Fix POSIX backend queue fallback handling

src/plugins/posix/posix_backend.cpp

@@ -201,6 +201,11 @@ nixlPosixBackendReqH::checkXfer() {
 
 nixl_status_t
 nixlPosixBackendReqH::postXfer() {
+    if (!io_queue_) {
+        NIXL_ERROR << "POSIX I/O queue is not initialized";
+        return NIXL_ERR_BACKEND;
+    }
+
     num_confirmed_ios_ = 0;
 
     for (auto [local_it, remote_it] = std::make_pair(local.begin(), remote.begin());
@@ -240,6 +245,12 @@ nixlPosixEngine::nixlPosixEngine(const nixlBackendInitParams *init_params)
         NIXL_ERROR << "Failed to initialize POSIX backend - no supported io queue type found";
         return;
     }
+    if (!io_queue_) {
+        initErr = true;
+        NIXL_ERROR << "Failed to initialize POSIX backend - unavailable io queue type requested: "
+                   << io_queue_type_;
+        return;
+    }
     NIXL_INFO << absl::StrFormat("POSIX backend initialized using io queue type: %s",
                                  io_queue_type_);
 }
@@ -332,9 +343,13 @@ nixlPosixEngine::checkXfer(nixlBackendReqH *handle) const {
 
 nixl_status_t
 nixlPosixEngine::releaseReqH(nixlBackendReqH *handle) const {
+    if (!handle) {
+        return NIXL_SUCCESS;
+    }
+
     try {
-        auto &posix_handle = castPosixHandle(handle);
-        posix_handle.~nixlPosixBackendReqH();
+        (void)castPosixHandle(handle);
+        delete handle;
         return NIXL_SUCCESS;
     }
     catch (const nixlPosixBackendReqH::exception &e) {

test/unit/plugins/posix/meson.build

@@ -1,25 +1,37 @@
-# SPDX-FileCopyrightText: Copyright (c) 2025-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
-# SPDX-License-Identifier: Apache-2.0
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-# http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-# Using globally defined has_posix_plugin from the root meson.build
-if has_posix_plugin
-    nixl_posix_app = executable('nixl_posix_test', 'nixl_posix_test.cpp',
-                                dependencies: [nixl_dep, nixl_infra, absl_log_dep],
-                                include_directories: [nixl_inc_dirs, utils_inc_dirs],
-                                install: true)
-
-    # Register the test with the test suite
-    test('posix_plugin_test', nixl_posix_app)
-endif
+# SPDX-FileCopyrightText: Copyright (c) 2025-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Using globally defined has_posix_plugin from the root meson.build
+if has_posix_plugin
+    posix_test_compile_defs = []
+    if has_linux_aio
+        posix_test_compile_defs += ['-DHAVE_LINUXAIO']
+    endif
+    if has_io_uring
+        posix_test_compile_defs += ['-DHAVE_LIBURING']
+    endif
+    if has_posix_aio
+        posix_test_compile_defs += ['-DHAVE_POSIXAIO']
+    endif
+
+    nixl_posix_app = executable('nixl_posix_test', 'nixl_posix_test.cpp',
+                                dependencies: [nixl_dep, nixl_infra, absl_log_dep],
+                                include_directories: [nixl_inc_dirs, utils_inc_dirs],
+                                cpp_args: posix_test_compile_defs,
+                                install: true)
+
+    # Register the test with the test suite
+    test('posix_plugin_test', nixl_posix_app)
+endif

test/unit/plugins/posix/nixl_posix_test.cpp

@@ -60,6 +60,40 @@ namespace {
         return std::string((line_width - str.length()) / 2, ' ') + str;
     }
 
+    bool
+    has_supported_test_queue(bool use_uring) {
+        if (use_uring) {
+#ifdef HAVE_LIBURING
+            return true;
+#else
+            return false;
+#endif
+        }
+
+#if defined(HAVE_LINUXAIO) || defined(HAVE_LIBURING)
+        return true;
+#else
+        return false;
+#endif
+    }
+
+    void
+    print_unsupported_test_queue_error(bool use_uring) {
+        std::cerr << "Unsupported POSIX test queue configuration: ";
+        if (use_uring) {
+            std::cerr << "io_uring was requested, but this build does not include liburing support."
+                      << std::endl;
+        } else {
+            std::cerr << "this build does not include Linux AIO or io_uring support." << std::endl;
+#ifdef HAVE_POSIXAIO
+            std::cerr
+                << "POSIX AIO may be available in the plugin, but this test requires Linux AIO "
+                   "or io_uring."
+                << std::endl;
+#endif
+        }
+    }
+
     constexpr char default_test_files_dir_path[] = "tmp/testfiles";
 
     // Custom deleter for posix_memalign allocated memory
@@ -217,8 +251,8 @@ read_write_test (int num_transfers,
         params["use_uring"] = "true";
         params["use_aio"] = "false";
     } else {
-        // Explicitly request AIO
-        params["use_aio"] = "true";
+        // Use the backend's compiled default queue. Startup validation rejects POSIX AIO-only
+        // builds.
         params["use_uring"] = "false";
     }
 
@@ -234,7 +268,7 @@ read_write_test (int num_transfers,
     std::cout << absl::StrFormat ("- Total data: %.2f GB\n",
                                   (float (transfer_size) * num_transfers) / gb_size);
     std::cout << absl::StrFormat ("- Directory: %s\n", test_files_dir_path_abs_path);
-    std::cout << absl::StrFormat ("- Backend: %s\n", use_uring ? "io_uring" : "AIO");
+    std::cout << absl::StrFormat("- Backend: %s\n", use_uring ? "io_uring" : "default");
     std::cout << absl::StrFormat ("- Direct I/O: %s\n", use_direct_io ? "enabled" : "disabled");
     std::cout << std::endl;
     std::cout << line_str << std::endl;
@@ -246,9 +280,12 @@ read_write_test (int num_transfers,
         std::cerr << std::endl << line_str << std::endl;
         std::cerr << center_str("ERROR: Backend Creation Failed") << std::endl;
         std::cerr << line_str << std::endl;
-        std::cerr << "Error creating POSIX backend: " << nixlEnumStrings::statusStr(status) << std::endl;
+        std::cerr << "Error creating POSIX backend: " << nixlEnumStrings::statusStr(status)
+                  << std::endl;
         if (use_uring) {
-            std::cerr << "io_uring was requested but may not be available. Try running without -U flag to use AIO instead." << std::endl;
+            std::cerr << "io_uring was requested but may not be available. Try running without -U "
+                         "flag to use the default queue."
+                      << std::endl;
         }
         std::cerr << std::endl << line_str << std::endl;
         return 1;
@@ -498,8 +535,8 @@ test_posix_repost (std::string test_files_dir_path_abs_path, bool use_uring) {
         params["use_uring"] = "true";
         params["use_aio"] = "false";
     } else {
-        // Explicitly request AIO
-        params["use_aio"] = "true";
+        // Use the backend's compiled default queue. Startup validation rejects POSIX AIO-only
+        // builds.
         params["use_uring"] = "false";
     }
 
@@ -779,17 +816,22 @@ main (int argc, char *argv[]) {
                        "  -s transfer_size      Size of each transfer in bytes (default: %zu)",
                        default_transfer_size)
                 << std::endl;
-            std::cout << absl::StrFormat ("  -d test_files_dir_path Directory for test files, "
-                                          "strongly recommended to use nvme device (default: %s)",
-                                          default_test_files_dir_path)
+            std::cout << absl::StrFormat("  -d test_files_dir_path Directory for test files, "
+                                         "strongly recommended to use nvme device (default: %s)",
+                                         default_test_files_dir_path)
                       << std::endl;
             std::cout << absl::StrFormat ("  -D Use O_DIRECT for file I/O") << std::endl;
-            std::cout << absl::StrFormat ("  -U Use io_uring backend instead of AIO") << std::endl;
+            std::cout << absl::StrFormat("  -U Explicitly use the io_uring backend") << std::endl;
             std::cout << absl::StrFormat ("  -h Show this help message") << std::endl;
             return (opt == 'h') ? 0 : 1;
         }
     }
 
+    if (!has_supported_test_queue(use_uring)) {
+        print_unsupported_test_queue_error(use_uring);
+        return 1;
+    }
+
     // Convert directory path to absolute path using std::filesystem
     std::filesystem::path test_files_dir_path_obj (test_files_dir_path);
     std::filesystem::create_directories (test_files_dir_path_obj);