Subject: Re: First cut at git port to Cygwin

From: Elfyn McBratney <[email-masked]>
Date: Sat, 8 Oct 2005 18:38:13 +0100

On Sat, Oct 08, 2005 at 09:11:03AM -0700, Linus Torvalds wrote:
 > 
 > On Fri, 7 Oct 2005, Alex Riesen wrote:
 > > 
 > > Make read_cache copy the index into memory, to improve portability on
 > > other OS's which have mmap too, tend to use it less commonly.
 > 
 > I really think that you should just get rid of the mmap.
 > 
 > As it is, you're just slowing the code down on sane architectures. That's 
 > not good.
 > 
 > So I'd suggest something like this instead.
 > 
 > Totally untested, of course.
 > 
 > 		Linus

Slightly adjusted diff below so it compiles ;)  (Note: only the second
die() un hunk #1 was changed.)

Best,
Elfyn

----
diff --git a/read-cache.c b/read-cache.c
--- a/read-cache.c
+++ b/read-cache.c
@@ -454,13 +454,39 @@ static int verify_hdr(struct cache_heade
 	return 0;
 }
 
+static void *map_index_file(int fd, size_t size)
+{
+	void *map;
+#ifdef NO_MMAP
+	map = malloc(size);
+	if (!map)
+		die("Unable to allocate index file mapping");
+	if (read(fd, map, size) != size)
+		die("Unable to read %z bytes from index", size);
+#else
+	map = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
+	if (map == MAP_FAILED)
+		die("index file mmap failed (%s)", strerror(errno));
+#endif
+	return map;
+}
+
+static void unmap_index_file(void *map, size_t size)
+{
+#ifdef NO_MMAP
+	free(map);
+#else
+	munmap(map, size);
+#endif
+}
+
 int read_cache(void)
 {
 	int fd, i;
 	struct stat st;
 	unsigned long size, offset;
-	void *map;
 	struct cache_header *hdr;
+	void *map;
 
 	errno = EBUSY;
 	if (active_cache)
@@ -475,16 +501,15 @@ int read_cache(void)
 	}
 
 	size = 0; // avoid gcc warning
-	map = MAP_FAILED;
-	if (!fstat(fd, &st)) {
-		size = st.st_size;
-		errno = EINVAL;
-		if (size >= sizeof(struct cache_header) + 20)
-			map = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
-	}
+	if (fstat(fd, &st))
+		die("unable to fstat index file");
+
+	size = st.st_size;
+	errno = EINVAL;
+	if (size < sizeof(struct cache_header) + 20)
+		goto corrupt;
+	map = map_index_file(fd, size);
 	close(fd);
-	if (map == MAP_FAILED)
-		die("index file mmap failed (%s)", strerror(errno));
 
 	hdr = map;
 	if (verify_hdr(hdr, size) < 0)
@@ -503,8 +528,9 @@ int read_cache(void)
 	return active_nr;
 
 unmap:
-	munmap(map, size);
+	unmap_index_file(map, size);
 	errno = EINVAL;
+corrupt:
 	die("index file corrupt");
 }

-- 
Elfyn McBratney
Gentoo Developer/Perl Team Lead
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