From efc4ee7b3773beca3b9b169a8f4d01ad391a9bdb Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Wed, 22 Jan 2025 16:06:51 -0500
Subject: [PATCH v2.7 07/35] aio: Implement support for reads in smgr/md/fd

This implements the following:

1) An smgr AIO target, for AIO on smgr files. This should be usable not just
   for md.c but also other SMGR implementation if we ever get them.
2) readv support in fd.c, which requires a small bit of infrastructure work in
   fd.c
3) smgr.c and md.c support for readv

There still is nothing performing AIO, but as of this commit it would be
possible.

As part of this change FileGetRawDesc() actually ensures that the file is
opened - previously it was basically not usable. It's used to reopen a file in
IO workers.

Discussion: https://postgr.es/m/uvrtrknj4kdytuboidbhwclo4gxhswwcpgadptsjvjqcluzmah%40brqs62irg4dt
Discussion: https://postgr.es/m/20210223100344.llw5an2aklengrmn@alap3.anarazel.de
Discussion: https://postgr.es/m/stj36ea6yyhoxtqkhpieia2z4krnam7qyetc57rfezgk4zgapf@gcnactj4z56m
---
 src/include/storage/aio.h              |   6 +-
 src/include/storage/aio_types.h        |  10 +-
 src/include/storage/fd.h               |   3 +
 src/include/storage/md.h               |   7 +
 src/include/storage/smgr.h             |  14 ++
 src/backend/storage/aio/aio_callback.c |   5 +-
 src/backend/storage/aio/aio_target.c   |   2 +
 src/backend/storage/file/fd.c          |  40 ++++++
 src/backend/storage/smgr/md.c          | 176 +++++++++++++++++++++++++
 src/backend/storage/smgr/smgr.c        | 124 +++++++++++++++++
 10 files changed, 382 insertions(+), 5 deletions(-)

diff --git a/src/include/storage/aio.h b/src/include/storage/aio.h
index 8bc43c33505..d02c3d27fae 100644
--- a/src/include/storage/aio.h
+++ b/src/include/storage/aio.h
@@ -112,9 +112,10 @@ typedef enum PgAioTargetID
 {
 	/* intentionally the zero value, to help catch zeroed memory etc */
 	PGAIO_TID_INVALID = 0,
+	PGAIO_TID_SMGR,
 } PgAioTargetID;
 
-#define PGAIO_TID_COUNT (PGAIO_TID_INVALID + 1)
+#define PGAIO_TID_COUNT (PGAIO_TID_SMGR + 1)
 
 
 /*
@@ -180,6 +181,9 @@ struct PgAioTargetInfo
 typedef enum PgAioHandleCallbackID
 {
 	PGAIO_HCB_INVALID,
+
+	PGAIO_HCB_MD_READV,
+	PGAIO_HCB_MD_WRITEV,
 } PgAioHandleCallbackID;
 
 
diff --git a/src/include/storage/aio_types.h b/src/include/storage/aio_types.h
index a5cc658efbd..b0b9a2a5c97 100644
--- a/src/include/storage/aio_types.h
+++ b/src/include/storage/aio_types.h
@@ -60,11 +60,15 @@ typedef struct PgAioWaitRef
  */
 typedef union PgAioTargetData
 {
-	/* just as an example placeholder for later */
 	struct
 	{
-		uint32		queue_id;
-	}			wal;
+		RelFileLocator rlocator;	/* physical relation identifier */
+		BlockNumber blockNum;	/* blknum relative to begin of reln */
+		BlockNumber nblocks;
+		ForkNumber	forkNum:8;	/* don't waste 4 byte for four values */
+		bool		is_temp:1;	/* proc can be inferred by owning AIO */
+		bool		skip_fsync:1;
+	}			smgr;
 } PgAioTargetData;
 
 
diff --git a/src/include/storage/fd.h b/src/include/storage/fd.h
index e3067ab6597..b77d8e5e30e 100644
--- a/src/include/storage/fd.h
+++ b/src/include/storage/fd.h
@@ -101,6 +101,8 @@ extern PGDLLIMPORT int max_safe_fds;
  * prototypes for functions in fd.c
  */
 
+struct PgAioHandle;
+
 /* Operations on virtual Files --- equivalent to Unix kernel file ops */
 extern File PathNameOpenFile(const char *fileName, int fileFlags);
 extern File PathNameOpenFilePerm(const char *fileName, int fileFlags, mode_t fileMode);
@@ -109,6 +111,7 @@ extern void FileClose(File file);
 extern int	FilePrefetch(File file, off_t offset, off_t amount, uint32 wait_event_info);
 extern ssize_t FileReadV(File file, const struct iovec *iov, int iovcnt, off_t offset, uint32 wait_event_info);
 extern ssize_t FileWriteV(File file, const struct iovec *iov, int iovcnt, off_t offset, uint32 wait_event_info);
+extern int	FileStartReadV(struct PgAioHandle *ioh, File file, int iovcnt, off_t offset, uint32 wait_event_info);
 extern int	FileSync(File file, uint32 wait_event_info);
 extern int	FileZero(File file, off_t offset, off_t amount, uint32 wait_event_info);
 extern int	FileFallocate(File file, off_t offset, off_t amount, uint32 wait_event_info);
diff --git a/src/include/storage/md.h b/src/include/storage/md.h
index 05bf537066e..9d7131eff43 100644
--- a/src/include/storage/md.h
+++ b/src/include/storage/md.h
@@ -14,11 +14,14 @@
 #ifndef MD_H
 #define MD_H
 
+#include "storage/aio_types.h"
 #include "storage/block.h"
 #include "storage/relfilelocator.h"
 #include "storage/smgr.h"
 #include "storage/sync.h"
 
+extern const PgAioHandleCallbacks aio_md_readv_cb;
+
 /* md storage manager functionality */
 extern void mdinit(void);
 extern void mdopen(SMgrRelation reln);
@@ -36,6 +39,9 @@ extern uint32 mdmaxcombine(SMgrRelation reln, ForkNumber forknum,
 						   BlockNumber blocknum);
 extern void mdreadv(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 					void **buffers, BlockNumber nblocks);
+extern void mdstartreadv(PgAioHandle *ioh,
+						 SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
+						 void **buffers, BlockNumber nblocks);
 extern void mdwritev(SMgrRelation reln, ForkNumber forknum,
 					 BlockNumber blocknum,
 					 const void **buffers, BlockNumber nblocks, bool skipFsync);
@@ -46,6 +52,7 @@ extern void mdtruncate(SMgrRelation reln, ForkNumber forknum,
 					   BlockNumber old_blocks, BlockNumber nblocks);
 extern void mdimmedsync(SMgrRelation reln, ForkNumber forknum);
 extern void mdregistersync(SMgrRelation reln, ForkNumber forknum);
+extern int	mdfd(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum, uint32 *off);
 
 extern void ForgetDatabaseSyncRequests(Oid dbid);
 extern void DropRelationFiles(RelFileLocator *delrels, int ndelrels, bool isRedo);
diff --git a/src/include/storage/smgr.h b/src/include/storage/smgr.h
index 4016b206ad6..856ebcda350 100644
--- a/src/include/storage/smgr.h
+++ b/src/include/storage/smgr.h
@@ -15,6 +15,7 @@
 #define SMGR_H
 
 #include "lib/ilist.h"
+#include "storage/aio_types.h"
 #include "storage/block.h"
 #include "storage/relfilelocator.h"
 
@@ -73,6 +74,8 @@ typedef SMgrRelationData *SMgrRelation;
 #define SmgrIsTemp(smgr) \
 	RelFileLocatorBackendIsTemp((smgr)->smgr_rlocator)
 
+extern const PgAioTargetInfo aio_smgr_target_info;
+
 extern void smgrinit(void);
 extern SMgrRelation smgropen(RelFileLocator rlocator, ProcNumber backend);
 extern bool smgrexists(SMgrRelation reln, ForkNumber forknum);
@@ -97,6 +100,10 @@ extern uint32 smgrmaxcombine(SMgrRelation reln, ForkNumber forknum,
 extern void smgrreadv(SMgrRelation reln, ForkNumber forknum,
 					  BlockNumber blocknum,
 					  void **buffers, BlockNumber nblocks);
+extern void smgrstartreadv(PgAioHandle *ioh,
+						   SMgrRelation reln, ForkNumber forknum,
+						   BlockNumber blocknum,
+						   void **buffers, BlockNumber nblocks);
 extern void smgrwritev(SMgrRelation reln, ForkNumber forknum,
 					   BlockNumber blocknum,
 					   const void **buffers, BlockNumber nblocks,
@@ -127,4 +134,11 @@ smgrwrite(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 	smgrwritev(reln, forknum, blocknum, &buffer, 1, skipFsync);
 }
 
+extern void pgaio_io_set_target_smgr(PgAioHandle *ioh,
+									 SMgrRelationData *smgr,
+									 ForkNumber forknum,
+									 BlockNumber blocknum,
+									 int nblocks,
+									 bool skip_fsync);
+
 #endif							/* SMGR_H */
diff --git a/src/backend/storage/aio/aio_callback.c b/src/backend/storage/aio/aio_callback.c
index 7392b55322c..6a21c82396a 100644
--- a/src/backend/storage/aio/aio_callback.c
+++ b/src/backend/storage/aio/aio_callback.c
@@ -18,10 +18,11 @@
 #include "miscadmin.h"
 #include "storage/aio.h"
 #include "storage/aio_internal.h"
+#include "storage/md.h"
 
 
 /* just to have something to put into the aio_handle_cbs */
-static const struct PgAioHandleCallbacks aio_invalid_cb = {0};
+static const PgAioHandleCallbacks aio_invalid_cb = {0};
 
 typedef struct PgAioHandleCallbacksEntry
 {
@@ -37,6 +38,8 @@ typedef struct PgAioHandleCallbacksEntry
 static const PgAioHandleCallbacksEntry aio_handle_cbs[] = {
 #define CALLBACK_ENTRY(id, callback)  [id] = {.cb = &callback, .name = #callback}
 	CALLBACK_ENTRY(PGAIO_HCB_INVALID, aio_invalid_cb),
+
+	CALLBACK_ENTRY(PGAIO_HCB_MD_READV, aio_md_readv_cb),
 #undef CALLBACK_ENTRY
 };
 
diff --git a/src/backend/storage/aio/aio_target.c b/src/backend/storage/aio/aio_target.c
index 3fa813fd592..aab86a358da 100644
--- a/src/backend/storage/aio/aio_target.c
+++ b/src/backend/storage/aio/aio_target.c
@@ -16,6 +16,7 @@
 
 #include "storage/aio.h"
 #include "storage/aio_internal.h"
+#include "storage/smgr.h"
 
 
 /*
@@ -29,6 +30,7 @@ static const PgAioTargetInfo *pgaio_target_info[] = {
 	[PGAIO_TID_INVALID] = &(PgAioTargetInfo) {
 		.name = "invalid",
 	},
+	[PGAIO_TID_SMGR] = &aio_smgr_target_info,
 };
 
 
diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index e454db4c020..be8c4c2d60d 100644
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -94,6 +94,7 @@
 #include "miscadmin.h"
 #include "pgstat.h"
 #include "postmaster/startup.h"
+#include "storage/aio.h"
 #include "storage/fd.h"
 #include "storage/ipc.h"
 #include "utils/guc.h"
@@ -1294,6 +1295,8 @@ LruDelete(File file)
 
 	vfdP = &VfdCache[file];
 
+	pgaio_closing_fd(vfdP->fd);
+
 	/*
 	 * Close the file.  We aren't expecting this to fail; if it does, better
 	 * to leak the FD than to mess up our internal state.
@@ -1987,6 +1990,8 @@ FileClose(File file)
 
 	if (!FileIsNotOpen(file))
 	{
+		pgaio_closing_fd(vfdP->fd);
+
 		/* close the file */
 		if (close(vfdP->fd) != 0)
 		{
@@ -2210,6 +2215,32 @@ retry:
 	return returnCode;
 }
 
+int
+FileStartReadV(PgAioHandle *ioh, File file,
+			   int iovcnt, off_t offset,
+			   uint32 wait_event_info)
+{
+	int			returnCode;
+	Vfd		   *vfdP;
+
+	Assert(FileIsValid(file));
+
+	DO_DB(elog(LOG, "FileStartReadV: %d (%s) " INT64_FORMAT " %d",
+			   file, VfdCache[file].fileName,
+			   (int64) offset,
+			   iovcnt));
+
+	returnCode = FileAccess(file);
+	if (returnCode < 0)
+		return returnCode;
+
+	vfdP = &VfdCache[file];
+
+	pgaio_io_prep_readv(ioh, vfdP->fd, iovcnt, offset);
+
+	return 0;
+}
+
 ssize_t
 FileWriteV(File file, const struct iovec *iov, int iovcnt, off_t offset,
 		   uint32 wait_event_info)
@@ -2498,6 +2529,12 @@ FilePathName(File file)
 int
 FileGetRawDesc(File file)
 {
+	int			returnCode;
+
+	returnCode = FileAccess(file);
+	if (returnCode < 0)
+		return returnCode;
+
 	Assert(FileIsValid(file));
 	return VfdCache[file].fd;
 }
@@ -2778,6 +2815,7 @@ FreeDesc(AllocateDesc *desc)
 			result = closedir(desc->desc.dir);
 			break;
 		case AllocateDescRawFD:
+			pgaio_closing_fd(desc->desc.fd);
 			result = close(desc->desc.fd);
 			break;
 		default:
@@ -2846,6 +2884,8 @@ CloseTransientFile(int fd)
 	/* Only get here if someone passes us a file not in allocatedDescs */
 	elog(WARNING, "fd passed to CloseTransientFile was not obtained from OpenTransientFile");
 
+	pgaio_closing_fd(fd);
+
 	return close(fd);
 }
 
diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
index f3220f98dc4..11d4d5a7aea 100644
--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -31,6 +31,7 @@
 #include "miscadmin.h"
 #include "pg_trace.h"
 #include "pgstat.h"
+#include "storage/aio.h"
 #include "storage/bufmgr.h"
 #include "storage/fd.h"
 #include "storage/md.h"
@@ -152,6 +153,15 @@ static MdfdVec *_mdfd_getseg(SMgrRelation reln, ForkNumber forknum,
 static BlockNumber _mdnblocks(SMgrRelation reln, ForkNumber forknum,
 							  MdfdVec *seg);
 
+static PgAioResult md_readv_complete(PgAioHandle *ioh, PgAioResult prior_result, uint8 cb_data);
+static void md_readv_report(PgAioResult result, const PgAioTargetData *target_data, int elevel);
+
+const PgAioHandleCallbacks aio_md_readv_cb = {
+	.complete_shared = md_readv_complete,
+	.report = md_readv_report,
+};
+
+
 static inline int
 _mdfd_open_flags(void)
 {
@@ -937,6 +947,61 @@ mdreadv(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 	}
 }
 
+/*
+ * mdstartreadv() -- Asynchronous version of mdreadv().
+ */
+void
+mdstartreadv(PgAioHandle *ioh,
+			 SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
+			 void **buffers, BlockNumber nblocks)
+{
+	off_t		seekpos;
+	MdfdVec    *v;
+	BlockNumber nblocks_this_segment;
+	struct iovec *iov;
+	int			iovcnt;
+
+	v = _mdfd_getseg(reln, forknum, blocknum, false,
+					 EXTENSION_FAIL | EXTENSION_CREATE_RECOVERY);
+
+	seekpos = (off_t) BLCKSZ * (blocknum % ((BlockNumber) RELSEG_SIZE));
+
+	Assert(seekpos < (off_t) BLCKSZ * RELSEG_SIZE);
+
+	nblocks_this_segment =
+		Min(nblocks,
+			RELSEG_SIZE - (blocknum % ((BlockNumber) RELSEG_SIZE)));
+
+	if (nblocks_this_segment != nblocks)
+		elog(ERROR, "read crossing segment boundary");
+
+	iovcnt = pgaio_io_get_iovec(ioh, &iov);
+
+	Assert(nblocks <= iovcnt);
+
+	iovcnt = buffers_to_iovec(iov, buffers, nblocks_this_segment);
+
+	Assert(iovcnt <= nblocks_this_segment);
+
+	if (!(io_direct_flags & IO_DIRECT_DATA))
+		pgaio_io_set_flag(ioh, PGAIO_HF_BUFFERED);
+
+	pgaio_io_set_target_smgr(ioh,
+							 reln,
+							 forknum,
+							 blocknum,
+							 nblocks,
+							 false);
+	pgaio_io_register_callbacks(ioh, PGAIO_HCB_MD_READV, 0);
+
+	FileStartReadV(ioh, v->mdfd_vfd, iovcnt, seekpos, WAIT_EVENT_DATA_FILE_READ);
+
+	/*
+	 * The error checks corresponding to the post-read checks in mdread() are
+	 * in md_readv_complete().
+	 */
+}
+
 /*
  * mdwritev() -- Write the supplied blocks at the appropriate location.
  *
@@ -1365,6 +1430,21 @@ mdimmedsync(SMgrRelation reln, ForkNumber forknum)
 	}
 }
 
+int
+mdfd(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum, uint32 *off)
+{
+	MdfdVec    *v = mdopenfork(reln, forknum, EXTENSION_FAIL);
+
+	v = _mdfd_getseg(reln, forknum, blocknum, false,
+					 EXTENSION_FAIL);
+
+	*off = (off_t) BLCKSZ * (blocknum % ((BlockNumber) RELSEG_SIZE));
+
+	Assert(*off < (off_t) BLCKSZ * RELSEG_SIZE);
+
+	return FileGetRawDesc(v->mdfd_vfd);
+}
+
 /*
  * register_dirty_segment() -- Mark a relation segment as needing fsync
  *
@@ -1841,3 +1921,99 @@ mdfiletagmatches(const FileTag *ftag, const FileTag *candidate)
 	 */
 	return ftag->rlocator.dbOid == candidate->rlocator.dbOid;
 }
+
+/*
+ * AIO completion callback for mdstartreadv().
+ */
+static PgAioResult
+md_readv_complete(PgAioHandle *ioh, PgAioResult prior_result, uint8 cb_data)
+{
+	PgAioTargetData *td = pgaio_io_get_target_data(ioh);
+	PgAioResult result = prior_result;
+
+	if (prior_result.result < 0)
+	{
+		result.status = ARS_ERROR;
+		result.id = PGAIO_HCB_MD_READV;
+		/* For "hard" errors, track the error number in error_data */
+		result.error_data = -prior_result.result;
+		result.result = 0;
+
+		pgaio_result_report(result, td, LOG);
+
+		return result;
+	}
+
+	/*
+	 * The smgr API operates in blocks, therefore convert the result from
+	 * bytes to blocks.
+	 */
+	result.result /= BLCKSZ;
+
+	if (result.result == 0)
+	{
+		/* consider 0 blocks read a failure */
+		result.status = ARS_ERROR;
+		result.id = PGAIO_HCB_MD_READV;
+		result.error_data = 0;
+
+		pgaio_result_report(result, td, LOG);
+
+		return result;
+	}
+
+	if (result.status != ARS_ERROR &&
+		result.result < td->smgr.nblocks)
+	{
+		/* partial reads should be retried at upper level */
+		result.status = ARS_PARTIAL;
+		result.id = PGAIO_HCB_MD_READV;
+	}
+
+	return result;
+}
+
+/*
+ * AIO error reporting callback for mdstartreadv().
+ *
+ * Errors are encoded as follows:
+ * - PgAioResult.error_data != 0 encodes IO that failed with errno != 0
+ * - PgAioResult.error_data == 0 encodes IO that didn't read all data
+ */
+static void
+md_readv_report(PgAioResult result, const PgAioTargetData *td, int elevel)
+{
+	RelPathStr	path;
+
+	path = relpathbackend(td->smgr.rlocator,
+						  td->smgr.is_temp ? MyProcNumber : INVALID_PROC_NUMBER,
+						  td->smgr.forkNum);
+
+	if (result.error_data != 0)
+	{
+		/* for errcode_for_file_access() and %m */
+		errno = result.error_data;
+
+		ereport(elevel,
+				errcode_for_file_access(),
+				errmsg("could not read blocks %u..%u in file \"%s\": %m",
+					   td->smgr.blockNum,
+					   td->smgr.blockNum + td->smgr.nblocks - 1,
+					   path.str));
+	}
+	else
+	{
+		/*
+		 * NB: This will typically only be output in debug messages, while
+		 * retrying a partial IO.
+		 */
+		ereport(elevel,
+				errcode(ERRCODE_DATA_CORRUPTED),
+				errmsg("could not read blocks %u..%u in file \"%s\": read only %zu of %zu bytes",
+					   td->smgr.blockNum,
+					   td->smgr.blockNum + td->smgr.nblocks - 1,
+					   path.str,
+					   result.result * (size_t) BLCKSZ,
+					   td->smgr.nblocks * (size_t) BLCKSZ));
+	}
+}
diff --git a/src/backend/storage/smgr/smgr.c b/src/backend/storage/smgr/smgr.c
index ebe35c04de5..607c14ee173 100644
--- a/src/backend/storage/smgr/smgr.c
+++ b/src/backend/storage/smgr/smgr.c
@@ -53,6 +53,7 @@
 
 #include "access/xlogutils.h"
 #include "lib/ilist.h"
+#include "storage/aio.h"
 #include "storage/bufmgr.h"
 #include "storage/ipc.h"
 #include "storage/md.h"
@@ -93,6 +94,10 @@ typedef struct f_smgr
 	void		(*smgr_readv) (SMgrRelation reln, ForkNumber forknum,
 							   BlockNumber blocknum,
 							   void **buffers, BlockNumber nblocks);
+	void		(*smgr_startreadv) (PgAioHandle *ioh,
+									SMgrRelation reln, ForkNumber forknum,
+									BlockNumber blocknum,
+									void **buffers, BlockNumber nblocks);
 	void		(*smgr_writev) (SMgrRelation reln, ForkNumber forknum,
 								BlockNumber blocknum,
 								const void **buffers, BlockNumber nblocks,
@@ -104,6 +109,7 @@ typedef struct f_smgr
 								  BlockNumber old_blocks, BlockNumber nblocks);
 	void		(*smgr_immedsync) (SMgrRelation reln, ForkNumber forknum);
 	void		(*smgr_registersync) (SMgrRelation reln, ForkNumber forknum);
+	int			(*smgr_fd) (SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum, uint32 *off);
 } f_smgr;
 
 static const f_smgr smgrsw[] = {
@@ -121,12 +127,14 @@ static const f_smgr smgrsw[] = {
 		.smgr_prefetch = mdprefetch,
 		.smgr_maxcombine = mdmaxcombine,
 		.smgr_readv = mdreadv,
+		.smgr_startreadv = mdstartreadv,
 		.smgr_writev = mdwritev,
 		.smgr_writeback = mdwriteback,
 		.smgr_nblocks = mdnblocks,
 		.smgr_truncate = mdtruncate,
 		.smgr_immedsync = mdimmedsync,
 		.smgr_registersync = mdregistersync,
+		.smgr_fd = mdfd,
 	}
 };
 
@@ -144,6 +152,16 @@ static dlist_head unpinned_relns;
 static void smgrshutdown(int code, Datum arg);
 static void smgrdestroy(SMgrRelation reln);
 
+static void smgr_aio_reopen(PgAioHandle *ioh);
+static char *smgr_aio_describe_identity(const PgAioTargetData *sd);
+
+
+const PgAioTargetInfo aio_smgr_target_info = {
+	.name = "smgr",
+	.reopen = smgr_aio_reopen,
+	.describe_identity = smgr_aio_describe_identity,
+};
+
 
 /*
  * smgrinit(), smgrshutdown() -- Initialize or shut down storage
@@ -623,6 +641,22 @@ smgrreadv(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 										nblocks);
 }
 
+/*
+ * smgrstartreadv() -- asynchronous version of smgrreadv()
+ *
+ * This starts an asynchronous readv IO with the IO handle `ioh`. Other than
+ * `ioh` all parameters are the same as smgrreadv().
+ */
+void
+smgrstartreadv(PgAioHandle *ioh,
+			   SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
+			   void **buffers, BlockNumber nblocks)
+{
+	smgrsw[reln->smgr_which].smgr_startreadv(ioh,
+											 reln, forknum, blocknum, buffers,
+											 nblocks);
+}
+
 /*
  * smgrwritev() -- Write the supplied buffers out.
  *
@@ -819,6 +853,19 @@ smgrimmedsync(SMgrRelation reln, ForkNumber forknum)
 	smgrsw[reln->smgr_which].smgr_immedsync(reln, forknum);
 }
 
+/*
+ * Return fd for the specified block number and update *off to the appropriate
+ * position.
+ *
+ * This is only to be used for when AIO needs to perform the IO in a different
+ * process than where it was issued (e.g. in an IO worker).
+ */
+static int
+smgrfd(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum, uint32 *off)
+{
+	return smgrsw[reln->smgr_which].smgr_fd(reln, forknum, blocknum, off);
+}
+
 /*
  * AtEOXact_SMgr
  *
@@ -847,3 +894,80 @@ ProcessBarrierSmgrRelease(void)
 	smgrreleaseall();
 	return true;
 }
+
+/*
+ * Set target of the IO handle to be smgr and initialize all the relevant
+ * pieces of data.
+ */
+void
+pgaio_io_set_target_smgr(PgAioHandle *ioh,
+						 SMgrRelationData *smgr,
+						 ForkNumber forknum,
+						 BlockNumber blocknum,
+						 int nblocks,
+						 bool skip_fsync)
+{
+	PgAioTargetData *sd = pgaio_io_get_target_data(ioh);
+
+	pgaio_io_set_target(ioh, PGAIO_TID_SMGR);
+
+	/* backend is implied via IO owner */
+	sd->smgr.rlocator = smgr->smgr_rlocator.locator;
+	sd->smgr.forkNum = forknum;
+	sd->smgr.blockNum = blocknum;
+	sd->smgr.nblocks = nblocks;
+	sd->smgr.is_temp = SmgrIsTemp(smgr);
+	/* Temp relations should never be fsync'd */
+	sd->smgr.skip_fsync = skip_fsync && !SmgrIsTemp(smgr);
+}
+
+/*
+ * Callback for smgr AIO targets, to reopen the file (e.g. because the IO is
+ * executed in a worker).
+ */
+static void
+smgr_aio_reopen(PgAioHandle *ioh)
+{
+	PgAioTargetData *sd = pgaio_io_get_target_data(ioh);
+	PgAioOpData *od = pgaio_io_get_op_data(ioh);
+	SMgrRelation reln;
+	ProcNumber	procno;
+	uint32		off;
+
+	if (sd->smgr.is_temp)
+		procno = pgaio_io_get_owner(ioh);
+	else
+		procno = INVALID_PROC_NUMBER;
+
+	reln = smgropen(sd->smgr.rlocator, procno);
+	od->read.fd = smgrfd(reln, sd->smgr.forkNum, sd->smgr.blockNum, &off);
+	Assert(off == od->read.offset);
+}
+
+/*
+ * Callback for smgr AIO targets, to describe the target of the IO.
+ */
+static char *
+smgr_aio_describe_identity(const PgAioTargetData *sd)
+{
+	RelPathStr	path;
+	char	   *desc;
+
+	path = relpathbackend(sd->smgr.rlocator,
+						  sd->smgr.is_temp ? MyProcNumber : INVALID_PROC_NUMBER,
+						  sd->smgr.forkNum);
+
+	if (sd->smgr.nblocks == 0)
+		desc = psprintf(_("file \"%s\""), path.str);
+	else if (sd->smgr.nblocks == 1)
+		desc = psprintf(_("block %u in file \"%s\""),
+						sd->smgr.blockNum,
+						path.str);
+	else
+		desc = psprintf(_("blocks %u..%u in file \"%s\""),
+						sd->smgr.blockNum,
+						sd->smgr.blockNum + sd->smgr.nblocks - 1,
+						path.str);
+
+	return desc;
+}
-- 
2.48.1.76.g4e746b1a31.dirty

