On Fri, 7 Oct 2005, Alex Riesen wrote:
quoted text
> 
> 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

----
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 inde
+#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");
 }
 
-
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