Skip unnecessary stat() calls in walkdir().

Some kernels can tell us the type of a "dirent", so we can avoid a call
to stat() or lstat() in many cases.  Define a new function
get_dirent_type() to contain that logic, for use by the backend and
frontend versions of walkdir(), and perhaps other callers in future.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Juan José Santamaría Flecha <juanjo.santamaria@gmail.com>
Discussion: https://postgr.es/m/CA%2BhUKG%2BFzxupGGN4GpUdbzZN%2Btn6FQPHo8w0Q%2BAPH5Wz8RG%2Bww%40mail.gmail.com

Author: macdice

src/backend/storage/file/fd.c

@@ -89,6 +89,7 @@
 #include "access/xlog.h"
 #include "catalog/pg_tablespace.h"
 #include "common/file_perm.h"
+#include "common/file_utils.h"
 #include "miscadmin.h"
 #include "pgstat.h"
 #include "portability/mem.h"
@@ -3340,8 +3341,6 @@ walkdir(const char *path,
 	while ((de = ReadDirExtended(dir, path, elevel)) != NULL)
 	{
 		char		subpath[MAXPGPATH * 2];
-		struct stat fst;
-		int			sret;
 
 		CHECK_FOR_INTERRUPTS();
 
@@ -3351,23 +3350,23 @@ walkdir(const char *path,
 
 		snprintf(subpath, sizeof(subpath), "%s/%s", path, de->d_name);
 
-		if (process_symlinks)
-			sret = stat(subpath, &fst);
-		else
-			sret = lstat(subpath, &fst);
-
-		if (sret < 0)
+		switch (get_dirent_type(subpath, de, process_symlinks, elevel))
 		{
-			ereport(elevel,
-					(errcode_for_file_access(),
-					 errmsg("could not stat file \"%s\": %m", subpath)));
-			continue;
-		}
+			case PGFILETYPE_REG:
+				(*action) (subpath, false, elevel);
+				break;
+			case PGFILETYPE_DIR:
+				walkdir(subpath, action, false, elevel);
+				break;
+			default:
 
-		if (S_ISREG(fst.st_mode))
-			(*action) (subpath, false, elevel);
-		else if (S_ISDIR(fst.st_mode))
-			walkdir(subpath, action, false, elevel);
+				/*
+				 * Errors are already reported directly by get_dirent_type(),
+				 * and any remaining symlinks and unknown file types are
+				 * ignored.
+				 */
+				break;
+		}
 	}
 
 	FreeDir(dir);				/* we ignore any error here */

src/common/Makefile

@@ -56,6 +56,7 @@ OBJS_COMMON = \
 	exec.o \
 	f2s.o \
 	file_perm.o \
+	file_utils.o \
 	hashfn.o \
 	ip.o \
 	jsonapi.o \
@@ -91,7 +92,6 @@ endif
 OBJS_FRONTEND = \
 	$(OBJS_COMMON) \
 	fe_memutils.o \
-	file_utils.o \
 	logging.o \
 	restricted_token.o \
 	sprompt.o

src/common/file_utils.c

@@ -14,19 +14,22 @@
  */
 
 #ifndef FRONTEND
-#error "This file is not expected to be compiled for backend code"
-#endif
-
+#include "postgres.h"
+#else
 #include "postgres_fe.h"
+#endif
 
 #include <dirent.h>
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <unistd.h>
 
 #include "common/file_utils.h"
+#ifdef FRONTEND
 #include "common/logging.h"
+#endif
 
+#ifdef FRONTEND
 
 /* Define PG_FLUSH_DATA_WORKS if we have an implementation for pg_flush_data */
 #if defined(HAVE_SYNC_FILE_RANGE)
@@ -167,30 +170,30 @@ walkdir(const char *path,
 	while (errno = 0, (de = readdir(dir)) != NULL)
 	{
 		char		subpath[MAXPGPATH * 2];
-		struct stat fst;
-		int			sret;
 
 		if (strcmp(de->d_name, ".") == 0 ||
 			strcmp(de->d_name, "..") == 0)
 			continue;
 
 		snprintf(subpath, sizeof(subpath), "%s/%s", path, de->d_name);
 
-		if (process_symlinks)
-			sret = stat(subpath, &fst);
-		else
-			sret = lstat(subpath, &fst);
-
-		if (sret < 0)
+		switch (get_dirent_type(subpath, de, process_symlinks, PG_LOG_ERROR))
 		{
-			pg_log_error("could not stat file \"%s\": %m", subpath);
-			continue;
+			case PGFILETYPE_REG:
+				(*action) (subpath, false);
+				break;
+			case PGFILETYPE_DIR:
+				walkdir(subpath, action, false);
+				break;
+			default:
+
+				/*
+				 * Errors are already reported directly by get_dirent_type(),
+				 * and any remaining symlinks and unknown file types are
+				 * ignored.
+				 */
+				break;
 		}
-
-		if (S_ISREG(fst.st_mode))
-			(*action) (subpath, false);
-		else if (S_ISDIR(fst.st_mode))
-			walkdir(subpath, action, false);
 	}
 
 	if (errno)
@@ -394,3 +397,73 @@ durable_rename(const char *oldfile, const char *newfile)
 
 	return 0;
 }
+
+#endif							/* FRONTEND */
+
+/*
+ * Return the type of a directory entry.
+ *
+ * In frontend code, elevel should be a level from logging.h; in backend code
+ * it should be a level from elog.h.
+ */
+PGFileType
+get_dirent_type(const char *path,
+				const struct dirent *de,
+				bool look_through_symlinks,
+				int elevel)
+{
+	PGFileType	result;
+
+	/*
+	 * Some systems tell us the type directly in the dirent struct, but that's
+	 * a BSD and Linux extension not required by POSIX.  Even when the
+	 * interface is present, sometimes the type is unknown, depending on the
+	 * filesystem.
+	 */
+#if defined(DT_REG) && defined(DT_DIR) && defined(DT_LNK)
+	if (de->d_type == DT_REG)
+		result = PGFILETYPE_REG;
+	else if (de->d_type == DT_DIR)
+		result = PGFILETYPE_DIR;
+	else if (de->d_type == DT_LNK && !look_through_symlinks)
+		result = PGFILETYPE_LNK;
+	else
+		result = PGFILETYPE_UNKNOWN;
+#else
+	result = PGFILETYPE_UNKNOWN;
+#endif
+
+	if (result == PGFILETYPE_UNKNOWN)
+	{
+		struct stat fst;
+		int			sret;
+
+
+		if (look_through_symlinks)
+			sret = stat(path, &fst);
+		else
+			sret = lstat(path, &fst);
+
+		if (sret < 0)
+		{
+			result = PGFILETYPE_ERROR;
+#ifdef FRONTEND
+			pg_log_generic(elevel, "could not stat file \"%s\": %m", path);
+#else
+			ereport(elevel,
+					(errcode_for_file_access(),
+					 errmsg("could not stat file \"%s\": %m", path)));
+#endif
+		}
+		else if (S_ISREG(fst.st_mode))
+			result = PGFILETYPE_REG;
+		else if (S_ISDIR(fst.st_mode))
+			result = PGFILETYPE_DIR;
+#ifdef S_ISLNK
+		else if (S_ISLNK(fst.st_mode))
+			result = PGFILETYPE_LNK;
+#endif
+	}
+
+	return result;
+}

src/include/common/file_utils.h

@@ -1,6 +1,4 @@
 /*-------------------------------------------------------------------------
- *
- * File-processing utility routines for frontend code
  *
  * Assorted utility functions to work on files.
  *
@@ -15,10 +13,28 @@
 #ifndef FILE_UTILS_H
 #define FILE_UTILS_H
 
+#include <dirent.h>
+
+typedef enum PGFileType
+{
+	PGFILETYPE_ERROR,
+	PGFILETYPE_UNKNOWN,
+	PGFILETYPE_REG,
+	PGFILETYPE_DIR,
+	PGFILETYPE_LNK
+} PGFileType;
+
+#ifdef FRONTEND
 extern int	fsync_fname(const char *fname, bool isdir);
 extern void fsync_pgdata(const char *pg_data, int serverVersion);
 extern void fsync_dir_recurse(const char *dir);
 extern int	durable_rename(const char *oldfile, const char *newfile);
 extern int	fsync_parent_path(const char *fname);
+#endif
+
+extern PGFileType get_dirent_type(const char *path,
+								  const struct dirent *de,
+								  bool look_through_symlinks,
+								  int elevel);
 
 #endif							/* FILE_UTILS_H */

src/tools/msvc/Mkvcbuild.pm

@@ -121,7 +121,7 @@ sub mkvcbuild
 	our @pgcommonallfiles = qw(
 	  archive.c base64.c checksum_helper.c
 	  config_info.c controldata_utils.c d2s.c encnames.c exec.c
-	  f2s.c file_perm.c hashfn.c ip.c jsonapi.c
+	  f2s.c file_perm.c file_utils.c hashfn.c ip.c jsonapi.c
 	  keywords.c kwlookup.c link-canary.c md5.c
 	  pg_get_line.c pg_lzcompress.c pgfnames.c psprintf.c relpath.c rmtree.c
 	  saslprep.c scram-common.c string.c stringinfo.c unicode_norm.c username.c
@@ -138,7 +138,7 @@ sub mkvcbuild
 	}
 
 	our @pgcommonfrontendfiles = (
-		@pgcommonallfiles, qw(fe_memutils.c file_utils.c
+		@pgcommonallfiles, qw(fe_memutils.c
 		  logging.c restricted_token.c sprompt.c));
 
 	our @pgcommonbkndfiles = @pgcommonallfiles;

src/tools/pgindent/typedefs.list

@@ -1515,6 +1515,7 @@ PGEventResultCopy
 PGEventResultCreate
 PGEventResultDestroy
 PGFInfoFunction
+PGFileType
 PGFunction
 PGLZ_HistEntry
 PGLZ_Strategy