Improve tuplestore's error messages for I/O failures.

We should report the errno when we get a failure from functions like
BufFileWrite.  "ERROR: write failed" is unreasonably taciturn for a
case that's well within the realm of possibility; I've seen it a
couple times in the buildfarm recently, in situations that were
probably out-of-disk-space, but it'd be good to see the errno
to confirm it.

I think this code was originally written without assuming that
the buffile.c functions would return useful errno; but most other
callers *are* assuming that, and a quick look at the buffile code
gives no reason to suppose otherwise.

Also, a couple of the old messages were phrased on the assumption
that a short read might indicate a logic bug in tuplestore itself;
but that code's pretty well tested by now, so a filesystem-level
problem seems much more likely.

src/backend/utils/sort/logtape.c

@@ -208,11 +208,9 @@ ltsWriteBlock(LogicalTapeSet *lts, long blocknum, void *buffer)
 	if (BufFileSeekBlock(lts->pfile, blocknum) != 0 ||
 		BufFileWrite(lts->pfile, buffer, BLCKSZ) != BLCKSZ)
 		ereport(ERROR,
-		/* XXX is it okay to assume errno is correct? */
 				(errcode_for_file_access(),
 				 errmsg("could not write block %ld of temporary file: %m",
-						blocknum),
-				 errhint("Perhaps out of disk space?")));
+						blocknum)));
 }
 
 /*
@@ -227,7 +225,6 @@ ltsReadBlock(LogicalTapeSet *lts, long blocknum, void *buffer)
 	if (BufFileSeekBlock(lts->pfile, blocknum) != 0 ||
 		BufFileRead(lts->pfile, buffer, BLCKSZ) != BLCKSZ)
 		ereport(ERROR,
-		/* XXX is it okay to assume errno is correct? */
 				(errcode_for_file_access(),
 				 errmsg("could not read block %ld of temporary file: %m",
 						blocknum)));

src/backend/utils/sort/tuplestore.c

@@ -501,7 +501,9 @@ tuplestore_select_read_pointer(Tuplestorestate *state, int ptr)
 								state->writepos_file,
 								state->writepos_offset,
 								SEEK_SET) != 0)
-					elog(ERROR, "tuplestore seek failed");
+					ereport(ERROR,
+							(errcode_for_file_access(),
+							 errmsg("could not seek in tuplestore temporary file: %m")));
 			}
 			else
 			{
@@ -509,7 +511,9 @@ tuplestore_select_read_pointer(Tuplestorestate *state, int ptr)
 								readptr->file,
 								readptr->offset,
 								SEEK_SET) != 0)
-					elog(ERROR, "tuplestore seek failed");
+					ereport(ERROR,
+							(errcode_for_file_access(),
+							 errmsg("could not seek in tuplestore temporary file: %m")));
 			}
 			break;
 		default:
@@ -834,7 +838,9 @@ tuplestore_puttuple_common(Tuplestorestate *state, void *tuple)
 			if (BufFileSeek(state->myfile,
 							state->writepos_file, state->writepos_offset,
 							SEEK_SET) != 0)
-				elog(ERROR, "tuplestore seek to EOF failed");
+				ereport(ERROR,
+						(errcode_for_file_access(),
+				 errmsg("could not seek in tuplestore temporary file: %m")));
 			state->status = TSS_WRITEFILE;
 
 			/*
@@ -936,7 +942,9 @@ tuplestore_gettuple(Tuplestorestate *state, bool forward,
 				if (BufFileSeek(state->myfile,
 								readptr->file, readptr->offset,
 								SEEK_SET) != 0)
-					elog(ERROR, "tuplestore seek failed");
+					ereport(ERROR,
+							(errcode_for_file_access(),
+							 errmsg("could not seek in tuplestore temporary file: %m")));
 			state->status = TSS_READFILE;
 			/* FALL THRU into READFILE case */
 
@@ -998,7 +1006,9 @@ tuplestore_gettuple(Tuplestorestate *state, bool forward,
 					if (BufFileSeek(state->myfile, 0,
 									-(long) (tuplen + sizeof(unsigned int)),
 									SEEK_CUR) != 0)
-						elog(ERROR, "bogus tuple length in backward scan");
+						ereport(ERROR,
+								(errcode_for_file_access(),
+								 errmsg("could not seek in tuplestore temporary file: %m")));
 					Assert(!state->truncated);
 					return NULL;
 				}
@@ -1013,7 +1023,9 @@ tuplestore_gettuple(Tuplestorestate *state, bool forward,
 			if (BufFileSeek(state->myfile, 0,
 							-(long) tuplen,
 							SEEK_CUR) != 0)
-				elog(ERROR, "bogus tuple length in backward scan");
+				ereport(ERROR,
+						(errcode_for_file_access(),
+				 errmsg("could not seek in tuplestore temporary file: %m")));
 			tup = READTUP(state, tuplen);
 			return tup;
 
@@ -1213,7 +1225,9 @@ tuplestore_rescan(Tuplestorestate *state)
 		case TSS_READFILE:
 			readptr->eof_reached = false;
 			if (BufFileSeek(state->myfile, 0, 0L, SEEK_SET) != 0)
-				elog(ERROR, "tuplestore seek to start failed");
+				ereport(ERROR,
+						(errcode_for_file_access(),
+				 errmsg("could not seek in tuplestore temporary file: %m")));
 			break;
 		default:
 			elog(ERROR, "invalid tuplestore state");
@@ -1276,14 +1290,18 @@ tuplestore_copy_read_pointer(Tuplestorestate *state,
 									state->writepos_file,
 									state->writepos_offset,
 									SEEK_SET) != 0)
-						elog(ERROR, "tuplestore seek failed");
+						ereport(ERROR,
+								(errcode_for_file_access(),
+								 errmsg("could not seek in tuplestore temporary file: %m")));
 				}
 				else
 				{
 					if (BufFileSeek(state->myfile,
 									dptr->file, dptr->offset,
 									SEEK_SET) != 0)
-						elog(ERROR, "tuplestore seek failed");
+						ereport(ERROR,
+								(errcode_for_file_access(),
+								 errmsg("could not seek in tuplestore temporary file: %m")));
 				}
 			}
 			else if (srcptr == state->activeptr)
@@ -1427,10 +1445,10 @@ getlen(Tuplestorestate *state, bool eofOK)
 	nbytes = BufFileRead(state->myfile, (void *) &len, sizeof(len));
 	if (nbytes == sizeof(len))
 		return len;
-	if (nbytes != 0)
-		elog(ERROR, "unexpected end of tape");
-	if (!eofOK)
-		elog(ERROR, "unexpected end of data");
+	if (nbytes != 0 || !eofOK)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+			   errmsg("could not read from tuplestore temporary file: %m")));
 	return 0;
 }
 
@@ -1469,14 +1487,20 @@ writetup_heap(Tuplestorestate *state, void *tup)
 
 	if (BufFileWrite(state->myfile, (void *) &tuplen,
 					 sizeof(tuplen)) != sizeof(tuplen))
-		elog(ERROR, "write failed");
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not write to tuplestore temporary file: %m")));
 	if (BufFileWrite(state->myfile, (void *) tupbody,
 					 tupbodylen) != (size_t) tupbodylen)
-		elog(ERROR, "write failed");
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not write to tuplestore temporary file: %m")));
 	if (state->backward)		/* need trailing length word? */
 		if (BufFileWrite(state->myfile, (void *) &tuplen,
 						 sizeof(tuplen)) != sizeof(tuplen))
-			elog(ERROR, "write failed");
+			ereport(ERROR,
+					(errcode_for_file_access(),
+				errmsg("could not write to tuplestore temporary file: %m")));
 
 	FREEMEM(state, GetMemoryChunkSpace(tuple));
 	heap_free_minimal_tuple(tuple);
@@ -1495,10 +1519,14 @@ readtup_heap(Tuplestorestate *state, unsigned int len)
 	tuple->t_len = tuplen;
 	if (BufFileRead(state->myfile, (void *) tupbody,
 					tupbodylen) != (size_t) tupbodylen)
-		elog(ERROR, "unexpected end of data");
+		ereport(ERROR,
+				(errcode_for_file_access(),
+			   errmsg("could not read from tuplestore temporary file: %m")));
 	if (state->backward)		/* need trailing length word? */
 		if (BufFileRead(state->myfile, (void *) &tuplen,
 						sizeof(tuplen)) != sizeof(tuplen))
-			elog(ERROR, "unexpected end of data");
+			ereport(ERROR,
+					(errcode_for_file_access(),
+			   errmsg("could not read from tuplestore temporary file: %m")));
 	return (void *) tuple;
 }