EQ(0, rbd_close(image));