cloud_storage: Make partition reader span ...

... multiple manifests. If the reader starts in one spillover manifest
it should be able to proceed to the next if needed.

(cherry picked from commit 2ba2f33)

src/v/cloud_storage/remote_partition.cc

@@ -625,6 +625,41 @@ class partition_record_batch_reader_impl final
               = co_await _partition->materialized().get_segment_reader_units();
 
             auto maybe_manifest = _view_cursor->manifest();
+            if (
+              maybe_manifest.has_value()
+              && _next_segment_base_offset == model::offset{}
+              && _view_cursor->get_status()
+                   == async_manifest_view_cursor_status::
+                     materialized_spillover) {
+                // End of the manifest is reached, but the cursor is pointing at
+                // the spillover manifest. We need to reset the cursor to the
+                // next manifest and try to find the next segment there.
+                vlog(
+                  _ctxlog.debug,
+                  "maybe_reset_reader, end of the manifest is reached, "
+                  "resetting cursor to the next manifest");
+                auto stop = co_await _view_cursor->next_iter();
+                if (stop == ss::stop_iteration::yes) {
+                    vlog(_ctxlog.debug, "maybe_reset_reader, last manifest");
+                    co_return false;
+                }
+                try {
+                    _next_segment_base_offset
+                      = co_await _view_cursor->with_manifest(
+                        [&](const partition_manifest& m) {
+                            return m.get_start_offset().value_or(
+                              model::offset{});
+                        });
+                } catch (...) {
+                    vlog(
+                      _ctxlog.debug,
+                      "maybe_reset_reader, failed to get next manifest: {}",
+                      std::current_exception());
+                    co_return false;
+                }
+                // NOTE: maybe_manifest is invalidated at this point
+                maybe_manifest = _view_cursor->manifest();
+            }
             if (
               maybe_manifest.has_value()
               && _next_segment_base_offset != model::offset{}) {