Fix pg_upgrade around multixid and mxoff wraparound

pg_resetwal didn't accept multixid 0 or multixact offset UINT32_MAX,
but they are both valid values that can appear in the control file.
That caused pg_upgrade to fail if you tried to upgrade a cluster
exactly at multixid or offset wraparound, because pg_upgrade calls
pg_resetwal to restore multixid/offset on the new cluster to the
values from the old cluster. To fix, allow those values in
pg_resetwal.

Fixes bugs #18863 and #18865 reported by Dmitry Kovalenko.

Backpatch down to v15. Version 14 has the same bug, but the patch
doesn't apply cleanly there. It could be made to work but it doesn't
seem worth the effort given how rare it is to hit this problem with
pg_upgrade, and how few people are upgrading to v14 anymore.

Author: Maxim Orlov <orlovmg@gmail.com>
Discussion: https://www.postgresql.org/message-id/CACG%3DezaApSMTjd%3DM2Sfn5Ucuggd3FG8Z8Qte8Xq9k5-%2BRQis-g@mail.gmail.com
Discussion: https://www.postgresql.org/message-id/18863-72f08858855344a2@postgresql.org
Discussion: https://www.postgresql.org/message-id/18865-d4c66cf35c2a67af@postgresql.org
Backpatch-through: 15

Author: hlinnaka

src/bin/pg_resetwal/pg_resetwal.c

@@ -70,8 +70,10 @@ static TransactionId set_xid = 0;
 static TransactionId set_oldest_commit_ts_xid = 0;
 static TransactionId set_newest_commit_ts_xid = 0;
 static Oid	set_oid = 0;
+static bool mxid_given = false;
 static MultiXactId set_mxid = 0;
-static MultiXactOffset set_mxoff = (MultiXactOffset) -1;
+static bool mxoff_given = false;
+static MultiXactOffset set_mxoff = 0;
 static TimeLineID minXlogTli = 0;
 static XLogSegNo minXlogSegNo = 0;
 static int	WalSegSz;
@@ -118,6 +120,7 @@ main(int argc, char *argv[])
 	MultiXactId set_oldestmxid = 0;
 	char	   *endptr;
 	char	   *endptr2;
+	int64		tmpi64;
 	char	   *DataDir = NULL;
 	char	   *log_fname = NULL;
 	int			fd;
@@ -254,28 +257,30 @@ main(int argc, char *argv[])
 					pg_log_error_hint("Try \"%s --help\" for more information.", progname);
 					exit(1);
 				}
-				if (set_mxid == 0)
-					pg_fatal("multitransaction ID (-m) must not be 0");
 
 				/*
 				 * XXX It'd be nice to have more sanity checks here, e.g. so
 				 * that oldest is not wrapped around w.r.t. nextMulti.
 				 */
 				if (set_oldestmxid == 0)
 					pg_fatal("oldest multitransaction ID (-m) must not be 0");
+				mxid_given = true;
 				break;
 
 			case 'O':
 				errno = 0;
-				set_mxoff = strtoul(optarg, &endptr, 0);
+				tmpi64 = strtoi64(optarg, &endptr, 0);
 				if (endptr == optarg || *endptr != '\0' || errno != 0)
 				{
 					pg_log_error("invalid argument for option %s", "-O");
 					pg_log_error_hint("Try \"%s --help\" for more information.", progname);
 					exit(1);
 				}
-				if (set_mxoff == -1)
-					pg_fatal("multitransaction offset (-O) must not be -1");
+				if (tmpi64 < 0 || tmpi64 > (int64) MaxMultiXactOffset)
+					pg_fatal("multitransaction offset (-O) must be between 0 and %u", MaxMultiXactOffset);
+
+				set_mxoff = (MultiXactOffset) tmpi64;
+				mxoff_given = true;
 				break;
 
 			case 'l':
@@ -454,7 +459,7 @@ main(int argc, char *argv[])
 	if (set_oid != 0)
 		ControlFile.checkPointCopy.nextOid = set_oid;
 
-	if (set_mxid != 0)
+	if (mxid_given)
 	{
 		ControlFile.checkPointCopy.nextMulti = set_mxid;
 
@@ -464,7 +469,7 @@ main(int argc, char *argv[])
 		ControlFile.checkPointCopy.oldestMultiDB = InvalidOid;
 	}
 
-	if (set_mxoff != -1)
+	if (mxoff_given)
 		ControlFile.checkPointCopy.nextMultiOffset = set_mxoff;
 
 	if (minXlogTli > ControlFile.checkPointCopy.ThisTimeLineID)
@@ -808,7 +813,7 @@ PrintNewControlValues(void)
 				 newXlogSegNo, WalSegSz);
 	printf(_("First log segment after reset:        %s\n"), fname);
 
-	if (set_mxid != 0)
+	if (mxid_given)
 	{
 		printf(_("NextMultiXactId:                      %u\n"),
 			   ControlFile.checkPointCopy.nextMulti);
@@ -818,7 +823,7 @@ PrintNewControlValues(void)
 			   ControlFile.checkPointCopy.oldestMultiDB);
 	}
 
-	if (set_mxoff != -1)
+	if (mxoff_given)
 	{
 		printf(_("NextMultiOffset:                      %u\n"),
 			   ControlFile.checkPointCopy.nextMultiOffset);

src/bin/pg_resetwal/t/001_basic.pl

@@ -119,10 +119,12 @@
 	[ 'pg_resetwal', '-m' => '10,bar', $node->data_dir ],
 	qr/error: invalid argument for option -m/,
 	'fails with incorrect -m option part 2');
-command_fails_like(
-	[ 'pg_resetwal', '-m' => '0,10', $node->data_dir ],
-	qr/must not be 0/,
-	'fails with -m value 0 part 1');
+
+# This used to be forbidden, but nextMulti can legitimately be 0 after
+# wraparound, so we now accept it in pg_resetwal too.
+command_ok([ 'pg_resetwal', '-m' => '0,10', $node->data_dir ],
+	'succeeds with -m value 0 part 1');
+
 command_fails_like(
 	[ 'pg_resetwal', '-m' => '10,0', $node->data_dir ],
 	qr/must not be 0/,
@@ -143,7 +145,7 @@
 	'fails with incorrect -O option');
 command_fails_like(
 	[ 'pg_resetwal', '-O' => '-1', $node->data_dir ],
-	qr/must not be -1/,
+	qr/must be between 0 and 4294967295/,
 	'fails with -O value -1');
 # --wal-segsize
 command_fails_like(