Add buffer_std flag to MarkBufferDirtyHint().

MarkBufferDirtyHint() writes WAL, and should know if it's got a
standard buffer or not. Currently, the only callers where buffer_std
is false are related to the FSM.

In passing, rename XLOG_HINT to XLOG_FPI, which is more descriptive.

Back-patch to 9.3.

src/backend/access/hash/hash.c

@@ -287,7 +287,7 @@ hashgettuple(PG_FUNCTION_ARGS)
 			/*
 			 * Since this can be redone later if needed, mark as a hint.
 			 */
-			MarkBufferDirtyHint(buf);
+			MarkBufferDirtyHint(buf, true);
 		}
 
 		/*

src/backend/access/heap/pruneheap.c

@@ -262,7 +262,7 @@ heap_page_prune(Relation relation, Buffer buffer, TransactionId OldestXmin,
 		{
 			((PageHeader) page)->pd_prune_xid = prstate.new_prune_xid;
 			PageClearFull(page);
-			MarkBufferDirtyHint(buffer);
+			MarkBufferDirtyHint(buffer, true);
 		}
 	}
 

src/backend/access/nbtree/nbtinsert.c

@@ -413,9 +413,9 @@ _bt_check_unique(Relation rel, IndexTuple itup, Relation heapRel,
 					 * crucial. Be sure to mark the proper buffer dirty.
 					 */
 					if (nbuf != InvalidBuffer)
-						MarkBufferDirtyHint(nbuf);
+						MarkBufferDirtyHint(nbuf, true);
 					else
-						MarkBufferDirtyHint(buf);
+						MarkBufferDirtyHint(buf, true);
 				}
 			}
 		}

src/backend/access/nbtree/nbtree.c

@@ -1052,7 +1052,7 @@ restart:
 				opaque->btpo_cycleid == vstate->cycleid)
 			{
 				opaque->btpo_cycleid = 0;
-				MarkBufferDirtyHint(buf);
+				MarkBufferDirtyHint(buf, true);
 			}
 		}
 

src/backend/access/nbtree/nbtutils.c

@@ -1789,7 +1789,7 @@ _bt_killitems(IndexScanDesc scan, bool haveLock)
 	if (killedsomething)
 	{
 		opaque->btpo_flags |= BTP_HAS_GARBAGE;
-		MarkBufferDirtyHint(so->currPos.buf);
+		MarkBufferDirtyHint(so->currPos.buf, true);
 	}
 
 	if (!haveLock)

src/backend/access/rmgrdesc/xlogdesc.c

@@ -82,11 +82,11 @@ xlog_desc(StringInfo buf, uint8 xl_info, char *rec)
 		appendStringInfo(buf, "restore point: %s", xlrec->rp_name);
 
 	}
-	else if (info == XLOG_HINT)
+	else if (info == XLOG_FPI)
 	{
 		BkpBlock   *bkp = (BkpBlock *) rec;
 
-		appendStringInfo(buf, "page hint: %s block %u",
+		appendStringInfo(buf, "full-page image: %s block %u",
 						 relpathperm(bkp->node, bkp->fork),
 						 bkp->block);
 	}

src/backend/access/transam/xlog.c

@@ -7681,12 +7681,9 @@ XLogRestorePoint(const char *rpName)
  * records. In that case, multiple copies of the same block would be recorded
  * in separate WAL records by different backends, though that is still OK from
  * a correctness perspective.
- *
- * Note that this only works for buffers that fit the standard page model,
- * i.e. those for which buffer_std == true
  */
 XLogRecPtr
-XLogSaveBufferForHint(Buffer buffer)
+XLogSaveBufferForHint(Buffer buffer, bool buffer_std)
 {
 	XLogRecPtr	recptr = InvalidXLogRecPtr;
 	XLogRecPtr	lsn;
@@ -7708,7 +7705,7 @@ XLogSaveBufferForHint(Buffer buffer)
 	 * and reset rdata for any actual WAL record insert.
 	 */
 	rdata[0].buffer = buffer;
-	rdata[0].buffer_std = true;
+	rdata[0].buffer_std = buffer_std;
 
 	/*
 	 * Check buffer while not holding an exclusive lock.
@@ -7722,6 +7719,9 @@ XLogSaveBufferForHint(Buffer buffer)
 		 * Copy buffer so we don't have to worry about concurrent hint bit or
 		 * lsn updates. We assume pd_lower/upper cannot be changed without an
 		 * exclusive lock, so the contents bkp are not racy.
+		 *
+		 * With buffer_std set to false, XLogCheckBuffer() sets hole_length and
+		 * hole_offset to 0; so the following code is safe for either case.
 		 */
 		memcpy(copied_buffer, origdata, bkpb.hole_offset);
 		memcpy(copied_buffer + bkpb.hole_offset,
@@ -7744,7 +7744,7 @@ XLogSaveBufferForHint(Buffer buffer)
 		rdata[1].buffer = InvalidBuffer;
 		rdata[1].next = NULL;
 
-		recptr = XLogInsert(RM_XLOG_ID, XLOG_HINT, rdata);
+		recptr = XLogInsert(RM_XLOG_ID, XLOG_FPI, rdata);
 	}
 
 	return recptr;
@@ -8109,14 +8109,14 @@ xlog_redo(XLogRecPtr lsn, XLogRecord *record)
 	{
 		/* nothing to do here */
 	}
-	else if (info == XLOG_HINT)
+	else if (info == XLOG_FPI)
 	{
 		char	   *data;
 		BkpBlock	bkpb;
 
 		/*
-		 * Hint bit records contain a backup block stored "inline" in the
-		 * normal data since the locking when writing hint records isn't
+		 * Full-page image (FPI) records contain a backup block stored "inline"
+		 * in the normal data since the locking when writing hint records isn't
 		 * sufficient to use the normal backup block mechanism, which assumes
 		 * exclusive lock on the buffer supplied.
 		 *