From 90a656382d064da030e63a1bece551a18fd199b9 Mon Sep 17 00:00:00 2001
From: Jeff Hostetler <jeffhost@microsoft.com>
Date: Wed, 1 Nov 2017 15:05:44 -0400
Subject: [PATCH] dir.c: make add_excludes aware of fscache during status

Teach read_directory_recursive() and add_excludes() to
be aware of optional fscache and avoid trying to open()
and fstat() non-existant ".gitignore" files in every
directory in the worktree.

The current code in add_excludes() calls open() and then
fstat() for a ".gitignore" file in each directory present
in the worktree.  Change that when fscache is enabled to
call lstat() first and if present, call open().

This seems backwards because both lstat needs to do more
work than fstat.  But when fscache is enabled, fscache will
already know if the .gitignore file exists and can completely
avoid the IO calls.  This works because of the lstat diversion
to mingw_lstat when fscache is enabled.

This reduced status times on a 350K file enlistment of the
Windows repo on a NVMe SSD by 0.25 seconds.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
---
 lib/compat/win32/fscache.c |  5 +++++
 lib/compat/win32/fscache.h |  3 +++
 lib/dir.c                  | 39 +++++++++++++++++++++++++++++---------
 lib/git-compat-util.h      |  4 ++++
 4 files changed, 42 insertions(+), 9 deletions(-)

diff --git a/lib/compat/win32/fscache.c b/lib/compat/win32/fscache.c
index e9a6d13bde..ad9af19442 100644
--- a/lib/compat/win32/fscache.c
+++ b/lib/compat/win32/fscache.c
@@ -12,6 +12,11 @@ static struct hashmap map;
 static CRITICAL_SECTION mutex;
 static struct trace_key trace_fscache = TRACE_KEY_INIT(FSCACHE);
 
+int fscache_is_enabled(void)
+{
+	return enabled;
+}
+
 /*
  * An entry in the file system cache. Used for both entire directory listings
  * and file entries.
diff --git a/lib/compat/win32/fscache.h b/lib/compat/win32/fscache.h
index 1a69f44358..fc31c17863 100644
--- a/lib/compat/win32/fscache.h
+++ b/lib/compat/win32/fscache.h
@@ -7,6 +7,9 @@ int fscache_enable(int enable);
 void fscache_flush(void);
 #define flush_fscache() fscache_flush()
 
+int fscache_is_enabled(void);
+#define is_fscache_enabled() (fscache_is_enabled())
+
 DIR *fscache_opendir(const char *dir);
 int fscache_lstat(const char *file_name, struct stat *buf);
 
diff --git a/lib/dir.c b/lib/dir.c
index 27f033388e..285e091317 100644
--- a/lib/dir.c
+++ b/lib/dir.c
@@ -1156,16 +1156,37 @@ static int add_patterns(const char *fname, const char *base, int baselen,
 	size_t size = 0;
 	char *buf;
 
-	if (flags & PATTERN_NOFOLLOW)
-		fd = open_nofollow(fname, O_RDONLY);
-	else
-		fd = open(fname, O_RDONLY);
-
-	if (fd < 0 || fstat(fd, &st) < 0) {
-		if (fd < 0)
-			warn_on_fopen_errors(fname);
+	/*
+	 * Since `clang`'s `-Wunreachable-code` mode is clever, it would figure
+	 * out that on non-Windows platforms, this `lstat()` is unreachable.
+	 * We do want to keep the conditional block for the sake of Windows,
+	 * though, so let's use the `NOT_CONSTANT()` trick to suppress that error.
+	 */
+	if (NOT_CONSTANT(is_fscache_enabled())) {
+		if (lstat(fname, &st) < 0) {
+			fd = -1;
+		} else {
+			fd = open(fname, O_RDONLY);
+			if (fd < 0)
+				warn_on_fopen_errors(fname);
+		}
+	} else {
+		if (flags & PATTERN_NOFOLLOW)
+			fd = open_nofollow(fname, O_RDONLY);
 		else
-			close(fd);
+			fd = open(fname, O_RDONLY);
+
+		if (fd < 0 || fstat(fd, &st) < 0) {
+			if (fd < 0)
+				warn_on_fopen_errors(fname);
+			else {
+				close(fd);
+				fd = -1;
+			}
+		}
+	}
+
+	if (fd < 0) {
 		if (!istate)
 			return -1;
 		r = read_skip_worktree_file_from_index(istate, fname,
diff --git a/lib/git-compat-util.h b/lib/git-compat-util.h
index 61f054404a..1c09ea0c3b 100644
--- a/lib/git-compat-util.h
+++ b/lib/git-compat-util.h
@@ -1126,6 +1126,10 @@ static inline int is_missing_file_error(int errno_)
 #define flush_fscache() /* noop */
 #endif
 
+#ifndef is_fscache_enabled
+#define is_fscache_enabled() (0)
+#endif
+
 int cmd_main(int, const char **);
 
 /*