Restore smgrtruncate() prototype in back-branches.

It's possible that external code is calling smgrtruncate().  Any
external callers might like to consider the recent changes to
RelationTruncate(), but commit 38c579b should not have changed the
function prototype in the back-branches, per ABI stability policy.

Restore smgrtruncate()'s traditional argument list in the back-branches,
but make it a wrapper for a new function smgrtruncate2().  The three
callers in core can use smgrtruncate2() directly.  In master (18-to-be),
smgrtruncate2() is effectively renamed to smgrtruncate(), so this wart
is cleaned up.

Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/CA%2BhUKG%2BThae6x6%2BjmQiuALQBT2Ae1ChjMh1%3DkMvJ8y_SBJZrvA%40mail.gmail.com

Author: macdice

contrib/pg_visibility/pg_visibility.c

@@ -421,7 +421,7 @@ pg_truncate_visibility_map(PG_FUNCTION_ARGS)
 	}
 
 	if (BlockNumberIsValid(block))
-		smgrtruncate(RelationGetSmgr(rel), &fork, 1, &old_block, &block);
+		smgrtruncate2(RelationGetSmgr(rel), &fork, 1, &old_block, &block);
 
 	END_CRIT_SECTION();
 	MyProc->delayChkptFlags &= ~(DELAY_CHKPT_START | DELAY_CHKPT_COMPLETE);

src/backend/catalog/storage.c

@@ -418,7 +418,7 @@ RelationTruncate(Relation rel, BlockNumber nblocks)
 	 * longer exist after truncation is complete, and then truncate the
 	 * corresponding files on disk.
 	 */
-	smgrtruncate(RelationGetSmgr(rel), forks, nforks, old_blocks, blocks);
+	smgrtruncate2(RelationGetSmgr(rel), forks, nforks, old_blocks, blocks);
 
 	END_CRIT_SECTION();
 
@@ -1059,7 +1059,7 @@ smgr_redo(XLogReaderState *record)
 		if (nforks > 0)
 		{
 			START_CRIT_SECTION();
-			smgrtruncate(reln, forks, nforks, old_blocks, blocks);
+			smgrtruncate2(reln, forks, nforks, old_blocks, blocks);
 			END_CRIT_SECTION();
 		}
 

src/backend/storage/smgr/smgr.c

@@ -693,6 +693,26 @@ smgrnblocks_cached(SMgrRelation reln, ForkNumber forknum)
  * smgrtruncate() -- Truncate the given forks of supplied relation to
  *					 each specified numbers of blocks
  *
+ * Backward-compatible version of smgrtruncate2() for the benefit of external
+ * callers.  This version isn't used in PostgreSQL core code, and can't be
+ * used in a critical section.
+ */
+void
+smgrtruncate(SMgrRelation reln, ForkNumber *forknum, int nforks,
+			 BlockNumber *nblocks)
+{
+	BlockNumber old_nblocks[MAX_FORKNUM + 1];
+
+	for (int i = 0; i < nforks; ++i)
+		old_nblocks[i] = smgrnblocks(reln, forknum[i]);
+
+	return smgrtruncate2(reln, forknum, nforks, old_nblocks, nblocks);
+}
+
+/*
+ * smgrtruncate2() -- Truncate the given forks of supplied relation to
+ *					  each specified numbers of blocks
+ *
  * The truncation is done immediately, so this can't be rolled back.
  *
  * The caller must hold AccessExclusiveLock on the relation, to ensure that
@@ -704,8 +724,8 @@ smgrnblocks_cached(SMgrRelation reln, ForkNumber forknum)
  * to this relation should be called in between.
  */
 void
-smgrtruncate(SMgrRelation reln, ForkNumber *forknum, int nforks,
-			 BlockNumber *old_nblocks, BlockNumber *nblocks)
+smgrtruncate2(SMgrRelation reln, ForkNumber *forknum, int nforks,
+			  BlockNumber *old_nblocks, BlockNumber *nblocks)
 {
 	int			i;
 

src/include/storage/smgr.h

@@ -104,8 +104,10 @@ extern void smgrwriteback(SMgrRelation reln, ForkNumber forknum,
 extern BlockNumber smgrnblocks(SMgrRelation reln, ForkNumber forknum);
 extern BlockNumber smgrnblocks_cached(SMgrRelation reln, ForkNumber forknum);
 extern void smgrtruncate(SMgrRelation reln, ForkNumber *forknum, int nforks,
-						 BlockNumber *old_nblocks,
 						 BlockNumber *nblocks);
+extern void smgrtruncate2(SMgrRelation reln, ForkNumber *forknum, int nforks,
+						  BlockNumber *old_nblocks,
+						  BlockNumber *nblocks);
 extern void smgrimmedsync(SMgrRelation reln, ForkNumber forknum);
 extern void smgrregistersync(SMgrRelation reln, ForkNumber forknum);
 extern void AtEOXact_SMgr(void);