Expand the use of get_dirent_type(), shaving a few calls to stat()/lstat()

Several backend-side loops scanning one or more directories with
ReadDir() (WAL segment recycle/removal in xlog.c, backend-side directory
copy, temporary file removal, configuration file parsing, some logical
decoding logic and some pgtz stuff) already know the type of the entry
being scanned thanks to the dirent structure associated to the entry, on
platforms where we know about DT_REG, DT_DIR and DT_LNK to make the
difference between a regular file, a directory and a symbolic link.

Relying on the direct structure of an entry saves a few system calls to
stat() and lstat() in the loops updated here, shaving some code while on
it.  The logic of the code remains the same, calling stat() or lstat()
depending on if it is necessary to look through symlinks.

Authors: Nathan Bossart, Bharath Rupireddy
Reviewed-by: Andres Freund, Thomas Munro, Michael Paquier
Discussion: https://postgr.es/m/CALj2ACV8n-J-f=yiLUOx2=HrQGPSOZM3nWzyQQvLPcccPXxEdg@mail.gmail.com

src/backend/access/heap/rewriteheap.c

@@ -113,6 +113,7 @@
 #include "access/xact.h"
 #include "access/xloginsert.h"
 #include "catalog/catalog.h"
+#include "common/file_utils.h"
 #include "lib/ilist.h"
 #include "miscadmin.h"
 #include "pgstat.h"
@@ -1213,7 +1214,6 @@ CheckPointLogicalRewriteHeap(void)
 	mappings_dir = AllocateDir("pg_logical/mappings");
 	while ((mapping_de = ReadDir(mappings_dir, "pg_logical/mappings")) != NULL)
 	{
-		struct stat statbuf;
 		Oid			dboid;
 		Oid			relid;
 		XLogRecPtr	lsn;
@@ -1221,13 +1221,16 @@ CheckPointLogicalRewriteHeap(void)
 		TransactionId create_xid;
 		uint32		hi,
 					lo;
+		PGFileType	de_type;
 
 		if (strcmp(mapping_de->d_name, ".") == 0 ||
 			strcmp(mapping_de->d_name, "..") == 0)
 			continue;
 
 		snprintf(path, sizeof(path), "pg_logical/mappings/%s", mapping_de->d_name);
-		if (lstat(path, &statbuf) == 0 && !S_ISREG(statbuf.st_mode))
+		de_type = get_dirent_type(path, mapping_de, false, DEBUG1);
+
+		if (de_type != PGFILETYPE_ERROR && de_type != PGFILETYPE_REG)
 			continue;
 
 		/* Skip over files that cannot be ours. */

src/backend/access/transam/xlog.c

@@ -657,8 +657,9 @@ static void PreallocXlogFiles(XLogRecPtr endptr, TimeLineID tli);
 static void RemoveTempXlogFiles(void);
 static void RemoveOldXlogFiles(XLogSegNo segno, XLogRecPtr lastredoptr,
 							   XLogRecPtr endptr, TimeLineID insertTLI);
-static void RemoveXlogFile(const char *segname, XLogSegNo recycleSegNo,
+static void RemoveXlogFile(const struct dirent *segment_de,
-						   XLogSegNo *endlogSegNo, TimeLineID insertTLI);
+						   XLogSegNo recycleSegNo, XLogSegNo *endlogSegNo,
+						   TimeLineID insertTLI);
 static void UpdateLastRemovedPtr(char *filename);
 static void ValidateXLOGDirectoryStructure(void);
 static void CleanupBackupHistory(void);
@@ -3596,8 +3597,7 @@ RemoveOldXlogFiles(XLogSegNo segno, XLogRecPtr lastredoptr, XLogRecPtr endptr,
 				/* Update the last removed location in shared memory first */
 				UpdateLastRemovedPtr(xlde->d_name);
 
-				RemoveXlogFile(xlde->d_name, recycleSegNo, &endlogSegNo,
+				RemoveXlogFile(xlde, recycleSegNo, &endlogSegNo, insertTLI);
-							   insertTLI);
 			}
 		}
 	}
@@ -3669,8 +3669,7 @@ RemoveNonParentXlogFiles(XLogRecPtr switchpoint, TimeLineID newTLI)
 			 * - but seems safer to let them be archived and removed later.
 			 */
 			if (!XLogArchiveIsReady(xlde->d_name))
-				RemoveXlogFile(xlde->d_name, recycleSegNo, &endLogSegNo,
+				RemoveXlogFile(xlde, recycleSegNo, &endLogSegNo, newTLI);
-							   newTLI);
 		}
 	}
 
@@ -3680,9 +3679,9 @@ RemoveNonParentXlogFiles(XLogRecPtr switchpoint, TimeLineID newTLI)
 /*
  * Recycle or remove a log file that's no longer needed.
  *
- * segname is the name of the segment to recycle or remove.  recycleSegNo
+ * segment_de is the dirent structure of the segment to recycle or remove.
- * is the segment number to recycle up to.  endlogSegNo is the segment
+ * recycleSegNo is the segment number to recycle up to.  endlogSegNo is
- * number of the current (or recent) end of WAL.
+ * the segment number of the current (or recent) end of WAL.
  *
  * endlogSegNo gets incremented if the segment is recycled so as it is not
  * checked again with future callers of this function.
@@ -3691,14 +3690,15 @@ RemoveNonParentXlogFiles(XLogRecPtr switchpoint, TimeLineID newTLI)
  * should be used for this timeline.
  */
 static void
-RemoveXlogFile(const char *segname, XLogSegNo recycleSegNo,
+RemoveXlogFile(const struct dirent *segment_de,
-			   XLogSegNo *endlogSegNo, TimeLineID insertTLI)
+			   XLogSegNo recycleSegNo, XLogSegNo *endlogSegNo,
+			   TimeLineID insertTLI)
 {
 	char		path[MAXPGPATH];
 #ifdef WIN32
 	char		newpath[MAXPGPATH];
 #endif
-	struct stat statbuf;
+	const char *segname = segment_de->d_name;
 
 	snprintf(path, MAXPGPATH, XLOGDIR "/%s", segname);
 
@@ -3710,7 +3710,7 @@ RemoveXlogFile(const char *segname, XLogSegNo recycleSegNo,
 	if (wal_recycle &&
 		*endlogSegNo <= recycleSegNo &&
 		XLogCtl->InstallXLogFileSegmentActive &&	/* callee rechecks this */
-		lstat(path, &statbuf) == 0 && S_ISREG(statbuf.st_mode) &&
+		get_dirent_type(path, segment_de, false, DEBUG2) == PGFILETYPE_REG &&
 		InstallXLogFileSegment(endlogSegNo, path,
 							   true, recycleSegNo, insertTLI))
 	{

src/backend/replication/logical/snapbuild.c

@@ -123,6 +123,7 @@
 #include "access/heapam_xlog.h"
 #include "access/transam.h"
 #include "access/xact.h"
+#include "common/file_utils.h"
 #include "miscadmin.h"
 #include "pgstat.h"
 #include "replication/logical.h"
@@ -2061,15 +2062,16 @@ CheckPointSnapBuild(void)
 		uint32		hi;
 		uint32		lo;
 		XLogRecPtr	lsn;
-		struct stat statbuf;
+		PGFileType	de_type;
 
 		if (strcmp(snap_de->d_name, ".") == 0 ||
 			strcmp(snap_de->d_name, "..") == 0)
 			continue;
 
 		snprintf(path, sizeof(path), "pg_logical/snapshots/%s", snap_de->d_name);
+		de_type = get_dirent_type(path, snap_de, false, DEBUG1);
 
-		if (lstat(path, &statbuf) == 0 && !S_ISREG(statbuf.st_mode))
+		if (de_type != PGFILETYPE_ERROR && de_type != PGFILETYPE_REG)
 		{
 			elog(DEBUG1, "only regular files expected: %s", path);
 			continue;

src/backend/replication/slot.c

@@ -41,6 +41,7 @@
 
 #include "access/transam.h"
 #include "access/xlog_internal.h"
+#include "common/file_utils.h"
 #include "common/string.h"
 #include "miscadmin.h"
 #include "pgstat.h"
@@ -1442,17 +1443,18 @@ StartupReplicationSlots(void)
 	replication_dir = AllocateDir("pg_replslot");
 	while ((replication_de = ReadDir(replication_dir, "pg_replslot")) != NULL)
 	{
-		struct stat statbuf;
 		char		path[MAXPGPATH + 12];
+		PGFileType	de_type;
 
 		if (strcmp(replication_de->d_name, ".") == 0 ||
 			strcmp(replication_de->d_name, "..") == 0)
 			continue;
 
 		snprintf(path, sizeof(path), "pg_replslot/%s", replication_de->d_name);
+		de_type = get_dirent_type(path, replication_de, false, DEBUG1);
 
 		/* we're only creating directories here, skip if it's not our's */
-		if (lstat(path, &statbuf) == 0 && !S_ISDIR(statbuf.st_mode))
+		if (de_type != PGFILETYPE_ERROR && de_type != PGFILETYPE_DIR)
 			continue;
 
 		/* we crashed while a slot was being setup or deleted, clean up */

src/backend/storage/file/copydir.c

@@ -22,6 +22,7 @@
 #include <unistd.h>
 #include <sys/stat.h>
 
+#include "common/file_utils.h"
 #include "miscadmin.h"
 #include "pgstat.h"
 #include "storage/copydir.h"
@@ -50,7 +51,7 @@ copydir(char *fromdir, char *todir, bool recurse)
 
 	while ((xlde = ReadDir(xldir, fromdir)) != NULL)
 	{
-		struct stat fst;
+		PGFileType	xlde_type;
 
 		/* If we got a cancel signal during the copy of the directory, quit */
 		CHECK_FOR_INTERRUPTS();
@@ -62,18 +63,15 @@ copydir(char *fromdir, char *todir, bool recurse)
 		snprintf(fromfile, sizeof(fromfile), "%s/%s", fromdir, xlde->d_name);
 		snprintf(tofile, sizeof(tofile), "%s/%s", todir, xlde->d_name);
 
-		if (lstat(fromfile, &fst) < 0)
+		xlde_type = get_dirent_type(fromfile, xlde, false, ERROR);
-			ereport(ERROR,
-					(errcode_for_file_access(),
-					 errmsg("could not stat file \"%s\": %m", fromfile)));
 
-		if (S_ISDIR(fst.st_mode))
+		if (xlde_type == PGFILETYPE_DIR)
 		{
 			/* recurse to handle subdirectories */
 			if (recurse)
 				copydir(fromfile, tofile, true);
 		}
-		else if (S_ISREG(fst.st_mode))
+		else if (xlde_type == PGFILETYPE_REG)
 			copy_file(fromfile, tofile);
 	}
 	FreeDir(xldir);
@@ -89,8 +87,6 @@ copydir(char *fromdir, char *todir, bool recurse)
 
 	while ((xlde = ReadDir(xldir, todir)) != NULL)
 	{
-		struct stat fst;
-
 		if (strcmp(xlde->d_name, ".") == 0 ||
 			strcmp(xlde->d_name, "..") == 0)
 			continue;
@@ -101,12 +97,7 @@ copydir(char *fromdir, char *todir, bool recurse)
 		 * We don't need to sync subdirectories here since the recursive
 		 * copydir will do it before it returns
 		 */
-		if (lstat(tofile, &fst) < 0)
+		if (get_dirent_type(tofile, xlde, false, ERROR) == PGFILETYPE_REG)
-			ereport(ERROR,
-					(errcode_for_file_access(),
-					 errmsg("could not stat file \"%s\": %m", tofile)));
-
-		if (S_ISREG(fst.st_mode))
 			fsync_fname(tofile, false);
 	}
 	FreeDir(xldir);

src/backend/storage/file/fd.c

@@ -3156,17 +3156,11 @@ RemovePgTempFilesInDir(const char *tmpdirname, bool missing_ok, bool unlink_all)
 					PG_TEMP_FILE_PREFIX,
 					strlen(PG_TEMP_FILE_PREFIX)) == 0)
 		{
-			struct stat statbuf;
+			PGFileType	type = get_dirent_type(rm_path, temp_de, false, LOG);
 
-			if (lstat(rm_path, &statbuf) < 0)
+			if (type == PGFILETYPE_ERROR)
-			{
-				ereport(LOG,
-						(errcode_for_file_access(),
-						 errmsg("could not stat file \"%s\": %m", rm_path)));
 				continue;
-			}
+			else if (type == PGFILETYPE_DIR)
-
-			if (S_ISDIR(statbuf.st_mode))
 			{
 				/* recursively remove contents, then directory itself */
 				RemovePgTempFilesInDir(rm_path, false, true);

src/backend/utils/misc/guc-file.l

@@ -14,6 +14,7 @@
 #include <ctype.h>
 #include <unistd.h>
 
+#include "common/file_utils.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
 #include "storage/fd.h"
@@ -1017,7 +1018,7 @@ ParseConfigDirectory(const char *includedir,
 
 	while ((de = ReadDir(d, directory)) != NULL)
 	{
-		struct stat st;
+		PGFileType	de_type;
 		char		filename[MAXPGPATH];
 
 		/*
@@ -1034,9 +1035,17 @@ ParseConfigDirectory(const char *includedir,
 
 		join_path_components(filename, directory, de->d_name);
 		canonicalize_path(filename);
-		if (stat(filename, &st) == 0)
+		de_type = get_dirent_type(filename, de, true, elevel);
+		if (de_type == PGFILETYPE_ERROR)
 		{
-			if (!S_ISDIR(st.st_mode))
+			record_config_file_error(psprintf("could not stat file \"%s\"",
+											  filename),
+									 calling_file, calling_lineno,
+									 head_p, tail_p);
+			status = false;
+			goto cleanup;
+		}
+		else if (de_type != PGFILETYPE_DIR)
 		{
 			/* Add file to array, increasing its size in blocks of 32 */
 			if (num_filenames >= size_filenames)
@@ -1049,25 +1058,6 @@ ParseConfigDirectory(const char *includedir,
 			num_filenames++;
 		}
 	}
-		else
-		{
-			/*
-			 * stat does not care about permissions, so the most likely reason
-			 * a file can't be accessed now is if it was removed between the
-			 * directory listing and now.
-			 */
-			ereport(elevel,
-					(errcode_for_file_access(),
-					 errmsg("could not stat file \"%s\": %m",
-							filename)));
-			record_config_file_error(psprintf("could not stat file \"%s\"",
-											  filename),
-									 calling_file, calling_lineno,
-									 head_p, tail_p);
-			status = false;
-			goto cleanup;
-		}
-	}
 
 	if (num_filenames > 0)
 	{

src/timezone/pgtz.c

@@ -17,6 +17,7 @@
 #include <sys/stat.h>
 #include <time.h>
 
+#include "common/file_utils.h"
 #include "datatype/timestamp.h"
 #include "miscadmin.h"
 #include "pgtz.h"
@@ -429,7 +430,6 @@ pg_tzenumerate_next(pg_tzenum *dir)
 	{
 		struct dirent *direntry;
 		char		fullname[MAXPGPATH * 2];
-		struct stat statbuf;
 
 		direntry = ReadDir(dir->dirdesc[dir->depth], dir->dirname[dir->depth]);
 
@@ -447,12 +447,8 @@ pg_tzenumerate_next(pg_tzenum *dir)
 
 		snprintf(fullname, sizeof(fullname), "%s/%s",
 				 dir->dirname[dir->depth], direntry->d_name);
-		if (stat(fullname, &statbuf) != 0)
-			ereport(ERROR,
-					(errcode_for_file_access(),
-					 errmsg("could not stat \"%s\": %m", fullname)));
 
-		if (S_ISDIR(statbuf.st_mode))
+		if (get_dirent_type(fullname, direntry, true, ERROR) == PGFILETYPE_DIR)
 		{
 			/* Step into the subdirectory */
 			if (dir->depth >= MAX_TZDIR_DEPTH - 1)