core/reactor: don't check AIO block count when they are not needed

Only check for sufficient number of AIO blocks when the linux-aio
reactor backend was selected. Otherwise these blocks are not used
anyway, but the check might result in failure because it think there
aren't sufficient number of AIO blocks available.

Fixes: scylladb#2453

Closes scylladb#2454

src/core/reactor.cc

@@ -4415,6 +4415,12 @@ void smp::configure(const smp_options& smp_opts, const reactor_options& reactor_
         memory::set_dump_memory_diagnostics_on_alloc_failure_kind(reactor_opts.dump_memory_diagnostics_on_alloc_failure_kind.get_value());
     }
 
+    auto max_networking_aio_io_control_blocks = reactor_opts.max_networking_io_control_blocks.get_value();
+    // Prevent errors about insufficient AIO blocks, when they are not needed by the reactor backend.
+    if (reactor_opts.reactor_backend.get_selected_candidate().name() == "linux-aio") {
+        max_networking_aio_io_control_blocks = adjust_max_networking_aio_io_control_blocks(max_networking_aio_io_control_blocks);
+    }
+
     reactor_config reactor_cfg = {
         .task_quota = std::chrono::duration_cast<sched_clock::duration>(reactor_opts.task_quota_ms.get_value() * 1ms),
         .max_poll_time = [&reactor_opts] () -> std::chrono::nanoseconds {
@@ -4428,7 +4434,7 @@ void smp::configure(const smp_options& smp_opts, const reactor_options& reactor_
         }(),
         .handle_sigint = !reactor_opts.no_handle_interrupt,
         .auto_handle_sigint_sigterm = reactor_opts._auto_handle_sigint_sigterm,
-        .max_networking_aio_io_control_blocks = adjust_max_networking_aio_io_control_blocks(reactor_opts.max_networking_io_control_blocks.get_value()),
+        .max_networking_aio_io_control_blocks = max_networking_aio_io_control_blocks,
         .force_io_getevents_syscall = reactor_opts.force_aio_syscalls.get_value(),
         .kernel_page_cache = reactor_opts.kernel_page_cache.get_value(),
         .have_aio_fsync = reactor_opts.aio_fsync.get_value(),