aio: Basic subsystem initialization

This commit just does the minimal wiring up of the AIO subsystem, added in the
next commit, to the rest of the system. The next commit contains more details
about motivation and architecture.

This commit is kept separate to make it easier to review, separating the
changes across the tree, from the implementation of the new subsystem.

We discussed squashing this commit with the main commit before merging AIO,
but there has been a mild preference for keeping it separate.

Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Reviewed-by: Noah Misch <noah@leadboat.com>
Discussion: https://postgr.es/m/uvrtrknj4kdytuboidbhwclo4gxhswwcpgadptsjvjqcluzmah%40brqs62irg4dt

24 files changed, 356 insertions, 0 deletions

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 3d62c8bd274..7ec18bb7627 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -2638,6 +2638,57 @@ include_dir 'conf.d'
         </para>
        </listitem>
       </varlistentry>
+
+      <varlistentry id="guc-io-max-concurrency" xreflabel="io_max_concurrency">
+       <term><varname>io_max_concurrency</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>io_max_concurrency</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Controls the maximum number of I/O operations that one process can
+         execute simultaneously.
+        </para>
+        <para>
+         The default setting of <literal>-1</literal> selects a number based
+         on <xref linkend="guc-shared-buffers"/> and the maximum number of
+         processes (<xref linkend="guc-max-connections"/>, <xref
+         linkend="guc-autovacuum-worker-slots"/>, <xref
+         linkend="guc-max-worker-processes"/> and <xref
+         linkend="guc-max-wal-senders"/>), but not more than
+         <literal>64</literal>.
+        </para>
+        <para>
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry id="guc-io-method" xreflabel="io_method">
+       <term><varname>io_method</varname> (<type>enum</type>)
+       <indexterm>
+        <primary><varname>io_method</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Selects the method for executing asynchronous I/O.
+         Possible values are:
+         <itemizedlist>
+          <listitem>
+           <para>
+            <literal>sync</literal> (execute asynchronous-eligible I/O synchronously)
+           </para>
+          </listitem>
+         </itemizedlist>
+        </para>
+        <para>
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
      </variablelist>
     </sect2>
 
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 1b4f21a88d3..b885513f765 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -51,6 +51,7 @@
 #include "replication/origin.h"
 #include "replication/snapbuild.h"
 #include "replication/syncrep.h"
+#include "storage/aio_subsys.h"
 #include "storage/condition_variable.h"
 #include "storage/fd.h"
 #include "storage/lmgr.h"
@@ -2411,6 +2412,8 @@ CommitTransaction(void)
 						 RESOURCE_RELEASE_BEFORE_LOCKS,
 						 true, true);
 
+	AtEOXact_Aio(true);
+
 	/* Check we've released all buffer pins */
 	AtEOXact_Buffers(true);
 
@@ -2716,6 +2719,8 @@ PrepareTransaction(void)
 						 RESOURCE_RELEASE_BEFORE_LOCKS,
 						 true, true);
 
+	AtEOXact_Aio(true);
+
 	/* Check we've released all buffer pins */
 	AtEOXact_Buffers(true);
 
@@ -2830,6 +2835,8 @@ AbortTransaction(void)
 	pgstat_report_wait_end();
 	pgstat_progress_end_command();
 
+	pgaio_error_cleanup();
+
 	/* Clean up buffer content locks, too */
 	UnlockBuffers();
 
@@ -2960,6 +2967,7 @@ AbortTransaction(void)
 		ResourceOwnerRelease(TopTransactionResourceOwner,
 							 RESOURCE_RELEASE_BEFORE_LOCKS,
 							 false, true);
+		AtEOXact_Aio(false);
 		AtEOXact_Buffers(false);
 		AtEOXact_RelationCache(false);
 		AtEOXact_TypeCache();
@@ -5232,6 +5240,9 @@ AbortSubTransaction(void)
 
 	pgstat_report_wait_end();
 	pgstat_progress_end_command();
+
+	pgaio_error_cleanup();
+
 	UnlockBuffers();
 
 	/* Reset WAL record construction state */
@@ -5326,6 +5337,7 @@ AbortSubTransaction(void)
 							 RESOURCE_RELEASE_BEFORE_LOCKS,
 							 false, false);
 
+		AtEOXact_Aio(false);
 		AtEOSubXact_RelationCache(false, s->subTransactionId,
 								  s->parent->subTransactionId);
 		AtEOSubXact_TypeCache();
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 71c34027c88..2513a8ef8a6 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -88,6 +88,7 @@
 #include "postmaster/autovacuum.h"
 #include "postmaster/interrupt.h"
 #include "postmaster/postmaster.h"
+#include "storage/aio_subsys.h"
 #include "storage/bufmgr.h"
 #include "storage/ipc.h"
 #include "storage/latch.h"
@@ -465,6 +466,7 @@ AutoVacLauncherMain(const void *startup_data, size_t startup_data_len)
 		 */
 		LWLockReleaseAll();
 		pgstat_report_wait_end();
+		pgaio_error_cleanup();
 		UnlockBuffers();
 		/* this is probably dead code, but let's be safe: */
 		if (AuxProcessResourceOwner)
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index a688cc5d2a1..72f5acceec7 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -38,6 +38,7 @@
 #include "postmaster/auxprocess.h"
 #include "postmaster/bgwriter.h"
 #include "postmaster/interrupt.h"
+#include "storage/aio_subsys.h"
 #include "storage/buf_internals.h"
 #include "storage/bufmgr.h"
 #include "storage/condition_variable.h"
@@ -168,6 +169,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
 		 */
 		LWLockReleaseAll();
 		ConditionVariableCancelSleep();
+		pgaio_error_cleanup();
 		UnlockBuffers();
 		ReleaseAuxProcessResources(false);
 		AtEOXact_Buffers(false);
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index 0e228d143a0..fda91ffd1ce 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -49,6 +49,7 @@
 #include "postmaster/bgwriter.h"
 #include "postmaster/interrupt.h"
 #include "replication/syncrep.h"
+#include "storage/aio_subsys.h"
 #include "storage/bufmgr.h"
 #include "storage/condition_variable.h"
 #include "storage/fd.h"
@@ -276,6 +277,7 @@ CheckpointerMain(const void *startup_data, size_t startup_data_len)
 		LWLockReleaseAll();
 		ConditionVariableCancelSleep();
 		pgstat_report_wait_end();
+		pgaio_error_cleanup();
 		UnlockBuffers();
 		ReleaseAuxProcessResources(false);
 		AtEOXact_Buffers(false);
diff --git a/src/backend/postmaster/pgarch.c b/src/backend/postmaster/pgarch.c
index dbe4e1d426b..7e622ae4bd2 100644
--- a/src/backend/postmaster/pgarch.c
+++ b/src/backend/postmaster/pgarch.c
@@ -40,6 +40,7 @@
 #include "postmaster/interrupt.h"
 #include "postmaster/pgarch.h"
 #include "storage/condition_variable.h"
+#include "storage/aio_subsys.h"
 #include "storage/fd.h"
 #include "storage/ipc.h"
 #include "storage/latch.h"
@@ -568,6 +569,7 @@ pgarch_archiveXlog(char *xlog)
 		LWLockReleaseAll();
 		ConditionVariableCancelSleep();
 		pgstat_report_wait_end();
+		pgaio_error_cleanup();
 		ReleaseAuxProcessResources(false);
 		AtEOXact_Files(false);
 		AtEOXact_HashTables(false);
diff --git a/src/backend/postmaster/walsummarizer.c b/src/backend/postmaster/walsummarizer.c
index ccba0f84e6e..0fec4f1f871 100644
--- a/src/backend/postmaster/walsummarizer.c
+++ b/src/backend/postmaster/walsummarizer.c
@@ -38,6 +38,7 @@
 #include "postmaster/interrupt.h"
 #include "postmaster/walsummarizer.h"
 #include "replication/walreceiver.h"
+#include "storage/aio_subsys.h"
 #include "storage/fd.h"
 #include "storage/ipc.h"
 #include "storage/latch.h"
@@ -289,6 +290,7 @@ WalSummarizerMain(const void *startup_data, size_t startup_data_len)
 		LWLockReleaseAll();
 		ConditionVariableCancelSleep();
 		pgstat_report_wait_end();
+		pgaio_error_cleanup();
 		ReleaseAuxProcessResources(false);
 		AtEOXact_Files(false);
 		AtEOXact_HashTables(false);
diff --git a/src/backend/postmaster/walwriter.c b/src/backend/postmaster/walwriter.c
index 0380601bcbb..fd92c8b7a33 100644
--- a/src/backend/postmaster/walwriter.c
+++ b/src/backend/postmaster/walwriter.c
@@ -51,6 +51,7 @@
 #include "postmaster/auxprocess.h"
 #include "postmaster/interrupt.h"
 #include "postmaster/walwriter.h"
+#include "storage/aio_subsys.h"
 #include "storage/bufmgr.h"
 #include "storage/condition_variable.h"
 #include "storage/fd.h"
@@ -164,6 +165,7 @@ WalWriterMain(const void *startup_data, size_t startup_data_len)
 		LWLockReleaseAll();
 		ConditionVariableCancelSleep();
 		pgstat_report_wait_end();
+		pgaio_error_cleanup();
 		UnlockBuffers();
 		ReleaseAuxProcessResources(false);
 		AtEOXact_Buffers(false);
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index d96121b3aad..1028919aecb 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -79,6 +79,7 @@
 #include "replication/walsender.h"
 #include "replication/walsender_private.h"
 #include "storage/condition_variable.h"
+#include "storage/aio_subsys.h"
 #include "storage/fd.h"
 #include "storage/ipc.h"
 #include "storage/pmsignal.h"
@@ -327,6 +328,7 @@ WalSndErrorCleanup(void)
 	LWLockReleaseAll();
 	ConditionVariableCancelSleep();
 	pgstat_report_wait_end();
+	pgaio_error_cleanup();
 
 	if (xlogreader != NULL && xlogreader->seg.ws_file >= 0)
 		wal_segment_close(xlogreader);
diff --git a/src/backend/storage/aio/Makefile b/src/backend/storage/aio/Makefile
index 2f29a9ec4d1..eaeaeeee8e3 100644
--- a/src/backend/storage/aio/Makefile
+++ b/src/backend/storage/aio/Makefile
@@ -9,6 +9,8 @@ top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
 OBJS = \
+	aio.o \
+	aio_init.o \
 	read_stream.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/storage/aio/aio.c b/src/backend/storage/aio/aio.c
new file mode 100644
index 00000000000..828a94efdc3
--- /dev/null
+++ b/src/backend/storage/aio/aio.c
@@ -0,0 +1,90 @@
+/*-------------------------------------------------------------------------
+ *
+ * aio.c
+ *    AIO - Core Logic
+ *
+ * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *    src/backend/storage/aio/aio.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "lib/ilist.h"
+#include "storage/aio.h"
+#include "storage/aio_subsys.h"
+#include "utils/guc.h"
+#include "utils/guc_hooks.h"
+
+
+/* Options for io_method. */
+const struct config_enum_entry io_method_options[] = {
+	{"sync", IOMETHOD_SYNC, false},
+	{NULL, 0, false}
+};
+
+/* GUCs */
+int			io_method = DEFAULT_IO_METHOD;
+int			io_max_concurrency = -1;
+
+
+
+/*
+ * Release IO handle during resource owner cleanup.
+ */
+void
+pgaio_io_release_resowner(dlist_node *ioh_node, bool on_error)
+{
+}
+
+/*
+ * Perform AIO related cleanup after an error.
+ *
+ * This should be called early in the error recovery paths, as later steps may
+ * need to issue AIO (e.g. to record a transaction abort WAL record).
+ */
+void
+pgaio_error_cleanup(void)
+{
+}
+
+/*
+ * Perform AIO related checks at (sub-)transactional boundaries.
+ *
+ * This should be called late during (sub-)transactional commit/abort, after
+ * all steps that might need to perform AIO, so that we can verify that the
+ * AIO subsystem is in a valid state at the end of a transaction.
+ */
+void
+AtEOXact_Aio(bool is_commit)
+{
+}
+
+void
+assign_io_method(int newval, void *extra)
+{
+}
+
+bool
+check_io_max_concurrency(int *newval, void **extra, GucSource source)
+{
+	if (*newval == -1)
+	{
+		/*
+		 * Auto-tuning will be applied later during startup, as auto-tuning
+		 * depends on the value of various GUCs.
+		 */
+		return true;
+	}
+	else if (*newval == 0)
+	{
+		GUC_check_errdetail("Only -1 or values bigger than 0 are valid.");
+		return false;
+	}
+
+	return true;
+}
diff --git a/src/backend/storage/aio/aio_init.c b/src/backend/storage/aio/aio_init.c
new file mode 100644
index 00000000000..aeacc144149
--- /dev/null
+++ b/src/backend/storage/aio/aio_init.c
@@ -0,0 +1,37 @@
+/*-------------------------------------------------------------------------
+ *
+ * aio_init.c
+ *    AIO - Subsystem Initialization
+ *
+ * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *    src/backend/storage/aio/aio_init.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "storage/aio_subsys.h"
+
+
+
+Size
+AioShmemSize(void)
+{
+	Size		sz = 0;
+
+	return sz;
+}
+
+void
+AioShmemInit(void)
+{
+}
+
+void
+pgaio_init_backend(void)
+{
+}
diff --git a/src/backend/storage/aio/meson.build b/src/backend/storage/aio/meson.build
index 8abe0eb4863..c822fd4ddf7 100644
--- a/src/backend/storage/aio/meson.build
+++ b/src/backend/storage/aio/meson.build
@@ -1,5 +1,7 @@
 # Copyright (c) 2024-2025, PostgreSQL Global Development Group
 
 backend_sources += files(
+  'aio.c',
+  'aio_init.c',
   'read_stream.c',
 )
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 174eed70367..2fa045e6b0f 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -37,6 +37,7 @@
 #include "replication/slotsync.h"
 #include "replication/walreceiver.h"
 #include "replication/walsender.h"
+#include "storage/aio_subsys.h"
 #include "storage/bufmgr.h"
 #include "storage/dsm.h"
 #include "storage/dsm_registry.h"
@@ -148,6 +149,7 @@ CalculateShmemSize(int *num_semaphores)
 	size = add_size(size, WaitEventCustomShmemSize());
 	size = add_size(size, InjectionPointShmemSize());
 	size = add_size(size, SlotSyncShmemSize());
+	size = add_size(size, AioShmemSize());
 
 	/* include additional requested shmem from preload libraries */
 	size = add_size(size, total_addin_request);
@@ -340,6 +342,7 @@ CreateOrAttachShmemStructs(void)
 	StatsShmemInit();
 	WaitEventCustomShmemInit();
 	InjectionPointShmemInit();
+	AioShmemInit();
 }
 
 /*
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 4b2faf1ba9d..7958ea11b73 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -43,6 +43,7 @@
 #include "replication/slot.h"
 #include "replication/slotsync.h"
 #include "replication/walsender.h"
+#include "storage/aio_subsys.h"
 #include "storage/bufmgr.h"
 #include "storage/fd.h"
 #include "storage/ipc.h"
@@ -635,6 +636,12 @@ BaseInit(void)
 	 */
 	pgstat_initialize();
 
+	/*
+	 * Initialize AIO before infrastructure that might need to actually
+	 * execute AIO.
+	 */
+	pgaio_init_backend();
+
 	/* Do local initialization of storage and buffer managers */
 	InitSync();
 	smgrinit();
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 9c0b10ad4dc..0d3ebf06a95 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -72,6 +72,7 @@
 #include "replication/slot.h"
 #include "replication/slotsync.h"
 #include "replication/syncrep.h"
+#include "storage/aio.h"
 #include "storage/bufmgr.h"
 #include "storage/bufpage.h"
 #include "storage/large_object.h"
@@ -3255,6 +3256,18 @@ struct config_int ConfigureNamesInt[] =
 	},
 
 	{
+		{"io_max_concurrency",
+			PGC_POSTMASTER,
+			RESOURCES_IO,
+			gettext_noop("Max number of IOs that one process can execute simultaneously."),
+			NULL,
+		},
+		&io_max_concurrency,
+		-1, -1, 1024,
+		check_io_max_concurrency, NULL, NULL
+	},
+
+	{
 		{"backend_flush_after", PGC_USERSET, RESOURCES_IO,
 			gettext_noop("Number of pages after which previously performed writes are flushed to disk."),
 			gettext_noop("0 disables forced writeback."),
@@ -5311,6 +5324,16 @@ struct config_enum ConfigureNamesEnum[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"io_method", PGC_POSTMASTER, RESOURCES_IO,
+			gettext_noop("Selects the method for executing asynchronous I/O."),
+			NULL
+		},
+		&io_method,
+		DEFAULT_IO_METHOD, io_method_options,
+		NULL, assign_io_method, NULL
+	},
+
 	/* End-of-list marker */
 	{
 		{NULL, 0, 0, NULL, NULL}, NULL, 0, NULL, NULL, NULL, NULL
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 8de86e0c945..43c2ec2153e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -202,6 +202,12 @@
 #maintenance_io_concurrency = 10	# 1-1000; 0 disables prefetching
 #io_combine_limit = 128kB		# usually 1-32 blocks (depends on OS)
 
+#io_method = sync			# sync (change requires restart)
+#io_max_concurrency = -1		# Max number of IOs that one process
+					# can execute simultaneously
+					# -1 sets based on shared_buffers
+					# (change requires restart)
+
 # - Worker Processes -
 
 #max_worker_processes = 8		# (change requires restart)
diff --git a/src/backend/utils/resowner/resowner.c b/src/backend/utils/resowner/resowner.c
index ac5ca4a765e..d39f3e1b655 100644
--- a/src/backend/utils/resowner/resowner.c
+++ b/src/backend/utils/resowner/resowner.c
@@ -47,6 +47,8 @@
 
 #include "common/hashfn.h"
 #include "common/int.h"
+#include "lib/ilist.h"
+#include "storage/aio.h"
 #include "storage/ipc.h"
 #include "storage/predicate.h"
 #include "storage/proc.h"
@@ -155,6 +157,12 @@ struct ResourceOwnerData
 
 	/* The local locks cache. */
 	LOCALLOCK  *locks[MAX_RESOWNER_LOCKS];	/* list of owned locks */
+
+	/*
+	 * AIO handles need be registered in critical sections and therefore
+	 * cannot use the normal ResourceElem mechanism.
+	 */
+	dlist_head	aio_handles;
 };
 
 
@@ -425,6 +433,8 @@ ResourceOwnerCreate(ResourceOwner parent, const char *name)
 		parent->firstchild = owner;
 	}
 
+	dlist_init(&owner->aio_handles);
+
 	return owner;
 }
 
@@ -725,6 +735,13 @@ ResourceOwnerReleaseInternal(ResourceOwner owner,
 		 * so issue warnings.  In the abort case, just clean up quietly.
 		 */
 		ResourceOwnerReleaseAll(owner, phase, isCommit);
+
+		while (!dlist_is_empty(&owner->aio_handles))
+		{
+			dlist_node *node = dlist_head_node(&owner->aio_handles);
+
+			pgaio_io_release_resowner(node, !isCommit);
+		}
 	}
 	else if (phase == RESOURCE_RELEASE_LOCKS)
 	{
@@ -1082,3 +1099,15 @@ ResourceOwnerForgetLock(ResourceOwner owner, LOCALLOCK *locallock)
 	elog(ERROR, "lock reference %p is not owned by resource owner %s",
 		 locallock, owner->name);
 }
+
+void
+ResourceOwnerRememberAioHandle(ResourceOwner owner, struct dlist_node *ioh_node)
+{
+	dlist_push_tail(&owner->aio_handles, ioh_node);
+}
+
+void
+ResourceOwnerForgetAioHandle(ResourceOwner owner, struct dlist_node *ioh_node)
+{
+	dlist_delete_from(&owner->aio_handles, ioh_node);
+}
diff --git a/src/include/storage/aio.h b/src/include/storage/aio.h
new file mode 100644
index 00000000000..e79d5343038
--- /dev/null
+++ b/src/include/storage/aio.h
@@ -0,0 +1,38 @@
+/*-------------------------------------------------------------------------
+ *
+ * aio.h
+ *    Main AIO interface
+ *
+ *
+ * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/aio.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef AIO_H
+#define AIO_H
+
+
+
+/* Enum for io_method GUC. */
+typedef enum IoMethod
+{
+	IOMETHOD_SYNC = 0,
+} IoMethod;
+
+/* We'll default to synchronous execution. */
+#define DEFAULT_IO_METHOD IOMETHOD_SYNC
+
+
+struct dlist_node;
+extern void pgaio_io_release_resowner(struct dlist_node *ioh_node, bool on_error);
+
+
+/* GUCs */
+extern PGDLLIMPORT int io_method;
+extern PGDLLIMPORT int io_max_concurrency;
+
+
+#endif							/* AIO_H */
diff --git a/src/include/storage/aio_subsys.h b/src/include/storage/aio_subsys.h
new file mode 100644
index 00000000000..2a6ca1c27a9
--- /dev/null
+++ b/src/include/storage/aio_subsys.h
@@ -0,0 +1,33 @@
+/*-------------------------------------------------------------------------
+ *
+ * aio_subsys.h
+ *    Interaction with AIO as a subsystem, rather than actually issuing AIO
+ *
+ * This header is for AIO related functionality that's being called by files
+ * that don't perform AIO, but interact with the AIO subsystem in some
+ * form. E.g. postmaster.c and shared memory initialization need to initialize
+ * AIO but don't perform AIO.
+ *
+ * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/aio_subsys.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef AIO_SUBSYS_H
+#define AIO_SUBSYS_H
+
+
+/* aio_init.c */
+extern Size AioShmemSize(void);
+extern void AioShmemInit(void);
+
+extern void pgaio_init_backend(void);
+
+
+/* aio.c */
+extern void pgaio_error_cleanup(void);
+extern void AtEOXact_Aio(bool is_commit);
+
+#endif							/* AIO_SUBSYS_H */
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index 24444cbc365..f619100467d 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -318,6 +318,7 @@ extern PGDLLIMPORT bool optimize_bounded_sort;
  */
 extern PGDLLIMPORT const struct config_enum_entry archive_mode_options[];
 extern PGDLLIMPORT const struct config_enum_entry dynamic_shared_memory_options[];
+extern PGDLLIMPORT const struct config_enum_entry io_method_options[];
 extern PGDLLIMPORT const struct config_enum_entry recovery_target_action_options[];
 extern PGDLLIMPORT const struct config_enum_entry wal_level_options[];
 extern PGDLLIMPORT const struct config_enum_entry wal_sync_method_options[];
diff --git a/src/include/utils/guc_hooks.h b/src/include/utils/guc_hooks.h
index 9a0d8ec85c7..a3eba8fbe21 100644
--- a/src/include/utils/guc_hooks.h
+++ b/src/include/utils/guc_hooks.h
@@ -64,6 +64,8 @@ extern bool check_default_with_oids(bool *newval, void **extra,
 extern bool check_effective_io_concurrency(int *newval, void **extra,
 										   GucSource source);
 extern bool check_huge_page_size(int *newval, void **extra, GucSource source);
+extern void assign_io_method(int newval, void *extra);
+extern bool check_io_max_concurrency(int *newval, void **extra, GucSource source);
 extern const char *show_in_hot_standby(void);
 extern bool check_locale_messages(char **newval, void **extra, GucSource source);
 extern void assign_locale_messages(const char *newval, void *extra);
diff --git a/src/include/utils/resowner.h b/src/include/utils/resowner.h
index e8d452ca7ee..aede4bfc820 100644
--- a/src/include/utils/resowner.h
+++ b/src/include/utils/resowner.h
@@ -164,4 +164,9 @@ struct LOCALLOCK;
 extern void ResourceOwnerRememberLock(ResourceOwner owner, struct LOCALLOCK *locallock);
 extern void ResourceOwnerForgetLock(ResourceOwner owner, struct LOCALLOCK *locallock);
 
+/* special support for AIO */
+struct dlist_node;
+extern void ResourceOwnerRememberAioHandle(ResourceOwner owner, struct dlist_node *ioh_node);
+extern void ResourceOwnerForgetAioHandle(ResourceOwner owner, struct dlist_node *ioh_node);
+
 #endif							/* RESOWNER_H */
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 93339ef3c58..3c9e823f07e 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -1279,6 +1279,7 @@ IntoClause
 InvalMessageArray
 InvalidationInfo
 InvalidationMsgsGroup
+IoMethod
 IpcMemoryId
 IpcMemoryKey
 IpcMemoryState