aio: Add io_method=posix_aio for FreeBSD.

Add support for native kernel-based AIO on FreeBSD, using its vectored
I/O extension and kqueue for completion events.  (Earlier versions
worked on about 5 other OSes, but not very well.)

Author: macdice

.cirrus.tasks.yml

@@ -140,6 +140,7 @@ task:
 # - Specifies configuration options that test reading/writing/copying of node trees
 # - Specifies debug_parallel_query=regress, to catch related issues during CI
 # - Also runs tests against a running postgres instance, see test_running_script
+# - Uses io_method=posix_aio
 task:
   name: FreeBSD - Meson
 
@@ -162,6 +163,7 @@ task:
       -c debug_write_read_parse_plan_trees=on
       -c debug_raw_expression_coverage_test=on
       -c debug_parallel_query=regress
+      -c io_method=posix_aio
     PG_TEST_PG_UPGRADE_MODE: --link
 
   <<: *freebsd_task_template

meson.build

@@ -977,6 +977,21 @@ endif
 
 
 
+###############################################################
+# Library: posix_aio (FreeBSD only)
+###############################################################
+
+posix_aioopt = get_option('posix_aio')
+posix_aio = not_found_dep
+if cc.has_function('aio_readv',
+    args: test_c_args, prefix: '#include <aio.h>',
+    include_directories: postgres_inc)
+  cdata.set('USE_POSIX_AIO', 1)
+  posix_aio = declare_dependency()
+endif
+
+
+
 ###############################################################
 # Library: libxml
 ###############################################################

meson_options.txt

@@ -139,6 +139,9 @@ option('plpython', type: 'feature', value: 'auto',
 option('pltcl', type: 'feature', value: 'auto',
   description: 'Build with Tcl support (PL/Tcl)')
 
+option('posix_aio', type: 'feature', value: 'auto',
+  description: 'Build POSIX AIO support (FreeBSD only)')
+
 option('tcl_version', type: 'string', value: 'tcl',
   description: 'Tcl version')
 

src/backend/storage/aio/aio.c

@@ -69,6 +69,9 @@ const struct config_enum_entry io_method_options[] = {
 	{"worker", IOMETHOD_WORKER, false},
 #ifdef IOMETHOD_IO_URING_ENABLED
 	{"io_uring", IOMETHOD_IO_URING, false},
+#endif
+#ifdef IOMETHOD_POSIX_AIO_ENABLED
+	{"posix_aio", IOMETHOD_POSIX_AIO, false},
 #endif
 	{NULL, 0, false}
 };
@@ -90,6 +93,9 @@ static const IoMethodOps *const pgaio_method_ops_table[] = {
 #ifdef IOMETHOD_IO_URING_ENABLED
 	[IOMETHOD_IO_URING] = &pgaio_uring_ops,
 #endif
+#ifdef IOMETHOD_POSIX_AIO_ENABLED
+	[IOMETHOD_POSIX_AIO] = &pgaio_posix_aio_ops,
+#endif
 };
 
 /* callbacks for the configured io_method, set by assign_io_method */

src/backend/storage/aio/meson.build

@@ -9,6 +9,7 @@ backend_sources += files(
   'aio_io.c',
   'aio_target.c',
   'method_io_uring.c',
+  'method_posix_aio.c',
   'method_sync.c',
   'method_worker.c',
   'read_stream.c',